I am using LifePO4 batteries for my solar electric systems. With each battery comes a small manual. They all state to not use more than 4 batteries in any given string, rather in parallel or series configuration. What is the reasoning behind that warning? I have another tab open which is Batteryuniversity. After perusing chapters related to LjfePO4, I have not come across mention of this instruction.
Why no more than 4 batteries in any particular string?
- Thread starter HANKMARS
- Start date
- Joined
- Jun 21, 2012
- Messages
- 4,968
I got the following answer from Grok 4 on X.com:
The warning in LiFePO4 battery manuals against connecting more than 4 batteries in series or parallel is a common guideline from manufacturers to ensure safety, longevity, and optimal performance, particularly in consumer-grade setups like solar PV systems.
Grok goes on to say a whole lot more about it, but the gist of its comment is this: commercial LiFePO4 batteries DO contain a battery management system, but it is primitive and may not be suitable for more than four cells. You need a battery management system (BMS) for either series connections (to avoid overcharging with "dead" cells) as well as paralleled batteries (to avoid trying to charge shorted cells).
If you have access to Grok 4 I highly recommend you use it first before posting here. Saves a lot of time, usually. ChatGPT IS NOT THE SAME!
I'm not sure exactly how the different Groks are affected by one's verification status. Just last week I unsubscribed from X's verification plan. Pinching pennies at the moment. Shortly before that, I was chatting with Grok 2 about what happens when the fractals of an infinite perimeter, contained within the area of a finite circle, reach the size of sub-atomic particles. Grok mentioned that at that point, we were entering quantum mechanics or quantum physics. Approaching Grok first with inquiries is not a bad idea and I may very well do that but if he fails to find an answer or an explanation, I will then address my question to Electronics Forum.
- Joined
- Jun 21, 2012
- Messages
- 4,968
It takes a bit of experience to formulate AI inquiries in a manner that produces good results. And if you do use AI, treat like you would a brand new calculator you found under the tree... in 1960. I remember my very first Texas Instruments Four-Banger, a desktop job that ran off of shore power, not batteries, and "featured" tiny, red, LED numeric displays (that's why it needed power from a convenience outlet). Most important: it could add, subtract, multiply, and divide! I could now use my tables of logarithms much more efficiently, maybe even ditch my log-log deci-trig bamboo slide rule, so important for calculating reactance and resonance in tuned radio-frequency circuits... if only I could remember where to place the decimal point. Yeah, new tech is fun play with. But it is just that: technology. Don't get hung up on how the interface is presented. Try to look a little deeper to see how we got here. Use what works. Ignore what doesn't.
I found the earlier versions of Grok interesting but virtually useless. More training and more processors improved things, but I still could not trust the "answers" I was getting from Grok 2. It wasn't until Grok 4 that things finally became useful. Grok has been a tremendous help with my effort to demonstrate Earth-Moon-Earth (EME) communications using optical laser wavelengths, specifically 532nm emissions from inexpensive Chinese laser pointers. If interested in this type of amateur radio activity, please visit http://optical-eme.groups.io to see what progress (if any) is being made.
Good luck with those LiFePO4 (lithium-iron-phosphate) batteries!
I found the earlier versions of Grok interesting but virtually useless. More training and more processors improved things, but I still could not trust the "answers" I was getting from Grok 2. It wasn't until Grok 4 that things finally became useful. Grok has been a tremendous help with my effort to demonstrate Earth-Moon-Earth (EME) communications using optical laser wavelengths, specifically 532nm emissions from inexpensive Chinese laser pointers. If interested in this type of amateur radio activity, please visit http://optical-eme.groups.io to see what progress (if any) is being made.
Good luck with those LiFePO4 (lithium-iron-phosphate) batteries!
If overcharging due to cell failure of some type or other, which no doubt would result in further destruction, I feel free to chain as many batteries together as I deem necessary. The LiFePO4 batteries I have purchased do have BMS and supposedly guard against problems of over temperature, short circuits, low voltage, overcharging and a few other non-healthy conditions. Currently, my battery banks are my sole source of electrical power. I do have a gasoline powered 1800/2400peak watt generator but using it makes me feel like a cheater. I am constructing a monitoring system which should help me notice any anomalies before any real damage occurs. Even though commercial electricity is within four miles of me, I do not expect it to be coming down my road in my lifetime. Harnessing solar energy has become a relatively easy procedure but the storing of the energy is still the bottleneck. Even being raised in an era that still today prompts me to ask, "Where's my 'clicker' ?, I am not impressed with what industry has developed in the way of energy storage. My best guess is that a few of the elite of the one percent have made that quest taboo.
Attachments
- Joined
- Jun 21, 2012
- Messages
- 4,968
The storage of energy for later use was solved billyuns and billyuns of years ago here on Earth. The Sun provides the energy; life provides the storage. Ancient lifeforms lived and died under the Sun's rays, eventually leaving behind the seams of coal and the deposits of oil and natural gas. Isn't it just like us humans to squander those riches? Of course we now have nuclear energy to fall back on if wind, solar, and hydro fail to keep civilization hummin' along. Soon we will migrate our philosophy into outer space. Won't the neighbors appreciate that!
But, seriously, storing electrical energy is a huge problem. The only known way to do this efficiently and at scale is to use gravity to store potential energy and then release it as kinetic energy. This is commonly called an hydroelectric facility, which I'll just abbreviate as HEF.
Most HEFs rely on rain (another Sun-driven energy resource) to fill up a reservoir above a dam with lake water derived from snow-melt off of mountains. Or, sometimes, from underground streams of water like the Tennessee Valley Authority (TVA) did in 1933. Or, if you have a reliable source of intermittent electricity, say from a solar panel array or a wind farm, you can use that to PUMP water from a reservoir below a dam to another reservoir above the dam. Inside the dam are turbines and alternators to convert falling water (that's where the gravity comes into play) in to transmittable electricity. And this scales up nicely if there is enough money to build it.
So what's a poor guy in the wilderness, four miles from commercial electricity, to do? The telephone company faced a similar problem in the previous century with wired telephone service. They needed the phones to work even with widespread power outages. Their answer was to build brick houses with lots of lead-acid batteries inside to provide telephone power. As long as commercial electricity was available, AT&T (and others) could keep the batteries charged 24/7/365. It wasn't very efficient, it was labor intensive to maintain the batteries, and it mostly doesn't exist anymore with the advent of cheap cell phones and free long-distance connections to anywhere in the continental USA.
I played around with lead-acid batteries in my youth. I even imagined building a go-kart with a pair of large digital tape reel motors and a huge lead-acid battery for energy storage. But this was way before MOSFETs made this possible, and Tesla made it a commercial reality. I would not recommend using Li-ion battery technology for energy storage in the wilderness. If you try using modern versions of the lead-acid technology, you may find that this type of battery is maintainable by you, whereas nothing can be done with a Li-ion battery that won't hold a charge anymore.
As for the elites... well, like the poor, the elites will always be among us. It is best to try to move in their direction instead of the other way. Don't try to play "catch up" though! Take what the elites can provide in terms of technology and leave the rest alone. It is admirable to try to be self-sufficient and even "get back to Nature" if that is your thing, but no one can do it alone. That's why we come here, right? We are the electronic hobbyist elite. Maybe.
But, seriously, storing electrical energy is a huge problem. The only known way to do this efficiently and at scale is to use gravity to store potential energy and then release it as kinetic energy. This is commonly called an hydroelectric facility, which I'll just abbreviate as HEF.
Most HEFs rely on rain (another Sun-driven energy resource) to fill up a reservoir above a dam with lake water derived from snow-melt off of mountains. Or, sometimes, from underground streams of water like the Tennessee Valley Authority (TVA) did in 1933. Or, if you have a reliable source of intermittent electricity, say from a solar panel array or a wind farm, you can use that to PUMP water from a reservoir below a dam to another reservoir above the dam. Inside the dam are turbines and alternators to convert falling water (that's where the gravity comes into play) in to transmittable electricity. And this scales up nicely if there is enough money to build it.
So what's a poor guy in the wilderness, four miles from commercial electricity, to do? The telephone company faced a similar problem in the previous century with wired telephone service. They needed the phones to work even with widespread power outages. Their answer was to build brick houses with lots of lead-acid batteries inside to provide telephone power. As long as commercial electricity was available, AT&T (and others) could keep the batteries charged 24/7/365. It wasn't very efficient, it was labor intensive to maintain the batteries, and it mostly doesn't exist anymore with the advent of cheap cell phones and free long-distance connections to anywhere in the continental USA.
I played around with lead-acid batteries in my youth. I even imagined building a go-kart with a pair of large digital tape reel motors and a huge lead-acid battery for energy storage. But this was way before MOSFETs made this possible, and Tesla made it a commercial reality. I would not recommend using Li-ion battery technology for energy storage in the wilderness. If you try using modern versions of the lead-acid technology, you may find that this type of battery is maintainable by you, whereas nothing can be done with a Li-ion battery that won't hold a charge anymore.
As for the elites... well, like the poor, the elites will always be among us. It is best to try to move in their direction instead of the other way. Don't try to play "catch up" though! Take what the elites can provide in terms of technology and leave the rest alone. It is admirable to try to be self-sufficient and even "get back to Nature" if that is your thing, but no one can do it alone. That's why we come here, right? We are the electronic hobbyist elite. Maybe.
poor mystic
- Apr 8, 2011
- 1,106
- Joined
- Apr 8, 2011
- Messages
- 1,106
Hi 
I asked DeepSeek and got this reply:
Q: "why should no more than 4 lithium ion batteries be charged in series?"
Of course. This is an excellent and crucial safety question.
The directive to not charge more than 4 lithium-ion batteries in series using a simple balancing charger is a rule of thumb rooted in the fundamental characteristics of the batteries and the limitations of common, affordable charging equipment.
Here’s a breakdown of the reasons, from the most critical to the practical.
Also, Veritasium has made a YouTube video on Lithium Ion technology:
Hope it helps
I asked DeepSeek and got this reply:
Q: "why should no more than 4 lithium ion batteries be charged in series?"
Of course. This is an excellent and crucial safety question.
The directive to not charge more than 4 lithium-ion batteries in series using a simple balancing charger is a rule of thumb rooted in the fundamental characteristics of the batteries and the limitations of common, affordable charging equipment.
Here’s a breakdown of the reasons, from the most critical to the practical.
1. The Core Problem: Voltage Imbalance (Cell Divergence)
This is the single most important reason.- No Two Batteries Are Identical: Even batteries from the same manufacturing batch have tiny differences in internal resistance, capacity, and self-discharge rate.
- What Happens in Series: When you charge batteries in series, the same amount of current flows through all of them. However, because they are not identical, they reach their full charge (e.g., 4.2V) at slightly different times.
- The Danger of Overcharging: The charger only monitors the total voltage of the pack. For example, a 4S pack should charge to 16.8V (4 * 4.2V). If one battery reaches 4.2V first but the others are still at 4.1V, the total voltage is only 16.5V. The charger keeps pushing current until it sees 16.8V. By then, the first battery is being severely overcharged (e.g., to 4.35V or higher).
- Why Overcharging is Catastrophic:Overcharging a lithium-ion battery causes lithium metal to plate on the anode. This can lead to:
- Rapid Heating: Thermal runaway begins.
- Gas Generation: The electrolyte breaks down and creates flammable gas, causing the battery to swell.
- Fire and Explosion: The combination of heat, pressure, and flammable chemicals is extremely dangerous.
2. The Role of a Battery Management System (BMS)
A BMS is a crucial circuit board that manages a series battery pack.- What it does: A BMS monitors each individual cell's voltage.
- How it helps: If any single cell reaches its maximum voltage (e.g., 4.2V) during charging, the BMS will disconnect the charging circuit or bleed off excess energy (through a process called balancing) to prevent that one cell from overcharging, even if the overall pack voltage hasn't been reached.
- The "4 Battery" Rule of Thumb: Many inexpensive, off-the-shelf "balance chargers" commonly used for hobbies (drones, RC cars, etc.) have a limitation: they can only monitor and balance up to 4 individual cells in series (a "4S" pack). They have five wires: one for the total voltage and one for the connection between each cell.
3. Practical and Equipment Limitations
- Charger Capability: If your charger is only designed for up to 4S (16.8V), attempting to charge a 5S (21V) or higher pack will not work and could damage the charger or, more likely, simply not recognize the pack.
- Complexity and Risk: As you add more cells in series, the potential for voltage imbalance increases. Managing a high-voltage series pack (e.g., 10S, 36V) requires a much more sophisticated and dedicated BMS that is physically attached to the pack, not just an external hobby charger.
Summary: Safe Practice vs. Unsafe Practice
| Safe Practice (Using a 4S Balance Charger) | Unsafe Practice (Charging >4S without a BMS) |
|---|---|
| The charger monitors each of the 4 cells. | The charger only sees the total voltage. |
| If one cell is full, charging stops or it balances. | The charger cannot see that one cell is overcharging. |
| All cells are charged to their safe voltage. | One weak cell gets overcharged, leading to failure. |
| The system is within the design limits of common hobbyist equipment. | The system operates beyond the safe limits of the charger. |
Conclusion
You should not charge more than 4 lithium-ion batteries in series unless you have the proper equipment to manage the imbalance.- For 4S (14.8V) packs or less: A standard 4S balance charger is sufficient and safe.
- For 5S (18.5V) packs or more: You must have a dedicated Battery Management System (BMS) permanently attached to the battery pack that is designed for that specific number of cells. The BMS, not the external charger, is responsible for protecting each individual cell.
...................................
I'm not ready to say that DeepSeek is your friend, but that's a well-written answer which feels right to me.Also, Veritasium has made a YouTube video on Lithium Ion technology:
Hope it helps
Last edited:
A move back to nature is not the driving force for me but rather affordable land. I had intended to construct my own dwelling then came across a "foldable container house" and purchased it. Actually the first house I have purchased. What would be considered a starter house in Phoenix will run easily 200k and more like 400k.. Even in working years, house prices remained out of reach. Call me a non-conformist, but signing a thirty year contract is not acceptable in my opinion. Mortgage: the mort root part is indeed related to words such as mortality, mortal, rigamortise, etc. Anyway, I am learning much about batteries and thoroughly enjoy my current lifestyle. Thanks for your help on the forum. I'm sure I will have more questions.
- Joined
- Jun 21, 2012
- Messages
- 4,968
Ah! Affordable land. What a concept! Too bad that government can take it all away from you for any of several numerous reasons. Those reasons include eminent domain where the government offers you a "fair price" (an offer you cannot refuse) for your land; tax forfeiture where the government says you owe taxes and they will take your property if you don't pay up; adverse possession (non-government) where a "squatter" sits on your property unchallenged for a certain period of time and then government says they now "own" it. You can probably dig up a few more. I am now in the process of paying on my second mortgage. The first mortgage was small, about $19,000 IIRC, and I paid it off before the thirty years were up. We lived in that house for more than thirty years while watching the "family neighborhood" turn into a crime and drug-ridden environment as older folks died and transients moved in to take their place. When I finally retired in 2015, my wife and I found an "affordable" home using my G.I. Bill VA benefits. I don't expect to outlive the mortgage note. My wife will inherit the house, the land, and the mortgage but I doubt she will keep any of it. Monthly mortgage payments are a lot like monthly rent payments in the fact that most of the monthly payments go toward interest rather than reduction of principle. If my wife is "lucky" the house and the land it is on will appreciate because of inflation, meaning the mortgage payments are made with dollars that are worth less than the dollars the seller received. Good news for her, bad news for a potential buyer who must somehow come up with the inflated price. Kind of reminds me of the game "musical chairs" where someone is left standing (and holding the bag) while everyone else sits down when the music stops. It may not be the best game in town, but it is the only game... unless you want to go back to a feudal system where only the king owns land and "rents it out" to the peasants for a percentage of whatever is produced on the land. Sort of similar to Communism only without any semblance of recourse. Hmmm. Make that exactly like Communism: take from the peasants as much as they can deliver; provide the peasants the minimum they need to survive. Okay, end of rant about property "ownership" because you "own" only what you can defend "others" from taking.
A collapsible cardboard house? Sounds like a repurposed refrigerator crate. I see they can now "print" a house with concrete. Not sure how much that costs, but it's got to be more expensive than logs dolloped with mud, especially if you can cut logs from trees on your land. That would normally require two people to handle the crosscut saw unless you opt for a gasoline-powered chain saw.
I wonder, is there still "government land" that can be acquired for "free" by homesteading on it? Is such land locally taxable? Are you young enough to homestead?
A collapsible cardboard house? Sounds like a repurposed refrigerator crate. I see they can now "print" a house with concrete. Not sure how much that costs, but it's got to be more expensive than logs dolloped with mud, especially if you can cut logs from trees on your land. That would normally require two people to handle the crosscut saw unless you opt for a gasoline-powered chain saw.
I wonder, is there still "government land" that can be acquired for "free" by homesteading on it? Is such land locally taxable? Are you young enough to homestead?
Very interesting and informative and sound advice. I currently have 3 battery packs. Two packs consist of 4 li-ion 100 Ahr batteries connected in parallel, each supplying their own 12 V 3000 W inverter. The third pack consists of 4-12 V, glass mat, lead/acid, 35 Ahr batteries. Two sets, of 2 batteries connected in series, are connected in parallel producing a 24 VDC output which is fed into a 100 A, 24 to 12 V DC to DC converter, for a high current application I have. I was feeling ripped off or lied to about the lithium batteries until I did the calcs. Let's say I have a 2 A, 120 VAC device that I need to power. The inverter will be asking for 20 A at 12 VDC. Figure the efficiency coefficient is 50%, the inverter now needs 40 A. Maybe some voltage drops because cables might be a little under-sized and the batteries are expected to puke up 50 Amps. And that is for merely a 2 A load. So I am somewhat surprised at the performance I do get from my systems. I have no grid power available. I'm definitely having a learning experience. Figure some devices may momentarly draw 2 to 5 times their rated run current, and it is surprising more equipment isn't fried.Hi
I asked DeepSeek and got this reply:
Q: "why should no more than 4 lithium ion batteries be charged in series?"
Of course. This is an excellent and crucial safety question.
The directive to not charge more than 4 lithium-ion batteries in series using a simple balancing charger is a rule of thumb rooted in the fundamental characteristics of the batteries and the limitations of common, affordable charging equipment.
Here’s a breakdown of the reasons, from the most critical to the practical.
1. The Core Problem: Voltage Imbalance (Cell Divergence)
This is the single most important reason.
- No Two Batteries Are Identical: Even batteries from the same manufacturing batch have tiny differences in internal resistance, capacity, and self-discharge rate.
- What Happens in Series: When you charge batteries in series, the same amount of current flows through all of them. However, because they are not identical, they reach their full charge (e.g., 4.2V) at slightly different times.
- The Danger of Overcharging: The charger only monitors the total voltage of the pack. For example, a 4S pack should charge to 16.8V (4 * 4.2V). If one battery reaches 4.2V first but the others are still at 4.1V, the total voltage is only 16.5V. The charger keeps pushing current until it sees 16.8V. By then, the first battery is being severely overcharged (e.g., to 4.35V or higher).
- Why Overcharging is Catastrophic:Overcharging a lithium-ion battery causes lithium metal to plate on the anode. This can lead to:
- Rapid Heating: Thermal runaway begins.
- Gas Generation: The electrolyte breaks down and creates flammable gas, causing the battery to swell.
- Fire and Explosion: The combination of heat, pressure, and flammable chemicals is extremely dangerous.
2. The Role of a Battery Management System (BMS)
A BMS is a crucial circuit board that manages a series battery pack.
- What it does: A BMS monitors each individual cell's voltage.
- How it helps: If any single cell reaches its maximum voltage (e.g., 4.2V) during charging, the BMS will disconnect the charging circuit or bleed off excess energy (through a process called balancing) to prevent that one cell from overcharging, even if the overall pack voltage hasn't been reached.
- The "4 Battery" Rule of Thumb: Many inexpensive, off-the-shelf "balance chargers" commonly used for hobbies (drones, RC cars, etc.) have a limitation: they can only monitor and balance up to 4 individual cells in series (a "4S" pack). They have five wires: one for the total voltage and one for the connection between each cell.
3. Practical and Equipment Limitations
- Charger Capability: If your charger is only designed for up to 4S (16.8V), attempting to charge a 5S (21V) or higher pack will not work and could damage the charger or, more likely, simply not recognize the pack.
- Complexity and Risk: As you add more cells in series, the potential for voltage imbalance increases. Managing a high-voltage series pack (e.g., 10S, 36V) requires a much more sophisticated and dedicated BMS that is physically attached to the pack, not just an external hobby charger.
Summary: Safe Practice vs. Unsafe Practice
Safe Practice (Using a 4S Balance Charger) Unsafe Practice (Charging >4S without a BMS) The charger monitors each of the 4 cells. The charger only sees the total voltage. If one cell is full, charging stops or it balances. The charger cannot see that one cell is overcharging. All cells are charged to their safe voltage. One weak cell gets overcharged, leading to failure. The system is within the design limits of common hobbyist equipment. The system operates beyond the safe limits of the charger. Conclusion
You should not charge more than 4 lithium-ion batteries in series unless you have the proper equipment to manage the imbalance.
The "4 battery" rule is a simplified guideline to prevent hobbyists from accidentally creating a dangerous situation with the common chargers available to them. Always respect the limits of your equipment and the chemistry of lithium-ion batteries.
- For 4S (14.8V) packs or less: A standard 4S balance charger is sufficient and safe.
- For 5S (18.5V) packs or more: You must have a dedicated Battery Management System (BMS) permanently attached to the battery pack that is designed for that specific number of cells. The BMS, not the external charger, is responsible for protecting each individual cell.
...................................I'm not ready to say that DeepSeek is your friend, but that's a well-written answer which feels right to me.
Also, Veritasium has made a YouTube video on Lithium Ion technology:
Hope it helps
I'm 71. Doubt homesteading is a route for me. There is a lot of government owned land in Arizona. I was quite surprised how diversified the land is in AZ. A lot of desert but also huge tracks of Pondarosa Pine. Many lake area, not to mention the man-made reserviors. I am in central east Az. The foldable house is mostly metal. 720 square feet of floor space. The floor is a hash work of 1 1/2' tubular stell with a layer of marine grade OSB covered with a modern linoleum sort of material, but the black tar-like backing of linoleum is replaced with a poly of some sort. Total weight is 14,000 pounds. I'm very happy with it. Keeps me out of the rain and wind. You are right about government's arrogance related to taking land but I'm not going to head up the next revolution. Last year before I put this house here, my property taxes were 16 dollars. 8 dollars per acre. I'm diggin it.
- Joined
- Jun 21, 2012
- Messages
- 4,968
Wow! Sixteen bux property tax on two acres. However, now that you have "improved" the property by placing a house on it, the local guv'mint will probably try to tax it out from under you. Better hide those solar panels, too, lest someone figure out a way to tax sunlight.
I have visited Arizona several times since I have been alive. I've been alive for 81+ years. The latest visit was for a job interview with Hughes in Tucson after I graduated college in 1978. IIRC, they were making television-guided Maverick missiles back then. But I didn't take their job offer, because Hughes had a union shop that I was told would go out on strike if I so much as picked up a soldering iron. I began my electronics career as a hobbyist, was formally trained up in electronics after enlisting in the Air Force, spent eleven years working as a research electronics technician after my four-year Air Force enlistment, and attended college part-time while working full-time for the University of Dayton Research Institute (UDRI) to obtain a Bachelor of Electrical Engineering degree. I am a "hands on" type of engineer and would not be happy sitting at a desk, throwing schematics over the transom for someone else to build. Besides that, my "desk" would have been in a house trailer parked outside the main plant. Not an improvement, IMO, over my "ivory tower" job at UDRI.
I am not an amateur astronomer, but I appreciate the Big Sky country of the Western United States. I remember stopping one night around midnight in the northern pan-handle of Texas, probably to relieve myself, and noticing the only light for miles in any direction was a lone farm light on the distant horizon. The view of the stars (no Moon that night) was fantastic! I would love to live close to Tucson, near Kitt Peak Observatory, just so I could walk outside and see the Milky Way Galaxy at night. The "seeing" is terrible here in Venice FL, but at least I don't have to shovel snow anymore.
I "inherited" a beginners model Celestron telescope from my deceased brother a few years after his death. but until recently I had no use for it. Now I want to use it as a laser transmitter, sending an amplitude-modulated laser beam toward the Moon and receiving the signal back here on Earth. This is called "moon bounce" or Earth-Moon-Earth (EME) communication. It has been practiced by licensed amateur radio operators since the 1950s using VHF, UHF, and microwave frequencies, but AFAIK no one except professional astronomers with big telescopes and powerful lasers have done EME at optical frequencies. I plan to use a 532nm laser diode (Nichia NDG7H75) and my Celestron Nexstar 102GT Computerized Telescope (sold only at COSTCO) to create a collimated, 100mm diameter, amplitude-modulated, laser beam to the Moon.
A separate home-made "telescope" will be used for receiving the reflected signal: A 300mm diameter, acrylic, Fresnel lens whose sole purpose is to gather photons and project them onto the photo-cathode of a 1P21 photo-multiplier tube (PMT). The PMT is housed in a thermally insulated, light-tight, die-cast, aluminum Bud box called the Quantum Detector Module (QDM). Inside there is a narrow band-pass optical wavelength filter, located behind the entrance window, that filters out all wavelengths except for a narrow band centered on the 532nm emissions from the laser diode. This filter is needed to suppress background radiation from the Moon that is not caused by the transmitter laser. Without it, the PMT would not be able to "see" individual photons because its photo-cathode would be saturated with ambient moonlight.
The end of the box opposite the entrance window has the "cold" side of a Peltier heat pump attached. A heat sink attached to the "warm" side of the Peltier device dissipates the heat removed from the box. The exterior of the box is thermally insulated with a two-piece Styrofoam "blanket" held in place with rubber bands. This is to allow maintenance of the interior of the box, which may also contain a small 12 volt DC fan to circuilate the chilled air around the PMT. This entire contraption is attached to the Fresnel lens' telescope tube, which is "slaved" with an electronic servomechanism to the motion of the laser transmitter telescope.
Hams (licensed amateur radio operators) are allowed to use any frequency greater than 275 GHz and a maximum power output of 1500 watts, but I plan on initially using only one watt, or less, of optical power at 532nm wavelength, which is green light. The "transmit frequency" of green light is way greater than 275 GHz. The number of photons per second in a one watt beam of light is huge, but most of those photons never make it back to Earth. Instead the light is scattered or absorbed by the Moon's regolith, which reflects only about twelve percent of the light illuminating its surface. So, one watt gets sent to the Moon, but only about 120 milliwatts gets sent back toward Earth. That would be a lot if the reflection were specular and in the direction of the transmitter (as it would be with corner-cube retro-reflectors), but instead the reflection has a Lambertian (cosine) spatial intensity distribution.
The peak of this spatial distribution IS back toward the laser transmitter, but the radiation expands as if from a point source, because of the vast distance between the Earth and the Moon. Most of the reflected laser signal shoots right past Earth and is lost to outer space. For this reason, only a few photons per second will arrive back on Earth. And of this number, only a smaller few will enter the receiver aperture to be counted as PMT pulses. This is probably more than you wanted to know, but if interested I invite you to join the public-facing discussion group at https://optical-eme.groups.io
I realize that at age 71+ you might not be interested in my optical-eme project. You probably don't even have an amateur radio license. But you could become a "short wave listener" and try to receive my transmissions reflected from the Moon. Or not. I am nowhere near ready to send photons racing toward the Moon, but when I do it will be posted on the groups.io site for all to see. In the meantime, enjoy your life in sunny (most of the time) central eastern Arizona.
I have visited Arizona several times since I have been alive. I've been alive for 81+ years. The latest visit was for a job interview with Hughes in Tucson after I graduated college in 1978. IIRC, they were making television-guided Maverick missiles back then. But I didn't take their job offer, because Hughes had a union shop that I was told would go out on strike if I so much as picked up a soldering iron. I began my electronics career as a hobbyist, was formally trained up in electronics after enlisting in the Air Force, spent eleven years working as a research electronics technician after my four-year Air Force enlistment, and attended college part-time while working full-time for the University of Dayton Research Institute (UDRI) to obtain a Bachelor of Electrical Engineering degree. I am a "hands on" type of engineer and would not be happy sitting at a desk, throwing schematics over the transom for someone else to build. Besides that, my "desk" would have been in a house trailer parked outside the main plant. Not an improvement, IMO, over my "ivory tower" job at UDRI.
I am not an amateur astronomer, but I appreciate the Big Sky country of the Western United States. I remember stopping one night around midnight in the northern pan-handle of Texas, probably to relieve myself, and noticing the only light for miles in any direction was a lone farm light on the distant horizon. The view of the stars (no Moon that night) was fantastic! I would love to live close to Tucson, near Kitt Peak Observatory, just so I could walk outside and see the Milky Way Galaxy at night. The "seeing" is terrible here in Venice FL, but at least I don't have to shovel snow anymore.
I "inherited" a beginners model Celestron telescope from my deceased brother a few years after his death. but until recently I had no use for it. Now I want to use it as a laser transmitter, sending an amplitude-modulated laser beam toward the Moon and receiving the signal back here on Earth. This is called "moon bounce" or Earth-Moon-Earth (EME) communication. It has been practiced by licensed amateur radio operators since the 1950s using VHF, UHF, and microwave frequencies, but AFAIK no one except professional astronomers with big telescopes and powerful lasers have done EME at optical frequencies. I plan to use a 532nm laser diode (Nichia NDG7H75) and my Celestron Nexstar 102GT Computerized Telescope (sold only at COSTCO) to create a collimated, 100mm diameter, amplitude-modulated, laser beam to the Moon.
A separate home-made "telescope" will be used for receiving the reflected signal: A 300mm diameter, acrylic, Fresnel lens whose sole purpose is to gather photons and project them onto the photo-cathode of a 1P21 photo-multiplier tube (PMT). The PMT is housed in a thermally insulated, light-tight, die-cast, aluminum Bud box called the Quantum Detector Module (QDM). Inside there is a narrow band-pass optical wavelength filter, located behind the entrance window, that filters out all wavelengths except for a narrow band centered on the 532nm emissions from the laser diode. This filter is needed to suppress background radiation from the Moon that is not caused by the transmitter laser. Without it, the PMT would not be able to "see" individual photons because its photo-cathode would be saturated with ambient moonlight.
The end of the box opposite the entrance window has the "cold" side of a Peltier heat pump attached. A heat sink attached to the "warm" side of the Peltier device dissipates the heat removed from the box. The exterior of the box is thermally insulated with a two-piece Styrofoam "blanket" held in place with rubber bands. This is to allow maintenance of the interior of the box, which may also contain a small 12 volt DC fan to circuilate the chilled air around the PMT. This entire contraption is attached to the Fresnel lens' telescope tube, which is "slaved" with an electronic servomechanism to the motion of the laser transmitter telescope.
Hams (licensed amateur radio operators) are allowed to use any frequency greater than 275 GHz and a maximum power output of 1500 watts, but I plan on initially using only one watt, or less, of optical power at 532nm wavelength, which is green light. The "transmit frequency" of green light is way greater than 275 GHz. The number of photons per second in a one watt beam of light is huge, but most of those photons never make it back to Earth. Instead the light is scattered or absorbed by the Moon's regolith, which reflects only about twelve percent of the light illuminating its surface. So, one watt gets sent to the Moon, but only about 120 milliwatts gets sent back toward Earth. That would be a lot if the reflection were specular and in the direction of the transmitter (as it would be with corner-cube retro-reflectors), but instead the reflection has a Lambertian (cosine) spatial intensity distribution.
The peak of this spatial distribution IS back toward the laser transmitter, but the radiation expands as if from a point source, because of the vast distance between the Earth and the Moon. Most of the reflected laser signal shoots right past Earth and is lost to outer space. For this reason, only a few photons per second will arrive back on Earth. And of this number, only a smaller few will enter the receiver aperture to be counted as PMT pulses. This is probably more than you wanted to know, but if interested I invite you to join the public-facing discussion group at https://optical-eme.groups.io
I realize that at age 71+ you might not be interested in my optical-eme project. You probably don't even have an amateur radio license. But you could become a "short wave listener" and try to receive my transmissions reflected from the Moon. Or not. I am nowhere near ready to send photons racing toward the Moon, but when I do it will be posted on the groups.io site for all to see. In the meantime, enjoy your life in sunny (most of the time) central eastern Arizona.
Delta Prime
- Jul 29, 2020
- 2,987
- Joined
- Jul 29, 2020
- Messages
- 2,987
Have you ever got stuck outside with your electronics during an Haboob?
I have been an amateur astronomer since about age 12. I lived in central Iowa. My dad bought a used silo dome, cut out a section from top to bottom and attached castors to a plywood ring fitted to the bottom of the dome. The unit was placed on a circular foundation of maybe 3 feet high and had a wood frame floor. A hole was cut in the center of the floor where a 3" round steel tube was driven into the ground on which the 6" Edmond Scientific reflector telescope was mounted. Complete with clock drive and various eyepieces that I think went to a magnification factor of 500. We seldom used the highest magnifier lens because of earth vibrations from distant trains, wind shaking trees, etc. Around my area here in AZ, the amateur clubs convinced some of the area towns to cut back lighting so as to lessen light pollution. I tagged along for about a year with them. Drove to the top of Maui when I vacationed there for a couple weeks. I forget the name of that observatory but it was odd looking down upon the cloud tops. I just recently bought a pair of HAM walkie talkies but cannot figure how to use them. As a young person, a friend of mine was interested in HAM radio and we started a fund which would eventually be spent on radio equipment. Each week we would both put a few bucks in the fund which was managed by Wally, owner of The Starlight Lounge. A little bar and grill in my hometown. Wally was a family friend of my young friend. As we entered junior high, I became distracted by other interests and the ham equipment never got purchased. Prior to that time, my oldest brother and I would search a vintage "upright" radio that the folks bought at a yard sale. It had a HAM band section as well as AM. We would search for Morse code. At the time, the huge slide by plates of the tuning capacitor (I forget the actual name) where a complete mystery to me. At the age of 28 and somewhat discouraged by the rewards of hard labor, home construction, concrete work and other body racking jobs, I enrolled in an 2 year associates program at NIT in West Des Moines, Iowa. Somewhat with the idea of learning radio. The course did touch on radio but its main focus was microprocessor applications, which is much of a part of radio communications today. I was kinda looking for antenna design, propagation of different frequencies, attributes of am, fm, digital broadcast, etc. The nuts and bolts of the whole radio shmeer. Didn't find it. Anyway, with an AAS degree from an accredited school, it was time to get back to work on a new career. So I left my job at a Pester Derby convenience store and was immediately hired by Keystone Electric Manufacturing. It's all academic from that point. The night skies are indeed something to see here.
- Joined
- Jun 21, 2012
- Messages
- 4,968
Sounds like you have enjoyed a very interesting life. It's not looking very good in Des Moines IA if you can believe Fox News Channel. Oh, wait! I bet you don't even watch television. But how is it you have an Internet connection? Did you go with Startlink? I am thinking about getting a Starlink terminal if my wife and I decide to buy or rent some sort of recreation vehicle to tour the USA. That may well depend on whether her cancer stays in remission or not. It's "wait and see" for now.
When I was much younger, my father tried to teach me celestial navigation. He had been a bombardier on B-17s during WWII but stayed in the newly-formed Air Force after the war. He eventually was assigned the "observer" position on B-47 strategic bombers. The B-47 was our interim strategic bomber until the B-52s replaced it. The observer sat in a nose-well below the other two crew members, who sat in tandem much like in two-man fighter aircraft with a pilot in the front seat and an electronic warfare officer in the rear seat. The two "top" crew members sat on ejection seats that ejected upward (presumably after the canopy was ejected), but Dad's ejection seat ejected downward. Good if ejecting at altitude, not so good if close to the ground. Anyway, Dad had a sophisticated, wind-up, sextant that he used to "shoot the stars" with the sextant measuring the angle of the star above the local horizon. There was a ball-and-disk integrator built into the sextant that required Dad to keep a "bubble" centered on the star for about three minutes while the declination was measured. Of course you had to know what star you were "shooting" before the sextant could be of any use. And Dad needed a current ephemeris and an accurate clock to plot a position on a map. IIRC, he would shoot three stars and obtain three intersecting lines on the map. The three lines intersected in a small triangular area on the map. The position he was in when the three stars were plotted on the map was somewhere within that small triangle. I never did understand how those three lines were plotted, but when the sextant was used at altitude the B-47's position was constantly changing. Apparantly the size of the triangle of uncertainty depended on how far the B-47 flew from the first star shooting to the third one.
I was too young to understand any of this celestial navigation stuff. Worse than that though: I was severely near-sighted. I could barely see individual stars as more than blurry points of light. So, I never did learn the constellations and the names of the stars associated with them. I can usually locate Ursa Major (the Big Dipper) and the North Start, but I don't know their names. Celestial navigators use their knowledge of the constellations to identify the star they are "shooting," but because I could barely see them, I never could. Now that I am trying to "shoot the Moon" with a visible laser, I suppose it behooves me to learn to identify constellations on the celestial sphere. Unlike my father, I will probably never see the Southern Cross or the stars visible in the southern hemisphere.
What kind of Ham radio transceivers did you acquire? I have a Baofeng handy-talky (HT) that covers way more than the authorized ham bands, but I only use it for two meters. I also have a pair of Midland GMRS (General Mobile Radio Service) transceivers, which at low power levels, do not require an FCC license. I think you can use higher power for more range if you buy a license (no test required) from the FCC. I got these at a truck stop when we moved from Dayton OH to Venice FL. The range is limited, but they are handy for communications around the house and yard between me and my wife. They beat the hell out of CB (breaker, breaker, one nine, this is the WonderWizard calling...) for on-the-road communication with a fellow traveler in another vehicle. At one time I had several CB mobile radios, but with the advent of cellular telephone service CB appears to be only for lonely 18-wheel trucker rigs.
When I was much younger, my father tried to teach me celestial navigation. He had been a bombardier on B-17s during WWII but stayed in the newly-formed Air Force after the war. He eventually was assigned the "observer" position on B-47 strategic bombers. The B-47 was our interim strategic bomber until the B-52s replaced it. The observer sat in a nose-well below the other two crew members, who sat in tandem much like in two-man fighter aircraft with a pilot in the front seat and an electronic warfare officer in the rear seat. The two "top" crew members sat on ejection seats that ejected upward (presumably after the canopy was ejected), but Dad's ejection seat ejected downward. Good if ejecting at altitude, not so good if close to the ground. Anyway, Dad had a sophisticated, wind-up, sextant that he used to "shoot the stars" with the sextant measuring the angle of the star above the local horizon. There was a ball-and-disk integrator built into the sextant that required Dad to keep a "bubble" centered on the star for about three minutes while the declination was measured. Of course you had to know what star you were "shooting" before the sextant could be of any use. And Dad needed a current ephemeris and an accurate clock to plot a position on a map. IIRC, he would shoot three stars and obtain three intersecting lines on the map. The three lines intersected in a small triangular area on the map. The position he was in when the three stars were plotted on the map was somewhere within that small triangle. I never did understand how those three lines were plotted, but when the sextant was used at altitude the B-47's position was constantly changing. Apparantly the size of the triangle of uncertainty depended on how far the B-47 flew from the first star shooting to the third one.
I was too young to understand any of this celestial navigation stuff. Worse than that though: I was severely near-sighted. I could barely see individual stars as more than blurry points of light. So, I never did learn the constellations and the names of the stars associated with them. I can usually locate Ursa Major (the Big Dipper) and the North Start, but I don't know their names. Celestial navigators use their knowledge of the constellations to identify the star they are "shooting," but because I could barely see them, I never could. Now that I am trying to "shoot the Moon" with a visible laser, I suppose it behooves me to learn to identify constellations on the celestial sphere. Unlike my father, I will probably never see the Southern Cross or the stars visible in the southern hemisphere.
What kind of Ham radio transceivers did you acquire? I have a Baofeng handy-talky (HT) that covers way more than the authorized ham bands, but I only use it for two meters. I also have a pair of Midland GMRS (General Mobile Radio Service) transceivers, which at low power levels, do not require an FCC license. I think you can use higher power for more range if you buy a license (no test required) from the FCC. I got these at a truck stop when we moved from Dayton OH to Venice FL. The range is limited, but they are handy for communications around the house and yard between me and my wife. They beat the hell out of CB (breaker, breaker, one nine, this is the WonderWizard calling...) for on-the-road communication with a fellow traveler in another vehicle. At one time I had several CB mobile radios, but with the advent of cellular telephone service CB appears to be only for lonely 18-wheel trucker rigs.
- Joined
- Jun 21, 2012
- Messages
- 4,968
No. I do all my electronics inside of an air-conditioned, hypoallergenic filtered work space. If my electronics needs to survive during a Haboob dust storm, it would be hermetically sealed and some means provided to remove internal heat generated by its operation. The telescopes are not exposed unless they are in active use, and then not during a Haboob or any other form of storm.
Why do you ask, oh physics master? Do you think that I need to build an "observatory" like @HANKMARS did? Not going to happpen at my age with the limited funds I have available, unless someone starts a Go Fund Me begging operation...
Delta Prime
- Jul 29, 2020
- 2,987
- Joined
- Jul 29, 2020
- Messages
- 2,987
Forgive me, I was addressing the thread starter; given his region in Arizona and his previous questions which I responded to concerning powering electronics off grid.
I am not a physics master, but I am hoping to make a contribution by continuing my education at this fine institution where I also work, but I must admit academia seems far more attractive. Than being a practicing physicist…
I do not understand the question fully. Haboobs are seldom seen Those are the huge dirt storms, right?
I could use some tutorage in the field of radio communications. I'll get the model and make of my walkies and send along with a photo, I would appreciate any clues you may be able to give me. Regarding your father's work, and others from that era, I just stand in awe at what was accomplished with the technology of their day. Weather by design or happenstance, I feel that the average American intellect is spiralling downwards, but then again, I live a secluded life in the backwaters of society right now so my cross-section of a sample is mighty slim. My father was born in 1918. In his school days, Latin was still an everyday course of study. I think it was not even offered in my school days. Dad asked my older brother about Latin classes at college to which my brother replied that there were none. Dad then asked, "well, how do you know where words come from then?" "I don't," was my brother's reply. Good communication is so vitally important, IMO. During my time doing technical work, I had to extrapolate the true meaning of virtual chicken scratches and half statements, such were documents supplied by engineering. It was frustrating at the time but one has to push on through and perserveer if one wishes to remain employed. Funny how it takes a lifetime to acquire knowledge and tempermant to deal calmly and successfully with life's little ordeals. Perhaps we should start a conversation in the conversation compartment since we have veered off topic considerably.
- Joined
- Jun 21, 2012
- Messages
- 4,968
Not sure how the new owners of this website feel about posts wandering off topic. This happened all the time when this forum was called Electronics Point, back in June 2012 when I joined. I have only one conversation active right now, so it seems reasonable to start another one with you. I'll let you initiate that.
You didn't answer my question of how it is that you have Internet access, miles away from civilization, or at least commercial electrical power.
What kind of bandwidth do you have? Can you do Zoom or Google Meeting conversations requiring broadband Internet connectivity? I have (not recently) exchanged messages with other users here who still had only "land line" Internet access, sometimes apparently with very slow acoustic modems running 110 baud. That made it very difficult to have a true "conversation" without the patience of a saint. Turnaround time could take days or weeks.
I did notice, and responded, when @Delta Prime chimed in on this thread. Moving our discussion to the Conversations part of this app would allow us to exclude comments from other members of Electronics Lab. It would be your choice of who to allow "in" to the private conversations if you start a new conversation there. I generally avoid private conversations because the purpose of this forum is to freely exchange ideas and perhaps offer solutions to problems. Private conversations easily move into the realm of echo chambers unless carefully avoided. I post my opinions on X, but that's just a larger echo chamber. I don't have many followers on X, but I follow back almost anyone who follows me, for whatever that is worth. For whatever reason, a lot of the folks who request a direct message (DM) with me are women. I seldom respond to those "female" DM requests as I have been happily married for more than twenty-five years to my second wife.
If you want to exchange comments or DM me on X, please look up my name on the FCC website associated with my amateur radio license, AC8NS. I use my full name as my username on X. If you choose to use a different username than HANKMARS, let me know with a DM that mentions that.
You didn't answer my question of how it is that you have Internet access, miles away from civilization, or at least commercial electrical power.
What kind of bandwidth do you have? Can you do Zoom or Google Meeting conversations requiring broadband Internet connectivity? I have (not recently) exchanged messages with other users here who still had only "land line" Internet access, sometimes apparently with very slow acoustic modems running 110 baud. That made it very difficult to have a true "conversation" without the patience of a saint. Turnaround time could take days or weeks.
I did notice, and responded, when @Delta Prime chimed in on this thread. Moving our discussion to the Conversations part of this app would allow us to exclude comments from other members of Electronics Lab. It would be your choice of who to allow "in" to the private conversations if you start a new conversation there. I generally avoid private conversations because the purpose of this forum is to freely exchange ideas and perhaps offer solutions to problems. Private conversations easily move into the realm of echo chambers unless carefully avoided. I post my opinions on X, but that's just a larger echo chamber. I don't have many followers on X, but I follow back almost anyone who follows me, for whatever that is worth. For whatever reason, a lot of the folks who request a direct message (DM) with me are women. I seldom respond to those "female" DM requests as I have been happily married for more than twenty-five years to my second wife.
If you want to exchange comments or DM me on X, please look up my name on the FCC website associated with my amateur radio license, AC8NS. I use my full name as my username on X. If you choose to use a different username than HANKMARS, let me know with a DM that mentions that.
