You originally suggested a 1Meg Ohm resistor, I purchased some of those. Should I exchange them for a 10k?
Thanks,
-TheChad
Koford (Slot Car) Bench Power Supply Project
- Thread starter TheChad
- Start date
You originally suggested a 1Meg Ohm resistor, I purchased some of those. Should I exchange them for a 10k?
Thanks,
-TheChad
Your call. 1MΩ is just fine.
I personally would not go less than 10k. I was momentarily on a different train of thought. Sorry if it confused you.
The 10K would just drain it quicker is all, at the expense of more wasted power.
Okay, so I have gotten everything re-installed, except for the rectifier and the new main capacitor...
They were caulked down to the case, which was suggested before as a bad idea..... That said, the heat produced now should be MUCH less and caulking/gluing them down is the only option I really have...
The DC/DC board is installed on stand offs (Like a motherboard) that I drilled/tapped into the case.. Pictures to come.
Anyway, So what is recommended to caulk/glue down the Rectifier and Capacitor?
There are oh, about 10k different typed of caulk.. The Company (Koford) said they use "An Industrial Caulk" which means nothing...
I would really like a product that adheres quickly with out having to wait 24-48 hours to cure.. I've seen everything from Silicone to epoxy to RTV silicone... Epoxy is out because It would be permeate and never be removable. RTV Silicone is rated for high temp's but how much adhesion properties does it have? Then there's Silicone, which has 10k+ different flavors/applications, so which do you choose?
I went to Radio Shack and bought some Silicone Heat Transfer compound, which said it was "adhesive" but it's not, it doesn't even cure/dry, it just stays pasty..
Thanks,
-TheChad
They were caulked down to the case, which was suggested before as a bad idea..... That said, the heat produced now should be MUCH less and caulking/gluing them down is the only option I really have...
The DC/DC board is installed on stand offs (Like a motherboard) that I drilled/tapped into the case.. Pictures to come.
Anyway, So what is recommended to caulk/glue down the Rectifier and Capacitor?
There are oh, about 10k different typed of caulk.. The Company (Koford) said they use "An Industrial Caulk" which means nothing...
I would really like a product that adheres quickly with out having to wait 24-48 hours to cure.. I've seen everything from Silicone to epoxy to RTV silicone... Epoxy is out because It would be permeate and never be removable. RTV Silicone is rated for high temp's but how much adhesion properties does it have? Then there's Silicone, which has 10k+ different flavors/applications, so which do you choose?
I went to Radio Shack and bought some Silicone Heat Transfer compound, which said it was "adhesive" but it's not, it doesn't even cure/dry, it just stays pasty..
Thanks,
-TheChad
I use a hot glue gun for that sort of application - it's fairly quick drying. An alternative might be silicone bathroom sealer, but there is a faint smell of acetic acid when it is curing and I'm not sure whether the fumes would affect the components.
Well, I tried silicone, It didn't seem to want to hold. I also just tried hot glue in which it didn't want to hold either.... I don't know if my wife's small craft hot glue gun maybe didn't get hot enough? but I wonder too if the components wouldn't get too got and actually re-melt the glue...
-TheChad
-TheChad
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- Jan 21, 2010
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This is what you place between a component and a keatsink before you bolt the device to the heatsink. It's not adhesive but it is the correct stuff to use in this case. You use a very thin smear.
Can you post photos of what you're trying to stick into place. It might give us a better idea of what you're trying to do. In general "glue" is not the right answer for a permanent arrangement with electronics.
I need to adhere the Capacitor, it's a PCB mount, so it needs to be adhered to the bottom of the case and the wires are soldered to the top. I also need to adhere the Rectifier... So it's 1" x 1" metal. to the Metal power supply case..
-TheChad
@Chad
If the glue can be squeezed out of the glue gun, it is hot enough. Did you leave it long enough to harden properly?
Were you using the ‘bathroom sealant’ type of silicon rubber? Again, it needs time to cure.
@Steve
Chad said he wanted to hold a large electrolytic and a rectifier in place, and he had to use some type of ‘caulk’. My experience with both these adhesives is that they are well able to hold quite heavy items in place.
Hot glue is a plastic – it should not be a problem holding the case of an electrolytic in place.
For the rectifier, Chad is using a 12V transformer with a buck converter to get 4V at 1.3V, so the rectifier will dissipate only about 0.6W. I don’t know whether it has some form of heat sinking, but if hot glue isn’t up to the task, silicon rubber certainly is.
If the glue can be squeezed out of the glue gun, it is hot enough. Did you leave it long enough to harden properly?
Were you using the ‘bathroom sealant’ type of silicon rubber? Again, it needs time to cure.
@Steve
Chad said he wanted to hold a large electrolytic and a rectifier in place, and he had to use some type of ‘caulk’. My experience with both these adhesives is that they are well able to hold quite heavy items in place.
Hot glue is a plastic – it should not be a problem holding the case of an electrolytic in place.
For the rectifier, Chad is using a 12V transformer with a buck converter to get 4V at 1.3V, so the rectifier will dissipate only about 0.6W. I don’t know whether it has some form of heat sinking, but if hot glue isn’t up to the task, silicon rubber certainly is.
Yes, I used a bathroom type sealant, An Indoor/Outdoor silicone caulk... I gave it well over 24 hours to dry and while it was dryish, it was still soft and uncured... The hot glue, was hard, but the components pulled right up with little effort..
When Koford is manufacturing these power supplies, I can't believe they would use an adhesive that took 2-3 days to dry... I have to imagine they are being mass produced so the adhesive would need to dry in seconds or minutes.... They said it was an "Industrial Caulk" I went to the local industrial suppliers in town, and all the caulk they have was the same as the caulk Lowe's has.
Epoxy would work fine, but then It will NEVER come off, should these components need replacing, I would need to be able to remove them. I have spent more money on adhesives at this point then the entire rest of the project!
-TheChad
Okay, I connected the 1MΩ 1/2-watt resistor between the + & - terminals on the capacitor and found there was little to no difference what so ever in how long it took for the capacitor to drain the voltage off.. I also tried a 20k 1/4-watt resistor, with the same results...
It takes about ~30 seconds for the capacitor to drain it's running voltage of ~19.6v off. The results were almost the same if not exactly the same with either of the resistors installed between the terminals...
-TheChad
Which capacitor did you do this with? The one after the bridge rectifier, or the one after the new voltage regulator you installed?
The one in front of your voltage regulator, I am not concerned with, as the voltage regulator will most likely cause it to empty by itself. The capacitor on the output is the one I had in mind to connect the resistor to.
The big idea was to prevent the charge from holding for a significant time, but 30 seconds sounds fair to me. If adding these resistors did not decrease the time it takes to discharge, then I'm sure it is safe to say that the capacitor most likely drains through some of the components in the new voltage regulator circuit. If the resulting resistance leaking through the circuit is less than your resistor, it's safe to say the resistor won't change the discharge rate by much.
If the discharge rate is unacceptable, you can use lower value resistors. The downside is that will result in the voltage regulator working a little harder, as the extra current being put out will be V/R
You could also easily burn a smaller value resistor if the resulting current through it is too high. (This is separate from the current you are sending to your motor, but will be part of the total sum the regulator is responsible for)
tl;dr, I think 30sec is just fine and would not worry any further about it unless 30sec bothers you
I was operating under the assumption that the discharge rate would be closer to a few minutes.
Which capacitor did you do this with? The one after the bridge rectifier, or the one after the new voltage regulator you installed?
The one in front of your voltage regulator, I am not concerned with, as the voltage regulator will most likely cause it to empty by itself. The capacitor on the output is the one I had in mind to connect the resistor to.
The big idea was to prevent the charge from holding for a significant time, but 30 seconds sounds fair to me. If adding these resistors did not decrease the time it takes to discharge, then I'm sure it is safe to say that the capacitor most likely drains through some of the components in the new voltage regulator circuit. If the resulting resistance leaking through the circuit is less than your resistor, it's safe to say the resistor won't change the discharge rate by much.
If the discharge rate is unacceptable, you can use lower value resistors. The downside is that will result in the voltage regulator working a little harder, as the extra current being put out will be V/R
You could also easily burn a smaller value resistor if the resulting current through it is too high. (This is separate from the current you are sending to your motor, but will be part of the total sum the regulator is responsible for)
tl;dr, I think 30sec is just fine and would not worry any further about it unless 30sec bothers you
I was operating under the assumption that the discharge rate would be closer to a few minutes.
I have not gotten to the new capacitor on the output side of the voltage regulator..... I'm not even sure If I will need that one yet...
I am talking about the large smoothing capacitor on the output of the bridge rectifier. 30-seconds is acceptable, the only problem that it causes, is that the digital volt/amp meter draw's power form that capacitor, which means after I switch the power supply off, it takes about 25 seconds for the meter to power off... It doesn't affect the function or anything, but I would like to have the meter power off with the power supply or very quickly after...
I tried connecting the 1MΩ 1/2-watt resistor between the capacitor's + side and the digital volt/amp meter power and got a reading of 1.2v, I connected the 20kΩ 1/4-Watt resistor between the capacitor's + side and the digital volt/amp meter power and got a reading of 2.2v.
The meter needs to be @ a minimum of 4v to power on, and can be up to 32v, which is why I connected it to the capacitor off the rectifier, because it sits at ~19.6v.. Which is great, except that it takes about 25 seconds for the meter to power off (For the capacitor to drop down under 4v) after the power being turned off..
Thanks!
-TheChad
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Haha... well, I would not recommend adding lower value resistors to cause that larger cap to drain faster. The whole point of that one is to store a larger amount of energy, which will be difficult to quickly dissipate it. My laptop power supply has an LED that glows for a few seconds after unplugging it.
Let me think on a solution for you...
I think the simple solution is to just put a resistor between the capacitor and the meter power + .. Right?
But what value?
-TheChad
Not ideal, as the resistor would be in-line with the meter, which would vary the voltage to the meter as the meter changes it's current draw (displaying different numbers).
This could throw off the accuracy of the meter, and determining the ideal value capacitor will be pretty difficult.
The only thing I can think of, is to use a pair of transistor (darlington) that is tuned to turn on/off at somewhere in the 15-17V range.
This will cut power from the + power lead of the meter.
Would this be an acceptable solution?
Okay, Adhesive problem solved.. http://www.eclecticproducts.com/_tds/e6000_tds.pdf
It only has a 150-Degree Service temperature. I was hoping for something in the 400-Degree range, The KDPC 2502 Bridge Rectifier (http://www.digchip.com/datasheets/parts/datasheet/129/KBPC2502-pdf.php) has a 150-Degree Celsius max operating temp, which is ~ 302-Degree Fahrenheit or 2x the max service temp of the E6000 adhesive. But I don't think the Bridge Rectifier will get that hot with the new DC/DC Converter..
I will of course test this once I get everything completed.
Waiting for the E6000 adhesive to cure and I will finish connecting everything.
Now I just need to solve the power to the volt/amp meter issue... which we are working on...
-TheChad
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The meter has 5 wires, Power-IN (+/-), and the 3 lead wires for the volt (+/-) / amp (load) meter.. In other words, I believe they are completely separate circuits.... That said, and the wide range of the input power, I don't *THINK* the input power or any variation in it, would have any effect on the accuracy of the meter or it's display.. Of course I could be completely wrong..
However, you did say determining the ideal value resistor would be difficult?
I think if I could get the input voltage to the meter to be @ ~5v via a resistor on the capacitor between the meter, it would be perfect...
-TheChad
