NiMH Battery Pack Charger

[audioguru2]

I am probably going to buy a Mini LST sometime soon, so I want to build a charger before I get it. Here is the battery it uses: http://www.teamlosi.com/Products/Default.aspx?ProdID=LOSB1202. Can someone give me some help on charging batteries like this? Like, where can I find charging info and stuff on this battery?

All battery manufacturers have info on their websites. My favorite is www.energizer.com . At the top of the 1st page select Technical Info, then select Ni-MH Rechargable. You will see a link to their excellent tutorial and a datasheet to their AA cells.

 

[CPW]

I looked all over their website but they don't seem to have any info on the battery.

My favorite is www.energizer.com . At the top of the 1st page select Technical Info, then select Ni-MH Rechargable. You will see a link to their excellent tutorial and a datasheet to their AA cells.

Energizer does have a good site.

 

[audioguru2]

I looked all over their website but they don't seem to have any info on the battery.

The battery that you linked to doesn't have its physical size shown. So we can't know which standard size of Ni-MH cells are used. With a capacity of 1100mA/hrs, the cells could be old AA size because new ones are rated at 2500mA/hrs, or the cells could be AAA size with a very good mA/hr rating for that small size. It is difficult to see if N size cells were used.

 

[CPW]

Well, I'll figure it out when I get it.

Back to the charger's design. I decided I would still rather use peak detecting (lol, I keep changing my mind). Here is my plan for the charger and the program I will write for the microcontroller that monitors the battery:

First, the charger will begin charging at 1c. Second, there will be a loop that keeps checking the increase in voltage over every half a second or so, and when the increase starts to get larger, it will switch to a timed charge, right? Then third, it will use trickle charge to keep the battery fully charged. This is how the three-stage charge routine works right? Will this technique work?

Also, can someone give me an idea of the circuit I will need. I would like it to be as simple as possible. And remember, I am using a microcontroller to control the current and voltage going through the battery.

Thanks everyone.  ;D

 

[audioguru2]

Before charging begins, a voltage measurement should be made that the battery isn't already charged.
During charging, a voltage measurement should be made to determine if the battery has a shorted cell.

It seems that looking at the datasheet of a battery charger IC from Maxim or another semiconductor manufacturer would allow you to re-invent the wheel without leaving anything out.

 

[ante1]

It seems that looking at the datasheet of a battery charger IC from Maxim or another semiconductor manufacturer would allow you to re-invent the wheel without leaving anything out.

Very smartly put AG!  ;D

 

[CPW]

Do you think you could give me a link to one of those datasheets? Thanks.

Before charging begins, a voltage measurement should be made that the battery isn't already charged.
During charging, a voltage measurement should be made to determine if the battery has a shorted cell.

So if at the beginning of the charge the voltage is already 1.2 volts, it should cancel the charging? Also, how would I detect a shorted cell by measuring the voltage?

One more question. Let's say you have a battery that is partially worn down, to about 80% or so. Would the charger still work right or would it detect a sharp voltage increase to late?

Again, thanks everybody for the help.  ;D I will probably be able to make the first charger soon. It won't be perfect, but it will be a start.

 

[audioguru2]

Do you think you could give me a link to one of those datasheets?

Go to www.maxim-ic.com and look at their 48 battery charger ICs.
http://para.maxim-ic.com/cache/en/results/5099.html
You could also see the rechargable battery tutorials at www energizer.com and at other battery manufacturer's websites.

So if at the beginning of the charge the voltage is already 1.2 volts, it should cancel the charging? Also, how would I detect a shorted cell by measuring the voltage?

Without a load, a discharged battery will probably measure 1.2V per cell. So some battery chargers load the battery then measure its voltage.
During charging, if the voltage doesn't increase to what is expected then the battery must have a shorted cell.

Let's say you have a battery that is partially worn down, to about 80% or so. Would the charger still work right or would it detect a sharp voltage increase too late?

It should detect the voltage rise when the battery is fully charged.

Again, thanks everybody for the help.

 

[CPW]

Go to www.maxim-ic.com and look at their 48 battery charger ICs.
http://para.maxim-ic.com/cache/en/results/5099.html
You could also see the rechargable battery tutorials at www energizer.com and at other battery manufacturer's websites.

Thanks. I'll take a look at some of those datasheets.

Without a load, a discharged battery will probably measure 1.2V per cell. So some battery chargers load the battery then measure its voltage.
During charging, if the voltage doesn't increase to what is expected then the battery must have a shorted cell.

It may seem like a stupid question, but how would I put a load on a battery? Would I use a resistor? Also, how long would it take before I could be sure there is a short? If the voltage doesn't increase at all, would I be able to tell right away?

It should detect the voltage rise when the battery is fully charged.

So if the battery is 95% charged, I will still be able to detect a sharper than normal increase, indicating a full charge?

Thanks.  ;D

 

[audioguru2]

how would I put a load on a battery? Would I use a resistor?

Yes.

Also, how long would it take before I could be sure there is a short? If the voltage doesn't increase at all, would I be able to tell right away?

If the vol;tage doesn't rise to the volts that are expected then the battery must have a shorted cell. It shouldn't take much time but you need to experiment to find out exactly how long. Maybe a charger IC has the amount of time.

So if the battery is 95% charged, I will still be able to detect a sharper than normal increase, indicating a full charge?

I think the charger circuit will miss detecting the full charge. That's why the battery charger ICs have many redundant circuits (temperature and pressure etc.) to detect just before a battery cell explodes. hopefully their designers have thought of everything and you are just copying their ideas.

 

[CPW]

Thanks again for your help.

Yes.

Sorry to keep asking questions about something so simple, but what value do think I should use? 1K maybe? Or is that too low?

I think the charger circuit will miss detecting the full charge. That's why the battery charger ICs have many redundant circuits (temperature and pressure etc.) to detect just before a battery cell explodes. hopefully their designers have thought of everything and you are just copying their ideas.

So maybe I could check and see if the battery is almost fully charged, and if it is more than, say, 90% it will just use a trickle charge, or maybe a timed charge, then a trickle charge. That way I don't have to worry about missing the increase in voltage.

Thanks.  ;D

 

[CPW]

If anyone can help me out with the charger design (circuit), I would appreciate it. 

Sorry about the double post, but I would really like to complete this project and needed to get it back on the first page where people will see it.