# 10ah lithium polymer battery charger

Thread Starter

#### ross

Joined Jul 30, 2010
46
I'm trying to find out how I can charge up a 7.4v 10ah lithium polymer battery from a 12volt cigarette lighter socket I have found a circuit for a 7.4v 800mah lipo charger! Can I change components on this circuit so it will do 10amps? Or does anyone know of a circuit out there that will do the job better? Any help I can get will be muchly appreciated. P.S. I'm will be using the battery for a metal detector and I want to charge it up out in the bush.

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#### wayneh

Joined Sep 9, 2010
16,512
That circuit requires quite a bit of modification to handle a charging current of 10A, because it now uses the LM317 to directly supply the charging current. That's the limiting factor.

It watches the voltage across R7 and and limits current at 600mA. Changing the value of R7 to, say, 0.1Ω would increase that current limit, but again you are limited by the LM317.

There are plenty of circuits designed to use the LM317 to control much higher currents. I believe the datasheet describes at least one.

Are you sure you want 10A into that battery?

#### Audioguru

Joined Dec 20, 2007
11,249
Li-Po batteries with more than one cell like yours (7.4V is two cells in series) are always charged with a balancer circuit. The balancer makes certain that one cell is not over-charged and the other cell is not under-charged.
Your battery should have 3 or 4 wires to allow balanced charging of each cell separately.
The circuit is more complicated than the one you found.

#### bountyhunter

Joined Sep 7, 2009
2,512
I'm trying to find out how I can charge up a 7.4v 10ah lithium polymer battery from a 12volt cigarette lighter socket I have found a circuit for a 7.4v 800mah lipo charger! Can I change components on this circuit so it will do 10amps? Or does anyone know of a circuit out there that will do the job better? Any help I can get will be muchly appreciated. P.S. I'm will be using the battery for a metal detector and I want to charge it up out in the bush.
Charging Li cells at the c rate is risky. I wouldn't do it, I'd buy a second battery. It is always better to have a smart charger that balances the cells.

#### wirednuts

Joined Nov 13, 2011
20
i third that. do not use that circuit to recharge your bomb. in small batteries, like for model toys, its not much of a worry if it catches on fire because it will be a small blaze and usually you are outside when charging.

a 10ah pack, on the other hand, is a big battery with LOTS of potential risk. if that thing catches fire, you better just get away from it.... and watch your house burn down.

i wouldnt even think about using a 'dumb' charger like you posted... look into smart charging circuits that monitor each cell individually.

Thread Starter

#### ross

Joined Jul 30, 2010
46
That circuit requires quite a bit of modification to handle a charging current of 10A, because it now uses the LM317 to directly supply the charging current. That's the limiting factor.

It watches the voltage across R7 and and limits current at 600mA. Changing the value of R7 to, say, 0.1Ω would increase that current limit, but again you are limited by the LM317.

There are plenty of circuits designed to use the LM317 to control much higher currents. I believe the datasheet describes at least one.

Are you sure you want 10A into that battery?
10% of 10ah = 1amp charging rate. where did you get the idea it needs a 10amp charging rate?

Thread Starter

#### ross

Joined Jul 30, 2010
46
Thanks for the advice everyone,I think I will stick to the tried and true method of SLA battery's.

Thread Starter

#### ross

Joined Jul 30, 2010
46
Edit;Can I change components on this circuit to do 10amp hours. (charging) Sorry I just read my post again (its a poor choice of words) but hey there aren't any spelling mistakes lol

#### Audioguru

Joined Dec 20, 2007
11,249
The Li-Po battery in many RC models charge in less than 1 hour. I have seen many 3300mAh batteries charged at 2C (6.6A) but I have never seen a 10Ah Li-Po battery.

New 6th-generation ThunderPower Li-po batteries have a max charge rate of 12C.

#### wayneh

Joined Sep 9, 2010
16,512
Edit;Can I change components on this circuit to do 10amp hours.
Sure, set it to 500mA and leave it connected for 20 hours.

Thread Starter

#### ross

Joined Jul 30, 2010
46
The Li-Po battery in many RC models charge in less than 1 hour. I have seen many 3300mAh batteries charged at 2C (6.6A) but I have never seen a 10Ah Li-Po battery.

New 6th-generation ThunderPower Li-po batteries have a max charge rate of 12C.
I was thinking of buying two RC 5000mah li-po battery's and putting them in parallel to make 10ah? But it all seems too complicated to charge them,is there a car charger available or circuit that I can use so that I can charge them from 12v in the field separately then rejoin in parallel ? I don't get any replies to my questions on ebay.