Nothing to do with Arduino this time I know but as there are a few power experts around on this forum I though Id pick your brains.
Dont know if the rest of the world knows, but its been a bit cold and white here in the UK and the wife has requested that I speed up the charging of her heated gloves.
They take 3 aaa 1000mah batteries in a little pack, one in each glove.
The pack is connected to the glove by a 3.5mm jack plug.
The wife wants it as easy as possible and doesnt want to have to keep unscrewing the packs to take the batteries out.
Can anyone recommend a circuit for charging 3 aaa batteries insitu?
I realise its probably not the best practice to charge them in series.
But she would like to just be able to plug it into the battery pack rather than taking the batteries out and putting them in a multi cell charger when she gets in and they will be charged when she needs them next.
daveg360
I dont know at the moment. Ill have to charge up some batteries and check.
I thought the battery info would be enough providing 3000mah at 4.5 volts.
Although thinking about it a rechargeable aaa only puts out 1.3v fully charged.
So that would be 3000mah at 3.9v
I need to keep the battery packs the same size as they fit a pocket in the gloves and have the on/off button built in.
She wouldnt be happy with bits of wire hanging out and taped up battery packs.
Remember Im doing this for the wife.Wives are a lot fussier.
jabber
Interesting, sounds a bit too good to be true, doesnt it?
Id need two one for each glove.
No, 1000mAh at 3.9V: the voltages add when the batteries are in series, but the current capacity doesn't.
You're right that it's not the best practice to charge them in series: it'll probably shorten their lives a little bit. But probably not dramatically, and AAA NiMH batteries are fairly cheap.
The rule of thumb is that NiMH cells can be left charging at .1C indefinitely without serious harm: once they're charged, they can safely dissipate the excess energy as heat. That'll be less true if they're in a battery case, but you can avoid leaving them plugged in while you're on vacation. :
My suggestion: wire up a couple of LM317s as 100mA constant-current sources, with jacks that match the gloves. Then you can charge them overnight. If you want to get fancier, you could wire up a couple of comparators with LEDs that turn on when the voltage is either below, or at, "full charge" (depending on whether you want them to indicate "charging" or "charged").
Yeah, it'll shorten the batteries' life a little bit, but consider it a price of convenience.
What is " .1C ".
The only thing I can think of is degrees centigrade?
What voltage should I set the adjustable voltage regulator?
Is it just slightly higher than the cell voltage?
Ill check the data sheet for the constant currant method.
Oops, sorry: in battery-charging discussions, "C" refers to the battery's "capacity" in Amp-hours or mAH.
So, "charging at .1C" means that you'd feed a 1000mAH battery 100mA.
When you read about charging batteries, you'll often see statements like "We charge at 2.5C until the battery reaches blah-blah Volts, then back down to .1C", or "Don't try to charge this type at more than 3C because it would damage the cells".
...or if you really wanted to get fancy and make it as easy as possible for your wife, you could look into hacking a Powermat system to the gloves rechargeable batteries. This way she can just throw the gloves on top of the mat without having to take anything apart or plug anything in.
