Do you have a technical question that doesn't really fit a specific console? Want some general info on electronics, hacking, making cookies, etc? Here's the place to ask! Go nuts.
I bought a Li-ion battery from e-bay very cheaply, for £3.49 delivered! (about $7). Seems fine, just checked with my multimeter. I thought it was worth the gamble at this price!!
The battery is a Keene Electronics battery for Sony camcorder NPF950 7.2v 4650mAh Li-ion.
Its dimensions are 70x38x56mm and it weighs a fair bit, 300g.
I figured it was worth playing with, perhaps for my Nintendo 64 Advance project (if I add a battery pack) or my forthcoming GP2x project.
My question is this: on the terminals, there is a "-" and "+" (duh) on the two opposite ends of the battery (in pic) and a terminal marked "C" - the flat top one.
I don't want to buy a charger just for it as it would cost about 4x the battery cost, so I was wondering, if I was to hook up an adapter I have, for example the PSone adapter (7.5v, 3 amp) and connect the positive from the adapter to the positive on the battery and the negative to the negative, would that recharge it? (if so, how long would it take to do this recharge please and would it be safe?). If I used a 9v adapter, would that be better?? What's the "C" terminal for please?
If this is possible, presumably I could buy any NiMH or Li-ion battery pack from e-bay (if cheap) and recharge them in the same way? Is this right?
Is it safe and would it work??
I would be grateful for any helpful and knowledgeable comments you have to assist please.
If you want cheap, first take apart the battery and look for a protection circuit, and maybe a datasheet and the likes to see what it protects against (over/under voltage, and overcharging, as well as too much current draw).
If it has decent protection (as I imagine a sony battery has), you should be safe simply hooking up a 8V 100mAh power source and leaving it until the protection kicks in.
protection circuits are not designed to help you charge batteries, they are an emergency failsafe. in many cases they cannot be reset and you will brick your pack. If you are really unlucky the battery might explode anyways. Also, I wouldn't recommend taking it apart cause you wont learn much an you just risk breaking it. It is entirely possible to safely charge it without taking it apart.
The 'c' terminal is most likely a one-wire serial data line for reading off of the EEPROM that is part of the protection circuit. Maybe you could also read remaining charge from there, or reset the protection. Its not important though, and in most cases I think you can charge the battery without it.
To properly charge a lithium battery, you should charge it in two stages. The first, constant-current stage will charge the battery at some maximum current, usually around 0.5 - 2 times the capacity of the battery. Yes, that is a very large current. In your case, about 5 or 10 amps. By no means do you actually have to meet that current, its just an upper limit. To achieve these high currents, the voltage will probably have to be set fairly high, perhaps 5 or 6 volts per cell.
As the battery fills with charge, its voltage will begin to increase. When the battery is about 70% full, the charge method should be switched to constant-voltage. The charge voltage should be about 4.2v per cell, but subtract a bit off that (maybe 0.1v) for each additional cell in series, to account for cell imbalance. As the cell's voltage approaches the supply voltage, the current will taper off to zero. Charge is terminated when the current is about 20mA.
This is roughly how a 'smart' charger will charge a battery for you. In practice, its a biatch to do this manually, as you need a pretty fancy power supply, and you have to watch it constantly.
Since the initial c-c stage has an upper limit but no real lower one (it will only cost you in time - usually people want their batteries charged fast), The easiest way to go about charging batteries is to just use c-v the whole time. It is in no way possible to harm your cells in this way, it might just take a little longer (like, 12 hours instead of 2),
In your case, that calls for an ~8.3v power supply. You will definitely need something adjustable.
You cant use a typical transformer type AC adapter, as it is an unregulated power source, and the rated voltage is more of a guideline. the less current you draw from them, the higher the voltage will get. The open circuit voltage of a 2A, 9v adapter could be something like 15v. You could use it for the c-c stage, but as the battery got more full, the current would get lower and the voltage would get higher, and before you know it your face is on fire.
If you dont have one yet, consider getting a small 2A adjustable power supply. If you are cheap, take a non-adjustable one out of a computer and use an adjustable regulator (LM317) to get the voltage you need
