One for the electronics guys....

[Heliospherez]

I have a battery pack for a RC device that might be handy to charge from USB on my laptop - it's just an idea I have had....


Now assuming.....
My USB is 5V / 500mA - same as everyone elses.
The mains transformer charger that came with the battery pack is rated at 12V / 400mA
The battery pack is 12V.

Would I do any damage to the battery pack by charging off a USB cable - would it just take longer to charge to full capacity or would the battery pack get to 5V and not ever charge to full ? (I have wired correctly / polarity checked the USB cable)
Can I just leave the USB to trickle charge the 12V pack ?

 

[Jonny69]

It's not the current, you have to charge a 12V battery on a 12V source. 5V won't do it.

You won't damage the battery, technically, but a 5V source will only charge it to 5V. What will probably happen is the battery will try and discharge into the 5V supply because the voltage is higher and it'll damage the USB line.

If you want to charge it on the 5V you'll need a switched mode circuit in there to bump it up to 12V

 

[Heliospherez]

Cheers Jonny - I knew it wouldn't be that simple.