How do I reduce amps??

[jrm850]

I've charged ecig batteries with my bench power supply and it works ok, but I can't just leave it unwatched. I set it to 4.2v and adjust the current to around .8C. The current will start dropping when the cells reach roughly 4.2v. I pull it off when the current drops to about .05C.
Interestingly enough, Volt 808 auto batteries appear to have some current limiting built in because I can't get it to pull more than about .4c in stage 1.
Be careful if you can't monitor current.

 

[Str8V8ping]

Any 350ma current regulator should work . Maybe a LED current regulator .

 

[slimest]

I want to reduce my 12v 5 amp source to 12v 300ma to charge a 11.1v Li-Po

Never do it if you do not understand exactly how Li-Ion chargers work. If you just get a current limit, it's not enough for charge, the process is much more complicated. Better spend a few dollars and buy reliable charger. Believe me, it's better and safer.

 

[CraigHB]

Li-Ion chargers are a current limited voltage source, not just a regulated current source. Without both voltage and current regulation you can damage the battery.

If you're trying to build yourself a 3S Li-Ion charger, you should use one of the myriad of available charger controller chips for that purpose. You can stack three single Li-Ion controllers with 2 virtual grounds to build a small 3S balancing charger. In that case, you can use your 12V 5A power source to charge a 3S battery safely. Though, you'd actually need a source around 14V to fully charge 3 cells in series. Each charger controller has about 200mV overhead. You'd need a minimum of 13.2V from top to bottom at the controllers themselves, that is, negelecting voltage drops due to wiring and connectors.

It would be possible to simply use a current regulator on the 12V source, but you'd only take each cell to 4V. Li-Ions are very sensitive to terminal charging voltage. It's not linear. Charging a cell to 4V would only charge it up about half way.