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# understanding the basics, whatâs more important volts or amps when charging a battery from a generator? Answered

I am getting confused my high school electronics is being tested, i passed by the way ;) . I want to make my own electricity from solar and wind to charge up some batteries. What voltage must my system produce to charge two 12 volt batteries? In my wind generator I envisaged using a stepper motor, with this it is possible to use a voltage doubler circuit. The article I read on reuk.co.uk stated that if you doubled the volts you halved the amps.

So to get to the point, which is more important volts or amps? And why?. (please)
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## 3 Replies

NachoMahma (author)2010-05-03

.  Neither is more important. When charging a battery you want your voltage to be above the open circuit voltage but not so high as to cause too much current flow.
.  Automotive batteries are ~12.6 V when fully charged, so somewhere around 13.5-14.5 V will be your max charging voltage. Search for something like "automotive battery charging" for more info.

seandogue (author)2010-05-04

+1 for the NachoMahma

For fast charge you'll need up to 16VDC for a 12V lead acid pack, although for car batteries, the current draw may hamper that ability, especially if they're deep discharge batteries, which can draw substantial current during the fast and bulk charge regimes.

orksecurity (author)2010-05-03

To charge the batteries to 12 volts, you need a 12 volt source. To avoid damaging the batteries, you need to limit the maximum current applied to them; see their specifications for information about that.

V=IR. At a constant resistance, if you double the volts you halve the amps, by definition. The batteries are not a constant resistance.