Re: Portable batter packs and Solar Charging?

From Wear-Hard Mailing list Archive (WH) Maintained by R. Paul McCarty

On 12-Jul-06, at 12:56 AM, Craig M. Armstrong  wrote:

> On 7/11/06, Andrew Plumb <> wrote:
>> You could charge two 7.2VDC battery packs (one at a time or possibly
>> both in parallel), then connect them in series and fall comfortably
>> within the 10-15VDC range needed for that Xantrex.
>
> Interesting idea.
>
> My first thought is to get two of the before mentioned RC car
> batteries and one of the small Kensington inverters I saw at CompUSA
> yesterday (I think they're even smaller than the Xantrex).
>
> But, what would I need to do for a charging circuit to avoid
> overcharging/damaging the batteries?

If it's solar charging, unless you have great big panels all you're  
going to be doing is trickle-charging the packs, so chances are very  
slim that you'd be doing any damage.

> Would it be possible to simultaneously draw power from the batteries
> and charge them?

Yes and no.  If you're using the packs while you're also charging  
them, all you're really doing is creating a current-divider or  
balancing Norton's equations (see http://en.wikipedia.org/wiki/Norton% 
27s_theorem).  If the circuit hooked up is using less current than  
the charging source can provide then all all that happens is that the  
batteries get charged more slowly.  If the circuit hooked up is using  
more current than the charging source can provide then the battery  
would be making up the difference.

Caveat:  Make sure any device you plug in can handle the charging  
*voltage* which will be greater than the battery voltage.  Probably  
not a big problem for a solar source, but if in doubt you may want to  
at least limit maximum voltage to the device using a Zener diode.

If you're looking for something reasonably generic to supply  
regulated DC from a wide range of DC input voltages, take a look at  
the new PicoPSU ATX power supply:

http://www.logicsupply.com/product_info.php/products_id/596

Enjoy!

Andrew.

>
> Thanks,
>
> --
> Craig
>
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