[Tfug] FTGH: APC Back-UPS Pro 650

[Harry McGregor]

The best source for seal lead acid I have found (in town, or mail order,
once you consider shipping cost) has been battery factory on Oracle just
north of Grant.

Good prices, and good PowerSonic batteries.

                                Harry

Adrian wrote:
> On Wednesday 18 April 2007 17:52, Sean Warburton wrote:
> [snip]
>   
>> lead acid batteries. There are two of them (in the backup, they were
>> togeather...in parallel (I think? where the current lasts longer than one
>> battery, as opposed to in series, which yields more current/voltage,
>> right?). 
>>     
>
>
> Not quite... You actually want them in series, not parallel, for 2 important 
> reasons (in most applications that is).
>
> First, P=VI, so power is voltage times current. However, power is lost thru 
> resistance in the battery and connecting wires, given by V=IR. Reducing 
> factors to find power lost: P(loss)=RI^2. So for a given amount of power, if 
> you double the amount of current, you halve voltage, but you quaduple the 
> power lost (as heat). If you double the voltage, you halve the current 
> needed, and hence cut loses to 1/4.
>
> Second, batteries are rated in "Amp hours", the theoretical value based on a 
> discharge rate over a period of 20 hours (SAE standard). So an 8Ah battery 
> theoretically could supply 8amps for 1 hour... in reality, it could supply 
> something closer to 0.4amps for 20 hours. At a high discharge rate, its 
> capacity is drastically reduced.
>
> So by putting batteries in series you both decrease loss to resistance/heating 
> in the batteries and get a greater capacity out of the battery.
>
> Adrian
>
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