[Tfug] FTGH: APC Back-UPS Pro 650

[johngalt1]

----- Original Message ----- 
From: "Jeremy D Rogers" <>
To: "Tucson Free Unix Group" <tfug at tfug.org>
Sent: Monday, April 23, 2007 10:38 AM
Subject: Re: [Tfug] FTGH: APC Back-UPS Pro 650


>> > On 4/20/07, Sean Warburton <> wrote:
>> >> I'm sorry! I didn't know a series/parallel discussion 
>> >> would ensue...Here
>> >> was
>> >> how I found it: the positive went somewhere into the 
>> >> unit, and the
>> >> negative
>> >> went directly to the positive in the second battery. 
>> >> the negative from
>> >> the
>> >
>> > Umm.. so they were in series, not parallel. So if you 
>> > added more in
>> > series, you would increase the voltage. That doesn't 
>> > sound like a good
>> > idea.
>>
>> Actually, it is a good idea. UPSes are rated by power 
>> rating (VA, or KVA) A
>> formula for power is P=IV, where I is current and V is 
>> voltage. Another
>> formula for power is P=I^2 R
>>
>> As someone else in the thread pointed out, if increase 
>> teh voltage, you
>> lower the current ( I ). Then, I^2R (power) losses are 
>> reduced.  As a
>> result, power loss due to heat (resistance ( R ) in the 
>> wiring, connections
>> and circuitry) will be less for higher voltage in the 
>> battery bank.
>
> Yes, I understand that if the electronics are designed 
> from scratch,
> higher voltage is more efficient and there is great 
> benefit...
>
>> Low end UPSes typically use 24V battery storage. However, 
>> when you look at
>> the 2KVA-3KVA range, they use 48V battery packs to reduce 
>> lossses. In higher
>> capacity UPSes, they design the battery voltage to be 
>> even higher.
>>
>> Another way to look at it is: If your UPS uses a higher 
>> battery voltage, the
>> transformer used to boost the voltage to 115VAC will be 
>> smaller and more
>> efficient. The transformer (or inverter really), will not 
>> have to boost the
>> voltage as much, and pay for that difference with a high 
>> current.
>
> Right, but I'm not talking about the design from scratch.. 
> Sean was
> asking if he could just double the number of batteries 
> connected in
> series to his existing UPS.
I read that incorrectly.


> What I meant is that I wouldn't expect the
> components on the input/battery side that are used in 
> these devices to
> happily work with a sudden doubling or tripling of the 
> input voltage.

Yeah, I can understand how that would be confusing. Of 
course it would not work to add more batteries in series to 
increase the input voltage. Why would you do that? If your 
UPS is designed for 24 volts, that's all it can handle.

Nevertheless, you could for a 24 volt system add parallel 
sets of (2-12 volt batteries in series) to increase the 
runtime. (that is, provided the UPS can handle charging the 
increased load.)