[Tfug] FTGH: APC Back-UPS Pro 650

[George Cohn]

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).
>

Most of the UPS's that I've dealt with had serial strings in parallel. 
The 3 KV units had a separate battery box with eight large 12 volt 
batteries in them configured as four pairs of 24 volts (nominal) that 
plugged into the back of the main unit.

UPS's may also have groups of serial and parallel batteries to create a 
certain voltage.

For example, some of the large Nortel PBX's that I've worked on would 
have a string of three 12 volt and one 10 volt battery.  The actual 
terminal voltage was 52 volts.  Then they would place 4 or 5 of these 52 
volt strings in parallel to give you more hours of capacity.  Typically 
these strings were rated at 52 volts at 200 amps or more.

The 52 volts would then be regulated to 48 volts to power the PBX's.

During an A/C power failure, once the battery string terminal voltage 
dropped to 43 volts, the UPS would disconnect from the phone system to 
protect the batteries from being discharged to a point that would damage 
them.

The charger circuit put out 52 volts at up to 300 amps.  That's a little 
more than my DC welder provides.

Once had a tech hook the charger cables up backwards to a battery 
string.  Ever see about 3 inches of number 0 cable disappear in an 
instant?  Also destroys the batteries that quickly, not to mention, 
makes a very loud bang.

George Cohn