[NTLUG:Discuss] Off topic... Souping up a UPS.

[Mark Bickel]

> From discuss-admin at ntlug.org Wed Nov 28 12:17 CST 2001
> From: "Richard Geoffrion" <ntlug at rain.lewisville.tx.us>
> To: <discuss at ntlug.org>
> Date: Wed, 28 Nov 2001 12:15:36 -0600

Hi Richard,

As one of the hats I wear is "DC power specialist for telecom systems" allow
me to answer your questions. Answers inline below.

Cheers,
Mark.Bickel at ericsson.com

 
> I have an APC BackUPS 450.  it uses two 6volt 12Amp Hour  batteries
> connected in series. (straight lines equal conectors between the 
> positive and negative terminals of each battery)
 
Providing 12 Volts at 12 Ah of capacity.

> Does anyone know for sure what would the consequences would be if I replaced
> the batteries with two 12 volt 7.2Amp Hour batteries BUT I would connect
> them in parallel.  And...is this the proper way to connect them in parallel?

Which would provide 12 Volts at 14.4 Ah of capacity, and yes you should connect
them in parallel to provide the same nominal 12 Volts to the UPS' inverter. 

> How will this affect the recharging mechanism? 

Can't say for sure how this will affect the charging circuit ... Note that the
endpoint voltage for the battery is ~ 1.8 V/cell for typical Valve Regulated
batteries at deep discharge ~ 10.8 Volts for a 12 Volt battery; full charge
is ~ 2.15 V/cell or ~ 13 V for a fully charged battery (idle with no float).
So a larger battery will impose a larger current load on the charging circuit
after a discharge, which may or may not be a problem.

> How does the Amp Hours difference between the two voltage of batteries affect
> runtime?

Doing the math shows a theoretical 20% increase in battery backup capacity.

Note also that this almost assuredly voids the UL listing and any warranty on
the UPS, therefore I cannot recommend this "upgrade". Also if you are using 
APC' PowerChute software for Linux the "% battery capacity" reported would
likely be inaccurate (read low).

/Mark