UPS battery upgrade

[JazzMan]

Any fundamental reasons why I can't use the guts of my
Tripplite 800 UPS with a larger external battery?

JazzMan
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[[email protected]]

Any fundamental reasons why I can't use the guts of my
Tripplite 800 UPS with a larger external battery?

Because the power supply on the powergrid side may not handle the load to
charge that much. A dirt hack would be to have relays to switch batteries in
and out. So that powersupply never is overloaded.

 

[JazzMan]

Because the power supply on the powergrid side may not handle the load to
charge that much. A dirt hack would be to have relays to switch batteries in
and out. So that powersupply never is overloaded.

If the charging circuit is current limited, with voltage
level used to switch from charging to maintenance, wouldn't
the net result be that it takes longer to charge a larger
battery? Also, I assume that the charging cycle generates
less heat than the discharge mode, so presumably the
additional time charging wouldn't present any problems.
Would that be a good assumption?

As far as discharge, I guess the inverter heating is a
function of load vs time, with the system designed to
withstand its maximum output with the stock battery. I
can retrofit a cooling fan quite easily.

The reason I'm considering this is because I already have
a battery, it's about the size of a car battery but it came
out of a whole office UPS system and is designed for UPS
duty, and the battery just kicked the bucket in one of my
Tripplites. I can't afford to buy a new proper size battery,
but can kitbash something together that's ugly but functional.

JazzMan
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"Rats and roaches live by competition under the laws of
supply and demand. It is the privilege of human beings to
live under the laws of justice and mercy." - Wendell Berry
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[Jasen Betts]

Any fundamental reasons why I can't use the guts of my
Tripplite 800 UPS with a larger external battery?

check the owners manual.

some UPSs can't handle running their charging circuit for a
long enough time to charge a large external battery - the
charger overheats and dies which ruins the UPS.
Other UPSs can, typically the big expensive ones.

Bye.
Jasen

 

[Jasen Betts]

If the charging circuit is current limited, with voltage
level used to switch from charging to maintenance, wouldn't
the net result be that it takes longer to charge a larger
battery? Also, I assume that the charging cycle generates
less heat than the discharge mode, so presumably the
additional time charging wouldn't present any problems.
Would that be a good assumption?

No.
lead acid batteries are typically charged with constant voltage chargers, so
the charger will see a larger load. _if_ there is current limiting in there that
part will be working harder and it will get hotter...

the charging circuit uses separate parts from the discharging circuit.
it depends how finely they cut the margins when they designed it...

it may be fine,or putting bigger heatsinks in the charger section may be all
it takes.

As far as discharge, I guess the inverter heating is a
function of load vs time, with the system designed to
withstand its maximum output with the stock battery. I
can retrofit a cooling fan quite easily.

Bye.
Jasen

 

[ehsjr]

No.
lead acid batteries are typically charged with constant voltage chargers, so
the charger will see a larger load. _if_ there is current limiting in there that
part will be working harder and it will get hotter...

P, the power dissipated as heat in the limiting part, is equal
to the current, I, times the voltage across the limiting part.
The equation is P=VI

V is the voltage across the limiter, equal to Vin, the constant
voltage source, minus the battery voltage, which is the voltage
specified to meet the requirements of the UPS, and therefore
the same for the larger battery as for the original battery.
I is the limited current, and is the same for both batteries.
So P=VI will result in the same number for either battery.
The limiting part won't work harder and won't get hotter - but
it will take longer to charge the larger battery, as the
OP presumed.

Ed