two UPSs sharing a battery?

dualblade

Supreme [H]ardness
Joined
Nov 19, 2000
Messages
4,180
i have 2 smartups 1400 and the battery has failed in one of them. i was thinking of replacing the factory battery with sealed gel cell car batteries (so the gas isn't vented into my room) to gain additional capacity. it occurred to me that i might be able to hook the batteries (it takes 2, in series, to make the 24v required) to both the UPSs so they'd benefit from the increased capacity. if i wire the battery array to the 2 UPSs in parallel, it will preserve the voltage, but will this create an issue during charge time? the battery connectors are just + and - connectors so there's no special on-battery circuitry, and i was wondering if it will cause a problem if both UPSs try to charge the battery at once. will this just charge the battery twice as fast, or will it feed power from one UPS into another and damage them. if this will cause damage, does it help if i use two different sets of terminals (the batteries in question have 2+, 2- terminals)?
 

Rubycon

Weaksauce
Joined
May 1, 2006
Messages
125
While it's definitely possible to isolate each UPS' charging circuit from each other with diodes, a lot can go wrong here. Car batteries are not designed to be cycled deeply and if the UPS inverters are run for significant time this will lead to a very short lifespan.

If the batteries are placed in a remote location it's crucial to fuse the wiring at the battery terminal. A pair of SLA batteries with say 100a/h capacity with a cranking rating can develop well over 700 amperes in a short condition. (assuming the wire is of sufficient gauge) If the wire is too small (i.e. 10 AWG) it will heat up very rapidly and start a fire.

The safest way would be to purchase four batteries and use a pair on each UPS. Purchase batteries designed for deep cycle use and you should be OK. If the UPS load is near 100% be careful of inverter overheating conditions as these are not designed for continuous duty and the extended runtime you get with a larger battery system will put additional thermal stress on the inverters.
 

scoob8000

2[H]4U
Joined
May 4, 2002
Messages
2,832
You'd be best suited just replacing the batteries..

Check here: http://www.diversifiedbattery.com/

I've bought a few UPS batteries here, actually just last month I replaced my SUNET1400 batteries with a set of Powerstar batts from them for under $60 including shipping.

They have good customer service, and ship pretty fast.

Just my .02
 

dualblade

Supreme [H]ardness
Joined
Nov 19, 2000
Messages
4,180
While it's definitely possible to isolate each UPS' charging circuit from each other with diodes, a lot can go wrong here. Car batteries are not designed to be cycled deeply and if the UPS inverters are run for significant time this will lead to a very short lifespan.

If the batteries are placed in a remote location it's crucial to fuse the wiring at the battery terminal. A pair of SLA batteries with say 100a/h capacity with a cranking rating can develop well over 700 amperes in a short condition. (assuming the wire is of sufficient gauge) If the wire is too small (i.e. 10 AWG) it will heat up very rapidly and start a fire.

The safest way would be to purchase four batteries and use a pair on each UPS. Purchase batteries designed for deep cycle use and you should be OK. If the UPS load is near 100% be careful of inverter overheating conditions as these are not designed for continuous duty and the extended runtime you get with a larger battery system will put additional thermal stress on the inverters.

it was actually deep cycle car batteries that i had in mind, so that part may not be a problem. i can swing 2, but 4 would be cost and space prohibitive, so if possible i'd rather use the 2 for both ups. the ups that i have is fan cooled so i don't think inverter runtime would be an issue, and i wouldn't be using more than 3/4 capacity on either of them. i know enough about electrical circuits to use fusing and proper gauge wire, but not how to implement diodes to isolate charging circuits. if there's something that you can link me to or advice you can give me on what i need to do, i'd really appreciate it. i'd really like to make this work

also, and this part is not nearly as critical: is it possible to run the batteries in parallel and then step the voltage up from 12v to 24v? i thought it might be a nice feature to be able to remove one of the batteries if need be, or possibly even only purchase one battery. i would think that 1 deep cycle battery would have enough juice to run the 2 ups for quite a while. even if i decide to use 2 batteries, i like the idea of having one be removable, because i could borrow it and attach it to my dc/ac inverter when i want to have a portable projector setup.
 
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