Help me modify a Battery Backup

I just moved into an area that seems to have frequent and prolonged power outages. I bought a cheap APC's Back-UPS ES 500 series battery backup, but im disappointed with the battery life. This thing has a 12v lead acid battery. i've been thinking that i could attach a much larger 12v Car battery(or more in parallel) instead of the, "stock" one. This might allow prolonged usage during outages.

I have a few worries. I hear that lead-acid batteries can explode when overcharged. When the power comes back on, could the UPS overcharge the battery circut? Would it take forever to recharge the larger battiery(ies), because the UPS recharger was designed for a smaller battery? Does the UPS have circuitry to prevent modding like this?

Has anyone else done anything like this?

i doubt its anything more than a trickle charger in it. those produce so little power that if the battery is full it burn up the excess in the form of heat.
myself i have a inverter that i can hook up in my truck to get power.
it sounds like a great idea but make sure you do an full load extended test run and checking the heat of the inverter unit itself. some are only for a few minutes and cant handle a constant load.

The device doesnt get hot(even warm) after 10 min of operation (with about 250w draw). It takes about an hour to recharge the stock battery. If i had to guess, it probably wouldn't try to take the full ampers the car batteries have to offer(which i hope to see in the form of better battery life). For safty reasons, i would keep this device outside.

This PSU has powered a 15w light bulb for 1+ hours, so it "can" run for long times, but a 200+w load may be different.

Im just disappointed with the high end UPSs offered. Yeah, they have cool features, but their batteries just don’t have as much power as an array of car batteries.

Someone else asked this exact question a week or two ago. Someone posted that they'd done this sort of thing. Maybe you can find the thread and PM the expert. Sorry for the lack of substance.

im sure it would be fine but may not be capable of charging a battery that large.
what size battery is the stock one?

speaking as a mechanical engineer who has done this:

it will work, as long as the voltages are the same

as far as the charging circuit, it must be internally limited anyway or the battery would pull 20+amps after en extended runtime, so all is fine

I'll post some images and results if i get a chance to build it.

I posted in the other thread about the charger cicuit maybe not handling it but upon further investigation it will handle it but it will take forever to recharge. BTW use a deepcycle battery not a standard car battery. After a deep discharge you may consider boosting the charge on the batterie(s) by using a standard 10 amp charger. This is depending on the frequency and length of the outages. Last saturday we had a planned outage of 10 min at 2AM but it lasted 4+ hours....

E_tron said:

This thing has a 12v lead acid battery.

Click to expand...

I think if you look it has a Gel acid. I think these batteries used indoors are required to be gell cells beause lead acid batteries will off gass hydrogen....a potential of boom

BTW keep the batteries outdoors.

a deep cycle lead acid battery is what you're looking for in order to run your system for the longest in this situation.

Well here is a follow up on my project. I went out and bought two everstart deep cycle trolling motor batteries and hooked them up in parallel. No problems, the backup took to the batteries like they where its own, but as some of you suggested... the UPS's built in charger only provides like .5 amps of charge power, so charging is painfully slow. I've been getting great battery life. It ran through the 8 hour outage during Tropical Storm Matthew and the numerous smaller outages that followed. To aid recovery time manually, i went to a garage sale and bought a 6amp battery charger. I have the batteries and the charger sitting in a rubber tub outside about 10 feet away from the house with ventilation holes to prevent hydrogen build up. The UPS is inside the house and DC power is delivered via about 20 feet of speaker wire. The little buzzer inside the UPS got annoying, so i shorted the circuit to prevent it from buzzing with a little copper wire bridge.

Bottom Line:
about $140 torched
One APC battery backup warranty voided
and a lot of battery life

I don’t know if this was economical, but it was fun. I would post pictures, but my digital camera is... dead.

uh

do not short that buzzer, disconenct it

though chances are the driving circuits are already fried.

also, I hope that speaker wire is good for 25a or so.

other than that, good job

i actually tried to remove the buzzer, but it is so close to the pcb that i cant even work harden it off. I took the copper wire short off a few days after the long run and the buzzer came back to life, so apparently i'm not causing major damage to the chip that governs it. The buzzy is only intermittent (like two short beeps every minute), not constant.