Using a Motorcycle Battery in a UPS

[Tranzfusion]

I've got an old UPS - just some Chinese 750va which contains a single 12V 7 a/h battery.

I live in a rural town in Cambodia, so obtaining a replacement battery is impossible.

I bought a small motorcycle battery which is 12V 5 a/h and sealed. (Valve-Regulated Lead Acid (VRLA)

Are these safe to use in the current UPS?

Power only goes off a few seconds at a time (a few times a week) - and the ups will only power low voltage devices (eg. router) - so actual current draw will be low.

As its a smaller battery (5 a/h vs original 7/ah) - I'm assuming i won't have any issues of the invertor overheating? As if it does run until its flat, it will run flat quicker than the original battery?

Only thing i'm not sure off is the charging - will the current UPS know when the motorcycle battery is fully charged?

I have the battery in there now, and the ups works - and the unit charge light is on - after about 10 minutes i thought i'd stop charging it check online first to make sure its not going to be a problem. And after a bit of research i could only find posts regarding using larger batteries for extended times.

Hope someone here can help!

 

[Red Squirrel]

Yeah should work ok.

If you want a more serious setup look into an inverter-charger instead of a UPS though. Some UPSes may have a built in timer for when it shuts off, and some may not charge the battery properly (too high or low of a voltage). But typically, it should be fine.

The nice thing with using a bigger battery is better run time.

 

[Torn Mind]

The battery will always be 12.6 volts fully charged, assuming it has no "wear" from use such as sulfation or plate damage. Increasing amp-hours is not going to kill any inverter. Plugging in a device with a huge load such as a laser printer will. The batteries inside a UPS are also lead-acid, so they output the voltage.

 

[Tranzfusion]

Thanks guys, went off and bought some more and got 3 failed ups' working with the motorcycle batteries.

Have had them running for a few days now, and all seems ok - they have survived quite a few blackouts already

 

[Torn Mind]

Going with a deep cycle battery with more amp hours can allow the battery backup to last even longer, and they can handle being discharged to lower levels better due to their thicker plates.

 

[Mark R]

In general, deep cycle batteries can be used in place of standby batteries.

However, deep cycle batteries tend to have lower Ah capacity and higher cost, due to construction differences. Engine start batteries are slightly different again and while OK and not the best available choice if deep discharge is anticipated.

Of course, the above doesn't take into account cost and availability. If engine start batteries are available at a much lower price, they may be a preferable option.

 

[Red Squirrel]

Yeah be sure you get deep cycle and not a starting battery. Look for a AH rating. If it just has a CCA rating, it's probably not the best bettery. Some batteries are more of a hybrid, like marine batteries, those are ok too.

Sealed AGM or gel cells are good too but you're going to be paying 3-4 times the cost.

Keep in mind they do put out hydrogen but it's not really a huge amount. Just avoid sparks near the battery and make sure it's well vented.

This is my setup:



It's fully vented and there's an exhaust fan in the back aimed at a hydrogen sensor. If I start picking up a huge amount of hydrogen it could mean something is wrong and gives me time to go check. There's two fuses as well in case of thermal runaway or other short situation.

 

[Mushkins]

It's cool you got it working!

A coworker was helping me move a UPS the other day and was shocked at how such a small box could be so heavy. He was floored when I explained to him that this $800 box is essentially just a couple car batteries in a fancy metal case 😛

 

[Tranzfusion]

The sealed VRLA motorcycle batteries were $10 so I can't really complain.

We only need the UPS for very short (< 1 min) blackouts - and its just to keep routers connected (we work on laptops - so no issues there) - so the motorcycle battery replacement does the job.

Good to know I could re-purpose one with a large marine battery tough - maybe for my xbox 🙂

 

[Talikarini]

The main thing to watch is the UPS ratings compared to whats being drawn from them during the power outage. The small batteries should be fine for routers and modems, but for computers or gaming systems, it would be best to make sure it is rated for 500W (600VA or more), which should work fine for 30 or more minutes with a basic small marine deep cycle battery rated at 300A (or more).