UPS output voltage

Car "starter" batteries are a terrible choice. They're designed to deliver a *lot* of current for a small time. As a tradeoff, they aren't designed to deliver a lot of energy. If you "deep cycle" a car battery it will kill it. Once is enough. What you want is a "deep cycle" battery, or the sort of battery used in marine applications (i.e. trolling motors).

Concerned about H2 gas.

What about a deep cycle AGM battery?

Andy

Voltage of disconnected battery is 13.57 V.

Andy

His unit uses a single 12 volt SLA battery.

I wonder if the larger battery would overtax the float charge circuit? It will take a lot longer time to bring a car battery back to full charge. Not only that but the longer run time may overheat the inverter.

As long as you don't overcharge it, H2 shouldn't be much of a problem. However, your unit is suspect, so it could be a problem.

A good choice. That's probably what's in the unit now.

Re: BackUPS:

APC's SmartUPS series is dramatically better than their BackUPSes. I have about five of them--the IBM-badged ones go for cheap on eBay. When you get one, recycle the battery and replace it with a Panasonic or Powersonic brand.

Cheers

Phil Hobbs

Weight would be a factor. Also. if it overcharged small SLA batteries, it can boil off a large battery and even make it explode.

Yes. Most UPS designs are driven by two 12V batteries in series.

The biggest problem with a (most) UPS is the fact that they are very poor at designing in good battery charge management protocols into the charging circuitry. And since some form of lead acid battery is typically used, they usually have a degraded lifespan due to being "topped off" too often or too much or both.

KRW makes a correct statement.

"small time" has a broad definition.

Ever see one melt an open end wrench?

True statement number two. You are on a roll.

Any sort of lead acid replacement will suffer the same end result failure mode from the UPS overcharging it. A deep cycle is the right battery, but I would also choose a different chemistry as well.

LiFePo is far lighter in weight. and deep cycles just fine.

The fact is, this should NOT effect the UPS output voltage. After all, they are designed to operate throughout the discharge cycle of said back up batteries, so a proper designed UPS will deliver full output voltage from an input voltage range of about 30 volts all the way down to 10 volts! It should not waiver one iota.

In fact, from a PARD POV, it should run the best right at its low limit input voltage. The current at those lower voltages will be higher. So the batteries discharge even faster as they go.

PS (actually, the PARD remark works the other way around. When testing AC driven DC power supplies, the ripple voltage and noise (PARD) read on the output is typically lowest at "low line" on the input) At least on our designs it worked that way.)

A good proof of this is the fact that the batteries are two in series and there is no way to insure a balanced charge across them without a smart charge management system on each battery.

Seconds rather than hours.

Does DimBulb understand the word "energy"?

He's stuck with the charger he has.

If he had a UPS that used LiFePo4, then he should use LiFePo4 cells, sure. But that's not the case.

They are a drop-in replacement.

The batteries are a series of cells anyway. As long as the lead-acid cells are used together (so age together), they'll be fine. It's a little more complicated with some chemistries but LA batteries are just fine in series.

I looked at LiFePo prices. Rather expensive.

And if I recall correctly, they have fewer charge cycles.

Andy

I am going with a deep cycle AGM battery. 18 Ah $34

It has excellent ratings with 70% giving it a 5 star rating.

I'll report back my experience every 4 months or so.

I will also only have my computer,router and monitor protected and leave my printers on the unprotected side.

Andy

I connected a data cable from UPS to my computer and now I have a battery monitor applet.

It says I have 31 mins to empty.

wet batteries like car batteries tend to emit sulphuric acid mist, this quickly degrades things containing cellulose, so keep it away from paper, linen, cotton fabric etc. explosive gas (Brown's gas) is another risk, a ventilated outdoor location is probably best.

some do, I've seens small 650VA units with a single battery, and 1U units that used 8 6V 9AH batteries also floor standing units with