advice: marine battery connected to ups

[astroboy]

Hello,

 

I'm at my wit's end. After five years the UPS I had hooked up to a marine battery for power failures died; I believe the battery went bad since I had it hooked up to a trickle charger.

 

What I have now is an APC Back-UPS RS 1500 computer backup power supply, connected to  Deka Marine Master 12V battery. Item 599947 Model 24M7 at Loews, 12 V, 1000 Amp.

 

I removed the old battery and hooked up the wires to the marine battery. I have  a 100W light bulb plugged into the power supply. The APC is plugged into a wall outlet.

 

Here's what happens:

-I turn on the ON button. On Line light button comes on  and the 100W light comes on. A beeper beeps. 

-After a few seconds the 100W bulb goes off, so does the online light. Beeping stops. 

-A few seconds later, the 100W and beep come back on. The online light comes back on. The "onBattery", "Overload", and "Replace Battery" light all flash. This goes on for at least 10 minutes, when I turn the APC off. 

 

With the APC unplugged:

-I turn on the on button. It beeps, one beep about every five seconds. That's it. After about a minute the beep stops. 

 

The battery shows 12.8V, of course, it could be nearly discharged for all I know. 

 

Does anyone have an idea of what the problem is? Could it be that the battery is completely flat and I need to charge it up with a trickle charger? Or, is the APC simply incompatible with the marine battery?

 

Worst case: does anyone know of an electrician or computer shop near Vienna who could hook this thing up for me if I brought it into the shop?

 

Thanks,

 

Mark

[Origami]

This is only a guess.  But I suspect that the marine battery is drawing more current than the RS-1500 is designed for and is interpreting the excessive draw as a defective battery. This is causing the reset. In other words, the APC was not designed to use that battery.

 

The marine battery could also be dead. Normal open circuit voltage is around 13.6 volts, not 12.8.

 

It could be both or just one (the latter is likely).

 

If you have another battery that's known good, try it and see if the APC still acts the same. 

[astroboy]

Hi Tom,

 

It's a brand new battery. It should be 13.2 but I was thinking perhaps the probes on my voltmeter were a bit corroded. I was thinking the battery might be acting as a short, so to speak, but I put it on a trickle charger for an hour and it showed it to be completely charged up, so a short sort of thing shouldn't be a problem. Of course, batteries have an internal resistance, who knows how you'd measure that or even look it up, so that might be causing the upc to freak out.

 

I'll hook it up again, now that it's fully charged. It's a bit frustrating, five years ago I bought a UPS on amazon completely out of the blue and it worked like a champ through a dozen power outages. Now, after I've done the math for the amount of power the necessary pumps will draw I can't get things to work. I bought a UPS online after the old one failed (bad battery) and ozone came out of it immediately. Since it was 'as is' I suspect it was fried beforehand. But this UPS is from a reputable computer geek shop in Falls Church, they claim it's good and I expect they're correct. 

 

I'm thinking of Kirchoff's Law from first year physics: internal resistance of the UPS charger and battery. It could be that the current is going in the wrong direction, so to speak. Too bad there aren't any electrical engineers in the club with an instant answer. 

[Origami]

I'm an EE. Measuring battery resistance is straightforward but requires a load. Your voltmeter is unlikely to be off because of corroded leads. The volt meter has an input resistance of 1-10 megaohms typically. The serial resistance in a lead-acid type battery is going to be small. On the order of fractions of an ohm. This is because they can be called on to deliver a lot of current (hundreds of amps, intermittent) with little drop - maybe a couple of volts. For your 1,000 A battery, that would translate to about 2 milliohms of serial resistance. Because the voltmeter's input resistance is so high, there's very, very little current flowing through the leads. Thus, there's very little drop across the leads. 

 

If you want to check if the leads are the problem, set the meter to measure ohms and touch the two leads together. It'll probably drop to zero or very nearly so. In that case, it's not the leads.

 

On second thought, open circuit (no load) voltage on a lead acid battery can be as low as 12.6 volts. 13.8 on the high end. I've typically seen north of 13 on new batteries.