Need help with modified computer UPS

I took an old UPS and replaced the original battery (12V, 7Ah sealed acid-lead) with an automotive 12V 66Ah one. I have it powered for a day and a half and the LED on the fascia of the UPS indicates that the battery is still charging.

I measured the current flowing towards the battery and it is a measly 0.5 Amp. Is the battery ever going to fully charge at that rate? Is there something I can do to increase the charging current?

Neat Trick.

I’m fascinated by the possibilities.

It seems that the battery is willing but the UPS is weak. It can handle the computer OR the monitor, but not both of them at the same time.

The good news is that I have another old UPS, exactly the same model as the other one. Can I connect both of them on the same battery, so I can power the computer through the first and the monitor through the second?

Thanks! I’ll post a pic as soon as I find my camera :smack:

I’ve done this for years, actually on my second auto battery, Well scratch that, the 1st time it was a auto battery, what I have now is a deep cycle 95 AH marine battery.

The USP has no problem powering my computer and monitor (21 in CRT). I also have a 1000W/ 3000peak W voltage inverter attached to that battery for running other essentials (including the refridgerator).

I know I ran my computer/monitor way over an hour before starting up the generator, and it could have gone further.

It does take some time (days/weeks?) to fully recharge, but it gets there eventually.

I would not hook up 2 usp’s to a single battery, these things pulse the batteries to produce a modified sign wave, which is not a step wave, there is time at 0 volts along the way, So the battery is being switched from full load to zero load back to full many times per second, 2 ups’s doing this would seem to cause some interference in this pattern.

I would suggest making sure the connections are very good however, and you are using proper gauge wire. Thin wire or bad connections could cause the UPS not to get enough voltage and cut off.

Just to clarify, the inverter is usually off, and just turned on during power failures

I’ve run both of my APC UPSes off of car batteries for six years now. I have to replace the batteries every 12-18 months, so I’m thinking of trying a deep-cycle battery or something fancy like that. Anyway, it does take several days to charge, in my experience.

Now that I think of it I have run my inverter and UPS at the same time, so 2 UPS’s to the same battery might also work. I don’t think the modified sign wave would be a problem like I stated. If anything you may get introuble with the 2 charging at the same time, but I don’t really know.

Are you starting with new batteries, it seems like you should get more then that, unless you are running them very far down? I suggest looking into duel cycle batteries, sort of a combo of deep cycle and the standard one, though a true deep cycle would be better, I have found that duel cycles are about the same $'s as a standard car battery.

Lead acid batteries will eventually fully charge regardless of the rate, unless it is REALLY low.

With a wet plate battery, you’ll need to check the electrolyte level once in a while (once a month would be good) and top them up with distilled water if needed.

I’d have more reservations about this if you had “uprated” to a large sealed battery. Depending on the charging stratagy, it is possible that the charging circuit may not switch from a higher voltage “top up” mode to a slightly lower voltage “float” mode. They do this by noting when the charging current at the higher voltage drops below a certain threshold. That threshold needs to be scaled in proportion to battery capacity. If the battery is MUCH larger than the charger was designed for, then even the self discharge current can exceed the threshold, so the battery never enters the float state.

In a sealed battery, that problem can damage the battery. In a wet plate battery it just causes increased water consumption.

That water consumption by the way, produces hydrogen. Not a lot of it but it might pose a hazard if the battery is in a poorly ventillated location. My SWAG is that farts pose a greator hazard in the average home.

Wow, thanks for the idea. If I can fabricate an enclosure for this i’m going to make one for my car.

I connected the two UPS at the same battery. Now it lasts considerably longer, but still overheats and turns off after about 15 minutes.

I want to install a fan, but I do not want it to run all the time, only when the power is out. How can I do this?