I have a 4kVA UPS(uninteruptable power supply) I found it at a ham radio swap meet and paid 50 dollars for it. It has a digital readout of AC volts in/out, %Load, battery voltage, runtime. I used it for about 6 months and now it needs new gel batterys. There is 2 12 volt 32amp hour gel batteries hooked up in series for 24 volts and I don't want to spend over 100 dollars replacing them. I hooked 2 deep cycle lead acid marine batteries(about 2 years old) and the UPS seems to work fine, I unpluged the AC cord and at 40% load it ran for almost an hour before the 5 min alarm sounded at 22.5 volts so I pluged it back in. The charging circuit shows full charge at 27.4 volts. My question is can I keep using lead acid batteries to replace the gel batteries? Will it destroy the batteries or kill the UPS?

 

Should work OK as long as your lead acid batts are designed for deep discharge duty. Battery lifetime tends to have as much to do with how many deep charge cycles have gone through them then just age.

$50 for for a 4KW UPS was quite the deal, what do you power from it?

 

Depends on the charging circuit, if it's a sophisticated enough charging circuit the cell resistance is going to play a role in it's charge cycle. Replacing it with lead acid cells drastically changes that internal resistance, perhaps to the point where either the charger will over/under change the cells, or the charger itself will burn out prematurely, with unknown effects (dead short maybe?) Lots of flying hot acid and burnt metal and plastic everywhere... Be sure you know how the charging circuit is going to act to the new cells.

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It should be Ok as long as the batteries are mounted outside the UPS. The gassing from regular lead acid batteries will corrode the UPS. Also, wet cells generally are not as forgiving about deep discharges as Gel Cells are.

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I have the lead acid batteries mounted externally vented box. I don't plan to drain the batteries unless my power goes out. I power everthing in my computer room with the UPS. I have my computer/router/monitor/cable box/tivo/big screen tv/dvd player/clock radio/one lamp. I only get about 1 power outage a month on adverage but I get 2-3 power spikes a day(I see the other lamp in the room blink on and off and hear the ups kick on for a min). I finally got the power company to replace the step down transformer on my pole so I hope the power spike problem is fixed.

 

I have substituted a lead acid battery for the gel cells in one UPS and I find that it doesn't keep it fully charged. I check them about monthly and top them off using an external charger.

 

Don't they make surge strips that have voltage regulation to prevent spikes lik e that? They're not meant for hold up power, but they can protect from transients and couple cycle brownouts using capacitors instead of batteries. Putting one of those before the UPS might help things.

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