Old Belkin Rackmount UPS & Possible Points of Failure (battery charging-related)

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I bought this rackmount Belkin UPS new almost 20 years ago. It’s never had any issues until now, and I’ve never even had to replace the batteries.

We recently had a small blackout, and the UPS failed to switch over. Upon first glance, I immediately thought the batteries had finally reached end of life. Testing the batteries showed that they were depleted, but putting them on an external charger has brought them back to full charge. Replacing the batteries allows the UPS to function correctly, except for one problem. I put a multimeter on the leads from the UPS that connect to the batteries, and they do not appear to output anything at all. I’m fairly certain that all UPSes output charging voltage while powered down and plugged in, so I am guessing that I’ve found the problem.

While I’m allowing all charge to drain from the UPS before opening, I thought I’d ask the question here.

Do you think this will be serviceable? Could this be as simple as something like old caps? I’ve never worked on a UPS, but I’ve plenty of experience working on electronics.

I don’t think I would normally bother trying to repair a UPS, but this one in particular has proven to be one of the best that I own … and the rest of the internals appear to function normally.

Any help or suggestions would be greatly appreciated. :slightly_smiling_face:

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It could really be anything because UPSs can be fairly complicated inside. It might be the controller responsible for the charging and switching or a more simple SMD that just gave up because of the age.
I don’t think it’s worth investing time tryng to sort out all the issues on such an old UPS. It can be a blown cap today, tomorrow might blow another one, another day and inductor might go bad and so on.
Unless it’s a very special UPS, maybe a true sine wave with some specific features I’d just pick up a new one and won’t feel bad because 20 years for a device like that are truly a lot.

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The problem was a current-sensing relay that switches the charging on once the circuit detects adequate voltage from the batteries. The resistance that loads the sensing circuit needed to be increased, and now it works flawlessly! :relaxed:

I’m still amazed at the longevity of this UPS. It has outlasted multiple systems as they’ve become obsolete over the years, and it kinda has a special place in my heart. :smiling_face_with_three_hearts:

I’ll periodically check readings of the components to ensure it continues to operate without issue.

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