A year ago I got a SU3000RM and didn't have any batteries to test it with. So I had hooked it up to 2 small wall wart SMPS that were in series with eachother. (30V + 18V for 48v total) just to test to see if the unit would power up before purchasing batteries. It cold started doing this the first couple of times but it seems to have fried something. Possible a voltage spike from one of the SMPS wall warts. I didn't put any load on the unit at the time of testing with the wall warts because they were only rated for an amp or two.
Now the unit functions normally if you plug it in first, power it up and the power fails. (I now have batteries to test it properly) but won't do a cold start. Attempting to do a cold start causes the overload light to turn on an and the alarm beeps.
Any Idea where to start looking for problems? Bad MOVs?(are there any in the output circuit?) Bad diodes? Faulty FET?
It seems to be drawing more current on start up than it should but my DMM isn't quick enough to give a reliable reading.
It is a SU3000RM J3U with a 640-0734K PCB in it.Thanks for any advice
I'd start by querying the status registers to narrow down what the UPS thinks the fault is. Towards the bottom of this page gives you the bit definitions, and looking at the protocol will tell you how to get that data from the UPS : https://networkupstools.org/protocols/apcsmart.html
Start with registers 1, 2 & 3.
It'd also be interesting to check both the input and output voltage measurements and the power measurement to make sure they are about where they should be (Check voltages while plugged in and on mains, and the load with a known load of some kind).
None of the units I've seen have MOVs on the UPS side of the input isolation relay and that should be open for a cold start.
Thank you for your reply. Sorry for the delay in writing back. Things have suddenly become really busy at work and I haven't had much free time to play around with projects. I will definitely get a serial cable built and test this out as soon as I can. Hopefully in the next couple of weeks. I will get back to you with the results. Thanks again!
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