DIYbanter - View Single Post - APC Smart UPS SU3000RM Overloaded when started from batteries

Phil Hobbs

On 07/03/18 03:06, wrote:
I have a SU3000 that works from AC power and inverter will start if you remove power, but it wont start up from battery power.

Originally I didn't have batteries to test it so I used a couple of small power supplies in series to produce the 48V it requires to operate. They were only a 1 amp supply or so but it worked.

Now with nothing plugged in, it draws a lot more amperage on startup from battery and instantly goes to overload..
When using the power supplies I originally used to start it up, it draws too much power from them and they shut down, and it doesn't get a chance to do anything but beep once and the lights blink once.

So obviously the unit is using more power than before and not just a software issue.

I am thinking it may have a bad mosfet. Cant remove them until I get my hot air station. Does this seem like a reasonable place to start troubleshooting? Maybe the mosfets were damaged from using the power supply to power the unit?

Thanks in advance for any advice

You could put an ohmmeter from drain to source and from gate to source,
and see if any of them are shorted or have blown gates.

If your power supplies overshoot badly after a large load transient, you
could have had a transient overvoltage. Doesn't take much energy to
blow a gate.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com