Help! APC 1500 Smart UPS went up in SMOKE!

[BradC]

A lot has already been said but in general for every APC SmartUPS I've looked at :
- The screws holding the MOSFETS in are hex head not torx. You can remove them by removing one row at a time, then passing the allen key through the holes to get to the next row without de-soldering the heatsinks.
- There's no heatsink compound because you want maximum electrical conductivity to the heatsink
- You *may* have damaged the MOSFET driver circuit, but that should use off the shelf parts.
- The rest of the circuitry is usually powered by a small 24V->12V/5V SMPS. You may have damaged that converter, but odds on the downstream stuff has survived.
- The charging circuit uses the MOSFETs as diodes, but also relies on the inductance of the transformers to operate as a boost converter. It's pretty clever.
- You will very likely have smoked the main 24V rail filter cap. These are special, super low impedance electros and if you replace it with something "off the shelf" it's likely it'll die quickly under load.

The voltage divider that measures the battery voltage might have damaged the H-Bridge controller ASIC, but it's pretty high impedance so you might have gotten away with it.

To test it, I'd be applying mains through a dim-bulb tester (maybe a 40W light bulb in series with the input) rather than powering it from the DC side. You could then look at the waveforms on the MOSFETs and associated driver chip with a scope to see if the PWM ASIC has survived. If that's dead then it's scrap.

I had an old SU2200 fail where the MOSFET driver shorted and caused all the high side MOSFETs to release the magic smoke, but that was through-hole with discrete high side drivers and I could rebuild it piece by piece. Yours is a lot newer and uses the integrated MOSFET driver.

There's a schematic around somewhere for the "Grey Wolf", which is slightly older, but the topology is usually the same. See if you can find the schematic for an E1732-E5. It's an early SUA 1500 model, but they don't seem to change much in the actual inverter.

[thekidkevin93]

Thanks everybody for being patient with me and pitching in with advice

[MartinZ]

I have several APC SMT1500 UPSs and use them with large external AGM batteries. I currently have a large 400 amp 240V rectifier to prevent the UPSs from charging the batteries. But, this causes a 0.7V voltage drop. Can anyone tell me how to disable the battery charging circuit? I do have a proper AGM battery charger and maintainer, and a 24V generator.

I also had two previous generations of these 1500's catch fire. The SMT1500 I'm pleased with except the 980W limit, my refrigerator defrost cycle will trip it. What makes these SMT1500's acceptable is running 3 of them off a pair of very large AGM batteries.