ABB Low Riso - internal

[Andy D]

Have a 3kw ABB inverter. Trips out on Low Rsio at the 8 second countdown and consistently at 8 seconds. It is not a panel issue. I manually measured both attached strings to ground on both DC +/- legs and the lowest was 500K ohms. So I went so far as to connect a panel string from the sister 6kw inverter and got the same error, and we know that panel string is good because it works on the 6kw inverter.

Anybody have an idea what the internal fault is? (Please note, I am an EE with a good electronics lab at home. I component repair UPS units and have once replaced bad relays in one of my inverters, a well documented ABB issue.

TIA

[Andy D]

Ok, since nobody answered and I found the problem, I though I would document the fix here.

First these ABB inverters do have a documented problem on the internet for overheating power relays. These are on the flip out panel once the back cover is off. I have replaced these before when one de-soldered a pin after getting too hot.

Well there is another relay on that same board, a small blue rectangle about 3/8in square x 1.25in long. This is a special high isolation voltage reed relay that should not be substituted. I think it must have something to do with checking the Riso. On mine, the coil was open, should be about 680 ohms. Replaced with exact part and all is well.

I found this by comparing the startup sounds of the 6kw sister unit. At 8 seconds where the bad unit failed, the good unit had a weak clink sound. That must be that blue relay closing to measure the Riso.

Both the power relays and the Riso relay are available from www.digikey.com.

Riso Relay: 374-1110-ND

[bcroe]

First these ABB inverters do have a documented problem on the internet for overheating power relays. These are on the flip out panel once the back cover is off. I have replaced these before when one de-soldered a pin after getting too hot.

Are the relays overheating from coil power, or from contact current flow? If coil
power is the issue, you could insert a peak and hold ckt in series with the (DC I
presume) coil. A large cap in parallel with a resistor, the cap would transmit
full power long enough to pull in the relay, then the resistor would cut coil current
quite a bit. 2/3 voltage is less than half power. Bruce Roe