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

[DaveInCA]

I'd like to heartily thank Andy D for this information because it enabled me to repair a family member's ABB inverter!

Since this is the only place I found relevant information, I also wanted to post a few details in case this might be useful to someone.

Our ABB PVI-3.6-OUTD-S-US-Z-M-A inverter failed on startup with the "Riso Low" error showing 0.00 M-ohm along with the red GFI error LED. It had no prior Riso issues, and removing either of the 2 strings didn't affect it. FWIW I also tested each PV conductor using the cheapest "meghommeter" I could find on Amazon, but that was overkill here. This all points to the inverter and not the panels.

On the main board at the location marked K4 on the PCB is a blue MEDER LI12-BV14072 relay. Searching for this on digikey returns the
Standex-Meder Electronics LI12-1A85 relay, which has the same digikey part number Andy D posted above. (Also currently available from Mouser in the US and Farnell in the UK.) Replacing the original with this part fixed our issue. (Three weeks of normal operation so far, knock wood.)

There was no visible damage on the board or arcing to the insulation sheet. After removal, the coil tested open circuit (I should have tested it before removal). Also the rubbery black sealant material under the relay had melted onto the PCB. I can't say for sure that wasn't due to my desoldering though. (The new relay has two intact blobs of spongy goo.)

Please note: Our ABB PVI-3.6 was manufactured in 2016. I notice from YT videos repairing other issues on older units that the relay at K4 is a buff-colored one. It seems to be an Axicom D3496 with a totally different pinout from the MEDER one. From it's datasheet it should have a coil resistance of 720 ohms. It's an obsolete part whose direct replacement seems to be the Panasonic Electric Works TXD2-12V. I have no experience with those parts, please double check this information before using it. Anyone considering this "Riso Low" repair should at least confirm which relay their board has before ordering a replacement.

Again, thank you Andy D!

[sdold]

That's good news, Dave, hopefully Andy will stop by and see your post. It was nice of him to follow up with what he found.

[azdave]

I'd like to heartily thank Andy D for this information because it enabled me to repair a family member's ABB inverter! Since this is the only place I found relevant information, I also wanted to post a few details in case this might be useful to someone

Yes, thanks for the additional details. As the owner of two 10-year old ABB inverters, that info might be quite useful one day.