SUMRY 5kW and 6kW inverters

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Posts: 302
Joined: Tue, 24 Jul 2018, 09:59
Real Name: David Kerr
Location: Sydney

SUMRY 5kW and 6kW inverters

Post by doggy »

There are several of us with these inverters and there are references in a number of more general threads.

So I thought I would start a specif Sumry thread.

These LF inverters are well built. Excellent internal busbars, very heavy due to big toroids, quite efficient (standby 25W and 3kW efficiency 92% on my 5kW unit). They run very cool and the only slight annoyance I have is the constant speed loud fans which are on except for low loads up to about 500W. Soldering on sub boards is of excellent quality. Waveforms are good right up to maximum power. Very brief peak power is around 15kW.

One member imported one from China into France. It still worked despite a problem with one blown MOSFET- due to a fractured gate connection. The company provided a total replacement power module, the member installed it and all was well.

Mine worked fine until recently when I noticed the output voltage had dropped to around 190V. When I bought it, I set it for 239V and it output 236V all the way up to 5kW. I discovered that the LCD display still said 239-240V even though the output was low. I found that when it warmed up, the output increased to about 220V and sometimes even 230V. If I let it cool, the output dropped again.

So, I pulled it apart and traced some of the circuitry on the Control board and attached uP board.

Basically, the problem was two resistors (R423 and R46 on the back of the controller board) which have become very temperature sensitive. When they are cool, they are too low in value. When they heat up, they are higher resistance and almost okay.

I had my inverter set for 239 volts. It is possible that lower settings like 230V might not cause the problem to happen.

They measure the inverter voltage using two 1.5Mohm resistors in series then through a LM324 Operational Amplifier. The maximum voltage rating of good quality 1206 resistors is 200V. They have two in series because the peak voltage can be +-340V (so 170V each). I have replaced them with 4 750K 0805 resistors each with a rating of 150V and the total power rating the same. So now the resistors can withstand 600V rather than 400V. It is even possible that the original resistors had a less than 200V rating and voltage stress caused them to become temperature sensitive. I fitted the new resistors across the existing pads.

There are other series 1.5M resistors to measure the grid input volts. I am using the unit in an offgrid standalone configuration so those resistors are irrelevant for me. However, if I was using a Sumry in a grid-connected scenario, I would replace all the series 1.5M resistors to be safe.

To make the repair, I had to remove the side and top panels, remove all the 240V cabling from the control board, remove about 7 small cables (all the plugs and sockets are sealed with rubbery goo). Then remove the 4 fixing screws. The resistors are on the underside of the control board and they go from the toroid output to the small uP daughter board which has the LM324.

If you want to or need to do this repair, you will need SMD rework equipment. I was able to test the resistors in situ using non-conductive pressure pack cooling solution. Given that BOTH resistors were damaged, I am assuming they are under rated for voltage.

I noticed that the relays for switching inverter input and output are 40amp relays.

Best Regards,
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