My install and review of the AIMS Prius 2kW Pure Sine Wave Inverter for Backup Power Generator

If you have an interest, I would be happy to desolder the toroidal isolation transformer to see if it blocks the likely ground fault signal. Send me by 'conversation' a shipping address. You'll need to mount it safely. Perhaps on perf board inside a case, plastic would be OK, with some vents.

Bob Wilson

 

Yes, I was expecting a much higher reading between the DC cables and ground than 2 Megohms. This would be reading the DC cable to the Inverter/Converter input. I have the 2010 Repair Manual in a pdf file and need to see if I can find a Mohm value.

It will be interesting to see the AC signal with the oscope this weekend.

 

I sent you a PM 'conversation'.

 

Got it!

We're letting the seller have first crack at resolving the problem. If we get to a point where it looks like progress has stopped, this becomes a way we can move forward. But no need to preempt the seller.

Bob Wilson

 

I would say yes. I have an email string going between Jack Chen and AIMS tech support. I was waiting for a further answer from AIMS and plan to call tomorrow.

 

I an glad to hear that they have tested a sample inverter which did not have the problem. The first response was that the negative terminal is NOT connected to ground.

I looked at the inverter PCB on mine the best that I could and it was elevated above the case bottom by nylon insulators, albeit too short in my opinion. The solder terminals on the bottom side were awfully close to the case bottom.

If I do not hear anything this morning I am planning to call this afternoon.

 

I agree. It should not be difficult to determine where the connection is being made and repair it.

 

I received an email from AIMS this afternoon asking me to check the Inverter PCB to see if it reads continuity to case ground. If it does I need to send the unit back to them for testing to try to find where the 240VDC is grounding to the case.

I will test it when I get home tonight and let you know.

 

I talked with AIMS when I got home tonight and he recommended looking for any nylon insulators with metal washers instead of nylon washers. He also said that he would loosen the insulator screws one at a time and see if I could possibly find the one that was causing the connection to ground.

There are 12 screws on the bottom of case that go to the insulators that support the inverter PCB. I could only get to about 6 of these from the top of the PCB. I tried loosening one of these at a time and them move them around to see if I could get any type of change on the continuity reading to case ground. Nothing that I did would even make the meter resistance reading wiggle.

I started to loosen some of the screws from the bottom but began to get nervous that I may not be able to get the nylon insulators to line back up to re-insert the screws. I decided it was time to close everything back up and ship it to AIMS and let them dis-assemble and figure out where the PCB was making contact with the case .

He did tell me that there have been 3 people, with this model inverter unit, in the last couple of days that have reported the same connection between the DC negative connection and case ground.

 

I appreciate you leading the bleeding edge ! Yes this is just a minor detail. Once we get the repaired units back from AIMS we should be ready to go. They seem to be easy to work with and genuinely interested in finding and correcting this problem.

I wanted to fix the problem without having to ship it out but it was going to be more of a disassembly than I wanted to get in to. I think once they remove the board from the case the ground connection is going to be easy to find and repair.

I am just glad that I laid the unit on top of the HV battery case the second time and found this problem now rather than in a situation where you needed the emergency power.

 

I wanted to complete all testing today before shipping the inverter unit back to AIMS. I tested the DC cables to ground leakage current after replacing the fuse in the multimeter. The readings were DC+ 0.080 mA DC and 21.0 mA AC. The DC- readings were 0.150 mA DC and 22.0 mA AC.

I left the multimeter on the ammeter reading too long one time waiting for the value to settle out and the car triggered a ground fault alarm again ! The ground fault signal works very well!

I put an oscilloscope on the DC + and - cables to ground and read the ground fault signal. It is a 25 VDC, 2.5 KHz signal riding on top of the DC battery cables. See attached picture.

I connected the inverter with the unit isolated from chassis ground and connected a small table fan. I took a look at the inverter output and I am glad to report that we indeed have a "pure sine wave" output. See attached picture for the waveform.

I checked the DC input voltages with the inverter in operation and the DC - terminal remained at 0V and the DC+ terminal read 220 VDC. The ground to the negative terminal is a continuous ground.

I was concerned about the low megohm reading to ground of the DC battery cables (~2.0 Megohms). I opened the relay compartment to remove the inverter wiring harness and took a reading of just the cables going to the Inverter/Converter module. The Megohm readings improved very little with the wiring harness removed. This made me feel better about leaving the wiring harness connected permanently. I am still a little disappointed that the resistance to ground is not higher than it is.

After the final testing I took the inverter unit to the Mail Room to ship it back to AIMS. When the unit returns with the 220 VDC terminals isolated from ground I should be ready for the first emergency power situation.

 

Awesome! This is the first time I have seen anyone measuring the ground fault signal.

Now the isolation transformer wiring makes sense. With the windings in opposite phase, it would block the 2.5 KHz signal but pass the DC. Hopefully the design has something similar and it is just the fault to ground that is the problem.

Well done!
Bob Wilson

 

Would you ask him if two of these units can be frequency synchronized so we could provide 'whole house' power. Many homes in North America have two, 120 VAC feeds that are 180 degrees out of phase. This is fed to the main breaker box and then fans out to the rest of the house circuits. Having two units, frequency synchronized would allow whole-house power with a single, isolating switch where the utility line comes into the house.

Also ask what sort of output, overload protection is provided? Does the unit electronically limit output current to protect the power electronics and then trip 'offline'? Would it still work if two units were tied together and one tripped?

The reason I ask is we had an inrush, load problem that would trip the overload protection circuit. I had left the house on Prius power and taken the electric bicycle to run an errand. When I came back, there was a slow, oscillation as the overload circuit shutdown; after a pause, powered up; the inrush tripped the overload. I was amused but my wife had a different opinion.

Thanks,
Bob Wilson

 

I would recommend you emailing AIMS at [email protected] to get the answer to your questions. AHetaFan answered the ones on the overload protection but I think AIMS would need to answer your questions concerning the synchronized units and what would happen if one tripped.

The guy that I have talked to is Andrew Frey.