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NiHaoMike 02-25-18 10:20 PM

V/Hz scaling is just a bit of code. You'll be a lot more limited in how much you can apply, but going down to 200/100V and 50Hz should work fine. (Just ask the Japanese!) Even then, a 20% power usage reduction for motor loads and 30% for resistive loads is pretty substantial.

You'll do even better if you used 3 phase for the compressors driven with off the shelf VFDs.

randen 03-03-18 04:24 PM

Working Toward Off Grid
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I've had some contact with this bright young fellow in the video. He had converted a van to electric using an industrial motor and you guessed it a VFD (Variable Frequency Drive). Although it was an experiment limited to just some trips around the neighborhood he had won and was driving on electrons. This was some 8 yrs. ago

Saturday March 3 and I'm at it in the shop. Its getting exciting now. The inverter has been running although some little gremlins are present. The enclosure is being fitted with components. The fan cooled heat-sink was savaged from and old VFD and exposed on the exterior of the box. I have some rather large el-caps that will be pre-charged when inverter is initially turned on. Followed by full power with the closing of a high current relay.
I have the Gigavac (rated 400amps!!!) battery disconnect ready to be mounted in the front panel as well as a nice digital meter.

The processor can be seen just below the IGBT boards. The ribbon cables will be neatened once the board is mounted.

I've used a Vicor DC-DC to provide low voltage 400-12Volt to operate the processor and relay

Spring is coming along with sunny weather. Who wouldn't like to be running a household on solar.???


NiHaoMike 03-04-18 12:15 AM

Are you using classical PWM or some sort of Delta Sigma? The latter would require a FPGA but those are quite cheap! A Spartan 6 LX16 board goes for $20 nowadays and would be plenty to implement inverter logic with. Delta Sigma, if implemented correctly, boosts efficiency especially with IGBTs. From my understanding, it uses less transitions during particularly low/high parts of the cycle. (I tried to get similar results by programming a dsPIC to period skip during extreme duty cycles but it's just not the same.)

You can really do some cool tricks in power electronics using custom logic. One that I'm working on is a bidirectional DC/DC converter - easy to implement in theory but good luck trying to find an off the shelf ASIC that supports that kind of control!

randen 06-03-18 02:50 PM

Anyone working to off grid
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Here it is June 03 2018 and I'm claiming success on the 20 kw inverter. We had accomplished a load test and with a scope saw a pure sine wave 60 htz with no artifact of noise YAY!!

The batteries fully charged covered a load of 15 amps without breaking a sweat while our inverter delivered a 21 amp @240 volt rock solid. Our resistive test load was only capable of the 5kw. but I claim victory

Over the next short while the inverter will be mounted and conduit run with cabling that will carry the desired currents. A transfer switch will be placed between the grid and our power production so a seamless transition can be made from off grid and IF only If we require a back-up from the grid. But as the system is configured should have us through summer and fall totally off grid.

We have a 25 kw transformer filtering and splitting the 240 volt to 120 volt.

The solar panels will provide max 11.5 kws of charge and operational power and batteries will do their work while at night air-conditioning, lighting, cooking TV and my sons video gaming. It will be a bit of a change as during peak hours for grid power was a bad time for anything power hungry will now be the time to plug in, clothes drying, baking in the oven and charging the vehicles.

As the off grid excitement grows so may my system. Back of the napkin design states that additional battery power and possibly solar panels may be necessary but we are off to a good start. We heat with Geothermal and that is the holy grail to power all for all seasons and it seams its possible!!!

I will keep everyone updated as we power through summer OFF GRID as this looks to be a non issue.


gasstingy 06-08-18 09:34 AM


Originally Posted by randen (Post 59225)
Here it is June 03 2018 and I'm claiming success on the 20 kw inverter.
As the off grid excitement grows so may my system. Back of the napkin design states that additional battery power and possibly solar panels may be necessary but we are off to a good start.
I will keep everyone updated as we power through summer OFF GRID as this looks to be a non issue. Randen

I took some liberty shortening the parts I wanted to comment on.

Congradulations on the success of your work. :thumbup: I admit I am envious of your electrical skills. My greatest claim to electrician fame is that I've never owned a Volt Ohm Meter I didn't short out in less than three times using it.

Almost as soon as we brought our new Chevy bolt home my wife asked, "So, when will we add more solar?" I wanted to tell her, "Patience, Grasshopper" but chose against that. After considering my options, I told her it would be as soon as I could save the money to put in ~ 5kW more in panels and a Tesla Powerwall 2.0. Of course, life happens, so it could be Powerwall 4.0 by then. I like extra solar as much as I like "over-insulating" something, aka there's never too much.

I look forward to hearinig about your successes on your system.

randen 06-12-18 10:42 AM


A little set back, our inverter quit. It seems our driver circuit had been driven too hard overheated and failed. We think we have the culprit, It appears the higher voltages 390V to board level 15V is not being controlled tightly enough, so much for the boot-strap topology. We have the corrective components on the way. More conditioning and buffering for those little drivers. We are using the IGBTs similar to the Tesla Inverter drive. The IGBTs that I had used in the truck are the big brick type (expensive) were the TO247 case style are quite inexpensive <$20. It will be very nice to get everything stabilized and toward more robust.

Head meet wall. Persistence !!!!

We'll get there.


randen 06-18-18 07:57 AM

We have success.!! Our test performed upto 40 amps charging the car combined with our test dump load. A consistent load of 30 amps without breaking a sweat

A more permanent placement of the inverter is the next order of business as well as proper wiring.

It felt really awesome to charge the car on electrons that were collected a few days before


randen 06-18-18 08:11 PM

I have begun to operate off grid. Today at about 4:00 as a thundershowers rolled through I connected the inverter to the fuse Panel disconnected the grid and operated the house until
8:00. GSHP air conditioning made a pot of tea and played with cooktop
The batteries were already low from our testing last night but still operated extremely well

Tomorrow we expect some sunshine so charging the pack and charging the car plus running the air conditioning

Looking good so far


randen 06-22-18 07:23 AM

A little got ya. As the inverter was driving al the house appliances and the solar panels were cranking out 16 amps @375 v the inverter faulted as an overvoltage. It’s a slight oscillation on the voltage competitor. Errrr. Oh well a cap and resistor hopefully will settle that and give a more steady signal to the cpu


randen 06-29-18 02:15 PM

We had installed some signal conditioning but still the reported voltages are way off at the higher end. We are thinking the I/C was damaged during one of our other failures

Tonight we will replace that IC and try that

I had been installing the system a little more permanently with proper conduit and larger gauge wire

But yesterday while I was cutting and fitting the inverter was running the house complete with air conditioning refrigerator wine cooler as well as all the phantom loads not breaking a sweat
The solar panels produced more than enough power and actually almost topped up the pack

Very soon we should be able to leave the switch in the off grid position


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