Can You Power a 240 Volt Panel With Two 120 Volt Generators?

0:00 - Intro
1:13 - NEMA 2 Port 5-15P 3 Prong Male to L14-30R 4 Prong Female
1:39 - Power Banks Used
2:02 - Testing The Cord
3:29 - Testing Voltages Across Cord Outlet
4:53 - Power Inlet Box & Interlock Kit
6:48 - Measuring Our Power Demand
7:04 - Power ON!
7:45 - Power Difference Between Power Banks
8:24 - Commence Troubleshoot
10:07 - Supper Time, brb
11:03 - Testing The Breaker
11:50 - :(
12:42 - Turning On Again
13:46 - Power Frequency Mismatch
15:07 - SENSE Energy Monitor Extra Details
15:48 - Inside The Breaker
17:12 - Great Cord Option–With A Caveat
18:50 - SUBSCRIBE!!!

In this video we experiment to see if it's possible to power a 240v panel with two separate 120v sources and what implications that can have on your 240v equipment. Some things didn't go as planned though so we found ourselves in a troubleshooting situation.

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[donbeckham]

The reason you are seeing the voltage changing between the to hot legs is the two inverters are not running at EXACTLY 60 hz....so their phase is not synchronized. What is happening is as the inverters come into phase with each other you will see 0 volts. And the voltage will rise as they go out of phase until they reach 180 degrees our of phase, showing you a peak voltage, approx 240v.

You can tell exactly how many cycles apart they are by timing the how long it takes from peak to peak.

This is how power generation plants sync with the grid before closing their interconnect with the grid. They monitor the voltage between the interconnect and their generator. They adjust the RPM so the cycles are VERY close. Then they wait for the zero crossings match and close the circuit. You can do the same thing with multiple generators connected to your home at the same time.

[Tool-Meister]

The drifting phases assumptions are correct. Some inverters are equipped to automatically synchronize as a cooperating pair, providing center-tap style 120v/240v. I have a pair of Xantrex 2 kw inverters, new in 2007, that are configured so. They work flawlessly, including auto cut-over, auto phase synchronization, with an absolutely perfect waveform. The inverter pair easily power the 120v and 240 loads including the range-top, oven, HVAC (A/C, furnace blower, etc.), at 4 kw continuous, 6 kw peak/surge. Each inverter is also a 100 amp, fully computerized battery charger keeping my bank of golf-cart batteries in tip-top condition. The cascading power sources are mains, solar, and finally propane fueled generator. When the mains fail, the generator, solar panels, or batteries power the inverters which are always carrying the load.

[BZEUG]

I think the two separate battery banks are drifting in and out of phase with each other since their inverters are not electronically synced to each other in any way.

[ozzypozo]

What it impresses me is his wife. She looks so confident about her husband messing with the power while preparing dinner.
Lucky him. Lol

[WagTsX]

on the bright side, it was much better that you discovered that the breaker was faulty outside a real power outage or an emergency, which is why we must periodically test all power systems, especially those that are infrequently used. Cheers from Brazil.

[brucej]

Edited with more info: There are two reasons for the 240 volt problem. Number one as you mentioned the frequencies are probably not exactly the same. However, the second problem is that they are also not going to be in phase with each other.

Even if they were both electronically synced to be exactly the same frequency, it's unlikely they would be in phase with each other. If they WERE synced to be the exact same frequency but NOT synced to be in phase, you would see some STEADY voltage between 0 and 240 depending on the phase difference.

In any case, if you were to look at a graph of the two 120V sine waves above each other WITH ONE INVERTED, the voltage at any moment in time would be the sum of the 2 voltages at that point in time. (Or on the graph, if the sine wave displays are touching each other, it would be the voltage equivalent to the distance between the two points at that moment.)

Another way to think of it is that the voltage on the 240 connection is the sum of the instantaneous voltage of the two sources at any point in time. Please keep in mind that the instantaneous voltage can be positive or negative at any moment in time. (I don't want to complicate things but for those that might try to point this out, yes the meter probably measures RMS, and the graphs would show peak which can go much higher than 240, but the basic principle is there.)

I apologize if anyone else said the same thing but I haven't read all comments. An interesting experiment. I enjoy your channel.

[KillAtron]

I find the thinking process to be real cool. With all the new tech coming out this puts some new ideas in the air. thanks for demonstrating this to all of us.

[ericwilliams]

There’s an easier way to back feed your panel with 120 Volts. disconnect all your 240 Volt loads. Take a regular 120 V extension cord. Cut the end off and install an L 1430 plug and jumper the hots in the plug. when you backfeed your panel you will now have 120volts to both legs . Definitely need to keep the 240 loads off. Love your show……

[Barracuda]

Similar to a 120v generator feeding both panel legs with 240v breakers off. Best to use single breakers protecting eack leg separately. If one leg goes over current, only one leg will drop out.
Great video proof it can be done safely.

[stevesether]

The varying LED is an example of what in physics is called 'beats". You can hear the same thing happen when you have two different tones play that are slightly different frequencies.

With the beat frequency you can measure the difference in frequency between the two sources So if one is 59hz and the other is 60hz, you'd hear a beat frequency of 1hz.

Yours looked like a frequency of about 8-10 seconds, so you'd expect a difference between the two of something like .1hz. For example, one might be 59.8hz and the other is 59.9 hz.

[stevesether]

You should also turn off any multiwire branch circuits, since these circuits share a neutral. (Which of course should have a shared breaker). I'm not really sure what would happen with these circuits since they share a neutral, but at the very least you'd be out of code since they no longer will balance any load between the two phases, since as you observed they aren't.

[billm]

Southwest Missouri here, it was an interesting experiment. Really liked it. As others have mentioned using actual generators would be another interesting scenario thanks for the video

[mmarte]

Benjamin I did the same thing in my house. I have an eco flow and a APC. I connected a transfer switch I split the two hots with to 20 amps plugs. I connected one to the Ecoflow and the other to the APC or 3500 ways generator, if I choose to. Haven’t lost power but am ready if it does. Eco flow is the only one that can turn my boilers pump for oil heat.

[polywog]

Awesome video. I have been thinking along these lines as well. I have 24 250W solar panels. 12 go to one solar charge controller/inverter and 12 go to another. Each of these have their own 10KW battery bank. They each put out 120v. If I connected them together and connected a data cable between them I could configure the inverters to output 240V but the 2 units have to be on a shared battery bank. And my lithium battery banks are identical in configuration (4 12V 200AH) but each bank of 4 batteries are of a different manufacturer. Also I had read a data sheet from one of the manufacturers to not exceed 4 batteries in one bank. So, I have been hesitant to run my two inverters in sync with each other to get the 240v and sidelining a perfectly good bank of 10KW. So this has been on my mind a lot lately. Thanks for the additional thought material!

[inspector]

You nailed it… the frequency between the two separate power sources are not synchronized. One is probably running at something like 58hz. 😂and the other at 63hz. So there sine waves were sometimes in opposition and other times they were in parallel thus cancellation.

[WeatherNut]

What a fun and interesting test. Keep em coming!

Funny call @6:28
Interesting 0 volts on 1 leg. Didnt expect that @9:45

Haha at the rewind flashback @10:26
Cool flashlight and dust blowing! @10:55
Cool tip to test breakers @12:10

[ChrisCurtinATL]

I showed part of this to my wife and her comment 'yup, the husband is always the biggest kid'. Cool video and test.

[erosbarreras]

Speaking as an IT professional I would say the problem with your second leg is that you have a bug in the system!

[lawrencepevitts]

I think you're right about the frequency between the 2 power supplies. When I was in the service, sometimes we had to run 2 generators to handle a very large load. The generators had paralleling light that would flash when it was correct to add the second generator so the frequencies were the same.

[corashy]

I do this all the time. It is an option on military genset older 1s. You have to synchronize the gen. exciter circuit. Using a resistance and you need to set the rpms of both Gensets with a tachometer. I use a harbor freight model. There are even control boxes you can buy on Amazon that come with an idle solenoid and adjustable knob.