Unbalanced Generator Loads

[SVNeko]

I know running unbalanced loads on the legs of a 240v generator is not a good idea. But why not and how much is too much (considering that it is difficult to have an exact balance)?

[CaptainChip]

Without getting into physics.. basically if you have things on leg 1 pulling a total of 40 amps and leg 2 is only pulling 5 you have an unbalanced load. The probem, and damage, occurs because of something called negative sequence magnetic flux. Both leg 1 and 2 share a neutral wire. And because of physics and heat, you can damage your generator. No generator will have a perfectly balanced load between phases, but getting it close is important for extending the life of the electronics in your generator.
This is some complex sh*t, people get doctorates just to figure it out.

[CaptainChip]

This may leave you just as confused:
https://electricalsimplified.blogspo...rrent.html?m=1

[SVNeko]

OK, but what about guidelines for how far out of balance and for how long? I am asking because I usually run 2 230V chargers. One is out, so I am supplementing charging with a 100a 120v inverter charger. So, with other loads, I have about 10A on one leg and 10A on the other on an 8kw genset while charging for an hour or two. This will continue until I get the bad charger repaired.

[CaptainChip]

If you have 10 amps on each leg then it's balanced and there is no issue... was that a typo?

[Scott Berg]

After considering this on my boat we chose to wire it so as to have both shore power AND the genset run through our isolation transformer and picking up the 'neutral' for 120v service off of the transformer. Treating it as a 240v only genset isn't a perfect solution, but makes many things easier...

[Teknishn]

Originally Posted by SVNeko

OK, but what about guidelines for how far out of balance and for how long? I am asking because I usually run 2 230V chargers. One is out, so I am supplementing charging with a 100a 120v inverter charger. So, with other loads, I have about 10A on one leg and 10A on the other on an 8kw genset while charging for an hour or two. This will continue until I get the bad charger repaired.

SVNeko, Captain Chip is correct , no Gen-Set will have a perfect balance. I try to balance within 15% or less on larger generators, 10% or less on a generator such as yours. And yes, this is a kind of rocket science trying to determine how to balance between inductive loads (electric motors and compressors), resistive loads (electric stove tops, lighting), and those that fall into both categories (dryers, jacuzzis). There's more involved than just volts and amps when it comes to load balancing. Don't even ask about phase balancing or Lead/Lag coefficients!

If I have read and understood your last post correctly, and depending on what equipment you are operating on the non-inverter leg, then you are probably at a good place with load balancing until you get your bad charger repaired.

[SVNeko]

Originally Posted by CaptainChip

If you have 10 amps on each leg then it's balanced and there is no issue... was that a typo?

Yes, sorry, should be 20a on the other one.

[Teknishn]

SVNeko, what electrical loads are you running on the 20A leg? A bit more information would help in determining if you need to temporarily shift electrical loads from one leg to the other.

[SVNeko]

A 100a charger. Along with minor loads on the 110v outlets - iPad charging and such. There is a 80a charger and water heater loads that are on 240.

[Palarran]

I don't think it really matters much. The generator has a breaker in it that will trip if one line of the 230v is overloaded. In my case, I can have up to 50 amps of 115v power coming off one leg and 0 off the other. It would be worse, IMO, to run the generator at 50 amps 230v total as the heat is what kills the generator.

Would it be better to have 25 amps off each, sure. But the generator windings are designed to put out the maximum on each leg.

[ericoh88]

Would running off 230v from generator to a step down transformer 230v/115v to provide a balanced 115v output instead of trying balance the 2 legs of 115v?

[tanglewood]

Originally Posted by ericoh88

Would running off 230v from generator to a step down transformer 230v/115v to provide a balanced 115v output instead of trying balance the 2 legs of 115v?

Yes, you could do that. That's how my 120V service works - via a 240V to 120V transformer.

[CaptTom]

Originally Posted by CaptainChip

... something called negative sequence magnetic flux...

Another new thing I learned today from CF!

I can't wait to find a way to work this phrase into a conversation.

I always wondered about this too. Thanks! Not sure I still understand 100%, but I got enough out of the link above to get the gist of it.

[botanybay]

You could install an "autotransformer" this allows a load imbalance of up to the allowed value of the transformer and present a balanced load to the generator.

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