Generators in Parallel

System · November 2006

I live several miles off the grid in Alaska and get all of my routine electricity form solar power (850W, MX60, 720AH Trojan, 12V system). Occasionally I have a need to generate more power then my system and 1500 watt DR1215 inverter can provide and must turn to one of my two Honda generators. This has generally worked fine for me, but occasionally I even exceed the capability of my generators.

Case in point: I am looking to buy a planner to finish up rough-cut lumber, but the AC amperage requirement of the planner is beyond the capability of either my 1500 watt or 1000 watt generators.

In order to solve this problem, can I set up a separate control panel to which I can hook up both generators in parallel for 2500 watts? Any special considerations or thoughts on this hookup? Any alternative thoughts. I could go to a new inverter for the Solar system, but am trying to make do with what I have for the time being.

Thanks for your help.

BB. · November 2006

Re: Generators in Parallel

The only commercial small generators that I am aware of that can parallel are the Honda euX000i family (1000, 2000, 3000 watt models). And even then, they are only rated to parallel two of equal capacity (equal kW ratings)...

You cannot just plug two generators or a inverters together--depending on the phase difference when first connected, they can either add together (same voltage/phase, current outputs would add/share load)... Or they can be exactly out of phase (opposite polarities/phases, current from one generator is worst than a dead short to the other). Plus, they will want to walk out of phase because of frequency (generator RPM) drift...

I am sure that somebody/somewhere has probably got to gen-sets to sync together-but I cannot think of a simple method to do that safely... If you get them connected in phase, a couple of simple AC generators should lock together in phase (I think), but you will probably have one generator actually driving the other generator like an electric motor if the gas engine RPM's are not exactly the same--they might share the load as you draw power--but I am not sure how well...

I understand that you are in the "middle of nowhere" (or, you are living in the middle of paradise because everyone is elsewhere)--but your cheapest and best bet is probably to buy/find a cheap/throwaway gen-set with the rating you need... It will suck fuel like crazy, but if you can turn it on only when you need it (stack up timbers for processing). It would be cheaper (and probably more rugged) than a new inverter for your system--plus if something pops, you will still have your primary power system still available.

The only "simple" gen-set alternative alternative would be to use them to DC charge/supply your batteries and use a big inverter while running the planner... Although, I think you might spend about as much for fuel to run this option because of the multiple conversion losses (AC to DC to Battery to AC again)...

Hmmmm.... Thinking about how I would share two gen-sets if I had no other options available???? How about this:

A (relatively) safe method for combining the generator power for the planer would be to use several AC induction motors connected in parallel (both motors must be 1:1 ratios to each other for them to correctly share the load) to the planer--and connect 1 gen-set to each motor--a cluge that may work for you if you have the extra motors and room to mount...

-Bill

System2 · November 2006

Re: Generators in Parallel

BB

Thank you for your very thoughtful and informative reply. We do indeed live in paradise (although it got down to -31F last night, but it sure is pretty), for both the reasons you mentioned.

The duo generators sounds like a much more difficult proposition then I had hoped for. It just seemed like intuitively it should work. But I'm glad that I checked in with the NAWS forum. One of my generators is the EU 1000, but it would probably be better to go with one of your other two suggestions rather then attempt to keep every thing in balance with the parallel generator approach. Of your two suggestions, I am due to get a new inverter in the near future as I will be upgrading my system from time to time and I want to get away from the modified sine wave. The junker generator is a good idea, but they are hard to get people to part with up here -- and I'm looking for a near term solution as I'm making an addition to my main cabin now. I've had my eye on the 2700 watt Outback, so maybe this is the time to bite the bullet.

Thanks again for the help. Glad I checked in here first!

BB. · November 2006

Re: Generators in Parallel

See this thread for a knock-down fight on syncing multiple generators... Short answer, there is no short answer

:

http://www.fieldlines.com/story/2006/10/29/174256/03

I agree that it is possible to sync the generators--but there are a whole bunch of variables (size, models, behaviors, control theory, feedback loops, damping factors, etc.) that make it a very much hit and miss proposition to get them to sync and share in any reasonable manner.

I think I have read somewhere about AC generators jumping around (and off of their foundations for the larger units) when they are connected out of phase or slip phase between the generator(s) and the source.

-Bill

System2 · November 2006

Re: Generators in Parallel

Yikes!!! I went to that thread that you sent. No way am I going to try sync'ing two generators (even of the same name plate rating).

Thanks for sending. The inverter upgrade looks even better now.

Generators in Parallel

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