portable home genset question


Old 07-22-05, 09:00 AM
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portable home genset question

Are randomly selected portable home generator sets close enough in frequency and voltage to be used in parallel feed situations?

All references point out that the gensets to be parallelled must match frequency and voltage.

There's a ton of stuff through Google on parallelling generators. Most of it, though, is for big plants, and multi-phase.

I'm just wondering if the portables gensets bought out of Home Depot, Walmart, Lowes, etc, can be parallelled without problems? What I'm hoping is to hear from someone who's done it, and that it works.
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Old 07-22-05, 11:26 AM
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I don't think that's a good idea. The only thing controlling frequency on the cheap generators is a thumbscrew on the engine throttle glued to "about the right place" in the factory. You could tweak it, but the generator has no feedback controller to hold that setting as varying amounts of load are applied. Moreover it's not just the frequency that's important, it's the phase. Both generators must have the same frequency and be in phase with each other. This is much harder to achieve and requires synchronized controllers.

Most of these generators have at least a 15% margin of error on voltage; so it would be within spec to have nearly fourty volts difference between two consumer generators. For that reason, you aren't even supposed to run electronics from cheap generators; the voltage is just too unpredictable to not damage your loads.
Old 07-22-05, 05:42 PM
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I agree. I would not even use a cheap genset for anything even remotely critical or sensitive. Most from the places mentioned are cheap units. Unless of course they specify for sensitive equipment.

Small Honda inverter generators (EU series) have available parallel kits from the factory.

I must say I have never seen it done on any kind of genset. I can't see a reason for it either. One bigger unit is cheaper than two smaller ones. Unless you get one or both for free.
Old 07-22-05, 08:51 PM
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Well, I was never an EPCP operator on the boats, but if I recall you not only have to match frequency and voltage, but you have to sync the phases. Unless you have instrumentation to so this, I think it is a problem.

Why do you need to do this? An emergency gen. usually comes into play after the utility power has gone away......suddenly!
Old 07-23-05, 12:26 AM
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Good answers, guys. Thanks. I was just playing around with the possibility that might be an easy way to end up with a few kw more power from portables. Guess it's not doable, though. Just thought I'd ask the experts.
Old 07-23-05, 06:03 AM
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I think you will find that the generators will sync themselves. The closer they are to being in sync the better. Continually doing this will probably cause damage to both generators.

I don't recommend this.
Old 07-23-05, 06:21 AM
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As mentioned, you need to sync the outputs of the gens before actually interconnecting (paralleling) them. Even if you could sync them and close onto each other, small gens are relatively week sources of fault current, so when they waver out of sync, each would feed into a short circuit created by out of phase sources.
You can easily get double the KW by keeping them isolated and serving different loads.

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