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Old 02-03-2011, 06:19   #1
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Inverter vs. GenSet. Need Elect Advice

Mastervolt inverter. 24/220 1500w. Kohler 12kw gen.

Whole thing started with the inverter going into overheat alarm and shutting down. I blamed it on cold damp conditions in November on the east coast. The boat, and I, prefer the warm weather.

A technician diagnosed the problem as being caused by running the gen set while the inverter was on line. The inverter and the gen set both providing 220 to the system overloads the inverter. Does this make sense?

We have a remote gen set start setup at the helm station (very convenient) but it does not provide for taking the inverter offline. The inverter itself does not seem to provide this function. Seem like it would if this were really an issue.

What I have been instructed to do is to take the inverter offline and set switching selections to “off”. Manually start the gen set, then switch the selectors to gen set. Shutting down is the reverse of this process. This creates an 8 step process for starting and shutting down the gen set. Ending with the selector set back to inverter. All of this takes place down in the engine compartment and it can be difficult and unsafe to access this while offshore.

So here are the questions for my electrically astute friends out there.

Does running the gen with the inverter on line overload it?

Do you need to take the load off the gen set before shutting it down?

Any help would be appreciated.

Regards and fair winds,

S/V Vivo

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Old 03-03-2011, 11:05   #2
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Re: Inverter vs. GenSet. Need Elect Advice

I'm not sure 'overload it' is the correct term. The problem with having both sources on at the same time is that they are not synced up. The oscillator in the inverter would need to be synced to the genset such they can work in parallel. With them out of sync, I would imagine you would make smoke (which is apparently what you did).

You might look for an inverter that has an internal transfer switch, it will take itself offline when is sees either the genset or shorepower come online.

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Old 03-03-2011, 11:10   #3
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Re: Inverter vs. GenSet. Need Elect Advice

I believe the term is 'backfeed' rather that overload. running the gen set and inverter (if they power the same circuits) is just like trying to run shore power and the gen set at the same time. It's a no-no. Regardless of how the inverter is set up, it should not feed the same mains circuit at the same time as the gen set (or shore power either). Your electrician is correct.
Keep the dirty side down!
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Old 03-03-2011, 11:12   #4
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Re: Inverter vs. GenSet. Need Elect Advice

Is your invertor the type which can be assisted with shore or gen power when its not big enough to supply on its own?

If the shut down/start up procedure is the way forwards, see what ways you can simplyfy the opperation with remote switching solenoids and relays
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Old 03-03-2011, 14:05   #5
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Re: Inverter vs. GenSet. Need Elect Advice

If it isn't auto switching, mine wasn't, you can fit a contacter in the system, which automatically disconnects the inverter circuit when it senses an external voltage source.
No multiple switching required.
Like one of these, sorry U.K but you get the idea.
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Old 03-03-2011, 14:34   #6
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Re: Inverter vs. GenSet. Need Elect Advice

You need a tranfer switch and a positive lockout on the genset unless you have an inverter/charger that is specifically designed to be on line. when there is power on the AC mains from either shore power or the genset. My boat has both as I have an inverter, not an inverter charger (yet). When I was boat shopping I asked a prospective seller to demonstrate his genset. He did not have a lockout and started his generator. Flames began shooting out of several pieces of his equipment. He told me he had never started the genset while still plugged into shore power. On my boat the lockout switch is either in the shore power position or the genset position, it can't be on both. The transfer switch disconnects the inverter any time there is AC coming from either the genset or shore power. Even though the inverter may be switched on there is no AC connection between the shore power/genset and the inverter so it cannot be damaged by genset of shore power.

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