Generator question......

[OneLapper]

I recently installed a Westerbeke BT8 8k watt diesel generator in my bus.  The install went well all things considered; it was 90 plus degrees outside, I started the install 24 hours before a 800 mile camping trip, it was uphill both ways to get to the bus.... you know.

About the generator and installation:  I purchased the generator from a boat owner that pulled the unit during a repower.  The engine has 2150 hours on it and smokes a bit, but runs great otherwise.  The smoking is a piston oil control ring issue, I've ruled out low compression, bad injectors, injector timing, etc.  And that goes to reason because the boat was in Chesapeake Bay and the owner used the generator to run two small 120vac AC units, so it saw light loads it's entire life.  Before I installed the generator in the bus I used it at my house for two major outages.  I rewired the generator head's terminal block for 240vac and used it to power the house well pump, dryer, oven etc. (not all at once, though).  I was careful to balance each 120vac leg's load and the generator worked fine.

The problem:  I kept the generator at 240vac and temporarily wire it into the bus so I could run the two roof AC units, fridge, and TV/DVD/lights on separate legs.  The generator is 68 amps at 120, 34 amp at 240.  I could not get the AC units to start unless BOTH units were flipped on at the same time!  When either AC unit cycled off, the compressor wouldn't restart and the voltage on that leg would drop from 126-129vac to, say, 69-89 volts.  The other leg would stay at 126ish only when the AC unit's compressor was running.  There doesn't seem to be any fault tolerance with unbalanced loads at 240.  I solved the issue by rewiring the head for 120 and changing the positions of the breakers in my temporary breaker box to use the hot leg.  After switching to 120vac everything worked correctly, both AC units would run and cycle, fridge, TV, lights, even the inverter in charging mode (incoming line power set to 15 amps on the inverters control panel) all worked fine.  I put 20 hours on the generator while running the AC OTR and had only one problem when the generator's engine's alternator died, running it's battery down, thusly shutting the engine down.  I fixed it by using the bus 12vdc system to charge the generator's battery which kept the radiator fan and run solenoid working.

The question:  Is this a ground/neutral bonding issue?  Or is there something odd with the generator output at 240?  This generator does not have an electronic voltage regulator, it uses what is called a "compound" regulator..... which I have not heard of before.  I had planned on wiring the bus for 50 amp service, but if I can't get the generator to be happy at 240, I guess I'll go with 30 amp.  Unfortunately, that changes my plans of using toe kick heaters while on the pole at the campgrounds.  I have a Webasto for boondocking.  Maybe I really don't need 50 amps after all.......hmmm 

[Len Silva]

There is no reason you can't do both; have the shore power at 240v/50A and the generator at 120v 68A.  You wire the generator for 120 volts and tie the two legs together at the generator side of the transfer switch or plug or however you arrange the transfer.

Your experience is pretty normal for this size generator.  When wired for 240, each leg does not have the capacity to start a compressor.

[TomC]

This is why I have my generator (10kw) wired for straight 120vac-no worries about "balancing the load". When going down the road, I use the generator to run my roof top airs-usually two do the work, but sometimes will run all three. When at the power poll, I only use one leg of the 50amp plug. I can run all three A/C's on that and with a little pre planning, run both 10gal water heaters, and everything else without problems. I like the system so much I'm repeating it with my truck conversion.  Good Luck, TomC