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Old 06-21-2018, 04:25 PM   #21
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Yeah, my thinking has morphed into "build a DIY genset out of an old APU". I think that buying an old APU just for the 14 horse Yanmar in it, jury-rigging one or two large alternators onto it, and supersizing your inverter is the way to go for a roll-your-own genset. You've told me that minisplits are inherently soft-start, and run at under 1KVA in most cases. The specs on some of the pure sine 4-5 KW inverters say they tolerate a 300% overload for 20 seconds so running, say, and air compressor would not be a problem.

I'm willing to be shot down on this, but it sounds like it has real promise so far.

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Old 06-21-2018, 05:28 PM   #22
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Originally Posted by dan-fox View Post
So you're running a more conventional "genset"? Produces 120VAC which you then use both for charging (by feeding a charger that downconverts it) and for powering the 120VAC side of your bus systems? That is what I'm thinking of as the more "conventional" or "baseline" approach.



What Chris suggested, and I jumped on, also provides an alternate AC compressor. I'm not sure if on-the-fly changeover from one compressor to another is feasible or even possible, or if I'd be limited to running the A/C off that one compressor.



I'm interested in why you use the words "safer" and "more efficient". Easier to comprehend/design, for sure, but I don't see a clear advantage to either setup for those two metrics.


Gotcha, the safer and more efficient thinking came from how many amps are being sent at the higher voltage. You have to have very large cabling and you’re more susceptible to voltage drop over distance with the low-voltage.
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Old 06-21-2018, 06:25 PM   #23
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thats why id say if you are going to go with a second alternator and an inverter I would run a 24 volt alternator and 24 volt inverter.. if the alternator's purpose is to charge that one set of batteries which would be completely isolated from the bus batteries..



the disadvantages being that to charge you batteries in any other method requires 24 volt circuitry.. ie solar must end up with a 24 volt charge controller, to charge from shore you need a 24 volt charger.. but 200 amp alternator at 24 volts nets you 4800 watts... vs 2400 watts if you ran 12 volts over the same 200 amp capable cable.



-Christopher
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Old 06-22-2018, 11:33 AM   #24
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I've learned here that there's lots of good reasons to run solar/ inverter/ battery bank/ charging at 24 VDC vs 12 VDC. Point well taken on more expensive cabling and higher downside to accidental arcing. Also, I don't think I controlled for 24VDC input when I was fantasy shopping for high output inverters; for all I know they are all 12VDC input. I'll look some more.

Cummins Onan 5KVA RV diesel genset is 8 grand. There's a price point to shoot for right there.

New Leece Neville 24VDC 200 (250)A alternator is 2 grand. Good candidate to save $ by buying used.

AIMS 24VDC 5000W pure sine wave inverter is 1200. Not a whole lot of overload capability. I might gain some flexibility there by running 2 inverters; 1 pure sine for what needs it, one modified sine for stuff that has inrush current. At the cost of added complexity.

14 horse Yanmar is 1250 used on Fleabay.

This isn't cheap any way you look at it.
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