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Old 07-13-2019, 03:57 PM   #1
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12V DC Generator

I am curious if anyone has used a DC generator with an inverter instead of an AC generator. This can be as simple as a small gas (lawnmower) engine with an alternator.
I have a 5000W inverter than can run my roof air conditioners as long as the batteries (1000 AH AGM) have the juice.
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Old 07-13-2019, 04:07 PM   #2
bii
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Have a 2004 Mandalay diesel pusher.. Generator runs but will stop on really warm
Days. But starts up right a way. Message is 23. Help going on trip next week and
Will need it.
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Old 07-13-2019, 04:12 PM   #3
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Quote:
Originally Posted by bii View Post
Have a 2004 Mandalay diesel pusher.. Generator runs but will stop on really warm
Days. But starts up right a way. Message is 23. Help going on trip next week and
Will need it.
Hi sir, I can't help you with that.
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Old 07-13-2019, 04:19 PM   #4
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Probably need a 200 amp, rated output, alternator to power that size inverter.

Then your going to need more then a 4 HP lawnmower engine, more like 20 HP, turning the alternator at 3 or 4 thousand RPMs.

They make them.
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Old 07-13-2019, 04:36 PM   #5
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Probably need a 200 amp, rated output, alternator to power that size inverter.

Then your going to need more then a 4 HP lawnmower engine, more like 20 HP, turning the alternator at 3 or 4 thousand RPMs.

They make them.
Thanks, yes, I have seen a few DIY projects to build something similar to what you are saying. Curious if anyone is using it this way, maybe if alternator gets too hot when running ~ 8 hours?
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Old 07-13-2019, 04:47 PM   #6
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Quote:
Originally Posted by bii View Post
Have a 2004 Mandalay diesel pusher.. Generator runs but will stop on really warm
Days. But starts up right a way. Message is 23. Help going on trip next week and
Will need it.
Welcome to the forum but No Hijacking please. You need to start your own thread to ask questions. In the top left corner of the forum is a button that says New Thread.

Fault code 23 is low oil pressure. Could be the sensor, could be low on oil, probably needs to be serviced.
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Old 07-13-2019, 07:03 PM   #7
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Are you talking about a standard car altenator? Those are actually A/C with a rectifier bridge that converts it to DC. That being said, it would be more efficient to run a standard 120 or 120/240 volt generator to power the A/C directly. You would lose a lot of efficiency stepping up the voltage to run the A/C. Even a heavy duty car altenator would only be good for around 1200-2000 watts max.
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Old 07-14-2019, 09:05 AM   #8
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Are you talking about a standard car altenator? Those are actually A/C with a rectifier bridge that converts it to DC. That being said, it would be more efficient to run a standard 120 or 120/240 volt generator to power the A/C directly. You would lose a lot of efficiency stepping up the voltage to run the A/C. Even a heavy duty car altenator would only be good for around 1200-2000 watts max.
I should have mentioned that I am intending to supplement solar. I understand that using A/C directly off a generator is more efficient of course than going through the conversion and inversion. I also have an Onan 6500 watt gas generator, but there are a few reasons I am looking to do this:
-Generator uses 0.7 gallons per hour with no load, 1 gallon per hour at 50% load. A smaller engine with alternator for charging could reduce my gas usage even if not being as efficient.
-The generator is in a compartment under the bedroom, so for a variety of reasons I don't want to use it while sleeping.
-A small engine with alternator mounted could be placed outside on the ground and be more useful for keeping my batteries charged without switching my power back and forth from inverter to generator.
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Old 07-14-2019, 09:16 AM   #9
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I should have mentioned that I am intending to supplement solar. I understand that using A/C directly off a generator is more efficient of course than going through the conversion and inversion. I also have an Onan 6500 watt gas generator, but there are a few reasons I am looking to do this:
-Generator uses 0.7 gallons per hour with no load, 1 gallon per hour at 50% load. A smaller engine with alternator for charging could reduce my gas usage even if not being as efficient.
-The generator is in a compartment under the bedroom, so for a variety of reasons I don't want to use it while sleeping.
-A small engine with alternator mounted could be placed outside on the ground and be more useful for keeping my batteries charged without switching my power back and forth from inverter to generator.
Or you could buy and use a 2K inverter generator to place on the ground to help keep your batteries charged. Either connect it directly to the converter or in conjunction with a stand-alone battery charger. Then you won't need to worry about connecting welding cables to your DC generator.
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Old 07-14-2019, 09:50 AM   #10
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Or you could buy and use a 2K inverter generator to place on the ground to help keep your batteries charged. Either connect it directly to the converter or in conjunction with a stand-alone battery charger. Then you won't need to worry about connecting welding cables to your DC generator.
Something else I should have mentioned is that my inverter/charger are currently the same unit, so I can't use it to charge the batteries while running as an inverter. That's why I was looking for a DC generator, vs getting another A/C generator and a high amp converter.
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Old 07-14-2019, 10:13 AM   #11
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If you need to run a 12 volt generator, big enough to keep the batteries charged while running the A/C in the RV, then its the same as running a 120 volt generator to power the A/C.

Your not going to do this with a junkyard car alternator and old lawnmower engine.
A 20 HP, garden tractor, size motor, turning a huge $$ 250 amp DC alternator is going to be loud enough to wake everybody.

A 3600 watt portable inverter generator is quiet and already built. AND you don't have to deal with the heat of the 5000 watt inverter, while its converting your 12 volt battery power into 120 volt AC power running the A/C.

If this was fesable, someone would be doing it.
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Old 07-14-2019, 10:38 AM   #12
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Some bus converters ran dedicated 48 volt systems, which means all normal ac equipment ran off 48 volt dc to 120 volt ac inverters. Battery bank was 48 volts and generator was a 48-52 volt DC diesel run generator.
Believe most of them used lithium type batteries to utilize their fast charging ability. A lot easier to set up than a 12 volt system.
https://polarpower.com/products/dc-generators/
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Old 07-14-2019, 10:47 AM   #13
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Agree with twinboat. A DC generator (not a car alternator) big enough to feed a 5000W inverter (or even 2500W) is a major unit that needs a substantial engine. An Onan 7500 or 8000 Quiet Diesel genset works that way (it's a 20 hp diesel engine driving a big DC generator which in turns powers two built-in inverters.
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Old 07-15-2019, 05:25 AM   #14
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Ok. Convert mechanical energy to 12V, then convert 12V to 120V, then convert 120 into mechanical energy to compress the freon. Can anybody tell this dumb truck driver why the engine can not drive the compressor with a belt? Maybe also drive a small alternator?

BTW, might want to look at APU for trucks
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