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Old 12-28-2018, 02:21 PM   #1
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Truck Apu DC generator

I am kicking around the idea of getting a salvaged truck APU and using it for a generator. I am thinking that a large 12v or 24v alternator could be added in addition to the 120v generator or in place of it. If the set up correctly the engine rpm could be varied to provide the needed output currant/dc voltage. It would allow the engine to run more slowly/quietly for battery charging. If a larger DC load was placed on the system or 120v power was wanted the rpm could be increased. Most APUs are belt driven from the engine so swapping out components shouldn't be too hard. Has anyone tried this?

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Old 12-28-2018, 02:52 PM   #2
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No, but would not do both.

A rectifier/PSU/charger from AC to DC, or an inverter to go from DC to AC are not expensive even at high amps.

KISS for moving parts stuff for sure.

Only advantage I see over a quiet little Honda is if you want to use diesel, same fuel as your bus.
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Old 12-28-2018, 06:30 PM   #3
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No, but would not do both.

A rectifier/PSU/charger from AC to DC, or an inverter to go from DC to AC are not expensive even at high amps.

KISS for moving parts stuff for sure.

Only advantage I see over a quiet little Honda is if you want to use diesel, same fuel as your bus.
agreed, I'd go this route personally
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Old 12-28-2018, 07:54 PM   #4
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this guy has some good ideas, only real issue being having to carry gasoline.. actual truck APUs come in masny flavors from mild to wild..



some will connect to the truck's cooling system to keep the engine warm, or heat heating loops , some have as belt drivern A/C, others electric. every last one of them except maybe the newest most expensive are defimnitely not nearly as quiet as a honda generator.. in the trucking world, noise is no barrier.. trucks arent parked in RV parks or campgrounds where quiet-time is encouraged..



-Christopher
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Old 12-28-2018, 11:31 PM   #5
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Few generators are as quiet as Hondas. I would like to have just diesel for fuel. An APU would be louder but I don't think it would be too bad if it could be run at high idle around 1000 rpm vs the 1800 rpm to 3600 rpm needed for non inverting generators. I could use the heat from the APU coolant for heating the domestic water, interior or bus engine preheat. I will not be spending much time in RV parks so I wouldn't annoy anyone too much.

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Old 12-29-2018, 11:54 AM   #6
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If you need to carry propane anyway, that's a **great** option for a small inverter genset, better than gas.
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Old 12-29-2018, 11:10 PM   #7
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I am kicking around the idea of getting a salvaged truck APU and using it for a generator. I am thinking that a large 12v or 24v alternator could be added in addition to the 120v generator or in place of it. If the set up correctly the engine rpm could be varied to provide the needed output currant/dc voltage. It would allow the engine to run more slowly/quietly for battery charging. If a larger DC load was placed on the system or 120v power was wanted the rpm could be increased. Most APUs are belt driven from the engine so swapping out components shouldn't be too hard. Has anyone tried this?

Ted
I floated an idea pretty much identical to this on the forum a while back and got crickets. I priced out a used Yanmar diesel APU engine, a 200A 24V alternator, and a (4? 6?) kw inverter for significantly less than I could find a similarly sized diesel genset. This would come with the additional benefit of charging a 24V battery bank which could feed the inverter when parked, etc.

Then I jumped down the rabbit hole of DIY lithium ion battery packs. That's a whole different story. But I'm on board with the idea.
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Old 12-29-2018, 11:32 PM   #8
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Yes it can be done, for those who enjoy such projects and will be there to DIY the maintenance.

But IMO for most people an easy OTS solution is more practical, something breaks, buy a replacement
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Old 12-30-2018, 01:46 PM   #9
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I floated an idea pretty much identical to this on the forum a while back and got crickets. I priced out a used Yanmar diesel APU engine, a 200A 24V alternator, and a (4? 6?) kw inverter for significantly less than I could find a similarly sized diesel genset. This would come with the additional benefit of charging a 24V battery bank which could feed the inverter when parked, etc.

Then I jumped down the rabbit hole of DIY lithium ion battery packs. That's a whole different story. But I'm on board with the idea.
I came to the same conclusion you did as far as the pricing comparison between used diesel gen and apu. I've seen some fairly low hour salvage apu advertised for around $1500. Most were around 3kw. Many of them run 2 cylinder kubota engines rated from 9 to 13 hp. There are a couple that had 3 cylinder isuzu. It seemed the older models had perkins and yanmar.

The lithium will be a fun project.

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Old 12-30-2018, 01:50 PM   #10
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Yes it can be done, for those who enjoy such projects and will be there to DIY the maintenance.

But IMO for most people an easy OTS solution is more practical, something breaks, buy a replacement
I do like projects! Your right for the average person it's better to be plug and play.

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Old 12-30-2018, 05:00 PM   #11
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this thread really has me rethinking my onboard Mitsubishi L3e engine
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Old 12-30-2018, 05:50 PM   #12
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ha, that is too cool. It looks like you are tearing it out? ..I am trying to get it back in .



Nice, later Johan
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Old 12-30-2018, 06:39 PM   #13
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ha, that is too cool. It looks like you are tearing it out? ..I am trying to get it back in .



Nice, later Johan
engine is staying in... just pulling the R12 ac compressors, hoses, and alternator.
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Old 12-30-2018, 06:44 PM   #14
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If that ac system can be made to work you should do it.
You can't have too much ac in your bus.
But figure out how to run a generator off that engine as well.
Looks like fun!
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Old 12-30-2018, 07:02 PM   #15
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The lithium will be a fun project.

Ted
Check out jehugarcia on YT if you've a mind to. He's a relentless self-promoter, but he is also a fountain of good information on how to disassemble various things that have lithium ion batteries in them, how to test used ones and sort good from bad, how to build the good ones up into battery packs, RV house battery packs, off-grid house batteries, Tesla powerwall work-alikes, etc.
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Old 12-30-2018, 11:39 PM   #16
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I have a rig master apu on my peterbilt that runs a 2 cylinder perkins. It is nearly as quiet as a honda, but has so freek'n much more ac and dc power. It's a stand alone apu, so nothing is hooked into any of the truck's system. It has it's own air cond system and it's own heater. I think it is a 10k watt ac generator, and it has no issues running the block heater on the big c15 cat engine.
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Old 12-31-2018, 08:39 AM   #17
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And costs more than what many here pay for their bus
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Old 12-31-2018, 09:07 AM   #18
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this thread really has me rethinking my onboard Mitsubishi L3e engine
That looks like a nice set up if you can make it work.

Ted
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Old 01-01-2019, 10:31 AM   #19
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I have a rig master apu on my peterbilt that runs a 2 cylinder perkins. It is nearly as quiet as a honda, but has so freek'n much more ac and dc power. It's a stand alone apu, so nothing is hooked into any of the truck's system. It has it's own air cond system and it's own heater. I think it is a 10k watt ac generator, and it has no issues running the block heater on the big c15 cat engine.
It's good to know the perkins in the rigmaster isn't too loud. The reviews I read said it was louder than the kubota APUs.

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Old 01-05-2019, 04:14 PM   #20
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this thread really has me rethinking my onboard Mitsubishi L3e engine
I'm in the planning stages of a Skoolie and want to boondock/off grid a majority of the time. I initially looked at Cummins/Onan QD5000 generator to run a/c but even used they are north of $2500 and $8500-9k new

I then thought to myself, hey I can get a Kubota D902 (3 cyl diesel) used for ~$1000 then salvage the a/c compressors/evap/condenser + 12v alternator from a bus and roll my own apu for a fraction of the cost. (I have the means/skills to be able to pull it off) but it would still be a ton of work.

For me, the real benefit here is the efficiency. If you can spin one of those 3 cyl engines at 1500-1800 rpm you can sip fuel, and still stay quiet. Not gonna write it all out here, but I figured I could stay at around 0.25Gph diesel consumption with 30,000+ btu cooling at 1800-2000 engine rpm. Run my a/c for 10 hours for 2.5 gal of diesel? what's not to like.

Look up Kubota D902 power curve, then check out some of the Sanden compressor kw power needs vs cooling output in btu and with some calculations you will see that it could easily come together nicely. I ended up calculating that in order to run my engine most efficient/quietly at peak output I'd need a 10" engine pulley @1800-2000 rpm driving 6" compressor pulley, and 3" alternator pulley (which most are) to get that 30,000+ cooling output.
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