Truck Apu DC generator

[Booyah45828]

If I was like most of you with solar panels and large battery banks.

I would find a large (4kw or bigger) dc alternator at whatever voltage your bank is. Run that off a serpentine system similar to how I run my ac generator. I know the military used oddball direct current generators on some things, so I wouldn't think it would be difficult to locate something that would work.

I would then keep the 40 amp 12v alternator and essentially run all engine functions and controllers off of 12v. Have that paired with the bus 12v system.

Keep your 12v vehicle battery and your house battery system seperate. You could then run a large enough inverter to power your air conditioning/house needs. I think there are charge controller that have an autostart function to start the generator when your house batteries are low. Use solar charging for as much as possible, but have the generator as backup power.

If you really want to get creative, you could use an arduino setup to control engine speed relative to power demand.

[john61ct]

4kW is going to need a pretty big pony engine. More like a gelding

[milkmania]

Originally Posted by Booyah45828

snip*
I've been meaning to do a write up and post some pics, just haven't had the time. Ask any questions that you have.

we'll be waiting

[kcarsey]

Originally Posted by Booyah45828

If I was like most of you with solar panels and large battery banks.

I would find a large (4kw or bigger) dc alternator at whatever voltage your bank is. Run that off a serpentine system similar to how I run my ac generator. I know the military used oddball direct current generators on some things, so I wouldn't think it would be difficult to locate something that would work.

I would then keep the 40 amp 12v alternator and essentially run all engine functions and controllers off of 12v. Have that paired with the bus 12v system.

Keep your 12v vehicle battery and your house battery system seperate. You could then run a large enough inverter to power your air conditioning/house needs. I think there are charge controller that have an autostart function to start the generator when your house batteries are low. Use solar charging for as much as possible, but have the generator as backup power.

If you really want to get creative, you could use an arduino setup to control engine speed relative to power demand.

I think i'm leaning towards this idea. If I go with an "apu" type system, it will have it's own small engine alternator (40 amp) and small starting battery. I think those little Kubuta engine usually require about 500cca starting power. I would keep this completely isolated from all other systems.

Then I would just have two input sources for my house bank, my "main" belt driven alternator that the small kubota drives, in the ~140 amp range, + solar charger/controller. 140 amps is a lot less than 4kw (it's about 1680w) but still should be enough for my needs. My DC loads are going to be pretty light on this build. My biggest consumer will be a dc fridge/freezer which I expect will use around ~80Ah/day during summertime, and 2nd my laptop computer which uses around 80W of power, but will be on 6-8 hours a day. I have a whole spreadsheet with formulas in Google Drive if anyone want's to take a look.

I really like all the Magnum Energy stuff, including their pure sine inverters. They have several other add on options, such as a control panel, a dc shunt that can measure current usage and battery state of charge by measuring Ah in/out once calibrated to the bank size. They also offer an auto-start gen controller.


I already plan on building my own Ardunio thermostat to control this whole system from a heating/cooling perspective. This way I can control engine startup/shutdown etc. For example. if I have the unit set to a/c and it's mid morning and warming up, and the thermostat calls for cooling, it will auto-start the pony engine and start cooling down to whatever set temp I have. Say things cool off and there is no call for cooling for 15 minutes (for example) then the engine will shut down automatically to save fuel.

As far as engine speed, I'd only plan to have two speeds, low idle at ~1400-1500 rpm and high idle at 1800-2000. If I have my set point at 74F and I turn on the a/c and it's 80 in the bus, it'll start up and go into "high power" mode with high blower and high engine speed to cool things down, once it reaches the set point it'll drop to "low" mode, slow the engine, and turn the fan to low and cycle the a/c clutch in/out to maintain set temp. If I creep up in temp, say 1-2 degrees over set temp, I can switch back to "high" cooling mode, etc.

I will also be able to use the Magnum gen auto start controller to start the engine. All I need to do is isolate each with a shockley diode so that they won't back feed each other, and feed both to a single relay, sort of like a simple OR logic circuit. If a/c, OR charging go to +12, relay closes, then starts engine.

As far as engine control, any diesel engine gen controller can handle glow plugs, and engine startup, and also protection from low oil/over temp, etc. You just close a circuit, and the engine starts. Open circuit (relay) and engine stops.

@cadillackid As I have it figured now, with 2000 rpm max engine speed, 10" serpentine pully on my engine, 6" compressor pulley, that puts me at 3320 rpm on my compressor at "max" speed. I could always raise/lower that speed but I think 2000 would be an ideal max for compromise of power output/noise and fuel consumption.

This also puts my alternator at 6,600 rpm provided it has a 3" pulley, which is pretty common. Most alternator peak output at 6000 rotor rpm so that should give me my 140 amps pretty easily.

I have several "good" take off 6.0 Powerstroke alternators lying around that are 140 amp so that's why i'm going down this road. They are also 8 rib micro-v which I think would be perfect.

[cadillackid]

have a look at the Bosch SB200 alternators.. they are smaller in size and pack 200 amps.. they also reach at ;east 80% of their peak at really low RPMs. they can be run as 1 wire or with a sense wire.. the advantage of a true sense wire run to the batteries is that you dont over-charge the batteries by the alternator having no idea what the true BAT voltage is..



I run the SB200 on my DEV bus and its been fantastic.. I havent blown it up even when ive been running down the road on a hot summer day with 2 Bus A/C units running and pulling 1000 watts from my inverter to run a 3rd electric A/C...

-Christopher

[Booyah45828]

@kcarsey

Sounds like you have a good start to the plan. My thoughts were to run a pair of mini-split heat pumps ran off a battery bank which is why I spec'd such a large DC alternator. You can use a belt driven compressor but you'll have to engineer some sort of fan to cool not only the condenser but also the engine radiator.

You might want to take a look at the variable displacement compressors that have come out. I prefer those to clutch type on/off controlling.

The original design from blackrock Apu had a 6 piston sanden compressor, but I already had a rooftop AC unit installed so I removed it. So you definitely can run a compressor off an Apu for cooling.

[TJones]

Originally Posted by Booyah45828

@kcarsey

Sounds like you have a good start to the plan. My thoughts were to run a pair of mini-split heat pumps ran off a battery bank which is why I spec'd such a large DC alternator.

I am think along the same lines for AC. This would allow the engine to not have to necessarily run continuously for AC. I think a DC mini split could add to the efficiency of the system.

Ted

[cadillackid]

I like the idea of running an electric 110 volt A/C unit simply because that way you can run it on shore power when you want vs having to run your APU even if you are in an area where shore power is available..



that minisplit wont keep you real cool on the road, so i'd consider it as your parked A/C and not a good driving A/C solution.

-Christopher

[Yukon Cornelius]

Originally Posted by Booyah45828

If I was like most of you with solar panels and large battery banks.

I would find a large (4kw or bigger) dc alternator at whatever voltage your bank is. Run that off a serpentine system similar to how I run my ac generator. I know the military used oddball direct current generators on some things, so I wouldn't think it would be difficult to locate something that would work.

I would then keep the 40 amp 12v alternator and essentially run all engine functions and controllers off of 12v. Have that paired with the bus 12v system.

Keep your 12v vehicle battery and your house battery system seperate. You could then run a large enough inverter to power your air conditioning/house needs. I think there are charge controller that have an autostart function to start the generator when your house batteries are low. Use solar charging for as much as possible, but have the generator as backup power.

If you really want to get creative, you could use an arduino setup to control engine speed relative to power demand.

Up here on base we have one of them fancy controllers that will remote start a genset, I'm going to be having coffee with our APU/GEN, and elec distribution guy to find out the specs.

Lots of Milsurp Veh and support equipment have DC Gen, or DC Alt's on board. Just be aware that the aircraft gear is 28VDC and most of it is high current.

[kcarsey]

I'm very much a "homebrew" guy and like to build custom stuff, but some things are best left to professionals, especially at the right price.

Here's one example of a gen set controller that is diesel compatible and has all safety shutdown measures built in. Uses alternator output to detect if engine is "running" or not and that's how it knows how long to crank, when to stop cranking, etc. some even have CAN bus inputs or can use a magnetic trigger.

https://www.americasgenerators.com/C...enerators.aspx

There are tons of options out there for reasonable prices.

Regarding Engine cooling and Condensers, some of the Kubota engines comes as a "power pack", or come in small tractors so it's not hard to find a radiator and shroud and cooling fan. There are also options for pusher/puller radiator fans.

Condenser wise, I would hope to find a bus that already has a/c and condensers, or else salvage good used condensers from a bus and add them myself.

[john61ct]

You do not need an AC genset. If your DC output is solid, use an inverter for the few devices that need AC.

Use your shore charger when mains is available to support the loads.

Or use AC genset only, running both is IMO silly.

[kcarsey]

Originally Posted by john61ct

You do not need an AC genset. If your DC output is solid, use an inverter for the few devices that need AC.

Use your shore charger when mains is available to support the loads.

Or use AC genset only, running both is IMO silly.

Another nice thing about a Magnum Energy inverter, they are inverter/charger/ATS all in one. They have a mains input, and when power is detected from mains, they switch the inverted loads to mains, and start charging the house bank. Pretty nice all in one unit.