APU in a Conversion

[Lostranger]

Thanks to a different thread, and the input of several intelligent and helpful contributors, I have recently become aware of the wonders of the Auxiliary Power Unit. I've spent time and money repairing and sprucing up my Kohler 4.5 KW generator before mounting it in the bus as a backup for our solar power system, but I have decided that an APU makes more sense. The Kohler is dependable and more than large enough to meet our needs, but it could in no way be described as efficient by today's standards.

My question to the group is twofold:

1. Are any of you currently using an APU in your conversion or do you have experience with one in a truck. Any experience and/or knowledge based opinions would be welcome.

2. I'm particularly interested in the Thermoking Tripac Diesel APU. Apparently, this unit is intended to be used with a diesel burning heater in truck sleepers, but my research indicates that they have engine block heating capability, so I assume that feature could be tied to a heater core in our bus. I have a chance to buy one of these, but I would like to know more about them.

To summarize our needs and intended use: We want mechanic AC, battery charge capability, and backup for our primary heating system.

I still can't believe that I had missed the entire APU phenomenon until now, but I intend to make up for lost time. All civil comment is welcome.

Best to all

[Audiomaker]

I can't say I'm familiar with one brand vs another, but basically one could just look at it as a extra engine which is just powerful enough to run the accessories of an engine.

Having said that, some things to consider might be:

Some run @ 1800.  Most run at 3600rpm.
I don't know if any are variable at this time, but if it has a rectified alternator, variable throttle (per load) might be something that could be retrofitted.  Modern inverter generators are able to adjust their RPM to the load (and hence save fuel and noise).

You may, or may not wish to keep the original enclosure if the internals fit well into a compartment you can sound proof.

I've also seen them used in conduction with diesel fired heaters.  I think are air heaters, although that's really a separate system (which can be added separately if desired).

I also intend to install one in addition to my small (7kw) generator so I've bounced a few ideas around in my head...

Some of these include plans for diverter valves and plumbing so that in addition to coach heat, some may be diverted to warm the holding tanks for sub freezing weather, and the more or less fresh hot air exhaust from the radiator could be diverted under the coach for the same reason.
If you are planning to plumb to the coaches factory heater core, you might also consider a separate core for the back of the coach.
The idea is to use every bit of heat that lil' APU puts out above operating temperature.
By the way, even exhaust heat can be captured via heat exchanger pretty inexpensively.

If you tie into the engine's cooling system (which I recommend), be sure that some of the power of it's alternator are going to the coaches' batt's so that you can run the dash heater fans from the APU....that's pretty standard.

Kubota and Perkins are the most common motors I've seen on APU's, with a preference for Kubota for some, but I can't recall the reason.

Don't forget to plan in an Automatic Generator Start device so that your A/C can trigger the generator if you so desire.

All I can think of at the moment.

[luvrbus]

I never saw a APU with a fan or radiator the ones I see are tied into truck cooling system that is were the engine pre heat comes from and they are noisy little suckers running at 3600 rpm

I have one I was going to use the generator part but decided not to it is a 2 cylinder Kubota

[Audiomaker]

Oh... I'll make one more comment which is slightly off topic to your question...

A few years ago my (now ex) wife didn't pay the power bill and it was shut off.   By the time I found out about it, the power company had attached a $3000 deposit to the re-starting of our electrical service.
This was more money than I had, and we were forced "off grid" for a couple months.

I immediately went out an bought a little gas generator... then when that broke down...another... and when that broke down while fixing the first one... I rented a diesel generator, which was loud and used a lot of fuel... then I rented another generator which wasn't much better.
I spent two months chasing generators and problems, and building enclosures from plywood..etc.

What I found was the most reliable and best performing "generator" I had used during that whole time was 4 group 31 batteries tied to a 2kw inverter, tied to the engine of a "Trans Sport" mini van (3.8l inline 4 I think).
Simply, I found this mini van to use the least amount of fuel, be the quietest (I mean really quiet at idle), and it had absolutely no problem idling for weeks charging up that little battery bank.

My theory is that with the advanced EFI, and the large automotive exhaust system, and the large radiator, and the large oil capacity... that the engine was simply miles ahead of what you would expect from a standalone generator and certainly over engineered by comparison.
From that time on, I've dreamt of making a "power wagon" for emergency off grid use.  It would consist of a similar mini van, with the back filled with battery banks, a pair of 200amp alternators, and solar on top.   Funny thing is that you could put this together used for a about what most good generators cost....and drive it to the gas station to fill the tank!

The point is, as it relates to your topic, is that there's a lot of ways to skin a cat.

[luvrbus]

The best value out there is buy the light towers when outfits like United Rental sell those off I bought some for under $1,500 ea 1 was new but had been wrecked, you have everything to work with those units IMO

Wacker is the one I try to buy they have the good sound proof materiel,radiator,muffler,shutdowns,Kubota engine good generator head and auxiliary fans. A 6kw is easily made into a 8kw with a hp increase on the 1800 rpm Kubota 

[Seangie]

A 6k APU and we would be good to go on our bus.  We have a 15k genny now and its too much power.  80% of the time its just charging batteries and the other 20% of the time its used to run 2 roof airs.  It would be nice to have something that was much quieter and used less fuel.

-Sean

[Van]

Sean I'll trade ya my &k for your 15k, any thing I can do to help buddy just ask away

[Lostranger]

Thanks, guys. This is good stuff, and I appreciate it.

The more we have learned about solar, and the more we've been willing to reduce our electric demand, the smaller the generator need has become. I have three Thermoking/Isuzu 4 cylinder engines in the shed. Original plan was to stick an 8 or 10 KW single bearing induction head on one of those. Been done lots. Incredibly reliable and long running. May still eventually do that for my shop, but would now be extreme overkill for the bus. Those engines are 1800 rpm. As of now, 4.5 KW was still overkill. 2 KW would easily meet our backup need, even in winter. With an APU, batteries are charging anytime you're making heat or air.

lvrbus, I'm in full agreement about the engine speed issue. One of the reasons I redid the Kohler is the 1800 speed. I don't want any 3600 rpm engine howling away on the other side of my bedroom wall. I WILL end up with an APU that runs at 1800.

With that said, I WILL own this ThermoKing. An old friend has it, and he's practically giving it to me. Catch is that I have to drive to Pa to get it, but everyone needs a road trip now and then. The engine is probably a Yanmar. Definitely 2 cylinder. Has alternator and AC compressor. Self contained radiator. Coolant circuit to preheat truck engine. As I mentioned earlier, I'm pretty sure I can run that to a blower coil in the bus, and I MAY plumb that feed through the bus cooling system. I don't yet KNOW that it's an 1800 RPM unit, but knowing ThermoKing, I'll be surprised if it's not.

I'd still like to hear from someone who knows for sure about a ThermoKing Diesel APU.

Thanks again to all contributors.

[luvrbus]

I have the Thermo King a 2008 year model it has the Z482-E4B engine 3600 rpm two cylinder horizontal Kubota the one you are looking at may be the later technology but I don't think they have changed the engines

I was in Cummins today I saw their Comfortguard  APU used the 2 cylinder Kubota engine it looked like Thermo King with a Cummins label

[Homegrowndiesel]

Hey Los tRanger, I have an 1 cylinder and 3 cylinder Kubota diesel. I have used the water from both to heat water, domestic, and potable,  the power from both , for electric, and air conditioning , and I really do understand the output and use of both of these. I know that to heat, cool and power the  average over the road truck the APU's are sized pretty good. But if you want to Heat, Cool, and Power the sq ft of a bus, you will probably want a little more. Not saying, you can not use solar and other sources to accomplish the same thing. But I know my 3 cyl Kubota struggled to keep up in the bus @ 1800 rpm.

[Audiomaker]

Hey Los tRanger, I have an 1 cylinder and 3 cylinder Kubota diesel. I have used the water from both to heat water, domestic, and potable,  the power from both , for electric, and air conditioning , and I really do understand the output and use of both of these. I know that to heat, cool and power the  average over the road truck the APU's are sized pretty good. But if you want to Heat, Cool, and Power the sq ft of a bus, you will probably want a little more. Not saying, you can not use solar and other sources to accomplish the same thing. But I know my 3 cyl Kubota struggled to keep up in the bus @ 1800 rpm.

I have wondered about this.
My Kubota D905 is a cool running critter even with a small radiator.  However, it is losing a ton of heat to radiator exhaust.
The question becomes whether to tap the water circuit in parallel, or in series?
In parallel you would have a lot less heat to work with.  In series, you might never get the motor warm enough to keep the thermostat open.
Hmm.

[TomC]

The ThermoKing Tripac uses either the Kubota or Caterpillar (Perkins) 2 cylinder engine. It drives a large 12v alternator and air conditioning compressor. Most set the RPM of the engine down around 1500rpm to cool a truck sleeper-much quieter and you don't have to worry about the alternator being synchonized with 60htz since the alternator is only creating 12vdc and you're getting your 120vac juice from the inverter. It is a compact, light weight way to have auxiliary power.

I do not like having APU cooling mixed with the big engine. If one goes out-it will take the other with it. I'd rather have a small full generator like the Powertech 8.0 compact genset and just electrically power everything. Good Luck, TomC

[Audiomaker]

The ThermoKing Tripac uses either the Kubota or Caterpillar (Perkins) 2 cylinder engine. It drives a large 12v alternator and air conditioning compressor. Most set the RPM of the engine down around 1500rpm to cool a truck sleeper-much quieter and you don't have to worry about the alternator being synchonized with 60htz since the alternator is only creating 12vdc and you're getting your 120vac juice from the inverter. It is a compact, light weight way to have auxiliary power.

I do not like having APU cooling mixed with the big engine. If one goes out-it will take the other with it. I'd rather have a small full generator like the Powertech 8.0 compact genset and just electrically power everything. Good Luck, TomC

I think I'd be willing to take that risk (You can laugh at me over a beer later if it fails).
I don't own an APU, but I know that millions of OTR truckers do have them plumbed into their prime cooling systems, and during all the reading I've done about them, cooling system failure doesn't seem to be an issue.

I own that little Powertech you are speaking of and for electric heating I currently have (ugh) a 1500w room heater, and a fixed mount 230vac 4.5kw heater.   If I had to get warm fast (which I don't right now in early summer), you'd find me sitting outside next to the Powertech's radiator exit, not next to one of the heaters inside.
I cringe at the waste of it.

Now of course using a generator or APU, or any engine to heat a coach either electrically, or via water heat exchange may not be the first choice of heat sources, it never hurts to have options, and waste heat usually has to be compensated for in some other way (ie...burning more propane or whatnot).

Before next winter, I hope to test these thoughts by tapping my generator's water for heat....which seem ingenious to me except that it's old news to APU users.   I didn't know if tapping generators is common practice among RV'ers, but it doesn't seem to be.

Sean

[Lostranger]

I know that to heat, cool and power the  average over the road truck the APU's are sized pretty good. But if you want to Heat, Cool, and Power the sq ft of a bus, you will probably want a little more.

I should have made it clear, as I did on the thread where this idea came up, that I am not intending to use an APU to heat and cool forty feet of bus. The back sixteen feet (bed/bath/laundry) can be isolated. That's the only area we will cool while parked. We want to be able to sleep cool in the hottest weather. Even then the APU will be a backup. I'm installing a tiny window AC unit in the bulkhead over the head of our bed, and it will run on solar. I envision a separate APU-driven evaporator at the dash that we could use while traveling, but it would be isolable.

The heat I plan to extract would also be confined to the back of the bus, AND it would be a supplement/backup to our main heating system. We lived through last winter with inadequate insulation (currently being remedied), and I vowed to never again let my wife get cold. (She promised to share whatever climate control I provide.)

With the efficiency of our 1020 watts of Samsung panels and 60 amp MorningStar MPPT charge controller, our generator need is minuscule. If we spend part of next winter in Florida, that need may be nonexistent, but I'm not foolish enough to think we will never need to charge batteries. Still seems to me that an APU ties everything together. The times we need to supplement heat or cooling are the same times that batteries need topping. Voila!

Glad I started this thread. I thrive on an abundance of information. This intelligent and innovative group is a well spring. Thanks to all.

Jim

[Homegrowndiesel]

I agree Jim
The APU's are great, already set up with all you need. With your solar set up you are not going to need much. 
  With the hot water coming out of the apu, if you put a tee with valves you can direct the heat to your inside heat exchangers in the winter, if you load the apu with electric heaters, the hydronic side also puts out more heat. Here is a pic of what we have under our bed in our eagle. Running off of the Kubota, or our diesel heater (also tied into our detroit) it is all we need in any weather. The radiant heat is all you need in most weather, but if it is really cold the fans hooked to a thermostat take over.
  In the summer the apu will do fine for your bedroom when you are not harvesting enough solar. Sounds like a good plan, keep us posted.

Thanks, Bill