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Author Topic: APU (Auxiliary Power Unit)  (Read 5083 times)
Kenny
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« on: October 09, 2008, 10:00:58 AM »

Has anyone thought of or even used an APU (auxiliary power unit) in their conversion instead of installing separate water heating, generator and AC? For those who are unfamiliar with APU's, they are used in Semi-trucks due to no-idling requirements. It is a unit that typically mounts outside the cab and contains a small diesel engine with a generator, water heating for the vechile engine and cab and has an AC unit. If you search the Web there are many forms and options available. Anyone researched or used one of these?

Kenny
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Nick Badame Refrig/ACC
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« Reply #1 on: October 09, 2008, 10:31:33 AM »

Hi Kenny,

Have you ever heard an APU run?  They sound like a freight train.

In the past year and a half, I have had maybe 30 truckers here at the shop in for warranty work on the APU's. The generators

are usually ok but, everything else vibrates apart. Pipes crack, panels fall off, fuel lines break, and refrigeration coils crack.

I think all of them gennies are over 3000 rpm's and I think running thier truck engines is a better way to go.... Cheesy

Just my expierence
Nick-
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« Reply #2 on: October 09, 2008, 01:13:49 PM »

Nick,

Just curious about the brands of APU's you're seeing these failures on?  I have a Rigmaster with the two cylinder Perkins that runs at 2,800 so yes its got an extra 1,000 rpm's over most gensets.

I researched brands, I thought pretty well, but the trucker network doesn't have as much to compare to as the Bus Conversion experience.  It's going in my HDT to use it seperately and to also run back-up in my fiver for boondocking.  Rather than hanging it outside where it can be noisy I have a box I'm building around the APU with air ducted in at the least with multiple 90 degree bends and can add insulation to quiet it even more and run a stack with longer pipe and muffler system. 

I knew they were noisy so that is why I was going that way with my adaptation and I felt their boxes and mounting also contribute to that noise.  I could find very little feedback about the lives of them, but I see used ones on eBay all the time with 4-5,000 hours and mine has less than 400 when it was removed so if I can redesign early that would be great.  I am at the point where I could isolate the entire 400# unit with rubber mounts to further absorb vibrations if that would tame some of the failures.  These are hung solid on the truck frame rails and don't appear to have much isolation so I can see where the failures you mentioned are generated.....

Any thoughts from your view?  And lol, replacing with a regular genset isn't one, I need the HVAC as well.
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« Reply #3 on: October 09, 2008, 02:48:50 PM »

Here at Los Angeles Freightliner, we are a dealer for the Powertech APU which is 2 cylinder-either Kubota or Caterpillar- with a 5kw generator.  It is completely self contained with its' own cooling system.  So it is just a 5 kw generator-if that's enough-then use it.  Then under the bunk is a Dometic truck 14,000btu A/C with electric heat.  For engine heat, they just install an electric block heater.  The advantage to this is that the cooling system of the engine and the air conditioning system of the truck is left intact-whereas other systems tie into them.  Personally-I don't like the sound of the 2 cylinder engines-the 3 cylinder is much smoother and quieter.

In California, our illustrious CARB (California Air Resource Board) has come out with a rule that if the truck has a DPF (Diesel Particulate Filter) the APU has to have a DPF also.  So far, Thermoking is the only manufacturer that has a CARB approved Diesel engine powered APU.  On a new truck, with installation and 12% FET (Federal Excise Tax-required on all new trucks over 33,000lb gvw or ones that can tow a trailer), it costs $15,000.00.  Still a good deal that will pay for itself on a big rig doing 120,000 miles a year in about 3 years.

I would suggest instead, looking at the 7kw Powertech compact generator.  It runs at 1800rpm, has a brushless direct connected alternator (no belt drive) and uses a 3 cylinder Kubota that will last well past the 20,000 hour mark (I have a friend that his had 23,000 hours on it when he sold his truck).  Good Luck, TomC
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« Reply #4 on: October 09, 2008, 03:14:40 PM »

Nick,

Just curious about the brands of APU's you're seeing these failures on?  I have a Rigmaster with the two cylinder Perkins that runs at 2,800 so yes its got an extra 1,000 rpm's over most gensets.

I researched brands, I thought pretty well, but the trucker network doesn't have as much to compare to as the Bus Conversion experience.  It's going in my HDT to use it seperately and to also run back-up in my fiver for boondocking.  Rather than hanging it outside where it can be noisy I have a box I'm building around the APU with air ducted in at the least with multiple 90 degree bends and can add insulation to quiet it even more and run a stack with longer pipe and muffler system. 

I knew they were noisy so that is why I was going that way with my adaptation and I felt their boxes and mounting also contribute to that noise.  I could find very little feedback about the lives of them, but I see used ones on eBay all the time with 4-5,000 hours and mine has less than 400 when it was removed so if I can redesign early that would be great.  I am at the point where I could isolate the entire 400# unit with rubber mounts to further absorb vibrations if that would tame some of the failures.  These are hung solid on the truck frame rails and don't appear to have much isolation so I can see where the failures you mentioned are generated.....

Any thoughts from your view?  And lol, replacing with a regular genset isn't one, I need the HVAC as well.

Hi Russ,

I was trying to refrane from mentioning Powertech but, since Tom says there is a 1800rpm unit out there, thats great because
the 5k units are really bad..
The standard units are powertech gens and Dometic heating/cooling units as Tom also uses.

Nick-
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« Reply #5 on: October 09, 2008, 03:47:48 PM »

Check on the APU...I think you'll find that it's 400 HZ not 60 Hz. I sure hope I'm wrong.

Bob
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« Reply #6 on: October 09, 2008, 05:28:06 PM »

All truck units are alternator or inverter created 120vac 60cycle. Good Luck, TomC
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« Reply #7 on: October 10, 2008, 08:27:11 AM »

I was trying to refrane from mentioning Powertech but, since Tom says there is a 1800rpm unit out there, thats great because the 5k units are really bad..
The standard units are powertech gens and Dometic heating/cooling units as Tom also uses.

Nick,

I take it then that you weren't talking about Rigmasters?  I agree the two cylinders aren't as quiet or smooth, but with enclosures, mounts and muffling can change even a V-Twin HD.  The Rigmaster I have is a 6 kw which is more than I need for my fiver since I have two A/C's, a diesel fired heat system, solar panels and a lot of 12 v. items. 

Just looking for feedback on anything specific to this brand to watch for?

Thanks guys,

Russ
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Well no longer a bus nut, but over the years I learned a lot here and still come back to see what I can apply to the conversion of my KW T2000 for hauling my Teton fifth wheeler.
Nick Badame Refrig/ACC
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« Reply #8 on: October 10, 2008, 05:13:42 PM »

Hi Russ,

I never worked on a Rigmaster.

FYI, Powertech's are in a hush box. "sorta" metal inclosure...  and still very noisy!

Hopefully Rigmaster's unit is quieter.

Good Luck
Nick-
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« Reply #9 on: October 10, 2008, 08:48:03 PM »

You guys need to quit perpetuating the myth of fast running generators. My little water coolde Honda two-cyl runs at 3600 rpm and is smooth as silk and very quiet.

Since it is Honda I have no doubt it will last longer than I will.

I had a two-cyl Onan that ran at 1800 rpm and it shook the whole bus. It heated everything within 50' and could be heard across two counties!! It weighed twice as much as the Honda.

Even though it worked fine I I couldn't stand it any more. I took it out and spent $4200 and a lot of work on the Honda, gave the Onan to a friend. I didn't want to have any complaints from him if I took any money!!
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« Reply #10 on: October 13, 2008, 11:28:31 AM »

Hi Russ,

I never worked on a Rigmaster.

FYI, Powertech's are in a hush box. "sorta" metal inclosure...  and still very noisy!

Hopefully Rigmaster's unit is quieter.

Good Luck
Nick-

Thanks Nick, that took a load off my mind.  I knew that noise from a twin would be more than a triple, but didn't like the thought that parts might be falling off left and right.  After your comments I am considering mounting the entire unit on rubber to tame some of the wiggles.....

Russ
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Well no longer a bus nut, but over the years I learned a lot here and still come back to see what I can apply to the conversion of my KW T2000 for hauling my Teton fifth wheeler.
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« Reply #11 on: October 13, 2008, 03:14:41 PM »

One of the quietest generators I've ever heard are the Pandas that run at 3600rpm.  They are in there own hush box (but are pricey).  I was at a boat show in Newport Beach, Ca, they had a 8kw powered by the 2 cylinder Kubota running at 3600rpm in a hush box.  They fired it up and barely could here it over the outside noise-remarkable. 
Most of us do not need a 1800rpm generator that will last over 20,000 hours before overhaul.  I would consider a 3600rpm Diesel generator at 12kw if it is at least a 3 cylinder.  Then it would be lighter, probably cheaper also. 
We sold the Rig Master for awhile, but they were problematic.  The Powertech APU is a much more reliable unit.  As to noise of the truck mounted APU's-just remember that most of the time these units are being run in a noisy truck stop with reefer units, trucks passing all night long.  I agree that for a quiet campground use, they would be too noisy.  Good Luck, TomC
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« Reply #12 on: October 13, 2008, 04:36:50 PM »

For what those APUs cost they should be quiet, but they aren't.  I can understand why companies were reluctant to spend $5,000 and up on APUs until the fuel price crisis this year.

Recently, some idiot expeditor was parked in the RV or car parking area at a Flying J with his APU making a terrible racket.  He was 100 feet away or better and I couldn't hear my generator that wasn't 10 feet away!  He should have been parked with the rest of the trucks if he wants to make diesel racket.
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« Reply #13 on: October 14, 2008, 08:34:15 AM »

We sold the Rig Master for awhile, but they were problematic.  The Powertech APU is a much more reliable unit.  As to noise of the truck mounted APU's-just remember that most of the time these units are being run in a noisy truck stop with reefer units, trucks passing all night long. 

Tom,

What kind of problems did you experience?  Was is model or date specific, or all Rigmasters?  I think mine is an '06 and if like most companies, product improvements are ongoing.  The local KW dealer sells them and like everything mechanical around truckers, they tear up steel balls with rubber hammers and the issues they see aren't consistent, except getting parts rapidly.

Thanks for any feedback,

Russ
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Well no longer a bus nut, but over the years I learned a lot here and still come back to see what I can apply to the conversion of my KW T2000 for hauling my Teton fifth wheeler.
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« Reply #14 on: October 14, 2008, 04:37:33 PM »

I talked to our Powertech rep today.  He said that the APU's are having maintenance problems-meaning that the drivers are not doing regular checks on the oil, water, etc.  So the engines are having heating issues from irratic maintenance checks-do figure!  Whereas, other drivers with normal gensets on their trucks seem to be more astute about keeping up on the maintenance-hence like my friend that got 23,000 hours out of the CD8000 compact genset of Powertech.
The Rigmaster we were selling has a 1 cylinder Kubota that was noisy and vibrated.  Probably now are better.  Good Luck, TomC
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