Generator or APU?

[pugslyyy]

The issue with using a small generator is that there are not very many available with diesel engines. So this would require another fuel tank for the gasoline and the issues involved with that.

I think the some of the servicing issues of many of the APUs are related to interconnection of them with the AC and heating systems - that seems like it would messy. There is a nice Cummins/Onan unit that is used in many of the higher end RVs called the "QD series" which are available in a small as 3200 watt with an inverter-output (so the power quality is better). The QD series includes an acoustic enclosure so its quiet - but it does weigh over 200 pounds and is about 30"L x 18"H x 18"D. They cost about $5000 - so not cheap. They say it will run a big rooftop AC unit and also could power the radiant floor heating system in the winter.

Worth considering...

The APUs I've looked at all have small diesel generators on them (Kubotas, IIRC) - but you just don't find many used for camping because they are 3-5x the cost of a propane powered unit.

If you look at marine generators, there are a lot of compact diesel units. Keep in mind that marine generators are designed to run at sea level.

 

[DirtWhiskey]

Alright, just chatted with my uncle. It's important to remember that this is third-hand information and I have never even been near any of these units so here goes: Uncle likes the Thermoking/Tripac units because they have a national sales and repair presence and they are the quietest. They cost up to $13k (he mentioned that the last in-frame overhaul on his older Series 60 diesel was $11k !!!) depending on installation and still have problems running his microwave, but he could fix that by increasing his battery capacity. The big hauler companies usually see the APU's payback at year 2 running 200k miles per year. He recommended the isolated units that only share fuel with the main rig (no auxiliary systems) because, and I quote, "When one breaks, they both break". He then regaled me with stories of entire coolant systems being dumped on the freeways because of crappy APU connections. Expect typical shop-hour charges and $200 servicing appointments every 500-1000 hrs. His has a hydronic system that he loves, but he doesn't know if it's Esbar or Webasto.

He was happy with the original Rigmaster units. They went out of business (a common theme early), got bought and are now back in service. He has heard good but noisy things. Not to speak for anybody, but when I described our particular use, he said he would never consider it because of the typical low per year mileage of our use, cost, service and reliability issues. He said he could buy a half-decent used over-the-road rig for the price of an APU.

Hope this helps!

 

[Haf-E]

Yes - the kubotas are nice engines. I think a lot of the small trucking and marine APU's are expensive because they are made in low volumes. The Onan diesel units are made in higher volume and are more common - i.e. easier to get serviced and parts for. Ditching the waste heat connection and going with just an all-electric connection simplifies the system substantially. Also makes it easy to manage the system when "plugged in" to an AC connection also.

 

[LoRoad]

Alright, just chatted with my uncle. Hope this helps!

I hope it helps too! There's lots of good advice coming in from all over the place - Thanks to All!

 

[bee]

I work on a fleet of Carrier brand APUs. I was told the model we have runs about $10k (might be a wholesale price). The apu includes A/C, and electric heat. Ours is a 3500watt generator and has a separate alternator which pushes up to 50amps continuous to the battery (measured with an amp clamp). I don't understand the comment about having trouble getting them serviced, I would think some truck shops and definitely refrigeration trailer shops can fix them. Also the comment about them probably being 3 stage chargers, well they definitely are not. I don't know of any over the road oem alternator that is 3 stage.

They can be tied into the engine coolant which means that there is of course an increased chance of coolant leaks. If it concerns you, just put ball valves in the coolant line so that if the apu water pump goes bad or whatever, you can just isolate the system. "crappy connections" mentioned above would be the fault of the installer not the system.

The engine is bombproof, the rest of it is not. Circuit boards, capacitors and generators are pretty common problems. Overall I would consider there quality to be mediocre, but remember we have units with over 10,000 hrs on them.

I don't think I would want one in an rv or expedition vehicle. You will want to size your heat and air conditioning to your vehicle, these are meant to be used in over the road tractors and our drivers still complain that they don't cool well enough. For heat it would be more efficient to have a webasto which all of our trucks have in addition to the apu.

 

[bee]

I just learned about thermokings tripac apu. It is quite a bit different concept then the carrier brand I mentioned above. It uses a diesel espar d2 or d4 for heat. It has a belt driven a/c compressor for air conditioning, and an alternator to charge the batteries. It is not a generator so no 120v without an inverter and battery bank. Benefit would be the yanmar engine would only need to run for a/c and charging the battery bank. The Carrier apu needs the engine running because both heat and a/c are 120v electric.

 

[LukeH]

Lots of great information here, for and against each solution. But the bit I can't come to terms with is why anyone would want to get out into the great outdoors, switch off the truck and not want to enjoy the peace and quiet of where they are. The constant thrum of an internal combustion engine would spoil everything. The small 2 and 3 cylinder diesels we're referring to are nowhere near as smooth as a 6 cyl truck engine and will always be present. When you need A/C there's generally lots of sun so roof covered in solar and decent battery bank would do; the new idle laws have given rise to some very nice self contained 24v rooftop A/C units. When you need winter heat the small diesel heaters wouldn't make a dent in the battery bank you have for the A/C, even near the polar regions. Judging by the prices announced for the APUs you could really have a big solar/battery system for that money. EGN (I think) even cooked on battery power without a generator in his Kat 6x6. If the size of the battery bank is a problem the LiFePo batteries are more compact and cycle better.
Gosh that's almost a rant now I reread it. Please don't take it as one, I don't mean it to be; my apologies if I have offended anyone, it really isn't my intention. I just think there is an alternative to depending on another engine when you're stopped enjoying the shore of that lake, or the wide open space in front of you.

 

[DiploStrat]

Ni Marx, Ni Jesu

APU - auxiliary power unit VS a generator

Why would one be better than another in an Expedition Vehicle?

Just to play devil's advocate, why do you think you need either? If I read the website on your BAE truck correctly, you already have well over 200A of alternator. The BAE certainly has the capacity to carry 600 - 800Ah of battery. (My 3500 Chevrolet carries 600Ah.) Finally, you are designing your own roof; you should be able to carry between 500 - 1000w of solar without trouble. (I have 500w.)

Assuming that the 12v side of your 12/24v system produces between 14-15v at 70-20F, then you should have adequate voltage differential to charge a 12v battery bank quite nicely. If not, there are devices like the Sterling Alternator to Battery charger which work well with 13v systems: http://sterling-power-usa.com/12volt-210ampalternator-to-batterycharger.aspx (Available from Defender Marine for much less.) It is also possible that you could so something clever with the 24v side of your system for even greater efficiency.

For reference, my truck uses a Webasto Dual Top for water and camper heat, a 6k BTU A/C, a convection microwave, and an induction stovetop. You can see pictures here: http://www.pbase.com/diplostrat/ndeke_luka And I have been posting way too much in the 12v forum: http://www.expeditionportal.com/forum/forums/48-Power-Systems-12v-Solar-Gen

Free advice is worth what you pay for it and YMMV, but I suspect that you can do what you want using the alternator in your truck, coupled with a decent solar kit.

 

[egn]

As already mentioned I have an all electric camper without lpg. Energy is stored in 900 Ah/24V lead acid batteries that are normally charged by the 150A/28.8V alternator. This worked fine in the first 5 years of use, because we stay only a few days and then move forward. Then 2 years ago I installed 2 kWp solar on the roof. Since then we can stay for weeks without any power connection, at least during the sunny half of the year.

I see only two situations where a generator/APU would be of interest: AC in summer and power and heating in deep winter.

AC in summer may also be handeled, at least part of the time by highly efficient inverter AC units, providing about 4-6 times the cooling power you put as electricity in it. So 500 W power from solar gives a cooling power of up to 12.000 BTU. At least for our higly isolated cabin with solar modules protecting the roof from direct insulation, and the double pane coated glass windows this would be enough cooling power.

Longterm camping in really cold climate is more of an problem without some extra power source. Heating is no problem with a diesel furnace, but the electrical energy will be as solar power will provide only one 10th of power as in summer on average. Once I had planned to installed a water cooled generater to provide electricity and heat. But I stopped this because we currently don't do longterm winter camping and I am horrified by the necessary maintenance I would have to do on such a unit when the generator runs multiple hours a day. Annother problem is that this small units are not very efficient. You can expect only about 20 % efficient. Of course if we have the real requirement then there is no other solution. But the diesel fuel cells available in a few years may be the right option for me.

Coming back to the original question, I would go for a generator because I don't like integrated solution very much. The reason is that if one component failes you loose all other functions too.

 

[rblackwell]

Some other things to consider.

A "big" generator/apu is only required IF you want to run air conditioning (and maybe bake bread in your oven). Most battery chargers (or inverter/chargers) used for charging expedition vehicle house batteries are rated at or under 100amps. These can be effectively driven by one of those small 2000 watt Honda gas generators. Other big loads like microwave ovens, induction cook top are, by comparison with AC units, used for comparatively short periods - though we always run a generator when baking in our oven.

As pointed out above the drive engines alternator can also (with the right additional controllers, or on a very modern vehicle) can effectively charge the house batteries.

But do you really want to run a generator for hours in order to have AC - we do that for short periods like a hour or so for lunch but for hot nights we rely on fans. We prefer some "quiet" at night.


Solar panels are great in hot weather UNLESS you make a point of parking in the shade.

In hot weather we find our refrigerator is a big user of electrical power (not a surprise) - it was pointed out to be recently by a european expeditioner that good ventilation on the refers cooling unit, and the separation of the cooling unit from the cold box could greatly increase the efficiency of the refrigerator and reduce electrical use.

Cold weather and generators. IF you get a diesel generator or APU make sure that it has a cold weather/high altitude package available. We have an Onan 3.2 Quiet Diesel - no cold weather or high altitude package is available. At 4400 meters in the Pamir mountains it would not start (neither would our diesel cooktop or block heater). Fortunately the drive engine would start (though only because we have an intake manifold heater).

Truckers get around this by always having one of the engines running and not driving at extreme altitudes.

Do an "amps" budget. We typically use about 100 amp/hours per day (actually per night). If we spend a lot of time on our computers with the inverter going that can get to 150 ah. If we drive each/most days and there is some decent sun this is not really a problem. For example last year we traveled for about 7 months without plugging in and with little generator use - during, spring, summer and fall. But once Nov-Dec arrived (in Turkey) no sun, less driving and even with some shore power - we had to run the generator regularly to get the house batteries charged.

Loroad - if you spent 4-5 hours processing photos you could probably get you budget to over 200ah in a single night. You need a pretty big solar array to put back 200 amp/hours.

We have 755 amp/hour capacity in our camper using AGM batteries. These types of batteries need to be fully recharged regularly (repeated discharge and partial recharge kills them quick) hence I am very fussy about ensuring that they get fully charged every day if possible and never more than 2-3 days without getting fully re-charged. When all else fails I use the generator.

We have an Outback inverter/charger that puts out charging 100amps - it will take 4+ hours of generator time to put back 200 amp/hours. The point is - big battery banks are no good unless you have a way of put back the charge you took out

So do an amps budget and work out how you will replace the amp/hours used.

Personally I would go for a generator (and one with a cold weather package), plus make sure that the truck drive engine was equipped with an alternator that could deliver the correct voltage/current profile required to fully charge my house batteries. Even better - if there was space I would have a 2nd alternator on the truck engine dedicated to charging house batteries.

 

[LoRoad]

Rob, as usual you are chalk full of great advice. Thanks! Thanks to everyone actually.

I think what we are headed toward is electric only with supplemental diesel for heating and hot water. I really like the idea of an extra alternator to charge the house on a separate line.

 

[DocGary]

I have an APU on my 2012 Freightliner Cascadia. The unit is called Rig Master. In its application on my truck it serves to recharge the batteries and supply air. For heating the truck has a Webasto heater. I would be happy to take pictures of both units if anyone would like.

 

[LukeH]

Just another thought, which might be completely irrelevant depending on where you go with your rig:
The floor level of cab and body could be considered the wading limit; transmission and tanks have breathers to stop water ingress, the engine intake is above the cab.
But the APU will probably be slung at the same level as the tanks.
You could put it in a pressurised sealed box, like the military ones on the side of the KATs, but then you can't just turn it on from inside the camper, you have to exit, open the box etc.

 

[DocGary]

Here are a few pics of the APP. Sorry if they end being large I'm sending from my S4.

Sent from my SAMSUNG-SGH-I337 using Tapatalk

 

[AFBronco235]

Lets get back to the original question shall we. Generators and APUs aren't that different. In fact, a generator is just a type of APU that just provides electricity. If you all you need is voltage, then a generator is what you need. If you need anything else, you're almost better off building your own device. I know of guys who build 12V and 24V generators using a small engine and 1 or 2 alternators. All it takes is a little mechanical and electrical knowhow. Mechanical to mount everything on a frame and electrical to wire it all up. And even then, its pretty simple.

So lets start from scratch and ask some basic questions. What are your power needs? Is the system you're running going to be 12V or 24V or 120V? Do you plan on running the generator constantly or just use it to charge a bank of batteries? Do you need something simple and light or heavy duty and bulky that needs wheels?

If I were building a camp generator for a trailer rig, I'd make it a 12 volt system with 2 or 3 batteries wired in and mounted to the trailer. I'd have the generator as a separate package and made from an alternator and a 2 cycle gas motor, from either a chainsaw or weed eater to power it. Or if I wanted it to stay simple, I could also get a small 4 cycle motor, so I don't have to mix gas. I would use it to charge up the trailer batteries and run a converter from those to any 120V appliances I'd need. And if need be, since the generator portion is a separate package, I can just unplug it and move it to jump start/charge a dead vehicle battery in a pinch. Easy to clean, easy to use and you can get the materials for less than a small commercial generator. You can probably spend a little more, add a battery to your portable power package and one of those on board welder alternators and have yourself a welder as well! Nice to have on 4 wheeling trips where stuff breaks all the time.