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Old 01-14-2019, 08:08 AM   #1
Mini-Skoolie
 
Join Date: Feb 2018
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Ideal system for trips

Ok, I've been looking at buses for a while now, and discussing the needs and expectations and trying to design and figure out what systems would be needed for what we want.

Basically our use would be to use the bus for long trips, as a giant suv, and to sleep and cook on long trips. An rv really, but unlike many people, we don't plan on staying in the bus camping much, mostly just getting from point a to point b with needed sleeps in between.

Plan is to use it year round, so from hot summer heat, to freezing 30 below temperatures. Despite my past experiences with solar power, I've decided to not bother this time, other than maybe a battery maintainer for when its sitting unused.

So, I've been looking at heat and air conditioner systems, thinking of various scenarios. I've decided that for our uses, we're either going to be parked on the road or rest stop running the engine, or at a camp site with power to plug in. We don't plan on camping off the trail and running a generator. I've also looked up fuel burn rates for generators and idling engines, and the difference just isn't big enough to justify carrying a generator and gasoline.
So I've been considering a mechanical drive ac system for the bus, vs wall mount ac units, and it seems like why install 2 separate systems when one can potentially run from a large alternator or plugged in to grid power?
There are 320 amp alternators that say they produce 60% power at idle, or 192 amps. After the inverter that should be a reasonable way to have at least 15 amps vac and with a large inverter and batteries should have lots of amps for intermittent loads.

The little 5000 btu air conditioners run 400 to 600 watts each, so it should be able to run 2 or 3 of them really. Like any power needs, heat and ac are always the biggest loads.
I would plan to have 3 nice batteries in the compartment, and just replace the factory alternator with the super huge one. I don't plan on running stuff without the bus running, so house batteries seem like a waste of money. I simply don't plan on trying to figure out a way to run everything while the bus engine is off. It would require a generator or giant battery bank. Most generators are as noisy as an engine so I don't see a reason to go that way.

I see there are also some hybrid belt drive alternators that run from an engine belt and provide 120vac, but they won't have the same intermittent start power that a giant inverter and batteries would.


Has anyone ever actually figured out how much r value is gained by tearing apart the bus and insulating better? A part of me wants to, but seeing decent insulation being torn out makes me wonder if it's really necessary if there arent plans to live in it for extended periods.

I like the idea of hydronic heat, a heat exchanger for hot water, and 120vac air conditioning. It's a simple system that can run from the bus coolant system as well as pre warm engine, and I can add a 1500w electric heating element to the coolant, so that if it's cold to provide heat and load on the engine thus creating more heat. There could be an extra heating element for when plugged into electrical service. It seems like a simple system without doubling up equipment.
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Old 01-14-2019, 08:16 AM   #2
Mini-Skoolie
 
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So what I'm thinking is a 5000 watt inverter which is capable of high surge. I found one for about 500$ that maxes out at 41 amps 120vac.

A 320 amp alternator seems to be available from 200 to 500$, I'm assuming the cheaper ones probably wouldn't hold up well to constant high output.

So if I couple a powerful inverter, alternator, and 3 decent 12v batteries in the battery compartment, should that not be a decent way to have 120vac while the bus is running, so it will work as needed?
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Old 01-14-2019, 08:20 AM   #3
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on the subject of Air Conditioning on the road in Hot climates..



your little camper AC or minisplits arent going to keep you cool going down the road..



idling the engine is not legal in many areas, however running a generator hasnt been tagged as being illegal in most areas..



if it were my bus, Id have 2 AC systems.. an electric one desifgned for being parked.. you need a lot less cooling power to cool a stationary parked bus .. no 70 MPH wind blowing heat in, curtains over the big windshield vs sitting in the hot sun as you drive west in the afternoon, no engine heat to overcome..



all of the above heat-adders make it why you will likely want an engine driven air-conditioner for running on the road. insulating your bus heavily can most surely help with cooling loads.. but not totally..



for contrast, from the factory a 35 foot bus ordered with A/C will likely be equipped with 120,000 to 130,000 BTU of Air-Conditioning.. .. once insulated and converted, you can cut the number in half for going down the road.. but not much more than that and still be comfortable on those hot humid days..



for being parked in an insulated bus of 35 foot length, a couple 12,000 BTU minisplits will do the job nicely.. esp if you curtain the windshield, park in the shade, and the like that many do while camping.. and of course at night your cooling load is cut decently since theres no sun load on your bus..



-Christopher
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Old 01-14-2019, 08:29 AM   #4
Mini-Skoolie
 
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Thanks for the info.
That's a huge ac load requirement change from driving to parked.
I've also been eyeing up used APu systems from semis, they have a 2 or 3 cyl diesel engine with ac system and heat system. That might be cheaper than adding ac to the bus engine, and allow parked use as well, but probably burn more fuel down the highway I imagine.
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Old 01-14-2019, 09:14 AM   #5
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This is an age old story, and Christopher has it right 100%. Although I'm not cutting my AC in half, I spend too much time in sunny places for that!

Also, when looking at a huge output alternator, consider that that is a maximum number and unless you have a unit specifically designed for high output at idle speeds (bosch sb200 is what I have) it will actually have far far lower output at idle. Along with that, you don't really want to be running your alternator at or near full power any more than you want to drive your bus with the throttle mashed to the floor.

For heat, look into non-electric ways to heat your bus. Using electricity for this stuff when you don't have a tether to an external outlet is expensive.

Truck APUs are cool but they're made for truck cabs which are small spaces. 13.5k btu air conditioners are the norm for them, which is probably OK while you're parked if you have put any effort at all into insulation and heat loss, but worthless on the road.
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Old 01-14-2019, 09:35 AM   #6
Mini-Skoolie
 
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Yeah the heat definitely isn't such a large problem. A person has several cheap ways to heat with diesel be it little webasto style heaters or diesel air heaters etc.
But, if you have a several horsepower engine mounted to make power for air conditioning, that's also a source of heat already also. For eg if I ended up with a 1 cylinder diesel generator for air conditioning, why wouldn't that generator also be used for heat? If the engine waste heat is also used for cabin heat the efficiency would be high.
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Old 01-14-2019, 09:36 AM   #7
Mini-Skoolie
 
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Also I'd probably aim to use hydronic heat, and have it so I can circulate through the engine as well. If its 20 below, the engine will never start unless its warmed up. That's why diesel space heaters seem useless for this.
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Old 01-14-2019, 09:43 AM   #8
Mini-Skoolie
 
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So I take it a rear engine city style bus with factory air would be what to look for then. I mean theres no way it could be worth it to start with a 2000$ school bus and change everything about it ��
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Old 01-14-2019, 09:56 AM   #9
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https://www.ebay.com/itm/Brand-New-1...UAAMXQgb1RI1Jd

I'd be inclined to purchase a generator like this. Those chnagfa diesel engines from what I gather can pile the hours on no problem. They're originally off farm equipment and are wet liner. I'd think that since they say roughly 30% of engine power is wasted on exhaust heat and another 30% engine heat, if I can utilize either or both, reduce heating load by half or more, and have a simple hydronic system instead of multiple heat systems.
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Old 01-14-2019, 10:35 AM   #10
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Quote:
Originally Posted by Parkland View Post
So what I'm thinking is a 5000 watt inverter which is capable of high surge. I found one for about 500$ that maxes out at 41 amps 120vac.

A 320 amp alternator seems to be available from 200 to 500$, I'm assuming the cheaper ones probably wouldn't hold up well to constant high output.

So if I couple a powerful inverter, alternator, and 3 decent 12v batteries in the battery compartment, should that not be a decent way to have 120vac while the bus is running, so it will work as needed?
Not likely.

Here is a good read on inverter and battery sizing :

https://www.solarpaneltalk.com/forum...-size-tutorial

https://www.solarpaneltalk.com/forum...utorial-part-2

Also keep in mind that, with a 12v - 5kw inverter, you will be drawing about 550 amps DC at full output.

Another detail to consider is that automotive alternators are not rated for continuous duty.

Not trying to rain on your parade but I would hate to see you spend time & $$ on something that doesn't meet your expectations. Or worse, burn down your bus with your family in it.

Good luck.
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Old 01-14-2019, 11:13 AM   #11
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there are often school busses with factory air for sale i nthe southern / southwestern states... my red bus has it, many busses come with 2 engine driven A/C systems, so if you want to cut it im half, its easy to take one out. city busses oiften have one large compressor..



de-rating a factory A/C system is possible. Joeblack5 and his dory transit is a pewrfect example of how using a small pony engne to drive the engine driven compresors at a reduced capacity is possible.. thus you use the main A/C for noth parked and driving.. using an A/C with TxV vs orifice tube. and then varying the RPM of the pony engine, and amount of airflow across the inside evaporator works so that you can run up the capacity for highway use and lower it for comfortable over-nighting conditions without over-cooling. you have all kinds of options with hydronic heating.. using existing Bus heaters for heating the front areas.. heated floors make for a really nice indoor environment.. the webasto and similar coolant heaters are quiet and dont use a ton of fuel to operate.. a well insulated bus can be heated on 17000-20000 BTU of heat pretty well.

-Christopher
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