Genset.

[Bob Gil]

Would it be reasonable to think I could run one AC and the refrigerator off the batteries and the engine while going down the road?

I am trying to figure if I will need to run the 14 kw gen set while going down the road.

I plan on having at least 4 deep scycle battries and maybe 2 others set aside to start the engine.

Does that sound possible?

I still have not gotten my bus home but am trying to think ahead.

[Sean]

...  I've never understood the reasoning that you get the inverter to not have to run the genset.

As Jim said, the inverter running from batteries is quiet.  If you stay at national parks, as we do frequently, you will find that generator operating hours are restricted, in some cases quite severely.

We just wrapped up a stay at Furnace Creek in Death Valley, where generators are only allowed for four hours each day (two in the morning, and two in the afternoon).  We couldn't even brew a pot of coffee in the morning without the inverter, nor use the microwave to make dinner, etc.  Texas Springs campground, across the road, does not permit generators at all.

The story is the same throughout the national park system, as well as many other federal and state campgrounds.  We also end up spending nights on the street in residential neighborhoods, and nothing will attract a midnight knock on the door from the local constabulary like running the generator after the neighbors have retired for the evening.

We've even spent several nights indoors (we spend more time in the shop than I'd like to admit), where the generator is completely out of the question.  So, it all depends on how you use your coach, but I wouldn't trade my battery/inverter combination for anything.  In fact, I wish I had room for (1) more batteries and (2) more solar panels.

... Both are going to use fuel, and the genset is likely to be more efficient.

That's just plain incorrect.  A 6.5kW generator will use typically about .6 gallons per hour at full load.  By contrast, the Delco 50DN alternator, generating the same 6.5kW, will use roughly .1-.2 gallon per hour with the engine running at road speed.  "Stealing" a dozen horsepower from a ~450BHP engine working in it's power band is more efficient that using a smaller engine to do the same work.  Think of it this way -- what would make a more efficient generator: One 100hp engine, or two 50hp engines?  The larger the engine, the more work per unit fuel you will get out of it (generally speaking).

All of that assumes that you are driving at normal RPM on a flat, straight road.  The efficiency equation actually improves when you throw hills into the mix.  That's because power being generated by the alternator is completely free on the down side.  Where does this amazing free energy come from? It is the energy that otherwise would have been expended as waste heat in the brakes (or retarder, if so equipped).  Think of it as poor man's regenerative braking.

All of that being said, there is, of course, no way that the efficiency improvements of using the engine alternator over a generator will ever pay for a $2,000 inverter, at least not in the time most of us will own and use our buses.  So you need to justify the inverter for other reasons.  But once you've done that, then the cost/benefit equation for using the alternator vs. the generator is an easy one.

-Sean
http://ourodyssey.blogspot.com

[Sean]

Would it be reasonable to think I could run one AC and the refrigerator off the batteries and the engine while going down the road?

Bob,

That all depends on how big your engine alternator is.  You don't say in your post (or your profile) what kind of bus or engine you have, so it's hard to even guess here.

The alternator that was supplied as OEM equipment on the 2-stroke Detroits in many large 24-volt coaches is a 270-amp Delco 50DN.  The huge output was needed to run massive blowers for the passenger air conditioning system.  These alternators can put out nearly 7,300 watts when running at rated speed under full load, and are rated for 6.5kW continuous duty.  That was generally achieved by using oil cooling and direct gear drive.

Let us know what alternator you've got, and we can give you some guidance.

-Sean
http://ourodyssey.blogspot.com

[DavidInWilmNC]

Another point in favor of an inverter in addition to a generator is the refrigerator.  Unless one uses an LP absorption 'fridge, the generator will always be running just to keep the food cold - at truck stops (or wherever one buys diesel), in the winter when there's no need for the A/C's, etc.  Inverters can be expensive, obviously.  I didn't spend $2-3K on a true sine wave inverter.  I spent about $300 on a Vanner 3600 watt inverter/charger on eBay.  Buying used is always an option.  I've run small and medium sized refrigerators off inexpensive MSW inverters for years with no problems.  I've never had a problem with anything I've run off of my MSW inverters.  The biggest is only 1000 watts, so I obviously haven't tried to run an A/C from it, but I wouldn't hesitate to do this with my big inverter.  I don't look at an inverter as a substitute for a generator all the time, just some of the time.

David

[Nick Badame Refrig/ACC]

To give you an idea about running A/C's off your battery bank..

I did an expierement when i had a 840 amp hour Flooded lead acid batt. bank set up for 12v. [1000amp hr now]

My 3000w Xantrex RS3000 has an english language monitor panel that displays all parameters, amps, volts, in and out, battery charge state,

volts and amps, and incomming volts and amps of both legs of 50 amp. So this was a no brainer to do..Starting at 13.6 volts,

I ran 1 15,000 btu HP in A/C mode on a 90 deg. day with no incomming charge or landline/genset hooked up. The low voltage alarm

tripped at 10.6 volts and total run time was 44 min's

Not much...huh

FYI
Nick-

[H3Jim]

another option on the refrigerator is to get one of the ones that run on 12 or 24 dc, then you don't need an inverter or a generator to run it.  The downside there is that they are pricy.

[Devin & Amy]

My turn,
We use a 13.5kw kubota 3cyl. w/turbo, the turbo was a prototype from Dick Wright and it does seem to keep me closer to .75/gal. per hour.
We also have 6 AGM Batteries wired 24v for our house bank.
We love the inverter for its loadsharing ability, which is probably the best thing you could ever do for power management issues.
We plant trees for a living and at times we can be off-grid for a week or two. If you don't want to hear your genset run constantly you should IMO have a pretty good sustainable system.
One time in Yellowstone Nat. Park we parked just down the road from a geyser that was scheduled to blow in the next hour or so. My kids laid in their bunks and watched out the window for the eruption, We ran the fridge, 1 A/C, and cruised the internet on a sat. connection. There were about 100 people waiting in the viewing area, And we did not offend anyone with the noise of a genset.
FWIW
Devin

[Don4107]

Great thread.  Always interesting to see how others have skinned the cat.  I am holding off on sizing/shopping for the genset until I am much further along with the new bus.  I'll know better what size to look for after choosing and installing the rest of the gear.  Hoping that by then there is an inverted based genset designed for RV use. 

Old bus has 5.5KW and we never need more but it is a very simple layout with one noisy rooftop AC.  We are accustom to a little power management.  At any rate, I am planning on a layout that will be livable on a 30Amp pole and in fat city on 50.  With a Proheat doing the heat and hot water, that leaves the big loads of the ACs, the micowave, and battery charging.  Have not picked the refer type yet but leaning toward AC or DC with enough solar to support it. A SW series or equal inverter with power supplementing should make living on 30/50Amps pole or genset doable.  Since the rest of the system is designed for 50Amp I cannot see needing much more that 6.5KW from the genset.

If I had to buy a genset today it would be the Honda EU6500is converted to permanent installation by me.  I hate noisy Gensets and even worse noisy AC.  Why not start with a quiet unit right off?  Now if someone designs an inverter based diesel genset around 6 or 7KW in the mean time, that would be great as long as it is quiet.

Don 4107

[Tenor]

Don,
Don't forget about propane fridges!  They are very efficient.  Run one on your inverter while going down the road and fire it up once you reach a boondocking place.  Same thing for hot water.  I'm doing some of the same things mentioned above.  7.5 KW genset (gasoline, got a great deal on it) Xantrex 4024 Inverter to allow me to run several AC's while on the road, 50Amp Shore line, 12V lighting, propane furnace, stove and fridge (110 also).  I'll also have a 110 hotwater heater with a heat exchanger.  I'll have some solar panels to help charge the batteries.  I won't have a big battery bank to start, but I'm not going to use much 110 except while driving.  Good luck!

[Nick Badame Refrig/ACC]

Great thread.  Always interesting to see how others have skinned the cat.  I am holding off on sizing/shopping for the genset until I am much further along with the new bus.  I'll know better what size to look for after choosing and installing the rest of the gear.  Hoping that by then there is an inverted based genset designed for RV use. 

Old bus has 5.5KW and we never need more but it is a very simple layout with one noisy rooftop AC.  We are accustom to a little power management.  At any rate, I am planning on a layout that will be livable on a 30Amp pole and in fat city on 50.  With a Proheat doing the heat and hot water, that leaves the big loads of the ACs, the micowave, and battery charging.  Have not picked the refer type yet but leaning toward AC or DC with enough solar to support it. A SW series or equal inverter with power supplementing should make living on 30/50Amps pole or genset doable.  Since the rest of the system is designed for 50Amp I cannot see needing much more that 6.5KW from the genset.

If I had to buy a genset today it would be the Honda EU6500is converted to permanent installation by me.  I hate noisy Gensets and even worse noisy AC.  Why not start with a quiet unit right off?  Now if someone designs an inverter based diesel genset around 6 or 7KW in the mean time, that would be great as long as it is quiet.

Don 4107

Hi Don,

I do know an OEM that will sell to you but, that will have to be in a PM.
http://www.cumminsonan.com/www/pdf/specsheets/a-1502.pdf

Nick-

[Sean]

To give you an idea about running A/C's off your battery bank..

... The low voltage alarm tripped at 10.6 volts and total run time was 44 min's

Not much...huh

Nick,

Just to give the flip side, we regularly run one A/C all night on the batteries alone.  Generally, we don't do this unless the outside temp is pushing 90 or above.

The numbers:  We have 920 amp-hours of batteries, or 22kWh at nominal 24 volts.  Our A/C's are a tad smaller than yours: 13,500 BTU/hr each.  As I said earlier, I measure them out at about 1600 watts when running.  On a typical night, though, they do cycle on and off, so that's not really a continuous number.

Even if they don't cycle, 1600 watts times about eight hours is about 13kWh, or just over half our battery capacity.  With AGM batteries, we regularly go down to 70% depletion.  So one air conditioner overnight is very comfortably within the working capacity of the system.

Of course, one thing that let's us do this comfortably without, umm, losing any sleep, is the generator autostart feature of the inverter.  Should our overnight loads draw the batteries down below the thresholds that we've set, for whatever reason, then the generator will come on automatically, thus avoiding either damaging the batteries or having the whole system shut down on LBCO.

Of course, YMMV, etc.

-Sean
http://ourodyssey.blogspot.com

[TomC]

Don- Cummins/Onan is making a "hybrid" system that uses a small Diesel generator with inverter technology.  Interesting theory on paper, but I'm always leary about Onan since they use their own electronics, and they always seem to go out at some time at an expensive amount of money.  I just talked today to Wrico, and they are still using mechanical switching that is very reliable.  Personally, a good simple generator (read Powertech or Wrico) with a load sharing inverter with auto start should do the trick.  Good Luck, TomC

[Bob Gil]

  Finally got the profile to take.

Sean: I do not have an engine alternator  at this time, I was trying to see what I should get.

My bus was the one with the engine compartment fire.  It does not have the engine alternator that most have it is powered off of the belt on the blower.

I hope that I can one of the big ones i have for the Mack's to work on it.

By the way thanks to the group for menting Fleet Pride I found there is a new one about a mile from me.  They have only been there 5 months.  Their prices are great too.

[chazwood]

I wish there weren't so many ways to skin a cat. It'd sure make all the decisions a lot easier

[Sean]

...
My bus was the one with the engine compartment fire.  It does not have the engine alternator that most have it is powered off of the belt on the blower.

Do you know if your coach electrics (Starter, gauges, exterior lights, etc.) are 24 volt?  If so, you will be, IMO, better off putting in a 24-volt house system than a 12-volt one.

-Sean
http://ourodyssey.blogspot.com