Running a roof air off of engine generator

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Running a roof air off of engine generator

January 20, 2023, 08:25:12 pm

Opinions on this. I have a Delco-Remy 40SI 240 amp alternator I'm going to install. I think the Leese-Neville that I have is 200 amp. I have a Xantrex 3000 watt inverter.
My goal is this. To run the front roof air on only engine generator power while driving to supplement the dash air. Or as a back to dash air. I've looked at micro-airs soft start that advertises a 15 amp start up current. Do the numbers support being able to do this and keep the house batteries in a stable state? Not slowly draining them? And not overworking the alternator?

Re: Running a roof air off of engine generator

Reply #1 – January 20, 2023, 09:44:59 pm

Quick math says your need about 160 amps continuous. So, you will make some heat. And need to keep the alternator putting out at the required RPM.
Add in the transition taxes form 12v to 120 volt, plus whatever else you are running. It looks like a lose from here. Maybe you could add an additional alternator for a stand alone system . ?
In my case, I have 2000 watts of solar as well as additional alternator to run my very efficient mini split.

Re: Running a roof air off of engine generator

Reply #2 – January 20, 2023, 11:07:03 pm

Not sure what your wire size is coming off the isolator, but you will likely need 3/0 or 4/0 wire run to the batteries depending on the length of run.

It seems the newer coaches are adding more alternator power to reduce the need to run the genny while driving, so it is possible. It doesn't hurt to have more amps than needed.

Re: Running a roof air off of engine generator

Reply #3 – January 21, 2023, 08:17:33 am

Was at the Tampa show a few days ago and talked with a gentleman that is presenting the Prevost line of coaches. When he lifted up the door on the back exposing the Volvo engine, there were 5 alternators running off that engine. That allows them to run all 4 airs going down the road without the generator running using their inverters, which I believe they have 3 or 4 on board as well.
Quite interesting for sure. After looking at both the XL's and H3's, you can see why these rigs cost this much.
Not sure adding a larger alternator will solve your wanting to run an air going down the road. Additional items need to be looked at as well. Just a thought!

Re: Running a roof air off of engine generator

Reply #4 – January 21, 2023, 08:49:26 am

My coach came with a 340A alternator and it was set up to run 1 AC unit on the inverter. I think your 240 may be on the small side.

Re: Running a roof air off of engine generator

Reply #5 – January 21, 2023, 09:02:16 am

My Prevost had a 300 amp oil cooled alternator, 10 batteries and wouldn't even attempt to startup the air conditioner.

Re: Running a roof air off of engine generator

Reply #6 – January 21, 2023, 09:34:29 am

Quote from: Res777 – January 20, 2023, 08:25:12 pm

My goal is this. To run the front roof air on only engine generator power while driving to supplement the dash air. Or as a back to dash air.

The cost effective way to run your front air conditioner is off your built in diesel generator.
Any other way requires spending money up front and all of them still use diesel fuel to run the air conditioner: it takes for horsepower to make 3Kw of power.
If you want to take that power from your main engine, you need to add a 4Kw 120-240V alternator and its supporting cast. The frequency is going to go up and down with engine speed so you'll need as AC-AC converter to take the alternator's power and make it a stable 60Hz with 120-240V of battery to take care of stop lights and off ramps.
Any way you slice the problem, it can be done with enough money and engineering, but it's more cost effective to start the generator set and assign the loss of range to the air conditioned air.

Re: Running a roof air off of engine generator

Reply #7 – January 21, 2023, 11:25:18 am

Quote from: juicesqueezer – January 21, 2023, 08:17:33 am

Was at the Tampa show a few days ago and talked with a gentleman that is presenting the Prevost line of coaches. When he lifted up the door on the back exposing the Volvo engine, there were 5 alternators running off that engine. That allows them to run all 4 airs going down the road without the generator running using their inverters, which I believe they have 3 or 4 on board as well.
Quite interesting for sure. After looking at both the XL's and H3's, you can see why these rigs cost this much.
Not sure adding a larger alternator will solve your wanting to run an air going down the road. Additional items need to be looked at as well. Just a thought!

Prevost uses electric fans on the radiator instead of hydraulic motors so I expect that is the reason for 5 alternators. That does seem like an overkill. I still don't understand why the radiator is not facing fore and aft.

Pierce

Re: Running a roof air off of engine generator

Reply #8 – January 21, 2023, 11:34:46 am

Quote from: Pierce & Gaylie Stewart – January 21, 2023, 11:25:18 am

Prevost uses electric fans on the radiator instead of hydraulic motors so I expect that is the reason for 5 alternators. That does seem like an overkill. I still don't understand why the radiator is not facing fore and aft.

Pierce

The have a dedicated alternator for the fans, not all 5. However, they have either 3 or 4 three plus thousand inverters in the coach and that most likely is what is making it feasible to run all the airs going down the road. In my opinion, it is cheaper in our applications to just start the generator and run how many airs one wishes. A no brainer! We run our airs all the time going down the road, just saying!

Re: Running a roof air off of engine generator

Reply #9 – January 21, 2023, 11:34:57 am

Quote from: erniee – January 21, 2023, 09:02:16 am

My Prevost had a 300 amp oil cooled alternator, 10 batteries and wouldn't even attempt to startup the air conditioner.

Sounds like an inverter power supply issue. Regardless of the actual running amps into the batts , the inverters control's whether or not the ac will start. How long it will run is dependent on total amps available.
Maybe the alternator would run the ac with a better support system .
The math says that it should .

Re: Running a roof air off of engine generator

Reply #10 – January 21, 2023, 11:36:32 am

Prevost recently started using those electric fans. Mine didn't have that feature

Re: Running a roof air off of engine generator

Reply #11 – January 21, 2023, 11:37:36 am

Quote from: juicesqueezer – January 21, 2023, 11:34:46 am

The have a dedicated alternator for the fans, not all 5. However, they have either 3 or 4 three plus thousand inverters in the coach and that most likely is what is making it feasible to run all the airs going down the road. In my opinion, it is cheaper in our applications to just start the generator and run how many airs one wishes. A no brainer! We run our airs all the time going down the road, just saying!

Bad at math.
I went through a lot so that I don't rely on the genset all weekend . It's the noise and such. That I don't care for.

Re: Running a roof air off of engine generator

Reply #12 – January 21, 2023, 11:39:17 am

I love my generator even more. It's simple, reliable and does the job .

Re: Running a roof air off of engine generator

Reply #13 – January 21, 2023, 11:48:22 am

Quote from: Protech Racing – January 21, 2023, 11:37:36 am

Bad at math.
I went through a lot so that I don't rely on the genset all weekend . It's the noise and such. That I don't care for.

Mike, yours is not enclosed, I am assuming. Mine is very quiet and we don't even hear it in the bedroom when sleeping. Maybe that is why I run mine when needed. I would not like hearing all that noise all the time either.

Re: Running a roof air off of engine generator

Reply #14 – January 21, 2023, 11:51:51 am

Mine is quiet also. Propane went way up. And I have to fuel up every 80 hrs.
But yeah. Having solar actually has a ROI that I may see the end of.

Re: Running a roof air off of engine generator

Reply #15 – January 21, 2023, 01:45:16 pm

Robert,

I converted my 1991 Foretravel to run one roof A/C while driving. Here are some recommendations:

In reading your old posts you are planning (or already have) installed the 250A Sterling ProSplitR isolator. You will need this isolator (or similar with excite terminal) to use a Delco alternator. A Delco alternator will not work with the Foretravel OEM diode isolator.

I think the Delco 40SI 240 amp alternator is too small. Amperage loads from my testing:

Coach running load with head lights/running lights on ~70 amps

A/C running load ~150 amps

So you will have to supply ~220 amps with A/C on and with lights on. While the alternator you have is rated for 240 amps, this is not a continuous rating. The best practice is to run an alternator at ~75% of rated capacity for continuous use especially in hot weather - when you want to use the coach A/C. For a 220 amp continuous load I would suggest a minimum alternator rating of 300 amps (75% is 225 amps).

The alternator I used was a Delco 40SI 300 amp (Delco 8600300). For even more margin you could go with the Delco 40SI 320 amp (Delco 8600634). Be wary of cheap half price alternators that say "replaces" or "Delco type".

In addition to right sizing the alternator, you will need to increase the wire gauge from the alternator to the ProSplitR, and from the ProSplitR to the house batteries. The wire gauge from the ProSplitR to the engine battery should be ok as-is.

For the alternator to ProSplitR and ProSplitR to house batteries I would suggest 4/0 marine grade cable available from Bay Marine Supply. They can also make up your cables unless you want to get set up to make your own cables as a few forum members have done.

Keep us posted on your project.

Re: Running a roof air off of engine generator

Reply #16 – January 21, 2023, 03:20:10 pm

Robert, some additional thoughts:

Your Xantrex 3012 should be able to start the A/C, this has a surge rating of 6000 watts. I would try it before going to the trouble of buying and installing a soft start. In my build I used an Aims 4000 watt inverter and this started my A/C fine with no need for a soft start.

Re: Running a roof air off of engine generator

Reply #17 – January 21, 2023, 05:08:46 pm

Diesel generator needs to be run to prolong its life. Do like most, just run gen, use both roof air, microwave to heat things while driving, enjoy the good 120v life while driving.

Re: Running a roof air off of engine generator

Reply #18 – January 21, 2023, 06:25:27 pm

Quote from: Old Toolmaker – January 21, 2023, 09:34:29 am

The cost effective way to run your front air conditioner is off your built in diesel generator.
Any other way requires spending money up front and all of them still use diesel fuel to run the air conditioner: it takes for horsepower to make 3Kw of power.
If you want to take that power from your main engine, you need to add a 4Kw 120-240V alternator and its supporting cast. The frequency is going to go up and down with engine speed so you'll need as AC-AC converter to take the alternator's power and make it a stable 60Hz with 120-240V of battery to take care of stop lights and off ramps.
Any way you slice the problem, it can be done with enough money and engineering, but it's more cost effective to start the generator set and assign the loss of range to the air conditioned air.

I think you misunderstood my question. The house battery bank through the inverter would actually power the A/C. The soft start lowers the start up amperage from around 50 to 15. So not to overload the capacity of the inverter. The alternators job would be to maintain the house battery bank. So my concern would be overloading the alternator trying to do this. That was my question.

Re: Running a roof air off of engine generator

Reply #19 – January 21, 2023, 08:57:28 pm

Thanks all for the input. Honestly in the end even though I've already bought the alternator and the pro-R. It sounds like the easiest thing is just run the genny if I need additional cooling.

Re: Running a roof air off of engine generator

Reply #20 – January 22, 2023, 11:21:21 am

Maybe trade the alt for a 300 amp. ?
Math is close .

Re: Running a roof air off of engine generator

Reply #21 – January 23, 2023, 10:02:11 am

I have the same inverter and do it often, no problems. I run both at the same time if needed with genny on driving

Re: Running a roof air off of engine generator

Reply #22 – January 24, 2023, 09:04:32 am

My Cummins brand 12.5kw diesel generator burns anywhere from .5 to a little over 1 gallon per hour of diesel. That's pretty cheap to run however many a/c's you need.

Re: Running a roof air off of engine generator

Reply #23 – January 24, 2023, 09:44:19 am

I run the front air off the engine/inverter on my Wanderlodge. Two alternators and 3K watt inverter. I only run it on the days I only need one AC.

Re: Running a roof air off of engine generator

Reply #24 – January 24, 2023, 01:53:20 pm

Thanks for a real world report .

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