running a/c on inverter

[Pete Masterson]

I agree... It's a difficult calculation, but the 15Kw genny  in the Series 60 tends to use about 1/2 gallon per hour with one or two ACs operating. It picks up to 3/4 gph with a "full load" (which is more than the 3 ACs). The figures I have suggest that it affects the MPG by between 1/4 and 1/2 mile per gallon, depending on speed. Of course the overall effect may be higher due to rest stops, etc. where the engine may not be running but the generator is. 

Overall, I see about 1/2 mile per gallon reduction on average when I'm using the generator "a lot" between fill-ups. The typical cruising speed has a _much_ greater impact on fuel economy than the generator. By dropping from a 70 mph cruise to 60, I save over 1 mile per gallon... (Best I've gotten is about 7 mpg, worst 4.5 mpg -- and that was on my maiden trip, using the AC with generator and crossing Wyoming at 70+ mph.)

I don't exactly know how much the alternator will drag on the main engine, under load, since I've never had much alternator load for any extended period. But I'm sensitive to _anything_ that reduces engine power to the drive wheels, especially on grades (which we have in abundance in the west where I mostly travel). When climbing, I turn off the chassis AC and only turn on the fan override when temperatures suggest it wise -- as these are significant drags on engine performance. I'm sure that the alternator pulling a heavy load is going to cut into power availability -- so I don't see any real advantage to using the alternator vs. the genny for powering a 120 v AC.

Pete Masterson

'95 Blue Bird Wanderlodge WBDA 42

El Sobrante CA

"aeonix1@mac.com"

On Jul 1, 2008, at 8:52 PM, David Brady wrote:

Hi Bill,

No I'm not sure, but my gut feel is that the generator is more
efficient. I'll have to look more deeply to see if I can come up w/
numbers. I have one 300 amp alternator on my Series-60. Typically
alternators are 50% efficient. When generating electricity you're
better off generating high voltage and low current, which is what
you'll do with the generator, and not do with the alternator.
Add into this the losses at the inverter. This gives me the feeling that
the genny will offer more economy. But I might be wrong...

David Brady
'02 LXi, NC

Wilhelmus Schreurs wrote:

David:

Are you sure that running your big generator is more efficient to run one a/c, from the standpoint of burning fuel to the output of the a/c?

With your engines you have two alternators, so each one would put out 50 percent only and then have 50 percent left over for other items.

 

Bill 84 FC 35 SB  "$quanderlodge"
Terrace, B.C.  Canada

----- Original Message ----
From: David Brady net>
To: WanderlodgeForum@yahoogroups.com
Sent: Tuesday, July 1, 2008 8:25:03 PM
Subject: Re: [WanderlodgeForum] running a/c on inverter

My LXi is set up to run one AC off an inverter and the alternator, but
conventional wisdom is that you shouldn't do it. Steadystate current
draw from the alternator is 150Amps. I want to preserve my precious
alternator, so I always run the generator when I need my AC's.
Another point of view to consider the inefficiencies of the alternator
in generating DC and to add on to that the inefficiency of the inverter
to convert to AC to run the air conditioning. The generator is more
efficient at generating the needed AC.

David Brady
'02 LXi, NC

coreyg67 wrote:

I'm trying to figure out a way to run 1 of my A/C units on the inverters and alternator. I
would think with the two 2500 watt inverters, and the 300amp alternator, this would be a
doable venture. Can someone tell me if, and how to do this task?

Thanks
Corey & Jenni
1996 PT42'
Prosper, TX

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