running a/c on inverter

[David Brady]

From what I can find, running the genny should give us around

75% electrical generation efficiency at a powerfactor of around

1. Of course almost everything we power is inductive, including

the AC's, so the powerfactor is probably closer to .8 which gives

us an efficiency of around 65%.



With the engine alternator, the alternator has an efficiency of around

50% and the inverter 80% (probably optimistic) for a combined

efficiency of 40%.



If we assume the AC runs for an hour and is off for an hour, 50%

duty cycle, then the alternator will consume 50% more fuel to

power the AC's when the AC's are running, then the genny. When

the AC's are not running, the alternator has a free ride, while the

genny is still running.



The question then becomes: during the free ride, is the genny burning

the extra fuel that the alternator required during the AC run time.

Probably not. Also during this AC off time, the genny can provide

power to other 120V loads, personal computers, refrigerator, etc,

so the spent fuel is not a total loss.



David Brady

'02 LXi, NC



Wilhelmus Schreurs wrote:

David:

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