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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[Michael]

I agree with you David. Just doesn't make sense putting such a load
on the system. First you have to buy and maintain a huge battery
bank to buffer the current. And I think 150 amps is conservative not
to mention the surges. Alternators' ratings are at an ideal
temperature and rpm so don't believe they will support even 75% of
the rated load for long extended periods without damage. So if you
look at the expense, the weight, the storage space lost, the up keep
of the battery bank, the corrosion, etc... just doesn't add up. On
top of that you cannot run the A/C from your battery bank for more
than a few minutes without the huge alternator/engine running. So it
does little good parked.

Michael Putz
78FC35 "Putz'n Around"
Mesa, Az

--- In WanderlodgeForum@yahoogroups.com, David Brady
wrote:
>
> 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
> >
> >
> > ------------------------------------------------------------------
------
> >
> > No virus found in this incoming message.
> > Checked by AVG.
> > Version: 7.5.526 / Virus Database: 270.4.3/1527 - Release Date:
6/30/2008 6:07 PM
> >
>

[bumpersbird]

I have 6 Lifeline GPL-4DL Deep Cycle RV Battery in my coach.
The Tech's at Xantrex have stated that with the RV 3012 M inverters.
That running an A/C with their inverters and 6 batteries is well
within the capacity of this setup to run one A/C.

Batteries specs. click on link below.
http://www.lifelinebatteries.com/rvflyer.php?id=6

I would suggest that some of the newer rigs are capable of this
setup. If you had to build this setup, in a FC for example it would
not be cost effective. But in the case of the PT-42's according to
Wayne Clapp all I need is a single relay. So for me to up grade the
capabilities of my coach it's a no brainer.

I have finished the control box for the engine compartment cooling
fan controls look at new pics. It's over the top, I couldn't help
myself :}

Kurt Horvath
95 PT-42 WLWB
10AC





--- In WanderlodgeForum@yahoogroups.com, "Michael" <mike.putz@...>
wrote:
>
> I agree with you David. Just doesn't make sense putting such a
load
> on the system. First you have to buy and maintain a huge battery
> bank to buffer the current. And I think 150 amps is conservative
not
> to mention the surges. Alternators' ratings are at an ideal
> temperature and rpm so don't believe they will support even 75% of
> the rated load for long extended periods without damage. So if you
> look at the expense, the weight, the storage space lost, the up
keep
> of the battery bank, the corrosion, etc... just doesn't add up. On
> top of that you cannot run the A/C from your battery bank for more
> than a few minutes without the huge alternator/engine running. So
it
> does little good parked.
>
> Michael Putz
> 78FC35 "Putz'n Around"
> Mesa, Az
>
> --- In WanderlodgeForum@yahoogroups.com, David Brady
> wrote:
> >
> > 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
> > >
> > >
> > > ----------------------------------------------------------------
--
> ------
> > >
> > > No virus found in this incoming message.
> > > Checked by AVG.
> > > Version: 7.5.526 / Virus Database: 270.4.3/1527 - Release Date:
> 6/30/2008 6:07 PM
> > >
> >
>

[g_man1146]

I agree with David 100%. My '99 LXi has the capability to run one air
on the two 3000 watt inverters but we seldom (never?) have. If it is
hot enough to run one roof air going down the road it, IMO, is hot
enough to run all three with the generator. This provides uniform
cooling front to back and no excessive alternator use.

Rich D. '99LXi 43' CT


--- In WanderlodgeForum@yahoogroups.com, David Brady wrote:
>
> 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

[Al]

David,
I agree with you... It is easy to tell where a bird is located by
this type of question. In the deep South, my bird does not start up
and go unless the generator is running powering two a/c units on the
roof and the one in the dash. Or I can arrive baked to a crisp in an
37' oven. The dealth of a diesel engine is not using it.

Al Johnson
'96 BMC B100
Mandeville, Louisiana

--- In WanderlodgeForum@yahoogroups.com, David Brady
wrote:
>
> 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
> > 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
> > 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
> >>
> >> -----------------------------------------------------------------
-------
> >>
> >> No virus found in this incoming message.
> >> Checked by AVG.
> >> Version: 7.5.526 / Virus Database: 270.4.3/1527 - Release Date:
6/30/2008 6:07 PM
> >>
> >
> >
> > ------------------------------------------------------------------
------
> >
> > *Yahoo! Canada Toolbar :* Search from anywhere on the web and
bookmark
> > your favourite sites. Download it now!
<http://ca.toolbar.yahoo.com/>
> >
> >
> > ------------------------------------------------------------------
------
> >
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> > Checked by AVG.
> > Version: 7.5.526 / Virus Database: 270.4.3/1527 - Release Date:
6/30/2008 6:07 PM
> >
>

[Wilhelmus Schreurs]

Kurt:

I doubt very much that you would be able to run the BR a/c for very long on any kind of batteries on our coaches, you will either need the main engine running or the genset.

When running down the road, using the alternator/battery setup is the way to go, as the engine is running anyhow. If stationary,running the genset would make more sense.

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

----- Original Message ----
From: bumpersbird
To: WanderlodgeForum@yahoogroups.com
Sent: Tuesday, July 1, 2008 9:44:24 PM
Subject: [WanderlodgeForum] Re: running a/c on inverter

I would like to run BR A/C without the genny after 10PM quite time at
most places.

Not too concerned about daytime running. I usually have all three
airs going so running the genny is a given. I would still like the
choice and the option

Wayne Clapp is the tech. I was refering to

Kurt Horvath
95 PT-42
10 AC--- In "WanderlodgeForum%40yahoogroups.com", jvredden@... wrote:
>
> Wayne Clapp is at Buddy Gregg. He trained Kenny Rogers with
BlueBird. He is great:
>
> John Redden
> 91 PT 40
> Mooresville NC
> Sent from my BlackBerry® smartphone with SprintSpeed
>
> -----Original Message-----
> From: "bumpersbird"
>
> Date: Wed, 02 Jul 2008 01:59:16
> To: <"WanderlodgeForum%40yahoogroups.com">
> Subject: [WanderlodgeForum] Re: running a/c on inverter
>
>
> Corey,
>
> I'm working on that. I have two new inverters that need to be
installed
> in the next few weeks. There is a tech in Knoxville TN @ Buddy
Gregg's
> that said he could add a relay and make one A/C run off the batts.
I
> just don't know where that relay is. Probably behind the rear
closet
> wall there are a bunch of relays and electrics behind that wall. I
do
> have some blue prints, I'll try to look them over in the AM.
>
> Kurt Horvath
> 95 PT-42 WLWB
> 10AC
>
> --- In "WanderlodgeForum%40yahoogroups.com", "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
> >
>

[Pete Masterson]

The '95 and later 'birds with the DD Series 60 only have one 300 amp alternator.

Pete Masterson

'95 Blue Bird Wanderlodge WBDA 42

El Sobrante CA

"aeonix1@mac.com"

On Jul 1, 2008, at 7:38 PM, 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 <"dmb993@earthlink.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

---

No virus found in this incoming message.
Checked by AVG.
Version: 7.5.526 / Virus Database: 270.4.3/1527 - Release Date: 6/30/2008 6:07 PM

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[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

---

No virus found in this incoming message.
Checked by AVG.
Version: 7.5.526 / Virus Database: 270.4.3/1527 - Release Date: 6/30/2008 6:07 PM

---

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No virus found in this incoming message.

Checked by AVG. Version: 7.5.526 / Virus Database: 270.4.3/1527 - Release Date: 6/30/2008 6:07 PM

 

[Pete Masterson]

Keep in mind, the '95 and later 'birds with the DD Series 60 generally have six model 4D house batteries. These are about 200 amp hours each (20 hour rate) -- and weigh about 150# each. However, from my experience with an "all electric" coach with a home-style Amana refrigerator, I can assure you that it won't take too many hours of running an AC on battery/inverter to seriously deplete the house battery bank.

Later LXIs have 8 or 10 of the model 4D batteries, and would be even more capable of handling the load -- but they also have more loads (slides, for example) on the batteries. That's why BB put 'em in.

Pete Masterson

'95 Blue Bird Wanderlodge WBDA 42

El Sobrante CA

"aeonix1@mac.com"

On Jul 1, 2008, at 10:29 PM, Michael wrote:

I agree with you David.  Just doesn't make sense putting such a load 

on the system.  First you have to buy and maintain a huge battery 

bank to buffer the current.  And I think 150 amps is conservative not 

to mention the surges.  Alternators' ratings are at an ideal 

temperature and rpm so don't believe they will support even 75% of 

the rated load for long extended periods without damage.  So if you 

look at the expense, the weight, the storage space lost, the up keep 

of the battery bank, the corrosion, etc... just doesn't add up.  On 

top of that you cannot run the A/C from your battery bank for more 

than a few minutes without the huge alternator/engine running.  So it 

does little good parked.

Michael Putz

78FC35 "Putz'n Around"

Mesa, Az

--- In "WanderlodgeForum@yahoogroups.com", David Brady  

wrote:

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

------------------------------------------------------------------

------

No virus found in this incoming message.

Checked by AVG. 

Version: 7.5.526 / Virus Database: 270.4.3/1527 - Release Date: 

6/30/2008 6:07 PM

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[bumpersbird]

I'm getting the impression that you guys that can run the A/C off the
inverters never use it.

Corey it looks like we've been out voted on this one

I agree that if it's hot enough to use one A/C it's hot enough to run
all of them. I know that is usually the case for me. I like a cold
coach.

I would say the exception of winter the genny is running whenever
were in the coach. The MPG for all systems running is negligable so
it's not an economic question for me.

If it's truely just installing one relay I can do that later. The
only reason I was interested in it was for dry camping, After hours,
quite time A/C operation.

This does answer one question I had. Where to take the coach to have
the inverters installed.

I'll go to Nashville to the Xantrex service center instead of
Knoxville. One it's half the distance, Factory installation, I don't
have to change out the control wires for the remotes, and the hourly
rate is less.

I'm not so sure that the Alternator is as feable as some think it is.

Although it was one of the first things that I had to replace after
buying the Indulgance.

I inquired about replacing it with something better and was informed
buy everone I questioned that there is nothing better than what I
already have.

Some Prevosts use the same alternator as the one in my coach in
addition to a couple of bosch 150's giving them a lot of juice to
utilise. I would love to do that to my 42 but it doesn't look like it
would have any advantage that could overcome the engineering/cost
factor.

Kurt Horvath
95 PT-42 WLWB
10AC