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| running roof air on DC [message #89689] |
Thu, 24 June 2010 08:03  |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
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The electric fan thread drifted away a little and I've always been interested in the topic so i thought I'd bring it up fresh;
A Coleman 13.000 btu roof air draws 15 amps at 120 VAC
THat's 150 amps at 12VDC or 75 amps at 24VDC.
I think you can get a 100 amp 24 volt alternator and a 2000 watt 24V inverter for under $1000 and run the roof air with no problem.
Mounting the second alt. would not be so difficult.
Would it be worth the effort?
Is there a flaw in the math?
You'd be adding a constant 3hp drag on the engine so there would probably not be any gain in efficiency over running the generator.
If all that worked out then you could run the roof air for a couple hours on four golf cart batteries.
That might be enough to get you through a HOT night in a "no generator after 10:pm campground".
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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| Re: running roof air on DC [message #89693 is a reply to message #89689] |
Thu, 24 June 2010 08:30  |
Rick Denney
Messages: 430
Registered: January 2004
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| hertfordnc wrote on Thu, 24 June 2010 09:03 |
The electric fan thread drifted away a little and I've always been interested in the topic so i thought I'd bring it up fresh;
A Coleman 13.000 btu roof air draws 15 amps at 120 VAC
THat's 150 amps at 12VDC or 75 amps at 24VDC.
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Pulling 75 amps from a 100-amp alternative consistently might stress it a bit. And you'll need those batteries to handle the surge current of starting the compressor.
Also, a 2000-watt inverter can only supply 16 amps (if that's the surge rating, and if the rating is accurate), and you'll need 20 to handle the start-up surge. I would use a 3000-watt inverter for this application, just to provide some headroom.
Batteries may be more of challenge than you realize. The typical golf-cart battery provides 100 amp hours nominally. If you only use two thirds of the charge to avoid damaging the battery, and if that rating is real, then you'll get 65 amp hours in practice. You'll need four of those batteries to supply 24 volts, but you'll still only be able to use 65 amp-hours (at 24 volts). You'll run those batteries down in less than an hour of compressor time, and the compressor will be on full-time until the thermostat is satisfied.
When it's that hot at night, I either park in a place where I can run the generator, or I park in a campground with a power hookup.
Rick "finding it's not usually that hot at night in most desirable destinations" Denney
'73 Glacier 230 "Jaws"
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| Re: running roof air on DC [message #89698 is a reply to message #89689] |
Thu, 24 June 2010 09:02 |
GeorgeRud
Messages: 1380
Registered: February 2007
Location: Chicago, IL
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It seems that you are probably better off just to fire up the generator and let it take care of the rooftop AC. I also think that adding a second alternator may not be as easy as it appears at first - you start running out of room quite quickly, and those belts could become a real mess.
If it could be done easily, I imagine one of the SOBs would have started offering it as an option on some of those big diesel pushers.
George Rudawsky
Chicago, IL
75 Palm Beach
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| Re: running roof air on DC [message #89710 is a reply to message #89689] |
Thu, 24 June 2010 10:46 |
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I would keep it simple and stay away from the 24v system, there are pleanty of 3kw inverters out there and you could run the AC just fine off of a modified sine wave. I've used a small modified sine wave inverter on inductive loads (power tools) and have had good results. Usually only high end electronics need a pure sine wave. As for the alternator, using a high amp unit from Iraggi or quickstart may eliminate the need for a second alt. Iraggi units in excess of 400 amps can be had, and quickstart has a 350 dual rectifier unit. The advantage of adding a second Alt would be to have the high amp alt be dedicated to the house battery system, this would allow the 3kw inverter for the roof AC to be connected through the housd system and that would allow the inverter to be used for other things as well as the roof AC and as long as the main engine was running there would be no danger of discharging the house system... Just an idea how that could work...
73 Canyon Lands, (a.k.a. The Yellow Submarine) West Los Angeles CA
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| Re: running roof air on DC [message #89711 is a reply to message #89693] |
Thu, 24 June 2010 10:54 |
hertfordnc
Messages: 1164
Registered: September 2009
Location: East NC
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| Rick Denney wrote on Thu, 24 June 2010 08:30 |
When it's that hot at night, I either park in a place where I can run the generator, or I park in a campground with a power hookup.
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Guys who are fully retired and people on the west coast who drive a couple hours to any climate they want may not grasp the situation here in the HOT south.
I may only get a weekend to run out to the beach. The best campgrounds with beach access are state parks with no hook up and quiet hours.
So if the AC could run for part of the night it would definitely take the edge off.
Not to mention the other advantages of having such redundant power to cool the coach without running the generator.
This is not something I'm likely to pursue but it started in the thread on electric fans and I'm interested in the idea.
About the batteries- they're rated at 200 amps- Is it not realistic to expect 100 amps from them?
thanks
Dave & Ellen Silva
Hertford, NC
76 Birchaven, 1-ton and other stuff
Currently planning the Great american Road Trip Summer 2021
It's gonna take a lot of Adderall to get this thing right.
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| Re: running roof air on DC [message #89716 is a reply to message #89689] |
Thu, 24 June 2010 11:24 |
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A 200Ah battery should only be discharged 50% to prolong life so basically you will need 2x the amp hours listed on thd battery. I would say a bank of 8D batteries would best the golf cart batteries in this application. The best 8Ds are by Lifeline and they are AGM, AGMs of this type can be totally discharged 500 times and over 1000 times if discharged to only 50% I use one of these for my house battery and it has 255 Ah so 2 of these would be 510 and 4 would be 1020 ah. The only problem is they are not cheap. I was lucky I got a slightly used one for 160 on craigs list. It was about a year old. New they are around 600 dollars. They. Are also heavy 165# a piece. so to power the roof AC one needs to calculate the aH draw and that should give you the number of batteries needed...
73 Canyon Lands, (a.k.a. The Yellow Submarine) West Los Angeles CA
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| Re: running roof air on DC [message #89728 is a reply to message #89711] |
Thu, 24 June 2010 12:15 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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| hertfordnc wrote on Thu, 24 June 2010 08:54 |
| Rick Denney wrote on Thu, 24 June 2010 08:30 |
When it's that hot at night, I either park in a place where I can run the generator, or I park in a campground with a power hookup.
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About the batteries- they're rated at 200 amps- Is it not realistic to expect 100 amps from them?
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We, among our other vehicle obsessions drive a Solectria Electric Vehicle. We are currently running on 12V AGM batteries. They are 90 amp hr and we try to keep the discharge below 30. We drive the little rig daily and have for two years. The batteries were not new when we got it. Some of the thinking is, even with deep cycle, you get much better life if you only use the top 20% or so. This is seeming to be true. As some days we go in the morning, recharge and go again later in the day... lots of cycles.
As a side bar, I have a new extra Deka battery along with us in the coach. We are without hookup. (amazing to have Internet out here) These Deka batteries are expensive and when you pick one up you think it is nailed to the ground. On the other hand, I ran an inverter from the Deka alone for about three hours yesterday and one today and it is still at 12.6 with the inverter running.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
[Updated on: Thu, 24 June 2010 12:26] Report message to a moderator |
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| Re: running roof air on DC [message #89734 is a reply to message #89689] |
Thu, 24 June 2010 13:58 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
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Would it be worth the effort?
Is there a flaw in the math?
__________________________________________________--
I think you have the basic numbers as far as needs go but your batteries are short. If you are going to consider battery usage in such a deal, you need to go to the solar sites and get the work sheet. You will find the batteries only give back a small percentage of what they take to charge.
Is it worth the effort?????
I think if it will keep the fire breathing dragon in the back called an Onan off, it may be.
I have used the Onan on the road but have now regressed to just parked use.
I have two concerns with the Onan, one is it get VERY HOT in that cubical and on the road it is very difficult for you to monitor what is going on, should it catch fire, by the time you smell smoke it is likely too late.
If you could find a place to mount a 24v Gen/Alternator on the engine, your power would be more or less direct through the Inverter but the best part, NO ONAN.....
I think there might be a safety issue here and your solution, though costly and needing prototyping, might be a good one.
Good thought
LarC ( Once upon a time, I thought of running the ac from the engine, too bad the factory Air sucks so badly, well, it sure doesn't blow )
Gatsbys' CRUISER  08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
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| Re: running roof air on DC [message #89740 is a reply to message #89711] |
Thu, 24 June 2010 15:00 |
Rick Denney
Messages: 430
Registered: January 2004
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| hertfordnc wrote on Thu, 24 June 2010 11:54 |
Guys who are fully retired and people on the west coast who drive a couple hours to any climate they want may not grasp the situation here in the HOT south.
...About the batteries- they're rated at 200 amps- Is it not realistic to expect 100 amps from them?
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Heh. It's not even cool here in northern Virginia, and I grew up in Houston, and then lived in College Station, Austin, San Antonio, and Dallas. Tell me about heat. But I didn't go camping in August--that was hibernation season in Texas. Spring and Fall were our seasons, and even Winter.
And I just changed jobs in the recognition that I won't be retiring for at least 15 more years.
Okay, on the batteries. The ratings consider relatively slow discharge to the fully discharged state. You will be discharging them much more quickly, and you really don't want to ever discharge them fully. I think you need to at least double your battery bank to make this work. I use batteries quite a bit--I'll be using four large deep-cycle batteries this weekend for field radio operations. Theory says I only need two to last 24 hours; practice says I voltage got too low after 18 hours. Theory and reality don't always agree.
Don't underestimate the belt load, either. The 455 already has three belts--adding an additional belt or retasking the existing belts will be really complicated. Plus, people often still have problems with slipping belts--there is not a lot of headroom in the current design.
I think you'll be forced to convert your whole belt system to a serpentine belt, which is a good thing to do, but doing so will cost more than that thousand bucks all by itself unless you can do your own custom fabrication.
Rick "forewarned is forearmed" Denney
'73 Glacier 230 "Jaws"
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| Re: [GMCnet] running roof air on DC [message #89763 is a reply to message #89689] |
Thu, 24 June 2010 18:52 |
emerystora
Messages: 4442
Registered: January 2004
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On Jun 24, 2010, at 7:03 AM, dave silva wrote:
>
>
> The electric fan thread drifted away a little and I've always been interested in the topic so i thought I'd bring it up fresh;
>
> A Coleman 13.000 btu roof air draws 15 amps at 120 VAC
>
> THat's 150 amps at 12VDC or 75 amps at 24VDC.
>
> I think you can get a 100 amp 24 volt alternator and a 2000 watt 24V inverter for under $1000 and run the roof air with no problem.
>
> Mounting the second alt. would not be so difficult.
>
> Would it be worth the effort?
>
> Is there a flaw in the math?
Well, Yes. In your calculation you have assumed that your inverter is 100% efficient. None of them are. Typically it is going to be more like 90%. So instead of 150 amps at 12 VDC it will be more like 167 amps at 12 VDC.
Another important factor involves the wave form of your inverter and inductive loads (ie an appliance where an electrical coil is involved, which will include anything with a motor). Any waveform that is not a true sine wave (ie is a square, or modified square wave) will be less efficient when powering inductive loads - the appliance may use 20% more power than it would if using a pure sine wave. So, again depending on your inverter, that could step up the power requirement to 167 amps times 1.20 = 200 amps.
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: [GMCnet] running roof air on DC [message #89858 is a reply to message #89763] |
Fri, 25 June 2010 13:30 |
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Good point Emery, the inverters efficientcy should be taken into account, a good inverter is about 90% I believe an alt that makes about 200 amps at idle would be enough to get the job done. that means a high end, high amp unit from Iraggi or Quickstart. An alternator in that class will set you back about $500 or so. A dual alternator system should be used as the high amp unit can be dedicated to the AC and charging battery banks.
its totally doable, but it wont be cheap I'd low ball it and say about $1500 for everything not including batteries...
| emerystora wrote on Thu, 24 June 2010 18:52 |
On Jun 24, 2010, at 7:03 AM, dave silva wrote:
>
>
> The electric fan thread drifted away a little and I've always been interested in the topic so i thought I'd bring it up fresh;
>
> A Coleman 13.000 btu roof air draws 15 amps at 120 VAC
>
> THat's 150 amps at 12VDC or 75 amps at 24VDC.
>
> I think you can get a 100 amp 24 volt alternator and a 2000 watt 24V inverter for under $1000 and run the roof air with no problem.
>
> Mounting the second alt. would not be so difficult.
>
> Would it be worth the effort?
>
> Is there a flaw in the math?
Well, Yes. In your calculation you have assumed that your inverter is 100% efficient. None of them are. Typically it is going to be more like 90%. So instead of 150 amps at 12 VDC it will be more like 167 amps at 12 VDC.
Another important factor involves the wave form of your inverter and inductive loads (ie an appliance where an electrical coil is involved, which will include anything with a motor). Any waveform that is not a true sine wave (ie is a square, or modified square wave) will be less efficient when powering inductive loads - the appliance may use 20% more power than it would if using a pure sine wave. So, again depending on your inverter, that could step up the power requirement to 167 amps times 1.20 = 200 amps.
Emery Stora
77 Kingsley
Santa Fe, NM
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73 Canyon Lands, (a.k.a. The Yellow Submarine) West Los Angeles CA
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| Re: [GMCnet] running roof air on DC [message #89888 is a reply to message #89858] |
Fri, 25 June 2010 16:37 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Anyone getting serious about driving the ac a/c from the engine should check
out this:
http://www.diesel-plus.com/acpower_2.cfm
<http://www.diesel-plus.com/acpower_2.cfm>
Ken H.
On Fri, Jun 25, 2010 at 2:30 PM, Shan Rose <defconfx@gmail.com> wrote:
>
>
> Good point Emery, the inverters efficientcy should be taken into account, a
> good inverter is about 90% I believe an alt that makes about 200 amps at
> idle would be enough to get the job done. that means a high end, high amp
> unit from Iraggi or Quickstart. An alternator in that class will set you
> back about $500 or so. A dual alternator system should be used as the high
> amp unit can be dedicated to the AC and charging battery banks.
>
> its totally doable, but it wont be cheap I'd low ball it and say about
> $1500 for everything not including batteries...
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] running roof air on DC [message #90122 is a reply to message #89888] |
Sun, 27 June 2010 10:38 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
Karma: 0
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Senior Member |
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Anyone getting serious about driving the ac a/c from the engine should check
out this:
http://www.diesel-plus.com/acpower_2.cfm
<http://www.diesel-plus.com/acpower_2.cfm>
Ken H.
______________________________________________________
That is a good site.
One of the AirCon manufacturers had tried a system of battery/inverter for the big trucks.
In theory it would charge as you traveled down the road and would allow you to turn your truck off at the rest area and gave yo 4 to 6 hours run time ( I think, it has been awhile since I was the ad ).
It was only on the market a few years and was removed from the site. Either the unit was well engineered but too futuristic for the buying public or it had bugs to work out.
Just another note from an idea the manufacturers had.......
LarC ( joining of ideas may produce one good event )
Gatsbys' CRUISER 08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
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| Re: [GMCnet] running roof air on DC [message #90814 is a reply to message #90585] |
Fri, 02 July 2010 09:13 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
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Is this the product you speak of?
http://www.dometic.com/enus/Americas/USA/Truck/HVAC-Solutions/Battery-Powered-HVAC-Guide/
Scott
______________________________________________________
Yes, the DOMETEC version, though I was it on the Dometec website.
Not sure if it exists today unless they made an improved unit. I remember seeing it then " ( POOF ! ) ", it was gone.....
If it is still advertised, might be a good idea to check out the actual size of the air con and the battery bank they developed..
LarC ( Looking at technology as it grows, and has its bumps and slip falls )
Gatsbys' CRUISER 08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
_
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| Re: [GMCnet] running roof air on DC [message #90840 is a reply to message #90814] |
Fri, 02 July 2010 11:50 |
idrob
Messages: 645
Registered: January 2005
Location: Central Idaho
Karma: 0
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| Larry C wrote on Fri, 02 July 2010 07:13 |
Is this the product you speak of?
http://www.dometic.com/enus/Americas/USA/Truck/HVAC-Solutions/Battery-Powered-HVAC-Guide/
Scott
______________________________________________________
Yes, the DOMETEC version, though I was it on the Dometec website.
Not sure if it exists today unless they made an improved unit. I remember seeing it then " ( POOF ! ) ", it was gone.....
If it is still advertised, might be a good idea to check out the actual size of the air con and the battery bank they developed..
LarC ( Looking at technology as it grows, and has its bumps and slip falls )
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I have a friend who is a long haul trucker, and we have frequently discussed this problem. The Dometic unit was tried by his company (a major one, they have 2500 trucks) and found to be too heavy and too expensive, as well as not lasting long enough. The capacity is only 7000 to 10,000 btuh and the running time was in the range of 6 hours as I recall. That is not enough time. Space in the tractor and dead weight to haul are a big factor in the truck tractor business. At any rate, they did not adopt them for their rigs.
His company has been testing 50 new trucks (and my friend has one) an APU (aux. power unit) which runs on diesel fuel. It is a small two cylinder diesel which operates a second compressor/evaporator, and a generator for charging batteries plus an inverter to power truck needs, such as computers, refrigerators, and microwaves (remember they live in the truck). It also keeps the main engine warm in the winter so it may be shut down and will restart easily.
He is not all that keen on what they have at this point. The unit is somewhat noisy, especially the AC part. The start/stop is annoying when you are used to constant run noise. The inverter used is electrically "noisy" and gives his electronic equipment some issues.
For the GMC, the size, weight of batteries and low cooling capacity of the Dometic unit are all a problem.
Just some more information.
Rob Allen
former owner of '76 x-PB
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| Re: running roof air on DC [message #90943 is a reply to message #90847] |
Sat, 03 July 2010 10:41 |
Larry C
Messages: 1168
Registered: July 2004
Location: NE Illinois by the Illino...
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It wouldn't be much of s stretch to run a roof air conditioner with such a device although I don't see how you would mount it on the GMC as all the pulleys seem to be spoken for.
___________________________________________________________
With that kind of Alternator capacity, I would be looking at removing the vehicle compressor and install the the alternator in its place.
I have no numbers for efficeincy running the 120vac air cons vs the motor driven compressor, but the option of an AC feed on the road sounds interesting.
A smaller gen set, like the ONAN could be used booning.
If going with solar and batts, another option.....
In the case of Gatsbys' CRUISER  , the OEM AC is next to useless and the hang on under dash unit unit I had installed won't hold gas, still working on that one.
If I were ambitious and could find an alternator of that size, I might be inclined to set up for that type of system power to the roof air.
Lots of options, just sorry that GM did not pay attention to detail on the OEM Air Con
LarC ( The only major flaw in Gatsbys' CRUISER has always been ventilation and Air Conditioning on the road. Not a good mark for such a big company full of engineers )
Gatsbys' CRUISER 08-18-04
74 GLACIER X, 260/455-APC-4 Bagg'r
Remflex Manifold gaskets
CampGrounds needed, Add yours to "PLACES" />
http://www.gmceast.com/travel
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