Skip to main content ↑ ↓
Topic: Roof AC while driving, no generator.  (Read 1373 times) previous topic - next topic

Roof AC while driving, no generator.

I finally got my Micro Air Easy Start in on Saturday. This was the final piece of a puzzle I've been waiting to try out. My goal was to be able to run the front roof AC on just the batteries. Partly for boondocking but mostly for while we're driving down the road without having to use the genny. I'm pleased to report that it works as I had hoped.

 My two DC to DC chargers coming off the alternator provide enough juice in conjunction with the solar panels that I can run the roof air for 10+ hours depending on the strength of sunlight. In 90 degree and sunny weather I was comfortable but if it got much hotter I would need to turn the genny on and run the rear air too.

Here's my setup:
1) Front AC circuit was relocated to the sub panel 
2) 1440 watts solar / 600 ah lithium batteries
3) Two Victron Orion 30amp chargers
4) Micro Air Easy Start installed in the front AC unit

In the attached pictures you can see I'm pulling about 950 watts from my solar panels. That in conjunction with the 60 amps coming off the alternator result in a net draw of roughly -36 amps on the batteries when the roof air is running (shown under "current" in the battery app. The app only shows draw from one of the two batteries at a time so  18 X 2 = 36).

A few considerations:
1) I have a 2001, which means my AC roof ducts extend all the way to the front of the coach so the air can be focused on the front two seats. Not sure how well this would work in older models without that. 

2) It's not instant gratification like dash air. You really need to get the overall temp of the living room down before you feel the benefits. But when you do, it's 10x more comfortable in my opinion. No more sticky back against the leather captains chair.

3) It's definitely nice being able to control the air without getting up via a Bluetooth enabled thermostat.

Anyways, that's what I know  ^.^d

Big thanks to Gilles at OffTheGridRvs  for helping me scheme and installing most of the goodies.
1987 Grand Villa ORED
2001 U320 4010

Not all that wander are lost... but I often am.

Re: Roof AC while driving, no generator.

Reply #1 –
Elliott,
Great to know! I have all the pieces and parts, just don't have them installed yet. Quick question, how did you hook up the two 30 amp chargers? Did you run new cables to each battery bank?

I may have more questions for you later as I get into this install. I have the Victron 3000 watt inverter, battery monitor and chargers along with the lithium batteries. This is going to be a winter project. I have not purchased solar panels yet. Any recommendations?

Thanks
Kevin
Kevin and Donna
2000 Foretravel U295 Build #5613
2002 Jeep Wrangler
Motorcader #18561

Re: Roof AC while driving, no generator.

Reply #2 –
Quote from: Elliott –

Here's my setup:
1) Front AC circuit was relocated to the sub panel 
2) 1440 watts solar / 600 ah lithium batteries
3) Two Victron Orion 30amp chargers
4) Micro Air Easy Start installed in the front AC unit

In the attached pictures you can see I'm pulling about 950 watts from my solar panels. That in conjunction with the 60 amps coming off the alternator result in a net draw of roughly -36 amps on the batteries when the roof air is running (shown under "current" in the battery app. The app only shows draw from one of the two batteries at a time so  18 X 2 = 36).

A few considerations:
1) I have a 2001, which means my AC roof ducts extend all the way to the front of the coach so the air can be focused on the front two seats. Not sure how well this would work in older models without that. 

Big thanks to Gilles at OffTheGridRvs  for helping me scheme and installing most of the goodies.

Those of us with more primitive homes find that the front air can be adjusted to blow on the front seats just fine.

Thanks for the write up Elliot.
1992 Foretravel Grand Villa
U225 SBID Build No. 4134
1986 Rockwood Driftwood
1968 S.I.A.T.A. Spring
1962 Studebaker Lark
1986 Honda VF700C
1983 Honda VF750C
Charlie, the Dog was broken out of jail 24 Oct 2023
N1RPN
AA1OH (H)e who must be obeyed.

Re: Roof AC while driving, no generator.

Reply #3 –
Well I have to disagree. My AC is located 1/3 of the way back from the front and the ducts are only a few feet in front of that. Even with the fan on high I don't get enough air coming to the front seats. That and that massive windshield that is a huge heat sink means a pretty warm ride in any kind of warmer weather. I thought about extending the ducks forward but I don't know that the fan is powerful enough to really do the job properly. I know people that have done it, and their results were mixed. Since I now have my dash air fixed fingers crossed, between the dash air and the AC running it's plenty cool enough now.
I'm also able to run my front AC off of my victron lithium batteries and the inverter unfortunately I have no way to charge the batteries off the alternator at this time so only through solar and I find that on a warm day I can run it 6 to 8 hours but at the end of that my batteries are on the lower side say 40%. That can leave me at camp with not enough battery capacity to get through the night unless I either run the generator or plug in the shore power. That's why I really wanted to figure out a way to charge off the alternator when running as well but it's not a big issue yet so may not ever be.
'99 U320 40 WTFE
Build #5462,
1500 Watts Solar 600 amp Victron lithium
2012 Jeep Grand Cherokee Overland Hemi
Instagram bobfnbw
Retired

Re: Roof AC while driving, no generator.

Reply #4 –
Bob, don't you still have the boost switch functional? I can hit the boost switch and put 13.8 to 14.2 from the alternator to the lithium batteries. The 14.2 is the bulk rating on my lithium's so no harm as lone as I don't keep charging them after they are fully charged for very long. That puts over 100 amps in them for that time.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Roof AC while driving, no generator.

Reply #5 –
Chuck my boost switch doesn't work and I haven't really checked out why. Never really needed it. It might just be the solenoid that needs replacing but I suspect that it was disconnected when  am solar installed the lithium system.
'99 U320 40 WTFE
Build #5462,
1500 Watts Solar 600 amp Victron lithium
2012 Jeep Grand Cherokee Overland Hemi
Instagram bobfnbw
Retired

Re: Roof AC while driving, no generator.

Reply #6 –
I agree with "Old Toolmaker" about the house AC being able to cool the driver and co-pilot without dash air.  I run my house AC while going down the road and have adjusted the directional vents to blow forward towards the driver and the co-pilot and it keeps us plenty cool.  Maybe our AC units put out more cool air than yours.  As you say yours does not keep you cool enough so your setup must be different than ours. 
I use a Buck-Boost DC-DC converter 24/12 100A (12V Alternator Charge to 24V Lithium) to charge my lithium batteries off the alternator.  So between my solar panels (3320 watts) and the Buck-Boost my batteries stay topped off going down the road with my house AC on with sunshine. 
My boost switch is connected to three Orion 24/12-70A DC-DC converter IP20s so my 24V lithium pack can have its voltage output reduced to 12V to start the engine in an emergency.

Oscar & Janet Valent
2023 Coach House 261XLQD
Former 2004 U320 3820 PBBS
Former 2007 Newell Coach #815
2015 Jeep Grand Cherokee Summit

Re: Roof AC while driving, no generator.

Reply #7 –
I had another test tonight with more moderate temps (80 degrees). It got down right cold and I had to adjust it to warmer a few times once the living room was properly cooled down. It took two hours and ran my batteries down to 85%, so roughly 90ah consumed.

It was a solo drive and being able to make adjustments from the dash was great.
1987 Grand Villa ORED
2001 U320 4010

Not all that wander are lost... but I often am.

Re: Roof AC while driving, no generator.

Reply #8 –
Quote from: kjsifer –
how did you hook up the two 30 amp chargers? Did you run new cables to each battery bank?

I may have more questions for you later as I get into this install. I have the Victron 3000 watt inverter, battery monitor and chargers along with the lithium batteries. This is going to be a winter project. I have not purchased solar panels yet. Any recommendations?
Sorry, not sure how I missed your question Kevin. The Orions sit between the isolator and the boost solenoid.

As for solar panel recommendations, check out SanTan solar in the Phoenix metro. They're very popular amongst the DIYers for cheap panels. I believe you can get large residential panels there too; they look like crap but offer a lot of wattage per dollar.
1987 Grand Villa ORED
2001 U320 4010

Not all that wander are lost... but I often am.

Re: Roof AC while driving, no generator.

Reply #9 –
Quote from: valento –
I agree with "Old Toolmaker" about the house AC being able to cool the driver and co-pilot without dash air.  I run my house AC while going down the road and have adjusted the directional vents to blow forward towards the driver and the co-pilot and it keeps us plenty cool.  Maybe our AC units put out more cool air than yours.  As you say yours does not keep you cool enough so your setup must be different than ours. 
I use a Buck-Boost DC-DC converter 24/12 100A (12V Alternator Charge to 24V Lithium) to charge my lithium batteries off the alternator.  So between my solar panels (3320 watts) and the Buck-Boost my batteries stay topped off going down the road with my house AC on with sunshine. 
My boost switch is connected to three Orion 24/12-70A DC-DC converter IP20s so my 24V lithium pack can have its voltage output reduced to 12V to start the engine in an emergency.


So the math is that your alternators are charging at 100 amps to get this done ?  The AC draws at least 12 amps ?
  MY Delco  100 amp alt wont keep up without the boost engaged and both alts working hard to run my minsplit . It draws about 8- 9 amp . 

Re: Roof AC while driving, no generator.

Reply #10 –
Quote from: Protech Racing –
So the math is that your alternators are charging at 100 amps to get this done ?  The AC draws at least 12 amps ?
  MY Delco  100 amp alt wont keep up without the boost engaged and both alts working hard to run my minsplit . It draws about 8- 9 amp . 


Remember, the roof A/C 12 amp draw is 12 amps AT 120 VAC.

It will take around 150 amps from the alternator to produce that (some efficiency loss in inverter as well as in the wiring at that high amp current).
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Roof AC while driving, no generator.

Reply #11 –
Quote from: Protech Racing –
So the math is that your alternators are charging at 100 amps to get this done ?  The AC draws at least 12 amps ?
  MY Delco  100 amp alt wont keep up without the boost engaged and both alts working hard to run my minsplit . It draws about 8- 9 amp .
1400 watts of solar
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Roof AC while driving, no generator.

Reply #12 –
Quote from: wolfe10 –

Remember, the roof A/C 12 amp draw is 12 amps AT 120 VAC.

It will take around 150 amps from the alternator to produce that (some efficiency loss in inverter as well as in the wiring at that high amp current).
That's my math also.
12 amps x 10

Re: Roof AC while driving, no generator.

Reply #13 –
1400 watts solar = 11.67 amps under perfect conditions. Lately with the winter sun I am getting 80 amps at 13 volts out of my 2030 watts of solar.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Roof AC while driving, no generator.

Reply #14 –
Quote from: craneman –
1400 watts solar = 11.67 amps under perfect conditions. Lately with the winter sun I am getting 80 amps at 13 volts out of my 2030 watts of solar.

11.67 amps at 120v from 1400 watts. Perfect conditions almost never happen.  In the winter 80 amps at 13v is 1040 watts.  That is pretty typical for realistic conditions. 

Bottom line put all the solar you can fit and still leave some access room for servicing the roof top equipment.  60 cell mono panels are smaller and you mat be able to arrange more watts on the roof.  72 cell panels are longer and may be harder to arrange but have some advantages.  Probably not enough to make up for more watts from 60 cell panels.  I have 4 300 watt 72 cell panels now on our 36' coach with a satellite dish and can fit 2 more 400+ watt 72 cell panels and still leave room for access.  That would get me to 2000 watts which would be nice. If I switched to 60 cell panels I could get 7 400 watt panels for 2800 watts and still have access where I need it. Without the satellite dish I could get 8 60 cell panels or as much as 3200 watts. 

Draw an accurate roof plan and paper panels and see how they fit.  Make sure to account for the panel mounting brackets. Once you like what you have make full-sized cardboard templates and try them on the roof to be sure. Then shop for panels, cheap is not always best if you are trying to maximize potential.  And you will need more than one solar charge controller when you get that many watts. It helps with wiring, redundancy, and some management.  Good planning is your best tool here for success.  And it is not hard to do it yourself.  Lots of help available here.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Roof AC while driving, no generator.

Reply #15 –
Great to know Roger, I was just shopping for solar panels! Sounds like the price is going to go up significantly because of global supply chain issues.

Kevin
Kevin and Donna
2000 Foretravel U295 Build #5613
2002 Jeep Wrangler
Motorcader #18561
 

Re: Roof AC while driving, no generator.

Reply #16 –
In the older 42' the situation is far worse as far as the air reaching the driver.  The front ac is very far from the driver seat.  OTR AC is a must in addition to the front ac.  My only real complaint about my coach.