Running one Airstream A/C when towing?

[foobar]

Has anyone with a large set of solar panels, lithium batteries, a large inverter, and a DC-DC charger (to pull some current from the tow vehicle) tried running one A/C unit and one of the 12V DC refrigerators while towing?

Am wondering if this is possible or not.

One Dometic A/C unit draws about 16amps when running. Not sure what the 12v compressor driven Norcold fridges consume (4Amps or so?).

A tow vehicle can provide a minimum of 8A usually (and some can provide much more, up to 30A).

Assumptions:

1. Victron Multiplus II 2x120 or equivalent (3KVA inverter/charger)
2. Victron Orion 12/12 18 (DC-DC 12volts in, 12v out, 18A capacity)
3. 600watts of rooftop solar managed by Victron Smart Solar 150/85 MPPT
4. Only Dometic 13KBtu a/c and 8 cu ft Norcold 12v compressor fridge are powered
5. Big-A** battery bank (at least 600ah lithium, but I'll probably have >1200ah)

The tow vehicle should be able to supply at least 8A through the 7 pin connector and the DC-DC. The rest should easily be able to supplied by the solar panels via the MPPT charger. For the brief intervals when solar is blocked (going under bridges, etc), the inverter should be able to make up the shortfall by drawing from the batteries. This temporary battery draw should be able to be compensated by the average total power production from the solar panels when towing.

This should work, right? Any reason why this would be a bad idea? The A/C compressors should work fine unless the route contains long stretches of steep roads.

It sure would be nice to be able to stop and have a cool trailer to make/eat lunch and to have a cool trailer when you arrive at a campground in hot weather.

Your thoughts/concerns/hysterical-laughter-over-a-stupid-idea?

[2012FB]

I easily run 1 AC unit and DC fridge while traveling down the road.

400A of Battleborn
Multiplus II with Cerbo Kit
Orian-TR Smart 12/12V-30A charging from the truck.
270W Solar
Micro-Air EasyStart™ 364 (3-ton) Soft Starter on both units.
Micro-Air EasyTouch RV™ Thermostat with Bluetooth/wifi.

While I have not tried it I could probably run both AC units using the built-in Onan 2500i propane generator, but if it is that hot we should not be there.

It is very nice to have the trailer cooled down when pulling into a hot site or when we want to stop and fix a meal in the trailer or stop to eat in a restaurant while our dog is cool and comfortable in the trailer.

[foobar]

Originally Posted by 2012FB

I easily run 1 AC unit and DC fridge while traveling down the road.

400A of Battleborn
Multiplus II with Cerbo Kit
Orian-TR Smart 12/12V-30A charging from the truck.
270W Solar
Micro-Air EasyStart™ 364 (3-ton) Soft Starter on both units.
Micro-Air EasyTouch RV™ Thermostat with Bluetooth/wifi.

While I have not tried it I could probably run both AC units using the built-in Onan 2500i propane generator, but if it is that hot we should not be there.

It is very nice to have the trailer cooled down when pulling into a hot site or when we want to stop and fix a meal in the trailer or stop to eat in a restaurant while our dog is cool and comfortable in the trailer.

Thanks 2012FB. That's great to hear.

I forgot to mention that I'll have easystart on the A/C's (of course). I won't have quite as much amperage through the 7-pin connection to the tow vehicle as you do, but the higher solar production should compensate.

I'll also have the easytouch thermostat and cerbo capability too.

Are you also running your fridge from 12v DC? Or are you running the fridge off of propane?

[2012FB]

Originally Posted by foobar

Thanks 2012FB. That's great to hear.

Are you also running your fridge from 12v DC? Or are you running the fridge off of propane?

I have the new DC-only fridge and yes it is always running. I typically only run the AC for 30-60 minutes prior to arrival or stopping. Wonder if on a sunny travel day along with the 12V-30A from the truck if it would run all day. Next time I hook the truck up I'll see what the Cerbo shows for consumption and supply. Interesting.

[pteck]

I'm playing with this idea as well. I think having multiple current sources to support the draw, while also not sinking too much battery capacity so there's reserve for the next day is probably key.

I don't see a problem with a big bank and properly sized inverter to do the deed. I find my Dometic 15k Blizzard NXT to draw anywhere from 1300-1800 running watts depending ambient temp.

A thing I've noticed is that the interior of the trailer is not really hotter than ambient when underway. Even on super hot 110* days. Perhaps at speed, the aluminum skin temps are sufficiently kept at ambient by moving air, so the interior doesn't get super heated like a statically parked car. Therefore possibly running the A/C maybe 30 minutes prior could make things sufficiently comfortable.

Couple things I'm looking to add:
1) BT controlled thermostat to turn on the A/C prior to stopping
2) DC-DC charger. I already have a 20amp Renogy charger on the 7-pin. I provides an honest 20amps based on my shunt
3) Second 40amp DC-DC charger hooked up to the two vehicle via an separate Anderson plug umbilical. I only need to plug this in when I want more charging/current capacity.

Between the 400W solar (~15-25 amps, call it 20)
+ DC-DC on 7-pin (20 amps)
+ 2nd DC-DC on Anderson (40amps)
Total: 80 amps or ~1000W support

That should make sustainable A/C use even more viable.

[foobar]

Originally Posted by 2012FB

I have the new DC-only fridge and yes it is always running. I typically only run the AC for 30-60 minutes prior to arrival or stopping. Wonder if on a sunny travel day along with the 12V-30A from the truck if it would run all day. Next time I hook the truck up I'll see what the Cerbo shows for consumption and supply. Interesting.

I am considering running the a/c the entire time I am towing so the trailer is cool right after we finish setting up at the campground.

[foobar]

Originally Posted by pteck

I'm playing with this idea as well. I think having multiple current sources to support the draw, while also not sinking too much battery capacity so there's reserve for the next day is probably key.

I don't see a problem with a big bank and properly sized inverter to do the deed. I find my Dometic 15k Blizzard NXT to draw anywhere from 1300-1800 running watts depending ambient temp.

A thing I've noticed is that the interior of the trailer is not really hotter than ambient when underway. Even on super hot 110* days. Perhaps at speed, the aluminum skin temps are sufficiently kept at ambient by moving air, so the interior doesn't get super heated like a statically parked car. Therefore possibly running the A/C maybe 30 minutes prior could make things sufficiently comfortable.

Couple things I'm looking to add:
1) BT controlled thermostat to turn on the A/C prior to stopping
2) DC-DC charger. I already have a 20amp Renogy charger on the 7-pin. I provides an honest 20amps based on my shunt
3) Second 40amp DC-DC charger hooked up to the two vehicle via an separate Anderson plug umbilical. I only need to plug this in when I want more charging/current capacity.

Between the 400W solar (~15-25 amps, call it 20)
+ DC-DC on 7-pin (20 amps)
+ 2nd DC-DC on Anderson (40amps)
Total: 80 amps or ~1000W support

That should make sustainable A/C use even more viable.

Good points.

I will need to augment the 7-pin supply as well.

600watts of solar are probably only going to provide 400watts on average during the day. 8A from the 7pin is another 100w at best.

That leaves a deficit of about a 1000w on average. With the large battery bank I a planning to implement, that should be sustainable for journeys of 4 or 5 hours without depleting the bank.

But, it would be better to add a 40amp Anderson connection to supply another 500w to the equation.

[pteck]

Originally Posted by foobar

Good points.

I will need to augment the 7-pin supply as well.

600watts of solar are probably only going to provide 400watts on average during the day. 8A from the 7pin is another 100w at best.

That leaves a deficit of about a 1000w on average. With the large battery bank I a planning to implement, that should be sustainable for journeys of 4 or 5 hours without depleting the bank.

But, it would be better to add a 40amp Anderson connection to supply another 500w to the equation.

Sustainability is probably something to consider.

How do you intend to charge the battery for the next day? Or do you primarily do hook-up camping?

I tend to boondock or non-hookup camping. So deep reserves only go so far.

What type of charger do you have on the 7-pin? Seems like there's untapped potential there.

[foobar]

Originally Posted by pteck

Sustainability is probably something to consider.



How do you intend to charge the battery for the next day? Or do you primarily do hook-up camping?



I tend to boondock or non-hookup camping. So deep reserves only go so far.



What type of charger do you have on the 7-pin? Seems like there's untapped potential there.

Currently planning on using Victron Orion 12/12 18. That can handle 18A, but I don't know yet what my tow vehicle wiring can handle (2016 Porsche Cayenne S). So for now, I am assuming only the standard 8A.

[hawkspur]

I've done this with a MultiPlus II, 800w of solar, 600ah of lithium, and an Orion DC-DC charger (350w). It isn't sustainable but it works for the use case of starting it an hour or so before you stop so it's not 95 inside.

[jondrew55]

While this certainly goes against the grain of the thread, I'd be inclined to run a 2200 watt generator in my pickup to keep the trailer cooled if that were something that was important to me. On long trips, it's certainly nice to have a cool place to relax (other than the truck) when you do rest stops. Firing up the AC for a 30 minute stop won't do it. That was one of the nicest parts about owning our Class A. The generator was always running and the coach was nice and comfy.

[LilPeanut]

We have a classic 30 with 600ahr or lithium and 1000 of solar and a 40a dc-dc, 3k multiples and easy starts. We tend to travel in the south a lot and turn on the AC about 30 min before we want to stop. It cools things down pretty for us and the cats. We run it while we make lunch, get groceries or whatever, typical stop is 30 min to an hour. Then we are off again.

I have run it the whole way but I don’t think it was substantially cooler, or at least not enough to warrant the juice it takes.

A note on solar and DC to DC. Solar is great when the sun is out. But you can’t always count on it. The DC to dC is what I use when it is raining. I don’t do both.

[foobar]

Originally Posted by LilPeanut

We have a classic 30 with 600ahr or lithium and 1000 of solar and a 40a dc-dc, 3k multiples and easy starts. We tend to travel in the south a lot and turn on the AC about 30 min before we want to stop. It cools things down pretty for us and the cats. We run it while we make lunch, get groceries or whatever, typical stop is 30 min to an hour. Then we are off again.

I have run it the whole way but I don’t think it was substantially cooler, or at least not enough to warrant the juice it takes.

A note on solar and DC to DC. Solar is great when the sun is out. But you can’t always count on it. The DC to dC is what I use when it is raining. I don’t do both.

Good info and good points. Probably isn't worth it to try and run for the whole trip. With the Easytouch thermostat, it would be easy to fire up the A/C remotely about 30 minutes to an hour before we stop for lunch or before we arrive at the campground.

[dsatwork]

Don't think I would ever need to run the AC all day but have turned it on a 30 to 60 minutes before reaching destination.

Multiplus ll 50 2x120
DC to DC 30 AMP Charger
400 watts solar on roof
500AH lithium

[2012FB]

Originally Posted by jondrew55

While this certainly goes against the grain of the thread, I'd be inclined to run a 2200 watt generator in my pickup to keep the trailer cooled if that were something that was important to me. On long trips, it's certainly nice to have a cool place to relax (other than the truck) when you do rest stops. Firing up the AC for a 30 minute stop won't do it. That was one of the nicest parts about owning our Class A. The generator was always running and the coach was nice and comfy.

Our onboard Onan Generator will run both AC units going down the road just like your class A. Have not really had a need to have both AC units going, but it is there if needed. If boondocking we run the AC 30-60 minutes before arrival and let the Solar and Generator if needed replenish the batteries.

[Mollysdad]

IIRC LoLoHo added a huge alternator to their tow vehicle.
They ran the power back to the trailer with a dedicated cable, using the stuff you see charging golf carts.

https://www.youtube.com/watch?v=KTGDCSu1kwI

Might give you some ideas.
Personally, I wouldn't run an a/c for hours to save five minutes of cool down.
People with class A do it all the time.

[foobar]

Originally Posted by Mollysdad

IIRC LoLoHo added a huge alternator to their tow vehicle.
They ran the power back to the trailer with a dedicated cable, using the stuff you see charging golf carts.

Might give you some ideas.
Personally, I wouldn't run an a/c for hours to save five minutes of cool down.
People with class A do it all the time.

Yeah, I'm rethinking the original goal :-). Probably stick with just starting the A/C via remote control from the tow vehicle about a half hour before we stop for lunch, or before we expect to arrive at a campsite. Here in sunny Texas, it's been 98-105F everyday for the last several weeks, so 30minutes isn't probably going to cool the trailer down very much but it might at least blunt a little of the blast furnace effect

I am planning on a 1290ah Lithium battery bank, so I won't have any capacity issues.

[2012FB]

Originally Posted by foobar

I am planning on a 1290ah Lithium battery bank, so I won't have any capacity issues.

With that much capacity, you could easily install two Multiplus II running both AC units and have an ice box when you stop.

[GetawA-S]

Originally Posted by pteck

A thing I've noticed is that the interior of the trailer is not really hotter than ambient when underway. Even on super hot 110* days. Perhaps at speed, the aluminum skin temps are sufficiently kept at ambient by moving air, so the interior doesn't get super heated like a statically parked car. Therefore possibly running the A/C maybe 30 minutes prior could make things sufficiently comfortable.

This is absolutely relevant to this discussion.
Sitting at the campsite, the radiant heat gain from the sun is what causes the “blast furnace” effect.
Going down the road, the heat gain is balanced by convective heat loss to the air blasting over the trailer (similar to blowing on food to cool it). If you run your A/C going down the road, as soon as it gets the inside temperature below the air temperature, that enhanced heat loss becomes enhanced heat gain. It costs more to run than in the campsite. The extended operation will not make your trailer any more comfortable than just turning it on as you get near your stop, and we all know energy is not free, especially when it’s coming from $5/gallon gasoline.

We all love the Fido’s, but let’s not overthink this.

[foobar]

Originally Posted by 2012FB

With that much capacity, you could easily install two Multiplus II running both AC units and have an ice box when you stop.

True :-)

Original motivation is pet protection. Then I realized how nice it would be to have that much capacity here in Texas when boondocking in the somewhat warmer season called Texans affectionately call "summer", lol.

I plan to connect the 13K btu A/C to the always-on port on the multi-plus inverter and connect the 15K btu to the auxiliary output on the inverter. Power is not supplied to anything hooked up to the aux port. So critical loads go on the always-on port and the non-critical loads go on the aux port.

The idea is that when my wife and I are out hiking or playing tourist, if there is a power loss event, a single A/C can be maintained for 6+ hours with plenty of reserve capacity. This would keep any pets in the trailer safe and cool until we return.