Dual alternator/batteries/inverter to run A/C in camper?

[Mingoglia]

History and summary of what I'd like to accomplish:

On my truck, I specifically purchased the dual 220amp alternators because I had a crazy idea of being able to run an A/C in a yet to be purchased slide-in while going down the road. Over the years I've downsized my rigs from a big fiver, to a toy hauler, to not a slide-in with just a trailer for the toys. Main purpose is to get in and out of more remote locations. I've recently moved from Phoenix to Georgia, but drive back every few months towing my off-road buggy, and at times add a couple quads to that trailer. Would be nice to keep the interior of the slide-in cool for the dog, and for the quick side of the road lunches, without using a genset. Over the years I've always had built in gensets, with built in gas tanks, and have always kept my rig cool no matter where I was driving. With a slide-in, the built in gensets are propane, and obviously I don't want to blow through propane whereas previously I didn't care as I typically could run the generator for 75+ hours on my built in fuel tank.

My thought process so far:

Alternators are rated at a certain RPM higher than idle. In addition, I'm sure they're tested at 80 degrees in a lab somewhere, where in my case they'll be running in a much hotter engine compartment while driving potentially in 115 degree ambient air, on top of 160 degree black top, while in an even hotter engine compartment. Although my alternators are rated for a combined 440amps according to the propaganda, let's say they're only good for 50% of that taking the variables into account and at idle. This brings us back down to 220amp available anytime the engine is running. Does this sound like a fair assessment?

I'm not sure what the startup and running amps are for say a 11k BTU air conditioner, but I do know I've read countless times that people are running them on Honda EU2000i generators. Since I don't know what A/C I'll end up with (since I haven't decided on my slide-in yet), I'll just pull the specs of this genset and see what I'd have to "duplicate" in the power generation department. According to the specs, this generator is rated at a startup of 2000 watts (16.7 amp), and 1600 watts (13.3 amps) continuous. If you take the 12v amperage of 220amps from the alternator, that translates into 22 amps (inverting 12v to 120v) at 120v. I do know inverters aren't 100% efficient, but it looks like the continuous 13 amps should be able to easily be provided by the alternators, even at idle. I know there are plenty of 2000 and even 3000 or more inverters, and assume finding one that can run the A/C won't be an issue, though I'm not sure how hard it is on them. Hope some can chime in here...

Batteries/Inverter:

Honestly it's been a couple years since I've evaluated golf cart batteries and tried to understand amp hours and how it relates to what I'm trying to accomplish. Knowing space is tight, could batteries 2 golf cart batteries handle the load I'm talking, feeding a 2000 or 3000 watt inverter, providing 13amps of continuous power and any inefficiency overhead of the inverter? If so, does anyone have a frame of reference of how long? Are we talking 15 minutes, 30 minutes, 2 hours? I ask this question because although I plan to run the A/C going down the road there are obviously times when I want to run into Denny's for a Super Bird and a coke, and may or may not turn the truck off. I'd like to figure such stops into my realistic expectation.

Charging the coach batteries:

I think it goes without saying I'm not expecting the charge wire in the 7-way plug to be able to keep the coach batteries charged at the amperage draw I'm talking about. I had pictured running some appropriate gauge wire from the engine compartment along the frame and up into the slide-in, using connectors similar to the ones used for receiver mounted winches. This would obviously be about a 25' run. Would I literally run my coach batteries in parallel to my truck batteries to get all this amperage? Or is there some sort of charge controller needed in order to make this happen? I'm completely ignorant here on how this would work.

Hopefully this isn't too wordy, curious everyone's thoughts.

Mike

 

[Shadrach]

Sounds interesting. I would start by contacting one of the major investor manufacturers and see what they can tell you. You could try http://www.xantrex.com for example. Keep us posted on how this goes. David

 

[Tuesdak]

The surge current to start the AC compressor, even with a hard start kit, will trip the inverters off unless it's big enough. Electric motors surge till they get to like 90% of their normal RPM. Never mind the huge battery cable and ground you would have to run. This current level is NOT a connector, but, bolt on lugs to battery size cable. The big inverter would have to be truck mounted and run 110v to the camper. The surge current will cause trouble with the battery charge wire to the camper let alone running current. The truck voltage will be higher thus the recommendation to place the inverter in the truck and keep the amps off the charge line to the camper regardless of the camper's batteries.

Last time I tried this it was with an air compressor and the ground path was the weak point followed by not enough CCA on the batteries to start it on an inverter.

Better idea is to drop a diesel genset in the camper and maybe refill it off the truck fuel tank. I don't like the 3 fuel idea but gasoline gensets are simpler to fuel than propane. I don't like the idea of a gas generator running while going down the road.

I will try having the dogs ride in the cab with me and I will fire the AC off when needed for stops or in advance of stops. We will see how fast the camper AC cools things down. I'll carry some extra 20# propane bottles as on propane alone 40# only lasts around 23 hours of genset use. This is w/o the fridge, but, the fridge will run on 12v from the truck.

I would get a remote temp sensor you can see in the cab in case SHTF and temps start climbing in the camper for your dog's sake.

Alternate idea is to use the camper's window to the cab for AC. Install a second evaporator in the rear seat area on your truck's AC system (Like rear air Suburbans and vans) and use the camper window for airflow. This would be a custom expansion valve system with a sliding rear window in the truck and camper. You don't put the system in the camper for detach and removal reasons. I doubt fans into the cab without a second evaporator will be enough to cool the camper. The truck's AC system may not have enough BTU to cool the camper. I think the Camper's AC size is the same as the trucks AC size in BTU's. So a larger compressor (CFM) may be required as most dual air system have larger CFM compressors.

Arctic BREEZE 12v Truck AC is an idea.

Big Rig APU would be worth looking into although you are back to a small diesel genset at this point.

Better yet is a 4x4 motorhome that you cool the entire thing off while driving.

 

[Mingoglia]

Sounds interesting. I would start by contacting one of the major investor manufacturers and see what they can tell you. You could try http://www.xantrex.com for example. Keep us posted on how this goes. David

Thanks for the link. I didn't realize that company existed. Definitely looks like a great starting point.

 

[Mingoglia]

The surge current to start the AC compressor, even with a hard start kit, will trip the inverters off unless it's big enough. Electric motors surge till they get to like 90% of their normal RPM. Never mind the huge battery cable and ground you would have to run. This current level is NOT a connector, but, bolt on lugs to battery size cable. The big inverter would have to be truck mounted and run 110v to the camper. The surge current will cause trouble with the battery charge wire to the camper let alone running current. The truck voltage will be higher thus the recommendation to place the inverter in the truck and keep the amps off the charge line to the camper regardless of the camper's batteries.

Last time I tried this it was with an air compressor and the ground path was the weak point followed by not enough CCA on the batteries to start it on an inverter.

Better idea is to drop a diesel genset in the camper and maybe refill it off the truck fuel tank. I don't like the 3 fuel idea but gasoline gensets are simpler to fuel than propane. I don't like the idea of a gas generator running while going down the road.

I will try having the dogs ride in the cab with me and I will fire the AC off when needed for stops or in advance of stops. We will see how fast the camper AC cools things down. I'll carry some extra 20# propane bottles as on propane alone 40# only lasts around 23 hours of genset use. This is w/o the fridge, but, the fridge will run on 12v from the truck.

I would get a remote temp sensor you can see in the cab in case SHTF and temps start climbing in the camper for your dog's sake.

Alternate idea is to use the camper's window to the cab for AC. Install a second evaporator in the rear seat area on your truck's AC system (Like rear air Suburbans and vans) and use the camper window for airflow. This would be a custom expansion valve system with a sliding rear window in the truck and camper. You don't put the system in the camper for detach and removal reasons. I doubt fans into the cab without a second evaporator will be enough to cool the camper. The truck's AC system may not have enough BTU to cool the camper. I think the Camper's AC size is the same as the trucks AC size in BTU's. So a larger compressor (CFM) may be required as most dual air system have larger CFM compressors.

Arctic BREEZE 12v Truck AC is an idea.

Big Rig APU would be worth looking into although you are back to a small diesel genset at this point.

Better yet is a 4x4 motorhome that you cool the entire thing off while driving.

Thanks for spending the time with your detailed response. I've explored all the options, and owned many different setups over the years and all have had limitations. I believe the truck/slide-in is the best option at this point. I'm sure I can make this work with the right inverter and charging technology.

As for thermal monitors, I already have that covered. There's a product I use in my gun safe that monitors temperature, humidity, and if the door opens. It uses the Internet to send me text messages, or messages through the app. Since I have an Internet access point I travel with, my plan is to use that in combination with this device to always monitor the interior temperature. This obviously requires there to be Internet, but I can make sure I know what areas I park that do or do not have Internet. It actually gives me alerts when it loses Internet. There is a third party monitor that does this monitoring, so I'll at least know if the unit isn't online. While going down the road, I'll have the sliding rear window open and if the dog is in distress I'll know about it.

 

[zb39]

You can run AC off of an inverter. First you need a large inverter(3k is good 4k is better) Then a battery bank. 4 6volt GC wired in series and then parallel. 8 would be better. You have the duel alt, so 440a at 12v equals 5280 watts. At 70% that is a whisker under 3700 watts. With good cables and what not, this should work. Please keep us updated, your not the first to do this, I say go for it. Also only the small AC run off a 2k genet, like the polar cub. A 13.5 btu will take around 3k watts to run well. They are all a little diff and hard start kits are a good thing to have. But it is doable.

 

[CBari]

There was a company a few years back that had a pto-gen set for diesel trucks it would run off the truck while running down the road. It worked on the Allison and Ford Trans when I looked into, but at the time Dodge didn't have a trans that would work with it. I think the Aisin trans would. Just another option to think about. It was called Real Power.

 

[Mingoglia]

There was a company a few years back that had a pto-gen set for diesel trucks it would run off the truck while running down the road. It worked on the Allison and Ford Trans when I looked into, but at the time Dodge didn't have a trans that would work with it. I think the Aisin trans would. Just another option to think about. It was called Real Power.

That's a very interesting solution. Unless their website isn't updated, they still don't support a Ram application. They do support the ISB, but the commercial ones matched to the Allison 2000:
http://realacpower.com/products/applications/

On edit:
Looks like it works with the Aisin behind a Isuzu.
"12kW and 15kW Hot Shift PTO generator systems are now available for 2011 Isuzu N-Series vehicles equipped with an Aisin 6-speed Automatic transmission with PTO port"

 

[CBari]

Looking at their news sections I don't see any updates since 2013 maybe they will work with the Aisin. Let me know what you find out.

 

[AH64ID]

I have a pair of 300 AH 6 volts (33% larger than your standard GC battery) and with a 1500W inverter making 1500W of A/C power my batteries are not big enough, even thou they have the capacity to run the 1500W load for a while (70 minutes). The voltage drop I get is bigger than it should be, based on the amp draw vs the AH rating. With my batteries at 100% the 126A draw puts my output voltage down to 11.65V almost instantly.

Most slide-in campers have 13.5K BTU A/C units. They can draw up 2,000W on a hot day (115°F). 2,000W of AC power is 16.6A of AC power and around 185A of DC power required (including loss). To have 185A of DC power without a big voltage drop is going to take 800+ AH of battery bank to run without a constant 12V source. That's a LOT, and running amps not startup amps. Ignoring the voltage drop a pair of GC batteries at 100 % SOC would be able to give you approx 70 minutes of use before the SOC was 50%, but with the voltage drop from such a large amp draw the inverter would likely go into low voltage cutout long before that time.

That being said if your engine is running at idle you will have ~210A total output and idling at 1100 rpms would net you ~280A. That is with 200°F ambient air over the alternator. If the air is 75°F the output is ~250A and ~330A respectively.

Option 1) Run 4/0 cables (+ and -) back to the bed and use a set of HD quick disconnects. Then have a 3500w inverter in the camper that powers the 120V AC circuit. You will want at least 225AH of batteries in the camper (pair of 6V GC) but they are mostly acting as a capacitor and the engine will be the power supply. You will want a voltage sensing relay inline (either in the camper or underhood) to keep the camper from accidentally, and quickly, draining the trucks batteries.

Option 2) Install the same 3500W inverter in the pickup. This gives you a much shorter 12V run which means smaller cable. I would want to upgrade my truck batteries to a dual purpose battery over the OEM starting batteries, but even then you will only want to power the inverter with the engine running. Then all you do is plug the campers 120V 30A connector into the inverter.

There are advantages to both. Option 1 allows for the inverter to be used for other dry camping 120V needs and Option 2 will likely be a cheaper install, but has fewer uses.




Voltage Sensing Relay
https://www.bluesea.com/products/7620/ML-ACR_Automatic_Charging_Relay_-_12V_DC_500A

Alternator Output curves. The bottom one is the dual 220A alternators.
http://www.rambodybuilder.com/2016/docs/ram/ramaltoutcrv.pdf

 

[Mingoglia]

I have a pair of 300 AH 6 volts (33% larger than your standard GC battery) and with a 1500W inverter making 1500W of A/C power my batteries are not big enough, even thou they have the capacity to run the 1500W load for a while (70 minutes). The voltage drop I get is bigger than it should be, based on the amp draw vs the AH rating. With my batteries at 100% the 126A draw puts my output voltage down to 11.65V almost instantly.

Most slide-in campers have 13.5K BTU A/C units. They can draw up 2,000W on a hot day (115°F). 2,000W of AC power is 16.6A of AC power and around 185A of DC power required (including loss). To have 185A of DC power without a big voltage drop is going to take 800+ AH of battery bank to run without a constant 12V source. That's a LOT, and running amps not startup amps. Ignoring the voltage drop a pair of GC batteries at 100 % SOC would be able to give you approx 70 minutes of use before the SOC was 50%, but with the voltage drop from such a large amp draw the inverter would likely go into low voltage cutout long before that time.

That being said if your engine is running at idle you will have ~210A total output and idling at 1100 rpms would net you ~280A. That is with 200°F ambient air over the alternator. If the air is 75°F the output is ~250A and ~330A respectively.

Option 1) Run 4/0 cables (+ and -) back to the bed and use a set of HD quick disconnects. Then have a 3500w inverter in the camper that powers the 120V AC circuit. You will want at least 225AH of batteries in the camper (pair of 6V GC) but they are mostly acting as a capacitor and the engine will be the power supply. You will want a voltage sensing relay inline (either in the camper or underhood) to keep the camper from accidentally, and quickly, draining the trucks batteries.

Option 2) Install the same 3500W inverter in the pickup. This gives you a much shorter 12V run which means smaller cable. I would want to upgrade my truck batteries to a dual purpose battery over the OEM starting batteries, but even then you will only want to power the inverter with the engine running. Then all you do is plug the campers 120V 30A connector into the inverter.

There are advantages to both. Option 1 allows for the inverter to be used for other dry camping 120V needs and Option 2 will likely be a cheaper install, but has fewer uses.




Voltage Sensing Relay
https://www.bluesea.com/products/7620/ML-ACR_Automatic_Charging_Relay_-_12V_DC_500A

Alternator Output curves. The bottom one is the dual 220A alternators.
http://www.rambodybuilder.com/2016/docs/ram/ramaltoutcrv.pdf

Now that's exactly what I was looking for! So on option 1, are you saying 4/0 wire with Positive from the truck battery to positive to one of the GC batteries, and negative from the other battery in the truck to negative to the other GC battery (then of course the relay somewhere in there)?

Option 2 does sound interesting. Could probably use say some 10/2 wire and a receptacle in the truck somewhere? I do like the idea of having A/C running most of the way, than D/C.

When you're pulling this type of amperage from the alternators, does it noticeably bring down idle speed of the truck? Like a genset when you first turn the A/C, does it dip and then bring it back up? Should I assume this may drastically reduce the life expectancy of the alternators?

 

[AH64ID]

Yes that would get you the power from the alternators to the GC batteries without too much of s voltage drop during high amp use.

You would still need at least 0 and maybe 00 even if the inverter was in the truck as the amp draw is still very large.

I doubt it would effect the idle rpm since the batteries should provide the needed amp surge.

Yes I suspect it would shorten the life, but it may not be appreciable. I would always try to idle up to 1100 of you run the A/C while parked. This will ease the load on the alternators and improve engine bay airflow. I wonder if the snowplow fan option would be a good idea?

 

[Mingoglia]

Curious if anyone knows how the ambulances are set up power-wise? Do they have gensets in them, or is it all power generated from alternators? I would assume their equipment pulls huge amperage.

 

[Tuesdak]

The auto idle will recover as 8-9HP is not a problem for the ECM to adjust to. Like kicking the AC compressor on.

440 amps from the two alts at 14V is 6160 Watts.
745.7 watts = 1 hp
6160 / 745.7 = 8.26 HP

That's a lot of amps (plus available CCA from the batteries being 800 each so nearly 2000 amps available with the camper connector wire being small enough to ignore it's batteries.) and a good reason to keep the 12v high amp run as short as possible. The inverter will be putting out it's own heat. If you can keep things cool it won't affect the life. This is hard to do with the extreme heat of Phoenix at 121 degrees. After all R134A starts to give up at 105 degrees. (Increased condenser temp ~160F in front of the cooling stack, extreme head pressures, and higher current draw from the camper AC fighting it's high head pressures.) The batteries will take over during the startup surge. (Without the load batteries only last around 2 -3 years in the extreme heat.) The startup surge is where you pop diodes in hot alternators or burn out the weak connector or wire. Once it gets hot the resistance goes up and thermal runaway till it burns out. Damage to diodes may not show up till the next day after a heat cycle. We are not talking about a alternator running the edge of a thermal envelope like some vehicles have. Although in a hot location under the hood short term you should be ok.

If anything I'd proactively overhaul them every year with new bearings as high heat will dry the grease out. The next stressed parts will be the diodes, but, that would be replaced if they start acting up.

It's not uncommon for compressors to refuse to start even after a 5 min timer due to extreme outside temps causing head pressures to stay high. This would be an extended surge till the thermal limiter kicks off in the compressor pushing the heat limits of every single connection, inverter, and extreme amps on the 12v side.

Here is a interesting site describing inverter power for hard to start compressor loads in context of boats.

https://www.victronenergy.com/inverters/phoenix-inverter-compact
https://www.victronenergy.com/upload/documents/whitepaper-Engine-driven-inverter-system.pdf

 

[Shadrach]

Since you want to do this to a slide in camper there will be no room for a generator of any kind or a lot of batteries unless you get big 11'9" that is set up for an 2.5 ONAN. With a soft start kit on the A/C it would run the unit but if you are driving and therefor not in the camper you can't monitor it if here is a problem.

Another solution, especially if the camper is to stay on the truck all the time, is to go with a setup like a catering truck uses and drive the roof mounted A/C from your engine. Forget the dual alternators and go with dual A/C compressors, one for the Dodge and the other for the camper. If the camper is to come off the truck on a regular basis then you would need quick disconnect lines.

You will get all kinds of crazy ideas from here. :-laf

 

[Bill Stockard]

The last three Lance slide-in truck campers I've owned have been factory equipped with built-in LP gas powered generators. The generators burn considerably less fuel than running the truck engine to power the A/C through a Rube Goldberg wiring nightmare of charging batteries and using inverters. I have run the A/C overnight on warm nights with the built-in generator and the use of LP gas from two 40-lb. LP gas tanks is insignificant. The A/C compressor doesn't run continuously, but cycles off and on and as the night air cools it cycles off and on less often. It's simple and almost fool-proof to operate with only a push of a button on the control panel. Simplicity=reliability. Who wants to stay up half the night of interrupted sleep attempting to make a complicated system work?

Bill

 

[AH64ID]

The 2003 Lance 1121 had the option for the 3400W Generac. It's rated fuel consumption is .55 gal/hr at 1/2 load which is 14A and about what the A/C should be using along with incidentals. An overnight 8 hour run would burn around 4 gallons, or 60% of a standard 7 gal 30# bottle.

.55 gal/hr is going to be more fuel an hour than the engine will burn at idle even with the alternators pumping out some amperage.

Even no load operation is going to be around 0.3 gal/hr or 2.4 gallons overnight (35% of a 30# bottle).

I have not seen any slide-in campers with the large 40#, 9.4 gallon, bottles. Where did you get them to fit in the 1121? Lance specs show it came with 2 30# tanks.


Not saying the on-board generator isn't a bad idea just getting the published spec's out there.

 

[Bill Stockard]

The 2003 Lance 1121 had the option for the 3400W Generac. It's rated fuel consumption is .55 gal/hr at 1/2 load which is 14A and about what the A/C should be using along with incidentals. An overnight 8 hour run would burn around 4 gallons, or 60% of a standard 7 gal 30# bottle.

.55 gal/hr is going to be more fuel an hour than the engine will burn at idle even with the alternators pumping out some amperage.

Even no load operation is going to be around 0.3 gal/hr or 2.4 gallons overnight (35% of a 30# bottle).

I have not seen any slide-in campers with the large 40#, 9.4 gallon, bottles. Where did you get them to fit in the 1121? Lance specs show it came with 2 30# tanks.


Not saying the on-board generator isn't a bad idea just getting the published spec's out there.

The Generac RV generator is an inverter type variable speed generator. The engine speed varies with the electrical load. When only the A/C circulating fan is running the engine runs at just above idle speed which is less than 0.5 gal/hr. fuel consumption. With the compressor cycles on, the engine speed increases to just under 1/2 max engine speed. In such a small enclosed area the compressor run time is short. I know what the specification are, but in my experience running the generator for nights and days, the fuel consumption is less. Yes, I stand corrected, our formerly owned 2003 Lance 1121 was equipped with 30-lb LP gas horizontal tanks. Again, I refer to my statement, Simplicity=reliability. Why endure an interrupted night's sleep attempting to keep an over complicated system running?

Bill

 

[AH64ID]

I understood that the OP is looking to keep it cool while traveling and not while parked overnight.

 

[Mingoglia]

I understood that the OP is looking to keep it cool while traveling and not while parked overnight.

Yup. I'm not shy about using a genset. My prior rigs have always had gensets, and I'll run the darn thing all day in the summer if I need to. I've found that running (and maintaining) the genset and putting hours on it seems to make it last longer than having it sit trying to prevent the hour meter from ticking away, resulting in it gumming up and not working properly. Granted in the slide-in my philosophy will change somewhat as it will be LP.

As for this thread, as was said, this is for when going down the road during the summer. When I get to my destination, if it's hot, I'll either cycle the LP genset on or bring along a Honda 2000 or similar, or both. No way I'd idle my truck to keep batteries charged to run the A/C. That's a bit silly. Only exception may be on a road trip when I'm sitting at Denny's in view of the truck with the dog in it. In that situation, I'd have no issue high-idling for 30-40 mins. That's the exception though.