Running 110v a/c off alt and inverter while driving

[Mfitz]

Can this be done? I asked in another thread but never got a clear answer.

My truck camper already has a Coleman Mach 8, and I am trying to see if I can run it off my alternator and an inverter while driving (not while the truck is turned off). The battery bank is two group 31 12v batteries and I will have a DC-DC charger for them. I would love to switch over to lithium but it isn't in the budget right now, nor is swapping the Coleman for a 12v AC unit. Can it be done safely? My truck ('22 F350) has a dual alternator system so it will churn out fairly big amps for a vehicle.

 

[Skeptic]

Looking at the Mach 8 (Plus) specs, it shows as drawing 12.5 or 14.2 amps, or about 1,700 watts using the 14.2 amp figure. You'd have to look at your inverter to determine how much it can supply at a steady draw (not peak). My estimate you would need something beyond a 2,000 watt inverter to make that work. Work backwards from there to determine the 12 VDC draw that inverter would need, and then see how long your battery bank can provide that, factoring in the DC charging input from the alternator. Chances are the alternator can supply the inverter without having to pull from the batteries.

Not terribly complicated to work out, but take it one stage at a time in doing the math.

 

[carterd]

You also need to make sure your electrical system can handle the initial startup current draw of the air conditioner. Per the Airxcel website (they own Coleman-Mach):

• To calculate the max potential startup: Find the running amp draw for your system and multiply it by 2.5. With this information, your generator manufacturer should be able to assist you in sizing a generator suitable for your application.

You can reduce the startup current by installing a soft-start kit, which can reduce startup current by up to 75%. Coleman-Mach sells these to retrofit on existing systems. https://www.airxcel.com/softstart

 

[broncobowsher]

Worst case, 100% duty cycle. For the most part, everyone runs the A/C 100%.
Just a wild assumption you have an invertor that can take the start up load, it probably can if the fans are on low. I've seen invertor generators fire up A/C units they had no business running so long as they were started on the lowest fan settings.
A watt is a watt, and every time you change from one to another there is a loss in effiency. Quick ugly numbers, it is going to be drawing close to 200A. That is a lot for a 12V alternator to make (even a pair of them) for sustained periods of time.
But wait, you are running it through a DC-DC charger. What size is that? Bet it isn't 200A. In which case this will be the choke point. Say you have a 40A DC-DC going into the house battery but the invertor is pulling 200, the batteries are loosing 160A of current. That isn't going to run very long
You would be better off with a cheap 2kw invertor generator running on the bumper as you are driving down the road.

 

[burleyman]

If load amps are listed at 120vac, then multiply that times 10 for amps from a 12v battery and inverter. Add a few more battery amps for inverter loss of efficiency.

In testing for air conditioner operation, don't quickly shut down, then quickly attempt a restart without allowing time for things to settle. A generator or inverter often cannot handle that kind of compressor start current. That can cause someone to think they need a larger generator or inverter.

What bronco said above, about seldom shutting down in hot weather. A properly sized generator is cheaper than high output alternators and associated devices and wiring, any of which can fail.

I have seen many expensive, high output alternator installations, sometimes dual, with a 40-60 amp dc-dc charger throttling all that alternator capacity feeding multiple hundreds of amp/hour lithium batteries, begging for more. Tales of thousands of dollars worth of stuff to charge hungry batteries at low amp values, while smiling and happy.

 

[86scotty]

I'm confused. It's winter time. This isn't how forums work. There are usually piles and piles of similar threads on questionable AC setups in late Spring. Right now is the time that everyone asks about the cheapest way to HEAT a rig. You aren't in Australia, by chance, are you?

 

[Mfitz]

HaHa, not in Australia, just looking ahead to the summer. It sounds like this is a sketchy idea at best, and not my first, but that is why I ask those who know more than I do! I'll move on to plan B (fans while stationary in the trailer, maybe an exhaust fan that is highway wind-proof for while driving). Thanks all.

 

[Mfitz]

And yes, I tend to ask questions about sketchy heating setups in June- looking ahead!