[oldroad]

I have mounted a small 5000 BTU air conditoner on the cab of my tractor, powered by a 2000 watt inverter. The inverter would shut down after about 90 minutes, which was better than nothing. After about 45 days of use, the inverter quit altogether.



I think i have a 75 amp alternator and I do have two 135 Amp hours marine batteries (270 AH Total). I can run approx 90 minutes before AC shuts off. Can wait an hour and go another 90 minutes or so with air.



The inverter quit working entirely, and I'm thinking about getting a new one. What might be the weak link in my set-up? What do you recommend? What size inverter and alternator do i need?

 

[user_12345a]

Having the compressor start on the inverter may be hard on it - normal wattage for that size a/c is 400 to 500w, compressor can draw 4 to 6 times normal amps on startup.

You can reduce the startup duration with a small hard start kit.

I know this doesn't really answer your question.

 

[spitz1234]

Take a look at a soft start. A hard start only reduces the in rush period of a compressor.

Sent from my SM-G960U using Tapatalk

 

[user_12345a]

neither soft nor hard start impacts running current - only startup.

the problem may not be caused by the startup current.

 

[CaptTom]

Look carefully at the inverter specs. Is that 2KW for extended duration, or just peak? Also, a pure sine wave may play nicer with your air conditioner. And make sure the cables are of the correct gauge and length to supply the inverter with sufficient voltage. Finally, can the alternator keep up?

This comes up on boating forums all the time. People don't understand how much power it takes to run an air conditioner. It's not really the kind of thing a 12V system is designed to handle.

 

[surferdude2]

I think you are taking the wrong approach. Granted you can modify the tractor's electrical system to do what you want but it will be more expensive and less reliable than if you chose some other alternative. Inverters are inefficient devices.

Here are some typical examples of what those inverters need in terms of supply capacity that I copied froma quick search:

"If you max out the inverter at 2000 watts, you are pulling 2000 watts /12 volts = 166.6 DC amps per hour. If you use a 200 amp 12 volt battery you would divide 200 amp battery / 166.6 amps = 1.2 hours of run time."

"To obtain 3000 Watts AC at 120 Volts from an inverter, you must replace your 100 AMP alternator with an expensive 250 AMP alternator and install MULTIPLE heavy duty batteries."

From those examples, it looks like providing power a different way might be a better method. Consider getting a portable generator with could be mounted on the tractor. One sized to start and run a 5000 btu ac shouldn't be very big physically. For Example, click here. That may even be bigger than necessary but would likely last longer at a low load.

 

[Oso954]

You are going about it the wrong way. Ever see an electric powered A/C on a tractor or truck ? Every one I’ve ever seen use engine power to run the compressor and a small dc fan to provide air flow.

Cobbing together a cheap RV inverter with a small window type A/C may be cheaper, but it isn’t going to hold up long term. IMO, you would be better off salvaging a used diesel truck A/C system from a junkyard.

Where did you mount that inverter ? Is it shutting down do to low voltage or thermal overload? My guess would be that it might be thermal, depending where you mounted the inverter.

You would get better answers by posting a better description of the system. Right now we are guessing at what A/C you might have, what inverter, what the tractor alternator/battery are, etc.

 

[lenaitch]

There seems to be a number of sites on this, so you're not the first (apparently OEM a/c units tend to be troublesome). Many discussions seem to lay blame on heat and vibration as well as the a/c sucking the guts out of the inverter.
There are other threads about running a/c off and inverter in off-grid settings. It seems the efficiency of converting DC-AC is part of the issue but I'll let others rule on that.


https://www.mrright.in/ideas/appliances/inverter/can-air-conditioner-run-inverter-find/

 

[oldroad]

Inverter used was Jupiter brand, 2000 continuous / 4000 peak. # 2 Cables about 6 feet long.

I also tried a 1500 continuous before going to the 2000. It would start ok, but when inverter shut down, it did not want to restart.

The 2000 continuous would start and run an hour to 90 miunutes. It would pull down batteries somewhat. I could then run tractor an hour without AC on and restart for another hour of cold air.

I'm thinking the hard start kit would definitely be a plus, although I don't have starting problems. At this point, it would seem, the weakest link might be the alternator.

I thank you all for the replies. They were indeed useful. Thanks again.

 

[TarheelTerp]

Is there a reason an automobile type AC system isn't already on the tractor?
Isn't that how all the other tractors and combines are set up?

 

[oldroad]

It's an old Deutz brand tractor, complete with an auto styled AC. This particular model, when in like new condition, the AC put out very little air.

 

[user_12345a]

Why not fix the built in a/c?

putting out little air could just be caused by a blower issue.

 

[beenthere]

75 amps at 12 volts is only 900 watts. A bit light for the A/C.

 

[oldroad]

75 amps at 12 volts is only 900 watts. A bit light for the A/C.

We are only guessing at amps on alternator. Many of these are half that. Going to test with amp meter. We will see. Will update.

 

[oldroad]

Why not fix the built in a/c?

putting out little air could just be caused by a blower issue.

May end up going that route.

 

[taylorjm]

You know, maybe instead of trying to rig up an inverter and run a 120v a/c, you should look at the a/c units made to run on 12/24v. They make them for the sleeper units of trucks, excavators, etc. that run on 12v and would probably be more than enough to cool your cab. I would think 5000btu would be overkill and you could get away with something smaller. Here are some examples.

https://www.alibaba.com/product-det...pm=a2700.7724857.normalList.48.838f6221L5rZ6z

https://www.alibaba.com/product-det...pm=a2700.7724857.normalList.64.838f6221L5rZ6z

https://www.alibaba.com/product-det...m=a2700.7724857.normalList.160.838f6221L5rZ6z

 

[oldroad]

You know, maybe instead of trying to rig up an inverter and run a 120v a/c, you should look at the a/c units made to run on 12/24v. They make them for the sleeper units of trucks, excavators, etc. that run on 12v and would probably be more than enough to cool your cab. I would think 5000btu would be overkill and you could get away with something smaller.

I never thought of that. Will definitely check those and other units out. Thanks a lot.