Air Conditioners from Inverter (s)

[neoneddy]

This is for only on the road use.  I know a generator can solve a lot of this, but let's table that for the time being.

Right now I have an Aims 24v 3000w Inverter Charger and recently I bought a 24v 1000w Grid Tie inverter to help it.  Yes this works, The kil-a-watt showed 500-600watts going into my system, that's not really the point of the post, just some background.

For ACs I have a brand new Coleman Mach 3 Plus and a used / unknown state Coleman Mach 15 .    I've installed soft start capacitors in both.

I'm considering selling the Mach 15 and replacing it with a Mach 3 Plus for a total of 2 of those units, vs one of each.   

I'm suspect of my Mach 15 and here is why.

Right now, if I try and start the Mach 15 up while plugged in at home, it will start up fine most times, but I have to put it on fan low first for a few seconds, then move it to Cool and the compressor kicks on and the voltage drops from my home extension cord. (Yes looking to add a 30 amp service plug outside)   If I try and start the Mach 15 up while on inverter power it's similar except sometimes the inverter will start start vibrating loudly, if that goes on too long the  breaker will eventually pop (20 amp).  I've found if I let the fan run on low, I think that charges up the capacitors and it will start softer, and it's fine.   Now the Aims manual says the vibrating case noise is usually from something like  a hair dryer that only uses 1/2 of the sine wave causing an imbalance in the magnetic fields.   

Where the grid tie inverter comes in is I wanted to boost the power of the inverter as a whole, they don't support stacking on their own, but a grid tie doesn't care what the grid actually is.  Now I will say this is dangerous, always make sure there is a real load on the system before adding a grid tie inverter.  Mine tops out at 140v, but I've heard some go up to 170 and will fry stuff.   Other option is to go to a 4000w inverter, but I figured 3000w + 1000w would get me close and so far I can't fire them both up, even with the grid tie helping out.

Now my Mach 3 Plus is just happy as can be, it's never once given me any trouble.  I know it's made top to bottom to be as power efficient as it can be.   I'd go from a total of 28,500 BTUs of cooling to 27,000 BTUs .. probably not a big deal.

My Main question
Do you think my Mach 15 is not working right?
I kind of do.

[Jon]

Just a comment because I know folks are going to do what they feel best, but Inverter Service Co. folks are very much against running A/C units on inverters because it works them very hard. They urge the use of a generator for loads like an A/C.

[chessie4905]

Unless that extension cord is short and 10 ga. I wouldn't expect it to start easily,even if the internals are ok. You can remove top shroud and remove cover where capacitors are mounted and look for rust or corrosion on any of the push on connectors if it is still made that way.  I had an older one that had issues and found rusted push on terminals on some.I personally don't like the idea of running AC's through the inverters  because of the amount of load and somewhat fragility of some inverters. They are too expensive to replace. But, some have had great success doing this. Go buy a Harbor Freight generator with extended warranty and use synthetic oil in it.jmo

[bevans6]

My sense is that the older unit has failing start/run capacitors in the compressor.  The start cap creates a big lag in the AC input, lets the motor start, then a switch disconnects it as soon as the motor reaches design speed.  The run cap creates a similar lag, lets the motor run almost as a two phase motor and is always connected.  If either cap is failing the motor will start hard, and the run cap failing will make the motor run inefficiently, pull more power, etc.  Both caps charge and discharge at 60 hz, the idea of "letting the caps charge" isn't correct.  A failing cap can do all sorts of weird stuff, obviously.  If your motor is popping a 20 amp breaker, there is definitely something wrong.  If the inverter cannot supply the start in-rush current (very possible even though that inverter is rated at a big start load over-current, something like 300% for 20 seconds) then what can happen is the voltage can sag, causing the current to go up and pop the breaker.  So I would get a fast reading voltmeter on and see if you can see the voltage sag when the compressor starts.

I personally think running air conditioner  units from inverters is just fine.  You need to understand start current loads, etc, design for the loads, but basically they are just an ac motor load the same as any other.  Look at all the mini-splits that are going to inverter technology (although I know they do it differerently), and almost all small generators are inverters now - no real difference in the load output sections of those generators and the pure-sine inverters.  I do have questions about load sharing between the 3KW unit and the 1KW unit.  Even if they can match frequency and phase, I don't know how they would load balance.  I also don't think you will be able to start the second AC unit when the other one is running unless the inverter can draw on extra power from something.  Some of the magnum hybrids are supposed to be able to do that, but I never really looked into it.  I usually account for 2000 watts per AC unit, and I only run one on my inverters.  I use a Yamaha 3000KW SEB inverter generator with a boost feature designed for starting AC motors, and a Magnum 4024.

Bottom line, I think the old AC unit is toast.

[neoneddy]

I have the LCD panel for my inverter and it shows it dipping into 70-60v on ac when trying to start both.

Usually starting the Mach 15, it dips lightening quick to 78-90v and then pops back up. The Mach 3 never registers.

The Mach 15 works great on shore power, in fact I can run both on a 30 amp hookup no problem.  So I hope I can get some resale, but I'll swap it for a Mach 3 I think.

[TomC]

I have three Coleman 13,500. I run them through the generator, or land line. My inverter Trace 2,500 MSW runs my plugs, microwave, oven toaster, bathroom heater, TV, stereo, etc. No motor loads. No problems with any since installing in 1994. I also believe an inverter is just for occasional use, or low watt use items. Good Luck, TomC

[belfert]

I'm like Tom and only run my roof top A/C units from my generator.  I used to have one A/C unit hooked up to my Prosine 3000, but one A/C unit is rarely enough.  I have my big 50DN alternator hooked to my house system with a big solenoid so in theory I have enough power for over 6,000 watts from the alternator.

[Geoff]

 Agee with Tom.

Geoff

[neoneddy]

Re :belfert - what is your selenoid  setup like? Right now I'm just hard wired in.  I'm always plugged in or driving  right now.   Use a starting selenoid? If so what kind etc.

[buswarrior]

Beware that an inverter that is running an AC, is going to need to be kept cool.

Locked up in a closed baggage bay is not good.

happy coaching!
buswarrior

[neoneddy]

I'm happy to report after a bit of Apollo 13 level startup procedures I was able to run both Mach 3 plus ACs

Had to start up bus, then turn on grid tie inverter. The one I have is very touchy, which is good, at the slightest hint of low voltage or over voltage it shuts down. I'd rather that than burning up.   

Next I had to run both ACs on low for 30 seconds or so. This pre pressurizes whatever the compressors compress. I read that an AC will keep pressure for a few minutes, which is why cycling can prove efficient.   

Once the one hand settled in I was showing 40%load or so on the inverter, grid tie managing 600 watts or so.  I the. Switched on the other, a slight flicker of lights and up it came.  It would settle in around 80% usage for the AIMS. That is including the fridge and some other small draw items.

Eventually I'll upgrade to the 4000w model, but right now I'll roll this for a trip and see how it goes.