Inverters and air conditioners

[bevans6]

I've been searching various manufacturers web sites on and off for a couple of days, to find the source for that statement that it's not recommended to run air conditioners (or any significant motor load) from a high quality pure sine inverter.  To my mind that would include inverters, inverter-generators, air conditioners, refrigerators, air compressors, etc, in that generalized statement.

I know of the issues with running motors from modified sine wave inverters, and the reasons why that can be problematic to a greater or lesser degree based on the modified wave output scheme of the inverter.  I know that typical pure sine wave inverters have a very clean waveform and power motors in general very well.  I know that my generator, a Yamaha EF3000iSEB, is specifically designed with a battery boost feature to start air conditioners better.  I looked in my Magnum manual and found no recommendation to not run air conditions.  There are various discussions of how to size inverters vs loads so that motors start properly and don't cause issues.  But I have not been able to find a blanket recommendation to not run air conditioners or other motor loads from modern, high quality pure sine inverters.  Anyone?

Brian

[windtrader]

Please include following
But I have not been able to find a blanket recommendation to not run air conditioners or other motor loads from modified or pure sine inverters.

Curious since one of mine is connected via inverter, the other direct to gen/shore power. Not sure why, trying to sort out the logic. It will never run long from battery through the inverter. What I do is run the gen to charge the house battery then send power through the inverter to the AC. Doesn't make much sense.

Seems like I should just wire it the same as the other, right to the generator.

hope i'm not hijacking the thread briaan.

[Utahclaimjumper]

  Its not a mater of CAN'T,,its a mater of not very long without a battery bank the size of a shipping container.. Just not practical.>>>Dan

[windtrader]

So, if the battery bank is being charged by the alternator, and the AC runs through the inverter connected to the bank, it should cause no harm, right?

[Utahclaimjumper]

  Most modern generators today do produce AC current,, so no need for the inverter for that purpose, eh??>>>D

[Jon]

The manufacturers are in the business of making and selling inverters and in their advertising and spec sheets it is counter to their interests to start listing what you should not or cannot do with their product. The information about limiting their use to supply power to products that do not have such an inrush of current comes from Inverter Service Center from the Nashville area. They did not leave any room to misinterpret what they were suggesting. Their advice is driven by having to repair inverters and what they feel is the cause of needed repairs.

It is their opinion the only inverters they ever felt comfortable using for A/C loads was an early Trace model with three transformers that could handle an inrush of current up to 7000 to 9000 watts. As that inverter has not been produced for a long time and parts are no longer being made it has been replaced with newer inverters that list almost identical specifications, but in fact are not as robust.

Their suggestion is (made to Prevost owners) that as long as the coach has an efficient and fuel sipping on-board generator it is best to use the generator and run all three or four A/C units on board. A follow up comment was if that is not practical at the very least make sure the inverter has ample cool air flow and is kept cleaned and free of accumulated dust and lint because heat is going to shorten the life of the inverter.

I think debating this is a useless exercise because folks on either side of the discussion already have their minds made up.

[buswarrior]

Talk around the water cooler?

uninformed B.S. said out loud by idiot techs to a customer to shut them up?

typing on internet boards?

windtrader, you are set up to run that inverter fed AC going down the road, powered by the coach big alternator.
Simply a choice by the previous owner.

I can, if I choose, run a pair of mid 80's roof airs going down the road with a Trace 4024. Load on big alternator is somewhat less than running the coach HVAC, if it still worked.

Cooling the inverter while it is working hard to run big loads like AC is a VERY significant issue. It needs a lot of cool air, the inside of an unvented baggage bay is completely insufficient.

As to the choice of how to run, it all depends on what bits and pieces the busnut has available at the time.
Many of us piece the coach together over the years, as funds, opportunities and inclination come along.

Some don't have a generator that is readily installed for mobile use, YET, but have bought that excellent inverter as part of the final equation.

Some change direction mid course.

Prices of various things have changed over the years.

happy coaching!
buswarrior

[sledhead]

I have run down the road with the a/c on working off the inverter and the alternator and never had any problems . where I have seen the problem is using the micro wave .... it uses way more power on start up  . I agree with BW that the big alternator was sized up to run all day long with the bus a/c running and never had any problems

if you only need 1 a/c to cool off the coach when it is not to hot I can not understand the use of running the big genne when you do not need to . the engine is there to run the alternator when on the road

dave   

[PP]

When we first purchased our coach, it had the microwave/convection oven connected to the inverter along with a small chest type freezer in the basement. After lots of problems that I won't go into, the microwave is now on a regular circuit and the chest freezer has been replaced with a roll out tool box, which is much more practical for a bus owner  The inverter is now dedicated to the things that keep the wife happy, IE the TV, Dish box, DVD player, you get the idea 

[bobofthenorth]

The question Brian is asking is specifically related to inverter generators so he doesn't have the option of running his generator to avoid running his AC off his inverter.  I have one of those inverter generators and I have to admit I had never considered the inverter load implications related to that type of generator.  For whatever the datapoint is worth, my nominal 3100 watt inverter generator will puke the TV when the AC starts so I @$#/u/me there is a significant voltage drop at that moment.

[buswarrior]

Right, back on topic.

I have the same Yamaha as Brian, and I can cheat:

Use the Yamaha 3000 thru a Trace 4024.

I wonder how the TV would get along...?

Rig is lacking a battery set for casual experimentation.

happy coaching!
buswarrior

[windtrader]

I think debating this is a useless exercise because folks on either side of the discussion already have their minds made up.

Maybe for the old timers but us noobies learn from the comments. Yes, the way my coach was designed is that one (front) AC runs via the inverter that is fed by the alternator(bus) is running down the road without having to turn on the genset. Makes logical sense. The back AC is wired to run off the genset or shore power. Again, makes sense that the bedroom would most often need the cooling in the evening.

Given the rig has been wired this way from day one twenty years ago and logged many trips and the original electrical design and hardware are still working, I'm inclined to check this one off for now. Even though, the PO was mostly drove pole to pole, the front AC would still have got a workout while on the road.

Again, thanks to all for kindly sharing your vast knowledge. You have no idea how much it helps us new guys out, especially those not around a table at the local Elks lodge. Oops!

[Jon]

Windy,

If a coach has a 12 volt system and 12 volt alternator and inverter a typical A/C is going to draw about 130 amps at 12V. Keep in mind that requires a decent sized alternator because there are other loads on the system besides the A/C.

Loads on the alternator and the inverter generate heat. The greater the load the greater the heat and that heat has to be dealt with. There is no one single best answer because there are so many associated considerations including understanding that no matter how A/C units are powered energy (meaning some burning of fuel) is going to be required.

[TomC]

When I first bought my Trace inverters in 1994, I had the idea of stacking two together to give 5,000 watts and since I have the 50DN 130 amp alternator, was thinking of running at least the front roof A/C through the inverter for A/C going down the road. The gal selling me my inverter asked me what generator I had, and said a 10kw Diesel. She said, don't bother with the second inverter or running the A/C through the inverter, just run the generator-I'll be much happier. And that's what I did (and she gypped herself of selling me a second inverter). Since 1994, I haven't had any problems with generator, inverter or A/C's. Good Luck, TomC

[Jon]

And having two inverters does not mean you have twice the wattage by combining them unless the system and inverters are set up to sync phases. To use Tom's example he would not have had 5000 watts, but two 2500 watt power sources. Big difference.