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Auto generator start hard on air conditioners?


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I just installed an automatic generator start on my Onan 7500 watt generator in my 2006 Fleetwood Expedition motorhome. This was primarily installed to ensure the comfort of our cat in hot weather. I have been observing the operation today, and it is causing some concern. The generator will start at the set temperature, then the air conditioners will start. In about 20 minutes the MH will cool enough that the generator will stop, with the air conditioners still running. After another 20 minutes, the MH will have warmed enough that the generator will restart and the cycle repeats. The MH is equipped with an energy management system that allows the generator to start, run briefly, then the ACs start one at a time. My concern is when the generator shuts off with both ACs still running. I don't think that can be good for them if this keeps happening on a frequent basis. The ACs are original, still working well, and have required only capacitor and one fan motor replacement. I really don't want to shorten their life.


I appreciate any insight on this situation. Thanks!


Tom (in sunny Moab)

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Evidently the generator is set to shut off at a warmer temp than the AC. Not the greatest but probably ok, just pretend you have power failures ! BUT does the generator get a chance to run a lil bit before the ACs kick in ? Hopefully the Genny isn't starting under a load

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Without getting into all the electrical theory, all I can say is ITS MY OPINION ITS SAFER TO SHUT OFF THE AC FIRST. I never shut down my genset with the AC running. (however the wife and kids have and I saw no problems, so what do I know lol) Id say it depends on the gensets output control and switching circuitry (of which I'm unfamiliar unless I have the schematic) and if it kills the power to the AC instantly with no voltage drop or possible surges or back EMF or relay contact stress etc., which wouldn't be any worse then turning the AC off directly. Sorry, I just cant analyze it absent the control and relay and switching schematics, but can envision how with adequate switching and protection it could be just fine, I just don't know sitting here so I avoid doing it to be on the safe side???? If power is suddenly removed from an Inductor (a motor) that stored energy dissipates and voltage can rise and the energy gets discharged somewhere you know, perhaps via a discharged capacitor or resistor etc.


John T

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I didn't want to make my post too long, but I will add a bit more info.The AGS in question is the Onan EC30W. It will start the generator on low battery voltage, rising interior temperature and even falling interior temperature. All set points are easily programmable on the remote control. The remote control also contains the temperature sensor. I just realized that the temperature differential is also programmable. It came set for +/- 2 degrees. So if set at 80 degrees, the gen will start at 82 degrees, and shut down at 78 degrees. If I increase the differential there would be fewer cycles, but the issue of the gen shutting down with the air running remains. The AGS is doing exactly what it should, no issues with that. I have the AC thermostat set low (70 degrees) because if the AC thermostat shuts off the AC, the generator would keep running, because the temperature requirements of the AGS had not been satisfied.


I am pretty good with electrical stuff, but I don't have the technical knowledge of how the ACs might be affected by this repeated dropping of input power. I have an email in to Coleman (Airxcel) and hope they respond.


Thanks again for the advice, and keep it coming.




Edit: I just thought of something else. I have a Progressive Industries EMS installed such that both generator and shore power pass through it. It will shut off power on low voltage. I would have to look up the exact voltage, but I think it is about 108? So maybe that would shut down the power to the ACs before voltage drops too low. Or maybe repeated low voltage will cause harm to the EMS. Wow, maybe I worry too much! :)

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  • 3 weeks later...

Our rig has Precision Controls equipment for power management. If/when the generator starts loads are slotted in one at a time and after a sufficient amount of time so as not to harm the AC equipment. Not exactly sure how this work off hand. Your rig may have a similar system. We also have the EC-30 unit.

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