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Old 11-04-2015, 11:15 AM   #1
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Generator capabilities

Does anyone know if the Onan 8000 will safely run 2 -1500btu units and 1 -13500btu unit all at the same time? I am defiantly fixing to add a 3rd Ac to my 390bh berk.
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Old 11-04-2015, 05:24 PM   #2
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Don't really know the answer, but my guess would be no. Info that I found from dometic ac units called for minimum 3.5kw for one unit or 5kw for two. Logical ( or illogical) progression from this would seem to be minimum of 6.5-7kw for the third unit....although I don't know if it works this way. If that is the case, I think that you are not really leaving much reserve for the rest of the coach. Here is my reference
Dometic B59516 Brisk II RV Air Conditioner 15,000 BTU White

Also, what are the size generators in other coaches with 3 ac units?


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Old 11-04-2015, 05:41 PM   #3
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Charlestons have 10kw


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Old 11-04-2015, 05:57 PM   #4
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The running watts of all three would be a bit under 6KW. The problem is the high starting current when they switch on. Really marginal, IMO.

Since you tow with a truck, maybe a nice Honda 3KW inverter genny in the bed of the truck. Just run one of the A/C units off of that. It also serves as a back-up if you Onan is out of service.

If Santa owes you a really swell present this year, you can always ask for the new Honda 7KW fuel injected baby.
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Old 11-04-2015, 06:28 PM   #5
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It is the start up current that will trip the breaker. Turn on 1, lock it on by setting temp really low, turn on the next one, lock it on as well then finally the third one. If they all stay running and don't cycle you have enough power to run them. The inrush, or start current is the issue. Shed other load like HW Heater for example and fridge if it can run on invertor or propane. Charge batteries when on shore power.
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Old 11-04-2015, 07:01 PM   #6
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The running watts of all three would be a bit under 6KW. The problem is the high starting current when they switch on. Really marginal, IMO.

Since you tow with a truck, maybe a nice Honda 3KW inverter genny in the bed of the truck. Just run one of the A/C units off of that. It also serves as a back-up if you Onan is out of service.

If Santa owes you a really swell present this year, you can always ask for the new Honda 7KW fuel injected baby.

He drags the truck behind him. It's a Moho.



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Old 11-04-2015, 07:04 PM   #7
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I don't think you will have a propels with it. I'm sure someone will do the math but there have been people that have added a third A/C and had no issue. With no WH the biggest drain will be the microwave and the fridge. It should be fine.



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Old 11-04-2015, 09:09 PM   #8
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I run a 15 and a 13.5 routinely. I have accidentally turned on the third and the breaker hasn't tripped. However, if three are running and are cycling and two try to come on at the same time, I'd bet the breaker will trip.

Also, that will be putting some 'hard time' on your generator...running at higher loads and thus RPMs like that.

I just close up the rear sleeping area and just run the front two plus the chassis A/C. It keeps us plenty cool on our June/July drives from Colorado to Florida and back.
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Old 11-04-2015, 09:51 PM   #9
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I run a 15 and a 13.5 routinely. I have accidentally turned on the third and the breaker hasn't tripped. However, if three are running and are cycling and two try to come on at the same time, I'd bet the breaker will trip.

Also, that will be putting some 'hard time' on your generator...running at higher loads and thus RPMs like that.

I just close up the rear sleeping area and just run the front two plus the chassis A/C. It keeps us plenty cool on our June/July drives from Colorado to Florida and back.

Did you ever install a vent to replace the one you used for your third A/C?
Also how do you control the third AC? Is it run through the same thermostat? Also if hooked up to a campground do you ever have low voltage issues. Do you run a Auto Former? ( not sure that's correct or spelled right)



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Old 11-04-2015, 10:02 PM   #10
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Joker, did you add a third air conditioner after you bought the rig? If you did please tell us about it. There have been several discussions on if and how it would be done.
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Old 11-04-2015, 11:26 PM   #11
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My dealer said it can be done. They will install a shed switch. It will go where the vent is in the kitchen area. It will have controls on the unit itself. I will post more as I learn. It's gonna be a few weeks before they can get to. Thanks guys for all the input. I will probably only run front 2 units most of the hot days and turn one off to turn the bedroom Ac on when it gets close to bed time. It's just really hard to keep the living room area cool durn tx Summer's with no shade. Thanks again
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Old 11-04-2015, 11:57 PM   #12
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Yes, I had a new vent installed over the kitchen area to make up for the one that was filled in by the AC. I believe it's a safety requirement to have a vent in there since we have propane stoves. If you're having a new vent installed there, see if they can use the existing control wires from the old vent to operate the unit from the wall. Also, they may be able to salvage the old vent.

Mine is controlled off the existing thermostat. It has ability to control up to 4 units.

If you're having it done, consider having them add a heat strip too. It's easy to do while they're already working on the unit. Although mostly I just use a little ceramic unit that keeps that area warm enough.

I have tripped the pedestal breaker at Fort Wilderness a couple of times trying to run three ACs or two ACs and the vacuum. Oops. I can't remember tripping it anywhere else.

I think you want to make sure the front two ACs are on separate 'legs' of your power system so that you can run both at once.

I don't know what an autoformer is.
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Old 11-05-2015, 07:59 AM   #13
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Did you ever install a vent to replace the one you used for your third A/C?
Also how do you control the third AC? Is it run through the same thermostat? Also if hooked up to a campground do you ever have low voltage issues. Do you run a Auto Former? ( not sure that's correct or spelled right)

Phil, if we're talking about this issue in the context of whether the genny would be ok for 3 ac's, I see where you're going with the autoformer. But, at least with my setup, autoformer is connected to boost shore power only.



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Old 11-05-2015, 08:03 AM   #14
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Adding soft-start capacitors (sometimes called a hard-start kit) would really drop the inrush current; and that's where your biggest issue would be...

Since they'll be working on the unit, adding the cap's should be no big deal.
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Old 11-06-2015, 07:30 PM   #15
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I have two 15k's and plugged my buddy's RV into the engine block heater outlet in the electrical bay while dry camping at NASCAR races and ran both my AC's and he ran his while plugged into my coach and I've never had an issue blowing any CB's. We also had the TV's going, lights etc...

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Old 11-06-2015, 10:47 PM   #16
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I would check the the engineers at FR before installing a third AC unit. I had talked to them a few years ago when I looked a pitting a third on our 2012 390BH60. I was told in no uncertain terms that the unit was not designed for 3 AC both from a power and structural perspective.

You are much better off spending some time to limit heat coming into the unit.

Insulated and reflective covering on windshield. Awning and vertical covers to name a couple.

Over cooling at night will also make a huge difference. 2 15s will maintain the cool over the course of the day but they may struggle to drop temperature if the ambient temp is high.
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Old 11-06-2015, 11:21 PM   #17
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I would check the the engineers at FR before installing a third AC unit. I had talked to them a few years ago when I looked a pitting a third on our 2012 390BH60. I was told in no uncertain terms that the unit was not designed for 3 AC both from a power and structural perspective.

You are much better off spending some time to limit heat coming into the unit.

Insulated and reflective covering on windshield. Awning and vertical covers to name a couple.

Over cooling at night will also make a huge difference. 2 15s will maintain the cool over the course of the day but they may struggle to drop temperature if the ambient temp is high.

I don't disagree and I'm not ready to add a third yet. I will say after the last few weeks in South Florida in 90 degree plus that two 13.5 AC's are falling short. I can get the Moho cool to a point. When it's 95 and the sun is out I can get the inside down to about 78-80. It's better than 95 but still a bit warm. With out the sun I do better. I do have a windshield cover a driver side window cover. A door cover. All slide out windows have covers as well as window awnings on the two living room windows and the bedroom window. The covers a Magna Shade and are of excellent material.
The heat transfer in the front is bad. It's amazing how hot the cupboards are. The insulation in the front and rear caps is not working. I would love to see what is in there.



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Old 11-07-2015, 12:09 PM   #18
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For anyone interested I have a 13,500 heat pump in a box on a pallet ready to ship. It will be a steal to get it out of my garage.
Just thought I would give it a shot since it was on topic :-)
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Old 11-07-2015, 05:39 PM   #19
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In Arizona the heat is bad... I have (2) 13.5's and all the magnashades etc. I added a standalone 8k Ac that ducts to the exterior out the drivers window. Still not enough in my option for Az. Also looking to add 3rd Ac but still thinking of it...


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Old 11-07-2015, 06:11 PM   #20
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Well I have a near new (used less than 5 times) Penguin II 13,500 btu A/C heatpump in the factory box ready to ship and for sale.
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