Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

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Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

October 08, 2020, 09:01:02 pm

Our 6.5 kw propane generator used to be able to power both of our roof A/C units in our 94 GV.

But now after starting up great, the generator turns off after turning on one of the roof AC units. Any ideas?

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #1 – October 08, 2020, 09:30:18 pm

Other than checking the air filter for obstructions, does the governor rod move freely?

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #2 – October 08, 2020, 10:33:45 pm

What exactly happens when you start a heavier load:

Generator just stops (like it was turned off)?

Stumbles/surges before dying?

Other?

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #3 – October 08, 2020, 11:16:39 pm

Yes, the generator just stops like it was turned off. The A/C unit starts to turn on but then the generator just shuts off.

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #4 – October 08, 2020, 11:41:12 pm

Check propane supply to the generator for restriction, regulator. Supply adequate until load is increased.

How long does the generator run when roof AC turned on? Immediate shutdown would be supply of propane. 5 minutes could be overheating shutdown.

Pierce

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #5 – October 09, 2020, 08:51:49 am

With a 1994, I ASSUME the regulator is internal to the Onan generator and liquid propane fueled. If so, and you have ruled out other issues, it is very likely that the regulator is the issue. It is a good, common regualtor, but is "laid on its side". In that orientation, it is susceptible to clogging from the longer chain hydrocarbons found in propane.

It can be overhauled using the high temp/silicone gasket set or replaced complete.

Then many of us have converted to high pressure propane vs liquid to substantially reduce contaminants getting into the regulator.

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #6 – October 09, 2020, 11:31:15 am

We have a '92 with an Onan and it's fueled with vapor from the tank through a regulator at the tank and one at the generator. Yesterday was a 90 degree day, and time for the monthly generator run so for lunch I fired up the Onan, both air conditioners and used the microwave oven to cook lunches. At the end of an hour I gave the gennie 5 minutes unloaded to cool off and shut it down until next month or hurricane whichever comes first. So far we've been lucky this year.

ehyall2005, with a little luck, if your governor rod snaps back open after you pull the throttle closed by hand, before I worried too much, I'd run the generator under varying loads i.e. re-heating food in the microwave at reduced power settings, and trying to turn on a well rested air conditioner after the generator is thoroughly warmed up. If you want to get lucky, you need to make a place for lucky to happen.

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #7 – October 09, 2020, 11:47:20 am

Wolfe 10 quoted: Then many of us have converted to high pressure propane vs liquid to substantially reduce contaminants getting into the regulator.

I thought I knew about everything there is to know a bout propane, I worked around LNG plants many years. I certainly know the phase diagram,
And I have heard that some city buses run on compressed gas.

But who sells high pressure propane and what are the pressure ratings for the tank?

Regards

Klaus

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #8 – October 09, 2020, 11:48:52 am

He is referring to the head pressure of the propane tank vs liquid.

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #9 – October 09, 2020, 11:55:27 am

Quote from: kepeters – October 09, 2020, 11:47:20 am

Wolfe 10 quoted: Then many of us have converted to high pressure propane vs liquid to substantially reduce contaminants getting into the regulator.

I thought I knew about everything there is to know a bout propane, I worked around LNG plants many years. I certainly know the phase diagram,
And I have heard that some city buses run on compressed gas.

But who sells high pressure propane and what are the pressure ratings for the tank?

Regards

Klaus

Quote from: craneman – October 09, 2020, 11:48:52 am

He is referring to the head pressure of the propane tank vs liquid.

CORRECT.

"T" between tank vapor port and house regulator. Block off liquid tank port. Connect hose to generator to the "T".

BTW, this was a recommendation of an engineer at Marshall Gas who makes the RV house regulators.

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #10 – October 09, 2020, 12:39:47 pm

Quote from: kepeters – October 09, 2020, 11:47:20 am

But who sells high pressure propane and what are the pressure ratings for the tank?

Regards

Klaus

Residential and Commercial propane is sold in liquid form, about 150 PSI at 70F. The DOT cylinders and ASME tanks are designed to contain 240 PSI, up from the previous 220 PSI.

"High pressure propane" is the pressure at the tank in liquid form. From hot air balloons to fork lifts, liquid delivery or high pressure propane, has its pressure reduced and vaporized at the load, is used whenever there is a need for lots of BTUs.

At what pressure and temperature do you handle liquefied natural gas?

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #11 – October 09, 2020, 01:00:22 pm

Not sure I understand.

In a static condition (no gas flowing) both the gas phase and liquid phase are at identical pressure determined by the tank temperature .At 60 F this is around 95 psig. This pressure drops the moment you start flowing, dependent on the size of the vapor volume of the tank. The larger, the less pressure drop.

The 95 psig are then on the inlet side side of the pressure regulator. For propane most household consumers require around 10" to 11" of WC ( = 0 .4psig)

The pressure regulators are set to supply that amount plus the line losses in flowing condition.
While typing this, Old Toolmakers absolutely correct post came in.

So where does "high pressure propane" enter the picture?

Regards

Klaus

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #12 – October 09, 2020, 01:02:36 pm

High pressure= vapor pressure in the tank.

Not just theory-- many of us have made this conversion-- a good idea for the propane Onan's with internal regulator.

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #13 – October 09, 2020, 01:07:29 pm

Quote from: kepeters – October 09, 2020, 01:00:22 pm

Not sure I understand.

So where does "high pressure propane" enter the picture?

Regards

Klaus

In my area of interest, when propane is used to fuel motor vehicles, the tank is tapped for liquid propane and the pressure is reduced at the engine where a coolant warmed heat exchanger facilitates the vaporization of the liquid to the gaseous form and the gas is finally fed to the engine at low pressure.

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #14 – October 09, 2020, 01:28:25 pm

Tapping into the liquid line when you want to vaporize with additional heat is a very valid process if it is set up this way.
Here is a picture of my set up, which looks like the traditional regulator for the vapor phase to me.
The connector under the word Relief is probably for the liquid phase. But whenever one hooks up to liquid one still needs a vaporizer,
From the forum posts I conclude that Onan generators have one built in. But mine is not an Onan, and I also have a gas cook stove.

Regards

Klaus

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #15 – October 09, 2020, 02:40:48 pm

I think the administrator should change the topic line from 6500 KW to 6500 W
Regards

Klaus

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #16 – October 09, 2020, 03:31:20 pm

Quote from: kepeters – October 09, 2020, 02:40:48 pm

I think the administrator should change the topic line from 6500 KW to 6500 W
Regards

Klaus

Done-- good idea. at the 6500KW would have to be towed behind the coach (if sufficient towing capacity-- YA RIGHT)!

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #17 – October 09, 2020, 04:02:54 pm

In an reciprocating combustion engine it would require a 12000 HP slow running diesel and a gearbox, you could not tow that because of weight,
You could tow a Solar 10KW gas turbine driver.

Imagine showing up on a campground with that.

Greetings

Klaus

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #18 – October 09, 2020, 05:49:25 pm

Quote from: kepeters – October 09, 2020, 02:40:48 pm

I think the administrator should change the topic line from 6500 KW to 6500 W
Regards

Klaus

"I", and you can ask my partner on this, don't do decimal points. As far as I'm concerned it's 6500 blivets. If I must get into the mud then it's 6.5(10^3).

Oh. Klaus? LNG is a liquid at 1Bar A and -260F. So Dewar flasks.

Re: Onan 6500 kw Propane Generator Shuts off when turning on the roof A/C unit

Reply #19 – October 10, 2020, 12:14:51 am

I grew up on a farm and ranch. On our equipment, tractors, pickups, etc, we always ran on vapor only.

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