Onan 5500 LP Generator Problems

lcdrdean

Active Member
I need help with a peculiar problem. Last night we were dry camping and had the fridge running off propane. Since we wanted to watch TV and run the fireplace, I lit off the generator. It started and seemed to run fine so I switched the fridge to electric. The furnace however would not light. When I shut down the generator and lit off the furnace, it worked fine and we had heat through the night. So for a while last night, I ran the generator and watched TV with the fireplace going, but no heat from the furnace. After a couple of hours, the generator shut itself down. When I restarted the generator, it would only run for a few minutes, then shut itself down again. We went to bed with the furnace running running on battery with no problems. This morning, we shut off the furnace, lit off the generator and the fireplace and made coffee with the electric coffeemaker. The generator again ran for a while but then shut itself down.

Any ideas on what might be happening?
 

danemayer

Well-known member
I had some shutdown problems caused by insufficient propane flow to the generator. It ran fine off one tank, but was erratic on the other tank. One of the hoses needed to be replaced.
 

newbie

Northern Virginia
it sounds to me like a propane delivery problem. I have read here about the a faulty sail shutting down the fuel supply which sounds like a possibility here.

John
 

davidg

Active Member
The first thing I would do is to check my propane tanks to see how much propane was in both of them, if one is empty or low and the other full I would then swap them around making sure the arrow on the switch over valve is pointed towards the full bottle, then fire up the generator and furnace, if that doesn't work switch the arrow towards the bottle on the opposite side, if that doesn't help could be little trash causing some restriction in the line or the regulator on the switch over valve is not working properly. Bottom line you are not getting enough fuel.
Good luck.
 

newbie

Northern Virginia
I am confused. You would think I would be used to it by now.

Never the less, it certainly sounds like a propane delivery problem since both the furnace and generator are shutting down. I have not had problems with my gas flow so I really don't know much about it but for some reason, I thought the regulator, sensing too much propane flow would shut off the gas thinking there was a leak if too much was going through it. (I know regulators don't think but you know what I mean.)
 

branson4020

Icantre Member
John, I know you're right about some sort of excess flow control in the propane system. I've activated it by disconnectig a line without shutting of the bottles. I don't understand if its part of the valve on the bottles, or part of the regulator itself.
 

jimtoo

Moderator
I don't know about the regulator for sure, but don't think it does that.. all the newer bottles have excess flow checks in the valve or neck. In case of line breakage, or accident it shuts it down to a very small flow. Not enough to cook with or water heater use, but maybe enough for a refrigerator

Jim M
 

lcdrdean

Active Member
Hi all - finally figured out what the problem was. The dealer replaced the regulator, but that didn't help. What I found after doing a lot of research is that when the temperatures get cold, pressure in the propane tanks drop and don't deliver sufficient fuel to the generator. I have found that when it's cold, we can run the generator off a full bottle for about two hours.
 

danemayer

Well-known member
The Onan manual shows lp consumption at various loads. At full load, the 5500 LP unit consumes 4.7 #/hour. At half load, about 3.4#/hour. That would translate to roughly 8.5 hours at full load, 11.7 hours at half load. That's no doubt an ideal case. As the tank gets low, you're likely to not have enough pressure to keep running. The manual says you'll lose pressure at extremely low temps, but the lp generator is spec'd to run down to 0 degrees F. It also warns of losing power output as temps drop and altitude goes up.

If you're consuming a full 40# tank after 2 hours of runtime, that sounds prohibitively expensive and way above Onan's consumption spec. But if the problem is that you consume 10# of propane in 2 hours and then the generator stops due to low pressure, I'd guess you still have a problem with restricted flow. Gas pressure can be measured to see if the flow meets Onan's Installation Manual spec, which is 9 to 13 inches Water Column (WC) pressure at the genset.

I'd suggest having the dealer take the measurement to see if enough gas is getting to the generator.
 

newbie

Northern Virginia
Hi all - finally figured out what the problem was. The dealer replaced the regulator, but that didn't help. What I found after doing a lot of research is that when the temperatures get cold, pressure in the propane tanks drop and don't deliver sufficient fuel to the generator. I have found that when it's cold, we can run the generator off a full bottle for about two hours.

That doesn't seem right. I know you said you found the problem but it still seems like there is a problem.

My generator is gasoline so I don't have any experience with what your are describing but, in my area, a lot of people heat with propane using external, above ground tanks and never have a problem with flow. These are for gas furnaces which consume a lot more propane than a 5500 watt generator. I think you have another problem. Your set up should work even when it is really cold.

Unfortunately I don't know what the problem may be. Good luck getting it working though,

John
 

lcdrdean

Active Member
John - The furnace needs less pressure to work than the generator. Our furnace worked fine when the it was freezing outside, but the generator would only run for two hours on the full tank. If I switched to the other full tank the same thing happened. During the day when it was warmer, I could run the generator on the same tank as the night before when the generator shut down. From what I have read, as the temperature drops the pressure in the tank decreases, it gets to a point where it's not enough for the generator. Some people put heat wrap on their tanks to prevent the problem (or pour hot water over the tank). Here's a link that explains it much better than I can: http://www.propanecarbs.com/propane.html
 

Rodbuster

Well-known member
You mention that the pressure decreases when the temperature drops.
What type of temperature drop are we talking about here? Is the outside temperature 40 degrees, or 30 degrees or 10 degrees, etc.
The reason I'm asking is because I'm thinking of pruchasing an Onan 5500 (propane) for my Landmark Key Largo and I am trying to educate myself on the pros and cons.

Thank you
Rodbuster
 

2psnapod2

Texas-South Chapter Leaders-Retired
Rodbuster, I have the propane gen in my KL and it works great. Enough power to run both A/Cs and just about anything else. The only draw back I see is that it uses alot of propane, so it is truly a back up power soarce.

Micheal
 

danemayer

Well-known member
Rodbuster, if you get serious about purchasing the Onan 5500, make sure you get it from someone who you're sure will do the job right. It's been described as a complicated install, beginning with the Generator Prep option that you hopefully ordered from the factory.

Also keep in mind that it's expensive to run in terms of propane use. 12 hours of A/C on the generator will cost at least as much as staying in a commercial RV park overnight.
 
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