IDK if this is going to get any responses, but if you have any experience with using propane with a portable generator maybe you can explain what’s going on.
So I got a big generator, I previously only used gas, but as this was new and dual fuel, it seemed like propane might be a big win. Propane as far as I know doesn’t get old like ethanol gas does, won’t gum up small engine carbs like gas does.
However, it had some downsides - the tanks are not able to just have an extra gas can to refill while the generator is running if needed, and for some reason I can’t tell the manual gives 0 estimated runtime with propane, but lots for the gas fuel. Ok, well some searching found a Y connector with a kind of switch/indicator that is supposed to auto failover to the second connected tank if the first one empties so you can then change out the tank while the generator is running.
Now my problem. Power goes out last night, it’s 20F and I fire up the new generator for the first time. First hour, no issue, however it then starts almost stalling out and then restarting over and over again. I go look at it seems like the “switch” indicated it tried to change tanks but… maybe didn’t? It went straight up and down, not pointed to the other side (though IDK if I actually understand the switch, there were like 0 instructions with it from Amazon). OK, I’ll just figure out which tank is empty (wondering how it went empty in like an hour on a 20lb tank) and move the switch to the other one and then change out the tank with my spare. Did all this, no change. Cannot get the generator to run right, and cause constant brownouts to my house and the generator makes a sound like it’s backfiring every so often. I give up on backup power for the night.
Today, I go look at it again, and it starts up and runs fine today at 43F. However I haven’t put a load on it, but it wasn’t running right without a load last night, so I don’t think it was overloading the generator (and I know it wouldn’t given earlier uses when it was warmer). OK, well lets at least use the valves on the top of the 20lb tanks to test the switch over thing. I tried turning off one of the tanks (right), the one the switch / arrow is pointing towards. Nada, generator keeps running, switch doesn’t do anything. I turn off left and generator stalls out. Weird. I then reset, restart, and try turning off the left tank - no change keeps running. I then re-open left and close right, no change, generator keeps running. Just to not lose my mind, I also close left and as expected generator stalls out.
Ok, so - do I have a worthless amazon transfer thingy, is the propane just not working at 20F or below? This seems really weird as I have a 500 gallon tank for my entire life for heat and stove and it got down to like -15F a few times with no issue.(I asked my provider, they say they can’t hook up the portable generator, or even provide me a propane hose / valve/ anything I could hook it up to.) The 20lb tanks are brand new… So some googling seems to say maybe the tanks need to be warmer? I could get some tank heaters I guess and plug them into the generator also assuming it can run long enough for the heater to do anything and bootstrap stuff when it’s cold. However, I’m also concerned about not having any estimate how long it should run from what should be 40lbs of propane. I don’t know if the first tank leaked over the months since I set it up (the other 2 didn’t), but 1 hour seems really fast to run out, and I would expect at least 8 hours when the gas tank is supposed to be good for 18.
So - do I just give up on propane for this generator? It seems silly to keep propane for the warm months and then switch to gas for the winter…
I have no experience with dual fuel generators, but I have experience using propane for hours in cold weather. Propane is a liquid that evaporates into gas. Evaporation cools the system (that’s why we sweat). When you run a propane tank in cold weather for a long time, the evaporation slows down until the propane freezes entirely, even though the ambient temp is above the freezing point of propane at that pressure.
Easiest way around it is to keep your backup tank in a heated area, or to find a way to keep the tank warm, like submerging it in a tank of warm water.
This is the right answer. As LP gas converts from a liquid to a gas in the tank the latent heat of vaporization is provided by cooling the bulk of the liquid. Eventually, the liquid becomes so cold that it will not evaporate, it will not become a gas. You cannot use more of it until there is enough heat input to evaporate the fuel. This can happen in warmer weather when the withdrawal rate is too great, so that even then, you have to provide supplemental energy, heat, to allow the liquid to vaporize. LP gas, commonly “propane” but typically a blend of propane and butane, is difficult to use in cold weather for exactly this reason.
I have experienced this in hot weather using one of those propane-fueled things for burning weeds, with a small 1lb tank. When running it full bore the tank gets super cold and eventually can’t provide enough gas to keep the flame going until it warms back up.
Hot Air balloon pilot here. I burn up to 60 gallons of propane, twice a day, if weather and passengers permit.
The vapor pressure of propane at 20F is 55PSI, but if you’re drawing it off fast, the temperature in the tank can plummet, and the vapor pressure can drop a lot.
I use waterbed heaters wrapped around my tanks, and preheat to 83F. That gives me 150PSI at the burners. I have redundant thermostats ensuring the temperature does not exceed that set point.
Heat tape, for keeping water lines from freezing, could hold your tanks around 40-50F. Put a couple wraps of tape very low on the tank (you want to warm the liquid, not the vapor) and use Saran wrap to secure. Wrap blankets or fiberglass insulation around everything.
Larger tanks have greater thermal mass; drawing a given amount of vapor from a tiny tank will lower its temperature (and thus pressure) far more than the same amount of vapor from a large tank. Maybe try a 30# or 100# tank?
I’d plumb it into the house lines. The propane supplier won’t, but a plumber will.
I bought a 22KW propane generator. It’s supposed to be plumbed to a large tank, but due to the pandemic I could not get the 500 gallon tank plumbing installed (county permit office was issuing for “emergencies only”). So I tried a 20# cylinder. It iced up after 6 minutes and the generator stalled shortly after. So I bought a 100# tank. That ran for 5 hours until the generator stalled. The tank was still 1/3 full.
What’s happening is that there’s insufficient area for heat transfer. The propane has to vaporize, so it draws heat from the part of the tank in contact with the liquid. The environment provides that heat, but in a small 20# tank there’s not enough surface area to transfer the amount of heat needed to vaporize the quantity of propane required by the generator. The propane stops vaporizing once its temperature drops below the boiling point, and the generator starves. The 100# tank has the same problem when the propane level drops, reducing the surface area in contact with the liquid propane. In the large horizontal tanks, the propane is in contact with a large surface area, and the tank is supported off the ground to provide good air circulation.
Your options are to buy a bigger tank or provide more heat to the small tank. What worked for me was an old washtub filled with water. I put the tank in it, then left the garden hose trickling water into the tub to keep the water from freezing.
If you do opt for a large tank, buy a reconditioned one. They’re half the price of new and last about as long because older tanks were made with thicker steel. Buying will save you money because you’re free to buy from the cheapest supplier. Buy your propane in the summer when the price is low. Get a tank big enough enough to last the whole year. When you lease a tank, the leasing company is the only one that can fill it, so you won’t be able to shop around for the cheapest price. Mine paid for itself in 2 fills (compared my bills with my neighbor who leases their tank).
Your explanation makes sense to me, an uninvolved spectator with no particular knowledge of generators.
Maybe you direct the generator exhaust over the exterior of the tank? Would that be adequate heat?
My thought was to recall that my 20# propane tank has some sort of safety valve integrated into it that will clamp outflow if there is too big a surge in flow. Flow needs to be 0 for a minute or so for it to reset. But that doesn’t explain your experience with the larger tank.
Using generator exhaust is inviting overheating the tank. I’ve been around one when the relief valve pops, and that’s a big fire waiting for a spark. It doesn’t take a lot of heat - maybe 30 watts - to keep the pressure up. They make tank wrap heaters specifically for this purpose. But I needed power (this was during one of California’s infamous “Public Safety Power Shutoffs” used to avoid wildfires). So I used what I had; a washtub and water.
The standard 20# tank has only one safety device - an overfill protection mechanism that prevents filling the tank more than 80%. The propane regulator for portable propane appliances is where the flow limiting device is located. That heavily limits the flow of propane if it detects insufficient backpressure on the outlet side of the regulator when initially pressurizing it (turning on the tank valve).
I have no issue with the 500 gallon tank. It has plenty of surface area in contact with the propane and good air circulation around the entire tank.
Propane is very cold. If you’ve ever had some squirt out on your fingers when hooking up a tank you’ll know how cold.
At my job we have a propane powered forklift. When it’s anywhere close to freezing out, it’s a bear to cold start. It will behave how you describe, runs for a moment then dies.
As a result we have a plug in heated magnet we throw on the throttle body to preheat the system. Even then once you get it rolling you have to give it throttle until the engine reaches operating temp. Kinda like using a choke but the forklift is fuel injected, so an adhoc choke.
I’ve heard folks with propane car conversions will run the engine on gas to heat everything up and then switch over to the propane. If that is possible with your generator that would be the next thing I’d try.
The reason your cooking gas works is because inside where the ignition is happening is presumably warm and also less complicated than running an engine.
I’m guessing your generator is outside/in an uninsulated space and the engine is having a hard time reaching operating temp with Sub-Zero propane feeding it. Keeping the tanks warm may help, but I think engine temp is a bigger factor.
I have no idea about run times on propane vs gas. I have heard that propane is less efficient, but cleaner burning.
I am far from an expert, but these are things I’ve seen and dealt with. Best of luck!
As a result we have a plug in heated magnet we throw on the throttle body to preheat the system.
You’d probably have better luck slapping that magnet on the bottom of the tank to warm the liquid. 80F is good (150PSI). Never exceed 120F (250PSI)
I’ll have to try that. Thanks!
Your propane is freezing, gotta torch the tank
(Don’t actually torch your propane tank, keep it in a heated area or heat trace it)
So I’m a propane guy (I’m in the biz) but not a generator guy, so I’ll give my knowledge on best guess.
So your 500gallon house tank you never had issue with never ran a higher demand thing like a generator. They suck more gas. Not an issue with a 500g tank though (which when full holds 400 gallons). The liquid doesn’t have to quickly boil off to make more gas because there’s so much more room and the size resists the rapid temp swings from the phase change going from liquid to gas.
A 20 pound cylinder only holds about 4.6 gallons of propane (and that’s if they actually filled it all the way. Many will only fill them to 15 pounds). So your issue is as the number one (at this time, anyhow) poster says. The tank was having to convert so much propane from liquid to gas so quickly that it dropped the tank down to a temp too close to below the boiling point of propane, so there wasn’t the 10 or more psi of pressure moving to keep your generator running. Once the liquid gets down to about -30f you wont have enough gas pressure. So you’d have to keep your tank warmer, which isn’t really an easy thing to do without being dangerous.
What you need to do is get a bigger tank(at least if this is made to be a permanent generator and not a movable/temporary generator).Call around to some propane companies. You’ll probably find someone who will lease you a 330 gallon tank for like $75 a year and hook the system up, but they probably won’t do it if it is a temporary style generator. If that’s the case, get yourself a 100 gallon tank if you think you can load/unload it from your vehicle when you need to go fill it back up. The 100 gallon ones are just tall versions of 20 and 30 pound tanks. Same fittings and stuff.
Now to answer your question about fuel and how long it should last. Like I said before, a 20 pound tank holds around 4.6 gallons of propane. Propane has almost 3/4 the energy as gasoline. So a 20 pound tank (if filled all the way and not just filled to 15 pounds) should last about as long as however long a bit over 3 gallons of gas lasts.
I’m not sure which generator you have but this one looks to run about 5 to 6 hours on a 20 lb tank. Others I’ve looked at seem to have the about the same runtime.
Propane has a freezing point of -44°F so it should work well at 20°F.
I don’t know why you’re experiencing the issues you’re running into but maybe look into the generator side to see if there’s anything that can be checked like the orifice for clogging.
Good luck!
That reference is garbage. The temperature at which a liquid becomes a gas is the boiling point. At atmospheric pressure the boiling point of propane is -44F. According to the textbook Organic Chemistry by Joseph M. Hornback, propane has a boiling point of -44° F (-42° C) at atmospheric pressure. 20F is is a problem because it is getting closer to the boiling point at atmospheric pressure so that more external energy is required than can move from the exterior of the tank to the interior to prevent bulk cooling to the the point where the tank can’t make pressure greater than atmospheric pressure.
