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Author Topic: rooftop air  (Read 9525 times)
tucsontattoo
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« on: April 18, 2006, 03:36:41 PM »

I have a 4106 conversion with 2 coleman roof air units, also have a onan 25 kw propane powered gen. would like to run my front air sometimes while driving but there seems to be some controversy about runing propane powered gen while moving. i know the way this bus is set up the gen wont start whjle moving. however my propane fridg works fine. is it possable to run this gen while in moton?
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« Reply #1 on: April 18, 2006, 04:07:13 PM »

Yes!
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Nick Badame Refrig/ACC
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« Reply #2 on: April 18, 2006, 04:31:46 PM »

SHAKE PROPANE


IT REFRIGERATES


AND FREEZES!


The Colder It Gets The Lower The PSI !???  Mabe it effects the air to fuel mixture???

That is the extent of my knolage on the subject!

Nick Badame-
« Last Edit: April 18, 2006, 04:35:23 PM by Nick Badame Refrig. Co. » Logged

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jjrbus
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« Reply #3 on: April 18, 2006, 05:12:45 PM »

Propane seems to be one of the alternate fuels for vehicles. If you can run a car on propane, I do not see why not a genset. But I am no expert!!
                                     Work?/Play safely Jim
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« Reply #4 on: April 18, 2006, 05:32:40 PM »

Nick,

I have a hard time buying that one. I run my frige all the time underway, no problems, and all those propane powered vehicles don't seem to have problems either.
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DrDave
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« Reply #5 on: April 18, 2006, 05:46:12 PM »

Most propane vehicles use LIQUID taps on the tanks and then heat exchangers to convert to vapor.

If the generator is a vapor-only setup, and liquid was to get into the vapor regulator it would/could
be a problem. But if the generator is fed LIQUID up to a heat exchanger from the tank and if you
have the right type of tank you should not have a problem.

Think Fork Lift tanks with liquid taps and heat exchangers down next to the engines with coolant
circulating to heat the propane to vapor.
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Nick Badame Refrig/ACC
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« Reply #6 on: April 18, 2006, 06:07:57 PM »

Gusc,

I just took  past expierences with res, and comm, heaters that if liquid makes it to the regulator, it will freeze up
and I have seen heaters that will actually burn through the heat exchanger if the mixture turns oxygen rich!
Big! Big! Hazzard!!
So, I figured a simular  situation could  Happen!

Nick-

Nick,

I have a hard time buying that one. I run my frige all the time underway, no problems, and all those propane powered vehicles don't seem to have problems either.
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« Reply #7 on: April 18, 2006, 07:11:11 PM »

Unless 30 years old or older, small gensets are vapor units. Don't work like fork lifts. I run my fridge on LP when underway...done this for 30 years...may burn the thing up next time too. Probably not.
Some states have laws that prohibit LP gas tanks being in "on" position while underway. Many northeast tunnels prohibit LP period. OOPS...
Your generator is 'locked out to comply with the RV safety guidlines. You may have some liability exposure if the genset caused a fire, and you could have issues with your insurance if you defeat the interlock. Still, if you ran the generator while underway, it wouldn't be any more of a fire hazard than when parked. May be less due to additional cooling air while underway. Be sure that all your flex lines are in good condition....if a fire started when underway, you'd never know it until too late.
Convert that thing to a nice safe diesel generator...and run it all you want!
How much does it cost to run that propane genset?
Cheers, JR
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« Reply #8 on: April 22, 2006, 06:36:32 AM »

I run my propane fridge all the time under way, never a problem, as for gen set safety i got to tell you i had a onan deisel in my bus ,it was my first gen set, you know one of those nice safe ones, well on a trip to california it caught fire on the road,nearly lost the whole rig but was able to get the fire out, damage to the bus was min, the investigation into the fire revealed a fuel leak developed at the fuel pump which sprayed fuel all in the compartment, it was in nevada, was a windy day,conditions with  heat and wind and fuel together with hot parts of the engine ignited the fuel, dont assume because its deisel its safe, gen sets running on the road can be a nigt mare for sure. I installed in dash engine driven a/c on mine and rarely operate the gen set even thogh it is brand new. if you go cross country 3000 miles from home in the 100 deg temps with no a/c that get your attn real quick.
Frank Allen
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« Reply #9 on: April 22, 2006, 07:55:34 AM »

If you have a large enough bus system alternator and an inverter you may want to consider this as an option:

I have a tie-solenoid between the house and bus batteries and this allows me to run the front air unit using the inverter. This works perfectly with my ducted air system blasting all of the air to the front of the coach. When the outside temp gets really hot, I start the genset and all three air units. You could hang meat in there if you wanted with all three units on and turned down.
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« Reply #10 on: April 22, 2006, 11:59:17 AM »

Well, I had to sign up for this one, I wasn't going to because I'm not sure I like the Mak board's new format.  But I couldn't resist jumping into this thread, because propane is not one of those topics that will tolerate misinformation.
So here's the scoop.  The three posts above this one have it right.  I'll try to consolidate and add a few comments...

First, Laws aside, running your genset on propane while underway is fine if the system is properly built.  Since it's very unlikely that your genset uses liquid propane, I'll not
comment on that part of it because liquid systems are very different and take a lot more "stuff" to make them safe and proper.  So a vapor system:

(1) Freezing Tanks.
If your tank is too small and you run a genset from it, it will freeze up.  Not from shaking though.  What makes it freeze is that when you draw vapor out of the tank, that vapor has to come from somewhere.  It comes from the liquid, which has to boil to turn into vapor. To boil you must have heat.  Forgetting about boiling things on a stove for a while, how liquids boil is that you put energy into them, and they turn into gas.  Or in the case of propane you use the latent heat already in the liquid to boil it. The energy gets used as the propane boils, and the liquid gets colder.   Propane is a gas at atmospheric pressure, and under a few hundred PSI it's a liquid. So instead of having to put a fire under a propane tank to make it boil, all you have to do is draw some gas out of the tank, the internal pressure reduces a bit, some liquid propane boils to replace what you've just removed, and the liquid gets a bit colder because the energy to boil it just came from the latent heat stored in the liquid.  Make sense?  Bottom line, if you're just using a little bit of propane from a big tank, it will never cool the tank down enough to freeze it.  If you're using a lot of propane from a small tank, the tank will freeze. 
  When a tank "freezes', the temperature and vapor pressure of the propane inside goes down and down to the point it won't boil anymore... tank frozen, no more gas will come out 'till it heats up again.  So for things that draw a lot of propane like cars and forklifts, it's a much better soultion to draw the propane out of the tank as a liquid and boil it externally using an external heat source like engine coolant via a heat exchanger... that way tank freeze ups are never an issue and you can draw as much out as you want.

Propane refrigerators are never an issue in an RV because they never draw enough out of a tank to freeze it. Same for stoves.  Gensets are ok but depending on your tank size and generator size, it's often "on the line".  A fully loaded 20KW genset will definitely freeze up a 5 gallon BBQ tank in short order.  But if the tank is 100 gallons, there'd never be a problem because the surface area of that big tank will transfer enough ambient heat into the liquid inside to keep it warm enough to work fine.  Somewhere inbetween, you'll find that your tank size/genset combo will work or not... the solution if it freezes is to use less electricity or get a bigger tank.

Ok, so much for that.  Now "ON THE ROAD"
And while I'm at it, FILLING PROPANE TANKS, because it all relates....

   Basically all the arguements for getting liquid propane accidentally into your genset's regulator are valid... it could cause trouble.
HOWEVER a properly designed tank system will limit your ability to fill it, to about 85% max. That leaves a lot of "slosh" room in the top of the tank, and even on a bumpy road or going up a grade, it's very unlikely that enough liquid if any will be able to get up to the top of the tank where the vapor is drawn out, and into the outlet, to do any damage. Unlikely I say, but not impossible.
If your vapor outlet is not right at the top of the tank, it's possible that liquid could get into it.  This happens when tanks are improperly mounted.
If you overfill your tank or the jerk at the propane station overfills it (called "stuffing in the propane industry) and there's little airspace left inside, yes liquid propane can and will probably get into your system.  But at that point you have a LOT more to worry about, because if the day heats up much at all, the liquid propane inside is going to expand and have nowhere to go, and  you're going to have a venting propane tank on your hands.  That will turn your "genset regulator getting liquid into it" into a problem that you won't even have to think about, because it's likely that you'll have a major fire or disaster on your hands that will make your genset problems trivial at that point.  Venting propane tanks are no fun and absolutely dangerous...you really never want to see one do it firsthand. Beleieve me, because I've seen it. Nasty.
 
 Bottom line, if the tank is NEVER overfilled, and your vapor outlet comes off the very top of the tank as it should, you'll never have problems getting liquid into your genset.
BEWARE- many larger propane tanks do not have OPD valves (overfill protection devices) as they are not required.  This means that the jerk at the propane station can and often will "stuff" your tank.  I've had it happen probably 15-20 times.  Some guys are good about it but face it, guys who work at filling stations are usually not rocket scientists, and many are clueless about the dangers of stuffing a tank.  Have you ever watched the guy see the 'pee" valve go off, then shut it and top your tank off to the next nearest gallon? Yup, the guy should be fired.  Dangerous.  As SOON as that pee valve makes white, the filling should be STOPPED right then and there.  NO FUDGING.
These days I watch the guys like a hawk and if they try to stuff the tank, I simpy reach over and turn the valve off myself.  If they argue, they loose. And it still happens...!!!

SAFETY SYSTEMS for PROPANE
TO be safe, there's a few things you should do, (A) to comply with some codes and (B) just for common sense.

(1) SHUTOFF VALVES:  Besides a shutoff valve on each appliance and a main shutoff valve as well, there should be an electrically operated solenoid shutoff valve placed just on the inlet of the genset, so that when the genset is turned off, the valve shuts. This is code and it's also common sense-necessary. You don't want your genset regulator leaking propane thru the system when the generator isn't running.

(2) TANK VENT:  Something most people don't know and unfortunately even the ones who do know, don't often do, is this:
There is a DOT regulation (It's been 20 years now and I don't remember the number) that says if you have a permanently mounted propane tank on your RV or propane powered vehicle, that you hard-pipe the tank overpressure relief vent out to the rear of the vehicle and aim it up at 45 degrees.  This is so that if the tank vents for any reason, the resulting plume of propane will exit out the rear of the vehicle and up, rather than under it where it puddle up, wait for a little spark and likely go *boom*.
  It's pretty easy to do- just plumb some 3/4" galvanized pipe from the tank to the rear of the vehicle and put a 45 on the end aiming up, and silicone a little cork in the hole.  Should it ever be necessary for the tank to vent, you'll be glad you did it!!!

(3) SAFETY SENSORS:  If you have propane on an RV, you'd be a total fool to not take advantage of the nice inexpensive safety detector devices avaliable these days, namely propane vapor detector alarm systems and CO detector alarm systems.  You should install both in appropriate places in your RV.  The propane sensors can also be had that automatically shut the main off if raw propane is detected, and those are the better ones if you can work them into your system.  Propane is heavier than air, so sensors should be mounted low in the space, like below knee level or on the floor.
And there's absolutely NO excuse for not having at least one CO monitor near your head where you breathe as you sleep.  Cheap insurance and keeps you alive if you have a problem.

(4) SO, running gensets on the road? If you have done the above homework and your system is proper, there's no reason not to do it except some codes (which I will acknowledge but not necessarily agree with).  Same goes with running the fridge while on the road.  Doing either is not as safe or as legal as shutting your propane system down when you drive, but that's your call not mine.  Personally? I do both. Never a problem.

(5) Where do I come from, preaching all this stuff ?  I've been involved in propane conversions of vehicles and small engines for 15 years now.  I've been through an intensive two-week propane school put on by the IMPCO corporation.  I use propane daily and work with propane systems that range from RV's to glassblowing torches to systems that create giant 200 foot propane fire-tornados.  None of this makes me an expert, that's for sure (expert=unknown drip under pressure) but I do understand the stuff and I've also seen what happens when you don't give it the respect it deserves. (kaboom, and all the windows gone for a three block radius, just from filling an RV tank under the wrong circumstances..no, it wasn't me, I was at my business two blocks away at the time )

My bus? 110 gallon propane tank, propane water heater, propane living space heater, propane stove, 8kw propane genset, propane fridge.  I run the fridge on the road 100% of the time and the genset often on really hot days.  I have two propane detectors, two CO detectors, the required hard-plummed tank vent system, and all the valves I should.  Whole thing is done in 3/4 pipe with stainless steel bellows style hoses between the piping and the appliances (If you use these make sure they are rated for RV use... many are not and won't hold up to the vibration)
So do it right, be safe
« Last Edit: April 22, 2006, 12:02:09 PM by boogiethecat » Logged

1962 Crown
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niles500
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« Reply #11 on: April 22, 2006, 02:42:19 PM »

THANKS for signing on and providing the info BTC
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belfert
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« Reply #12 on: April 24, 2006, 05:59:13 AM »

My bus? 110 gallon propane tank, propane water heater, propane living space heater, propane stove, 8kw propane genset, propane fridge. I run the fridge on the road 100% of the time and the genset often on really hot days. I have two propane detectors, two CO detectors, the required hard-plummed tank vent system, and all the valves I should. Whole thing is done in 3/4 pipe with stainless steel bellows style hoses between the piping and the appliances (If you use these make sure they are rated for RV use... many are not and won't hold up to the vibration)
So do it right, be safe

What are your thoughts on using something like Pro-Flex CSST tubing for propane in a bus conversion?  Will it handle the vibration?  RV makers use a fair amount of copper for propane and I personally don't like that idea.

Brian Elfert
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« Reply #13 on: April 24, 2006, 06:22:43 AM »

Well, I had to sign up for this one, I wasn't going to because I'm not sure I like the Mak board's new format. But I couldn't resist jumping into this thread, because propane is not one of those topics that will tolerate misinformation.

Now see, that was not so hard, and welcome to the board. Your posts are always informative and welcome. Thanks for the valuable information on propane.
Richard
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« Reply #14 on: April 24, 2006, 06:31:16 AM »

Finally, some advice a guy can believe.
Thanks for the post boogiethecat.

I do however take issue with one item.
"expert(ekspert) prep. a hasbeen ( ie:washed up ), combined with: drip ( ignoramice) under pressure( stressed out)".
 Grin

Now if we could just get some respectable electrical advice.
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