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Old 02-18-2019, 03:28 PM   #1
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LPG for coach, and generator, or both...

Have a new fiver, five tanks. This is the basic setup that I can see:

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About to install a new Onan LPG genset.

Comments I've heard: "You can run anything else when you're running the generator, there's not enough gas".

Onan recommends going at the start of the chain for the same reason, and kind of hints at turning everything else off hard in case the gas being consumed starves something else out.

Another post here mentioned having a dedicated LP system for the generator.

So, I thought of this:

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Seems like with a couple of Y valves I could dedicate one take to generator and the rest to coach, vice versa, or almost anything. Is is a Bad Idea, or even hard?

Thanks, all!
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Old 02-18-2019, 06:11 PM   #2
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Most likely your regulator is not made to flow enough for the genset and other loads. Talk to a propane shop about getting one with higher flow, not higher pressure.
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Old 02-18-2019, 10:30 PM   #3
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Standard RV LP Regulator has a 160,000btu flow rating


SO....
40K btu furnace
12K Water heater
9k and two 5k stove top burners
2k oven
2k fridge
2k outside grill


That's 77,000 btu/hr demand (IF you ran everything at same time)


5.5K Onan LP Gen
.8 gallon/hr at half load & 1.1 gallon/hr at full load
1 gallon propane has 91,600btu


77,000 plus 91,600 -------168,600 btu demand (runnign everything at same time)


SO Two standard 160k btu 2 stage LP Regs on a split system WILL handle the demand
One side primary for RV and one side primary for gen with cross tie so either can supply RV and/or Gen


High capacity auto changeover regs are also available in 350k and 400k flow rates
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Old 02-19-2019, 06:52 AM   #4
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what you are thinking would obviously work. but you may need to install another regulator so that each tank feeds a low pressure regulator. in your diagram i believe the regular on the 30 lb tank is a high pressure regulator. but before you go to the effort to do it i'd just get the generator installed and then install the dedication valves if you find that you are actually starved for lpg fuel. for what it's worth we have a lpg onan 5500 and have not yet run into a situation where we were starved for fuel. but we don't push it to the limits either. we did have a regulator failure but that had nothing to do with the generator.
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Old 02-19-2019, 09:10 AM   #5
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FWIW .. my Sprinter Class C had an LPG Onan genny and had 2 separate regulators. I don't recall if the Onan was on it's own or not, but the coach also had a gas/electric fridge, gas/electric water heater, furnace & stove.
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Old 02-19-2019, 03:27 PM   #6
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Quote:
Originally Posted by khocke View Post
FWIW .. my Sprinter Class C had an LPG Onan genny and had 2 separate regulators. I don't recall if the Onan was on it's own or not, but the coach also had a gas/electric fridge, gas/electric water heater, furnace & stove.

Motorhomes have stacked LP Regs so one feeds coach and the other feeds the gen
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Old 02-20-2019, 09:52 AM   #7
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Quote:
Originally Posted by Old-Biscuit View Post
40K btu furnace
12K Water heater
9k and two 5k stove top burners
2k oven
2k fridge
2k outside grill
No fridge on gas. Would likely be running nothing on that list while on generator other than the water heater, maybe one or two top burners. Generator will be a little-used use case for us, but there are one or two days a year we're in a location with no shore power and requirement to drive both A/C units. In that case likely none of the other loads. I woudn't be running it in a cold weather situation unless the batteries needed to be recharged to keep the furnace blower spinning.

Quote:
That's 77,000 btu/hr demand (IF you ran everything at same time)

5.5K Onan LP Gen
.8 gallon/hr at half load & 1.1 gallon/hr at full load
1 gallon propane has 91,600btu

77,000 plus 91,600 -------168,600 btu demand (running everything at same time)

SO Two standard 160k btu 2 stage LP Regs on a split system WILL handle the demand
One side primary for RV and one side primary for gen with cross tie so either can supply RV and/or Gen
6.5K Onan QG
0.8 gal/h half load
1.2 gal/h full load

with 2x20 = 1x30 I have 70 lbs LPG, doing full load math that seems like a little more than 13 hours for generators only, and I can't see them running full power more than an hour or two, then half power to maintain. I think I'm good.

Seems like I'll be fine in any case with that math. I need to document the regulators I have. Need to find out size of gas line (looks like heavy rubber at that point) to determine fittings.

Quote:
High capacity auto changeover regs are also available in 350k and 400k flow rates
I'd appreciate any pointers. I like to improve and have spares.
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Old 02-20-2019, 09:54 AM   #8
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Quote:
Originally Posted by bigchick View Post
what you are thinking would obviously work. but you may need to install another regulator so that each tank feeds a low pressure regulator. in your diagram i believe the regular on the 30 lb tank is a high pressure regulator. but before you go to the effort to do it i'd just get the generator installed and then install the dedication valves if you find that you are actually starved for lpg fuel. for what it's worth we have a lpg onan 5500 and have not yet run into a situation where we were starved for fuel. but we don't push it to the limits either. we did have a regulator failure but that had nothing to do with the generator.

Sounds about like I use case. I like the "install it and see how it goes" approach, I need to find out if there's a gas line for a valve that will be blocked once the genset is in the nose. I'm not dying to pull it back out.
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Old 02-20-2019, 09:49 PM   #9
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Originally Posted by manowell View Post
No fridge on gas. Would likely be running nothing on that list while on generator other than the water heater, maybe one or two top burners. Generator will be a little-used use case for us, but there are one or two days a year we're in a location with no shore power and requirement to drive both A/C units. In that case likely none of the other loads. I woudn't be running it in a cold weather situation unless the batteries needed to be recharged to keep the furnace blower spinning.



6.5K Onan QG
0.8 gal/h half load
1.2 gal/h full load

with 2x20 = 1x30 I have 70 lbs LPG, doing full load math that seems like a little more than 13 hours for generators only, and I can't see them running full power more than an hour or two, then half power to maintain. I think I'm good.

Seems like I'll be fine in any case with that math. I need to document the regulators I have. Need to find out size of gas line (looks like heavy rubber at that point) to determine fittings.



I'd appreciate any pointers. I like to improve and have spares.

Those High Capacity Regs should be used as the 'only' supply for the WHOLE system


Oversizing does NOT make it better....
Regs are used that CAN provide FULL Flow but actually are operating within the mid-range area so reg has ability to control pressure in system


Oversized reg would be operating at the bottom end vs mid-range UNLESS huge demand was placed on it.
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Old 02-21-2019, 08:41 AM   #10
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Quote:
Originally Posted by Old-Biscuit View Post
Those High Capacity Regs should be used as the 'only' supply for the WHOLE system

Oversizing does NOT make it better....
Regs are used that CAN provide FULL Flow but actually are operating within the mid-range area so reg has ability to control pressure in system

Oversized reg would be operating at the bottom end vs mid-range UNLESS huge demand was placed on it.
Not really interested in over-sizing, but auto-fail over. RIGHT-sizing. I've order a set of Mopeka Tank Check monitors, have read good things about them. If they're accurate enough that allows advance planning to not need auto-switch or just leaving all the valves feeding. I like a reserve somewhere.
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Old 02-21-2019, 09:03 AM   #11
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i dont know that its enough gas. it the demand on the bottle created by the generator. using only one bottle (20lb) it may cause the bottle to freeze and loose pressure. the better alternative is to get a manifold so you can draw from both bottles same time. Larger regulator may cause this to happen sooner. Especially in cold temps.
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