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Old 01-04-2022, 10:36 PM   #1
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Default Dometic 3-way... pro's and con's of driving with propane on

I have a Dometic 3-way fridge (Model 8501) which has the options of running off LP, my 12v batteries or shore power.

When I plan to drive for a few hours, I leave the propane on (OH NO!) because I've been told if I switch it to DC, the draw from the fridge will not allow my 12v batteries to charge while driving. (Since I can't drive while plugged in, the only other option is turning the fridge OFF altogether and hope everything stays cold enough not to spoil.)

I've heard horror stories about explosions however I don't want to drain my batteries nor do I want spoiled food.

If you say it is really dangerous to drive with propane on, then please also provide a solution to my dilemma.

Thank you

P.S. I have a 2013 Roadtrek SS Agile, my battery system is two 224-amp hour Fullriver batteries in series. Not sure about the alternator.
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Old 01-04-2022, 10:53 PM   #2
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Originally Posted by AG_Ltd View Post
I have a Dometic 3-way fridge (Model 8501) which has the options of running off LP, my 12v batteries or shore power.

When I plan to drive for a few hours, I leave the propane on (OH NO!) because I've been told if I switch it to DC, the draw from the fridge will not allow my 12v batteries to charge while driving. (Since I can't drive while plugged in, the only other option is turning the fridge OFF altogether and hope everything stays cold enough not to spoil.)

I've heard horror stories about explosions however I don't want to drain my batteries nor do I want spoiled food.

If you say it is really dangerous to drive with propane on, then please also provide a solution to my dilemma.

Thank you

Your batteries will still charge while driving, maybe not as fast depending on how much current is available to the coach at max allowed by the alternator and/breakers and how much battery capacity you have to replace. What model and year you have would help as someone probably will know.


When we had a propane frig (compressor frig now for a long time) we always used DC while driving with the propane off as it was more convenient and somewhat safer besides, so no downside for us. It was in a 2007 Roadtrek 190 with 1820ah of coach battery and 80 amp alternator.


Not going into depth on the safe to drive with propane or not as too many very strong opinions on that from both sides.
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Old 01-04-2022, 11:00 PM   #3
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I think Booster is correct. Mine charges quite well with the fridge on DC.
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Old 01-04-2022, 11:11 PM   #4
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Originally Posted by AG_Ltd View Post
I have a Dometic 3-way fridge (Model 8501) which has the options of running off LP, my 12v batteries or shore power.

When I plan to drive for a few hours, I leave the propane on (OH NO!) because I've been told if I switch it to DC, the draw from the fridge will not allow my 12v batteries to charge while driving. (Since I can't drive while plugged in, the only other option is turning the fridge OFF altogether and hope everything stays cold enough not to spoil.)

I've heard horror stories about explosions however I don't want to drain my batteries nor do I want spoiled food.

If you say it is really dangerous to drive with propane on, then please also provide a solution to my dilemma.

Thank you
Can you get some a bag of ice for the road? Also consider a 12 volt refrigerator ice chest for the road? These use way less electricity than 12 volt dc for the 3 way refrigerator.
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Old 01-04-2022, 11:25 PM   #5
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I'd rather save propane for use when camping, and use 12V power for the fridge when on the road.
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Old 01-05-2022, 05:29 PM   #6
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The problem occurs when you stop and fail to turn the fridge away from DC. You could install a relay in the DC heater circuit controlled by ignition on voltage. Works for me.
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Old 01-05-2022, 05:58 PM   #7
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We have a 2007 Roadtrek 210 we bought new. We run on 12v going down the road, always have and have had no issues. Just don't try to cool the refrig down in the first place with 12v. My first choice for cooling is the propane, then the 110v AC.

That being said, we also have a Class C which we use for extended stays. The refrig is 110v AC or gas, no DC option for cooling. We go down the road just fine using the propane but you gotta remember to turn off the frig before pulling in to buy gasoline. Virtually all Class Cs are 110/propane refrigerators.

Think about travel trailers and fifth wheels. They have no option except to run on propane going down the road.

Some motorhome folks are really concerned about using propane and run their generators going down the road and using the 110v option on the refrigerators.

Where I live, compressed natural gas powered vehicles have been in use for a while. Like for about thirty years.

I check my propane connections and burners twice a year for integrity and use a sniffer like this to make sure everything is OK. I use this one and consider it a good tool to own.

https://www.amazon.com/Detector-Batt...xpY2s9dHJ1ZQ==
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Old 01-05-2022, 06:22 PM   #8
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Some motorhome folks are really concerned about using propane and run their generators going down the road and using the 110v option on the refrigerators."

Down the road I use ac from the inverter - noticeably better/hotter/more watts than dc. Battery is easily charged while driving.
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Old 01-06-2022, 01:22 PM   #9
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Down the road I use ac from the inverter - noticeably better/hotter/more watts than dc. Battery is easily charged while driving.
any idea on the amp draw vs 12v
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Old 01-06-2022, 02:07 PM   #10
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any idea on the amp draw vs 12v
I could guess at whatever the inverter inefficient watt cost is while charging vs dc. Some other forum members here would have a better guess.

Supposedly 90% efficient which I don't believe. So maybe 11-16% loss?

I should have mentioned that some absorption refrigerators make little or no more heat than dc. There is a noticeable difference with mine. I mostly drive on ac, once in awhile on propane.
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Old 01-06-2022, 03:52 PM   #11
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The heating elements in mine are 135W DC & 160W AC so fridge cooling performance is better when running the fridge from the inverter while driving.

With engine running it would be approximately 10A on DC or 13A on AC from inverter.
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Old 01-06-2022, 04:36 PM   #12
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The heating elements in mine are 135W DC & 160W AC so fridge cooling performance is better when running the fridge from the inverter while driving.

With engine running it would be approximately 10A on DC or 13A on AC from inverter.

It would be interesting to see what actual voltage the heater element is rated at. If the 135 watts is at 12v, at 14v it would be like 157watts and 14v is more typical of what it would see while driving. It would also indicate that DC would work better when driving than when sitting.
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Old 01-06-2022, 05:15 PM   #13
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It would be interesting to see what actual voltage the heater element is rated at. If the 135 watts is at 12v, at 14v it would be like 157watts and 14v is more typical of what it would see while driving. It would also indicate that DC would work better when driving than when sitting.

That had not dawned on me booster, slow here. It appears that if the refer is rated the same ac or dc in watts, the ac will produce more heat - Like the recent Dometic 8501 cited in an earlier post. I checked, Dometic cites about the same watts, but it appears that Dometic does rate the refer at 12 and 120 volts. They cite amps and watts with both ac and dc. So, it appears that I would also be driving using ac with a 8501.

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Old 01-06-2022, 07:18 PM   #14
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Good catch Booster. I found a tech data sheet from 1997.

RM2410
160W AC 120V 1.3A 92 Ohms
125W DC 12V 10.4A 1.15 Ohms

Looks like DC would equal AC performance as long as you get at least 13.6V to the fridge.
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Old 01-08-2022, 02:30 AM   #15
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Where I live, compressed natural gas powered vehicles have been in use for a while. Like for about thirty years.
Compressed natural gas and propane are somewhat different animals. Natural gas is lighter than air and disperses quickly as a result. Propane is heavier than air and pools like water.
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Old 01-08-2022, 02:51 AM   #16
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We have a 2007 Roadtrek 210 we bought new. We run on 12v going down the road, always have and have had no issues. Just don't try to cool the refrig down in the first place with 12v. My first choice for cooling is the propane, then the 110v AC.

That being said, we also have a Class C which we use for extended stays. The refrig is 110v AC or gas, no DC option for cooling. We go down the road just fine using the propane but you gotta remember to turn off the frig before pulling in to buy gasoline. Virtually all Class Cs are 110/propane refrigerators.

Think about travel trailers and fifth wheels. They have no option except to run on propane going down the road.

Some motorhome folks are really concerned about using propane and run their generators going down the road and using the 110v option on the refrigerators.

Where I live, compressed natural gas powered vehicles have been in use for a while. Like for about thirty years.

I check my propane connections and burners twice a year for integrity and use a sniffer like this to make sure everything is OK. I use this one and consider it a good tool to own.

https://www.amazon.com/Detector-Batt...xpY2s9dHJ1ZQ==
Do you check all connection? Some of mine are hidden behind cabinets etc. How do you do it? A "sniffer" sounds like a very good idea but don't know how to get to allllll connections.
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Old 01-08-2022, 02:55 AM   #17
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Good catch Booster. I found a tech data sheet from 1997.

RM2410
160W AC 120V 1.3A 92 Ohms
125W DC 12V 10.4A 1.15 Ohms

Looks like DC would equal AC performance as long as you get at least 13.6V to the fridge.

I am starting to wonder if at least some of the reputation for poor cooling on DC while driving was on vans with an isolator in place that would drop the voltage .7v, but even back then most alternators ran at 13.8v or so and wouldn't be as low as 12v would be at 13.1v and would be lower than on AC.
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Old 01-08-2022, 03:24 PM   #18
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Originally Posted by AG_Ltd View Post
I have a Dometic 3-way fridge (Model 8501) which has the options of running off LP, my 12v batteries or shore power.

When I plan to drive for a few hours, I leave the propane on (OH NO!) because I've been told if I switch it to DC, the draw from the fridge will not allow my 12v batteries to charge while driving. (Since I can't drive while plugged in, the only other option is turning the fridge OFF altogether and hope everything stays cold enough not to spoil.)

I've heard horror stories about explosions however I don't want to drain my batteries nor do I want spoiled food.

If you say it is really dangerous to drive with propane on, then please also provide a solution to my dilemma.

Thank you

P.S. I have a 2013 Roadtrek SS Agile, my battery system is two 224-amp hour Fullriver batteries in series. Not sure about the alternator.
Where did you get the information your batteries would not charge while driving if your refrigerator was on DC? Is that in your owner's manual from Roadtrek or from reading on the Internet? I've had two absorption refrigerators with two different upfitters, Pleasure-way and Great West Vans and had battery charging while driving and running the refrigerator on DC. I doubt Roadtrek would be any different because that was back in the days when one lead-acid battery would suffice. That is why 3-way. Drive on DC, AC when on shore power and propane when not on shore power. It was a pretty simple concept but needing to pay close attention on what source of power you were on.

Compressive refrigerators came to be popular when people started desiring more battery power so they could leave a refrigerator on one source usually DC without worries all the time. We found them a bit more stable maintaining temperature in hot climates.
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Old 01-08-2022, 06:00 PM   #19
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Where did you get the information your batteries would not charge while driving if your refrigerator was on DC? Is that in your owner's manual from Roadtrek or from reading on the Internet? I've had two absorption refrigerators with two different upfitters, Pleasure-way and Great West Vans and had battery charging while driving and running the refrigerator on DC. I doubt Roadtrek would be any different because that was back in the days when one lead-acid battery would suffice. That is why 3-way. Drive on DC, AC when on shore power and propane when not on shore power. It was a pretty simple concept but needing to pay close attention on what source of power you were on.

Compressive refrigerators came to be popular when people started desiring more battery power so they could leave a refrigerator on one source usually DC without worries all the time. We found them a bit more stable maintaining temperature in hot climates.

Hi Davydd,

Thank you for circling back around to the original question. (This thread got way too complicated for me to understand. Shoots, my head spins simply trying to keep staight: AC DC LP propane gas 12v 110 etc. but I'm doing my best.)

A well-meaning friend told me she drives with her fridge OFF because if she believes it keeps her 12v batteries from fully charging. Thank you (all) for correcting this misconception.

I'm a healthy, curious, solo retired/senior explorer with NO experience (or interest in, if we’re being honest) in things mechanical but I’ve never let that stop me from pursuing new things! I love boondocking at high elevations, so my fridge turning off has been a real problem. (The Dometic manual says if you go to elevations over 5500 ft, “find shore power”. HA! Lot of help that is…NOT!)

My Roadtrek has a 3-way fridge which I have a love-hate relationship with because for the past 6 years I've thought it has not been reliable because when on propane, it inexplicably shuts itself off, even at elevations well below 5500. (Yes, it’s been “in” to at least a dozen shops saying they have “good RV techs”, who each took it apart, “diagnosed” the issue, cleaned and blew, none of which made any difference…)

But last month while kvetching about this, another RT friend said “what is your battery level?”. 90% capacity I said… “Not the capacity… the voltage…” “10.7” I said.. THERE he said. That’s your problem! Your batteries are too low. Go get new batteries and tell me if the problem persists, I bet it won’t…

…and VOILA! With new batteries the fridge has stayed on on LP. Mind you, I’m at 1820 elevation. (The last time I had new batteries installed was 5 years ago so this could be the culprit.)

With new batteries, I'll now see if my fridge stays on LP, and test it at elevation. It will be later this year but I will post my results.

Thanks Davydd, and everyone else too, for your help!!!

[Sidebar:] Related but separate topic: I’m considering getting an Isotherm 115 for all the advantages of the compressor fridge, but am going to wait and see how well/if my Dometic performs adequately with good batteries. The compressor/Isotherm thread on the Sprinter Source forum
https://sprinter-source.com/forums/i.../#post-1129863
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Old 01-08-2022, 08:19 PM   #20
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I just read the posts on the Sprinter forum link and have to say that they seem to be using way more power than they should be. You shouldn't need 4-6 AGM batteries and 200 watts of solar to run a 115 liter frig.


220ah with 200 watt should be fine in most cases unless extreme conditions, I think, unless that model uses more power than it is rated at. If the ventilation is poor, like we see in the majority, probably, of installations the frig can easily use twice the power it should. That is likely their issue.



The Freedom 115 uses that new style electronic control and when I tested a similar control from them on our new 85 it used more power than the mechanical relay did, and way more power than the mechanical relay and the compressor speed turned down.
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