My Dometic RV fridge is sucking my batteries dry and I can't determine why?!

Cal said:

Exactly my sentiments.

First off, an absorption fridge isn't meant to be run off a battery. It consumes way too much power. The fridge ac usage is meant for shore power. An absorption fridge operates sparingly off propane. That should be the primary energy source.

Per spec, the Dometic DM2862 consumes 440W ac power. No way should consumption be much higher than that. If it is, then something else is going on. Perhaps a measurement error or something like the converter being active and is causing an exorbitant load. But it's not the fridge. If the fridge was at room temperature prior to making the measurements then it will be at 100% duty cycle for a number of hours. Once it starts cycling power at perhaps 70% duty cycle, in 24 hours it should consume: 440W * 70% * 24 = 7.4 kWh. This data should have been known before starting the project!

How much power does the new fridge consume? Per spec, it has an energy consumption of 339. Not sure what that means. This article says a fridge like the new one consumes about 150 Ah in 25 hours. That's 1.8 kWh in 24 hours, or about 4 times more efficient on ac. It's still a lot of energy where long periods of clouds in the winter could run down the battery. That wouldn't be a problem with a propane fridge.

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If it's a frost-free fridge, that could account for any higher-than-normal running current albeit just for a short time once a day. Actual running should be less than the "rated" current. My home refer only draws .75 amp @115 vac. when running. Thats 83 watts. Figure in 50% duty cycle = <1kw a day.

I noticed my two whirlpool fridges, one 10 CF and the other, 22 CF both have the same LRA. Wonder if they both use the same compressor?

Checkthisout said:

Wonder if they both use the same compressor?

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…or at least the same motor.

In “playing experiment games” with fridges- 6 now I think- I’m finally settled and happy with both the space and consumption of the current 7.5CF Element refrigerator. It confirmed for me my suspicious observations that with at least the 4.5- 7.5CF small fridges the primary difference is in the insulation and shelving. The 7.5 top freezer two door is consuming nearly identical daily kW as the 4.7 (4.5?) magic chef. Element 7.5 visually has twice the freezer compartment insulation thickness as did the 4.7, and thicker fridge insulation. Anecdotally it runs/cycles less often which seems to my mind to be why it uses less watts.

Your fridge could be parts-bin mechanicals with merely a different carcass.

12VoltInstalls said:

…or at least the same motor.

In “playing experiment games” with fridges- 6 now I think- I’m finally settled and happy with both the space and consumption of the current 7.5CF Element refrigerator. It confirmed for me my suspicious observations that with at least the 4.5- 7.5CF small fridges the primary difference is in the insulation and shelving. The 7.5 top freezer two door is consuming nearly identical daily kW as the 4.7 (4.5?) magic chef. Element 7.5 visually has twice the freezer compartment insulation thickness as did the 4.7, and thicker fridge insulation. Anecdotally it runs/cycles less often which seems to my mind to be why it uses less watts.

Your fridge could be parts-bin mechanicals with merely a different carcass.

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The bigger one takes more refrigerant. I was thinking they both have the same compressor and motor but the big one has a larger evaporator and condensor.

littleharbor2 said:

Haven't read all 8 pages of this thread but I have one question. Is the converter drawing power from the onboard AC system? If so it ought to be disabled. It should only be drawing power from a shore power source, otherwise it is trying to charge the house batteries from ......THE HOUSE BATTERIES! That is guaranteed to drain them

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No need to read all 8 pages. If you had read to the third sentence in the OP's first post, you would know that's not the case. OP indicates 48V system, and you can see the two EG4 batteries in the picture. The 12V converter can't charge the 48V onboard shore power battery.

Cal said:

First off, an absorption fridge isn't meant to be run off a battery. It consumes way too much power. The fridge ac usage is meant for shore power. An absorption fridge operates sparingly off propane. That should be the primary energy source.

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It uses essentially exactly the same amount of heat energy from propane as it does from AC. Propane is just far more BTU dense than batteries. A fridge that size will deplete a 30# bottle of propane in 2-3 weeks if it's the exclusive draw on the bottle.

The 30# bottle holds the equivalent energy to a 808kWh battery.

Cal said:

How much power does the new fridge consume? Per spec, it has an energy consumption of 339. Not sure what that means.

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339 is the annual kWh usage. 339/365 = 0.93kWh/day



That testing is done based on the performance in steady closed door 90°F ambient conditions. That's supposed to approximate and is more conservative than testing at 75°F ambient with some number of door openings.

Compressor fridge generally also has auto defrost which increases efficiency and convenience by a healthy margin.

The ammonia fridge will use more propane btus that electric btus because of the loss of heat up the flu. Maybe 70% of the heat generated by the flame gets absorbed by the boiler.

Yes definitely dump the propane, and go all electric. Preferably at a higher dc voltage.

There may be times when there is no sun, and no shore power.....
A small "silent" gasoline generator can recharge your battery occasionally, during the bad times.

sunshine_eggo said:

It uses essentially exactly the same amount of heat energy from propane as it does from AC. Propane is just far more BTU dense than batteries. A fridge that size will deplete a 30# bottle of propane in 2-3 weeks if it's the exclusive draw on the bottle.

The 30# bottle holds the equivalent energy to a 808kWh battery.



339 is the annual kWh usage. 339/365 = 0.93kWh/day

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That testing is done based on the performance in steady closed door 90°F ambient conditions. That's supposed to approximate and is more conservative than testing at 75°F ambient with some number of door openings.

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Not sure you got your math right. A 30# bottle holds 7 gallons of propane. For 16 years I've been purchasing propane in gallons for my motor home. Gallons is my reference point. The tank has a capacity of about 12 gallons. I can go for 7 weeks before requiring fill-up. Propane usage is for the fridge and the cook-top. The cook-top gets quite a bit of use, daily for breakfast and about every third day for dinner. Another person reported that they can go for 2.5 months with fridge as the only load. That would be equivalent to 12gal / 10 weeks = 1.2 gal/week. Your estimate for a 30# bottle is 2.3 to 3.5 gal/week. OK, kind of close.

Regarding estimated yearly electricity use; 339 kWh/year = 930 Wh/day = 78 Ah/day on a 12V battery. The compressor RV fridge I mentioned had a consumption of 150 Ah/day (real data). That's almost twice the consumption. It might get hotter in the RV and the inverter is not 100% efficient. If it's 80% efficient then 78 Ah/day increases to 97 Ah.

BTW, the fact that the LiFePO4 battery is 48V doesn't mean the 12V converter can't charge the 12V battery, resulting in an error in measuring the absorption fridge power usage.

Cal said:

Not sure you got your math right. A 30# bottle holds 7 gallons of propane. For 16 years I've been purchasing propane in gallons for my motor home. Gallons is my reference point. The tank has a capacity of about 12 gallons. I can go for 7 weeks before requiring fill-up. Propane usage is for the fridge and the cook-top. The cook-top gets quite a bit of use, daily for breakfast and about every third day for dinner. Another person reported that they can go for 2.5 months with fridge as the only load. That would be equivalent to 12gal / 10 weeks = 0.12 gal/week. Your estimate for a 30# bottle is 7gal/3 weeks = 2.3 gal/week. That's quite a difference!

Regarding estimated yearly electricity use; 339 kWh/year = 930 Wh/day = 78 Ah/day on a 12V battery. The compressor RV fridge I mentioned had a consumption of 150 Ah/day (real data). That's almost twice the consumption. It might get hotter in the RV and the inverter is not 100% efficient. If it's 80% efficient then 78 Ah/day increases to 97 Ah.

BTW, the fact that the LiFePO4 battery is 48V doesn't mean the 12V converter can't charge the 12V battery, resulting in an error in measuring the absorption fridge power usage.

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20 degrees at night, maybe 40 during the day, 27 foot traveler I used to have.

A 30lb bottle of juice (7 gallons) lasted 19 days running furnace, hot water, cook top and fridge.

I was conscious to turn the water heater and furnace off if I I left for a hike or whatever but I kept it very comfortable inside.

The 30k Btu furnace would run like 3 hours on a gallon of propane.

I think a fridge burner is like 1200 btus so if on constantly and never cycled off it would run a loooooonnnnggg time.

So your math checks out!

Petenebraska said:

Well yes, that's my position too. But my installer and leggo my @sunshine_eggo make a reasonable argument for leaving the 12v legacy system in tact. Instead of removing that in exchange for a dc2dc converter, the 12v converter and 12v battery act as a buffer against slide and jack power surges where a dc2dc converter might fail

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I have a Dc to Dc converter 24 volts to 12 volt with no battery to run the slides and leveling.

-I measured 250 watts about 10
Amps at 24 VDC pushing out my 13’ slide out

-I measured up to 50 amps at 12 volts, 600 watts on leveling jacks. I level my RV one jack at a time, not auto level. I never did like auto level and find manual leveling quicker.

I do think auto level would use more power.

For me the 24 volt to 12 volt converter leveling with no 12 volt battery works fine.

As only one of three people I’ve read on the forums that has done this, Honestly, anyway you’re comfortable building your system is fine as long as you understand it.

I guess I should be looking for a propane leak.

Cal said:

Not sure you got your math right. A 30# bottle holds 7 gallons of propane. For 16 years I've been purchasing propane in gallons for my motor home. Gallons is my reference point. The tank has a capacity of about 12 gallons. I can go for 7 weeks before requiring fill-up. Propane usage is for the fridge and the cook-top. The cook-top gets quite a bit of use, daily for breakfast and about every third day for dinner. Another person reported that they can go for 2.5 months with fridge as the only load. That would be equivalent to 12gal / 10 weeks = 1.2 gal/week. Your estimate for a 30# bottle is 2.3 to 3.5 gal/week. OK, kind of close.

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Definitely got the equiv battery capacity wrong. Ran it for 30 gallons vs. #. It's 189kWh.

Pretty easy to find online references reasonably consistent with my numbers. Additionally, I could see the 1W difference when my fridge opened and closed the propane valve. It specs at 1300BTU/hr. Duty cycle was right around 60%, thus 18,720 BTU/day. Thus I used .87#/day. This was with the unit closed the entire time - never opened and a 7.5 cu-ft model vs. the OP's 11 cu-ft model. I got a little over a month on a 30# bottle. I was basing the 2-3 weeks on the fact the the OP's fridge is larger, and it's in use daily. Plus, I'd rather have someday say it lasted a week longer than I said it would.

Cal said:

Regarding estimated yearly electricity use; 339 kWh/year = 930 Wh/day = 78 Ah/day on a 12V battery. The compressor RV fridge I mentioned had a consumption of 150 Ah/day (real data). That's almost twice the consumption. It might get hotter in the RV and the inverter is not 100% efficient. If it's 80% efficient then 78 Ah/day increases to 97 Ah.

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The energy star ratings are based on test data. Whatever the case, your numbers or the DoE, it's a lot better than the 600Ah the RV fridge would use on AC power.

Cal said:

BTW, the fact that the LiFePO4 battery is 48V doesn't mean the 12V converter can't charge the 12V battery, resulting in an error in measuring the absorption fridge power usage.

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Not sure if this is directed at me, or why you're saying it. I never claimed the 12V converter can't charge the 12V battery. I said it couldn't charge the 48V as my comment was in the context of an "infinite loop" where the battery is powering the inverter is powering the converter is charging the same battery, etc., until the battery depletes itself.

Checkthisout said:

20 degrees at night, maybe 40 during the day, 27 foot traveler I used to have.

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Cool ambient reduced the load on the fridge. When it's temperatures like that, my absorption fridge power consumption drops to about half was it does on a 75° day.

Checkthisout said:

A 30lb bottle of juice (7 gallons) lasted 19 days running furnace, hot water, cook top and fridge.

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You sure you didn't have a failover circuit where the value switches to the second bottle?

Checkthisout said:

I was conscious to turn the water heater and furnace off if I I left for a hike or whatever but I kept it very comfortable inside.

The 30k Btu furnace would run like 3 hours on a gallon of propane.

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Yep. But what that says is that in 19 days, you didn't run the furnace more than 21 hours total, yet you kept it very comfortable inside... that's running your furnace a little over 1 hour per day. That does not seem possible in 20-40°F weather.

Checkthisout said:

I think a fridge burner is like 1200 btus so if on constantly and never cycled off it would run a loooooonnnnggg time.

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21,548BTU/# * 30# = 646440 BTU

646440BTU/1200BTU/h = 539 hours - 22 days.

Checkthisout said:

So your math checks out!

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Maybe his does, but yours appears to be in error.

sunshine_eggo said:

I guess I should be looking for a propane leak.



Definitely got the equiv battery capacity wrong. Ran it for 30 gallons vs. #. It's 189kWh.

Pretty easy to find online references reasonably consistent with my numbers. Additionally, I could see the 1W difference when my fridge opened and closed the propane valve. It specs at 1300BTU/hr. Duty cycle was right around 60%, thus 18,720 BTU/day. Thus I used .87#/day. This was with the unit closed the entire time - never opened and a 7.5 cu-ft model vs. the OP's 11 cu-ft model. I got a little over a month on a 30# bottle. I was basing the 2-3 weeks on the fact the the OP's fridge is larger, and it's in use daily. Plus, I'd rather have someday say it lasted a week longer than I said it would.



The energy star ratings are based on test data. Whatever the case, your numbers or the DoE, it's a lot better than the 600Ah the RV fridge would use on AC power.




Not sure if this is directed at me, or why you're saying it. I never claimed the 12V converter can't charge the 12V battery. I said it couldn't charge the 48V as my comment was in the context of an "infinite loop" where the battery is powering the inverter is powering the converter is charging the same battery, etc., until the battery depletes itself.



Cool ambient reduced the load on the fridge. When it's temperatures like that, my absorption fridge power consumption drops to about half was it does on a 75° day.



You sure you didn't have a failover circuit where the value switches to the second bottle?



Yep. But what that says is that in 19 days, you didn't run the furnace more than 21 hours total, yet you kept it very comfortable inside... that's running your furnace a little over 1 hour per day. That does not seem possible in 20-40°F weather.



21,548BTU/# * 30# = 646440 BTU

646440BTU/1200BTU/h = 539 hours - 22 days.



Maybe his does, but yours appears to be in error.

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Well, ok. I ran the fridge on gen whenever it was running. Probably 4 hours a day.

The RV furnace only ran for like 5-7 minutes every hour to maintain the place WHEN I was INSIDE and hot water was only turned on whenever. I was outside the majority of the day and yes the low ambient temps were good for the fridge fuel consumption.

So yeah, it looks like we're all doing mostly correct math but failing to account for each other's widely variable ambient conditions.

Checkthisout said:

Well, ok. I ran the fridge on gen whenever it was running. Probably 4 hours a day.

The RV furnace only ran for like 5-7 minutes every hour to maintain the place WHEN I was INSIDE and hot water was only turned on whenever. I was outside the majority of the day and yes the low ambient temps were good for the fridge fuel consumption.

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You must have exceptional insulation in your RV. My Montana with it's "arctic" insulation package is like the other four RVs I've owned - Mediocre at best. Walls and ceilings may be decent, but floors, doors and windows are atrocious. My perspective is also skewed by the fact that my furnace runs what seems to be about 1/2 the time in similar conditions in a 37' 5th wheel with 4 slide outs. I've depleted a 30# bottle in as little as 3 days keeping it 60°F inside with overnight temps in the mid teens to mid 20s.

We had a 420# tank installed at the trailer in April. I think we've been there maybe 24 nights total, and we've used about 1/3 of the tank. Since July the new big NMC battery has been enough to power the fridge almost exclusively on AC, so about 30 gallons of propane have been consumed mostly by the furnace.

Checkthisout said:

So yeah, it looks like we're all doing mostly correct math but failing to account for each other's widely variable ambient conditions.

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Perhaps my problem is that I think everybody else's stuff is as shitty as mine. ?

I guess I need to get out the FLIR and find the holes.

sunshine_eggo said:

Perhaps my problem is that I think everybody else's stuff is as shitty as mine.

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Including heat, water, cooking; as of yesterday morning I’ve used ~60+ gallons of propane since July in a 24’ camper kept at 60 when I’m not ‘home’ and 70*F when I am, and I cook a lot.
I have a 100-gallon tank. Filled 2nd week of February and end of July. Took 53 gallons in July.

So for me that would be like 8-9 30lbs cylinders.
For you that’s a 60 gal tank and like 3-4 30lbs cylinders used if I calculate correctly.

12VoltInstalls said:

Including heat, water, cooking; as of yesterday morning I’ve used ~60+ gallons of propane since July in a 24’ camper kept at 60 when I’m not ‘home’ and 70*F when I am, and I cook a lot.
I have a 100-gallon tank. Filled 2nd week of February and end of July. Took 53 gallons in July.

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Man... I really need to hunker down and find out where my losses are. Even if I used 2X what you did in the same situation, I'd be ecstatic. One of my big gripes is having to winterize. If I could trust that my tank wouldn't go dry even maintaining 45-50°F in the interior, I would be thrilled.

12VoltInstalls said:

So for me that would be like 8-9 30lbs cylinders.
For you that’s a 60 gal tank and like 3-4 30lbs cylinders used if I calculate correctly.

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Not sure what you mean. 420# is 100 gallons, i.e., my tank is 100 gallons, and I'm down about 30 gallons since April. RV fridge/cooking/water heater was the only use from April to September. Furnace has only been used for the last 2.5 months.

We're NOT there 85-90% of days. Typically only there 2 nights 2 times per month.

sunshine_eggo said:

Man... I really need to hunker down and find out where my losses are.

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You may want to check propane pressure with a manometer. They are simple to build. Just some plastic tubing, formed in a U-shape and filled with some water. Connect one side of tube to the low pressure side of regulator. See how many inches the water column rises (typical is 10 to 11 inches).

By chance you don't have a neighbor tapping into your line?

littleharbor2 said:

By chance you don't have a neighbor tapping into your line?

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LOL... Both neighbors are > 1/4 mile away and have their own 500 gallon tanks.

I've seen traveling RVs that somewhen got a refill of suppliers' tank dregs, enough the ammonia-cycle burner & target heat plate are smothered in a oily carbon velvet that halts decent heat transfer - a gentle brushing to get pilot light flame reshaped back as intended & the lower flue cleared of cobwebs & soot build up could vastly inprove efficiency...

chrisski said:

I have a Dc to Dc converter 24 volts to 12 volt with no battery to run the slides and leveling.

-I measured 250 watts about 10
Amps at 24 VDC pushing out my 13’ slide out

-I measured up to 50 amps at 12 volts, 600 watts on leveling jacks. I level my RV one jack at a time, not auto level. I never did like auto level and find manual leveling quicker.

I do think auto level would use more power.

For me the 24 volt to 12 volt converter leveling with no 12 volt battery works fine.

As only one of three people I’ve read on the forums that has done this, Honestly, anyway you’re comfortable building your system is fine as long as you understand it.

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That's the kind of real world data I appreciate. Thanks for the info.

After thinking about it for a bit this weekend while getting my new fridge installed, I'm going to leave the 12v system installed while testing the draw of my new fridge (I'm really excited about it!!). I'm probably going to have to buy another battery or two in the future and that's going to be the real deciding factor on whether I have to get rid of my 12v battery and converter. To make room for any additional EG4 - 48v batteries, I'll have to take out the 12v battery. If I do, then I'll just remove it, install the 48s in it's place and install a dc2dc converter in between the two battery banks.

Zoomyn said:

I've seen traveling RVs that somewhen got a refill of suppliers' tank dregs, enough the ammonia-cycle burner & target heat plate are smothered in a oily carbon velvet that halts decent heat transfer - a gentle brushing to get pilot light flame reshaped back as intended & the lower flue cleared of cobwebs & soot build up could vastly inprove efficiency...

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I did watch a maintenance video about cleaning the back of the fridge and how important it is. It's a moot point now as I've already swapped the old Dometic for a new residential LG. The back of the Dometic wasn't grimey, but it was dusty. And I learned that the embarrassingly undersized little dinky computer fan that was supposed to circulate air was dead. So, I wasn't even getting any circulation to the cooling fins?! However, even correcting that with larger fans would probably still leave the original issue of Dometic absorption fridges just pull a lot of juice.

I'm glad it's gone. This one is better by miles!

Thanks!

Less power, more space for food. Whats not to like.

Got a new fridge installed yesterday. Only thing left is a little insulation and a trim piece.

Removal and install was really easy. No, I'm not going to post a video...there are enough of those boring things out there amongst the interwebs as it is. Here are some pics of the transformation. I made the cavity about 5" larger and slid it in (that's what she said...) Everything is plugged in, running smoothly and cold!

Thank you, everyone, for your input. I'm going to leave the 12v system installed for the time being while I do some testing. I may get around to swapping it out for a dc2dc converter if I need the space for more batteries.

....but that will be another thread! ?

Happiness is, (like a new set of tires), a new fridge. ?

I read the first two pages and then skipped ahead to the last page. I have a Dometic absorption refrigerator in my three season toy hauler. Until I installed a Victron 12/3000 this year I almost never used the AC option to run the fridge. Yeah, it sucks almost 400 watts. So I run it only during the day (with plenty of sun) on AC. A DC compressor fridge will be purchased when the 16 year old absorption fridge goes to that big junk yard in the sky. Otherwise, the absorption fridge is working OK.

I've camped in temperatures down to -8°F. The furnace is going a LOT in that case. But everything still worked. I've done a lot of work on the trailer to make it able to withstand such low temperatures, though it still has the OEM single paned (drafty) windows.

I retained a small 12v lead acid battery (the main house battery is LiFePO4) so that I could start the generator no matter what. That battery is isolated from the rest of the DC system. Because of that, I still have an AC-DC converter to charge the 12v lead acid battery when the generator is running. The 12v lead acid battery has its own solar panel and controller to keep it charged otherwise. This is a legacy part of the system and I'll eventually get around to replacing it with a DC-DC charger, but I'm in no hurry.