Fridge on DC (battery power)

[jmai]

I have a 2001 Roadtrek 190 that uses the standard Dometic, 3 way power fridge. It works fine on gas and AC settings, but poorly on DC (battery). I also have a solar panel with 2 AMG house batteries.

My question concerns the DC setting and battery switch. My Roadtrek only has a converter, not an inverter. AC is provided by shore power or generator.

What component will provide DC power with both the engine on and the engine off and with the battery switch on and off as described below?

Engine on-Battery switch off-the alternator should provide the DC voltage for the fridge.

Engine on-Battery switch on-alternator and house batteries ?

Engine off-Battery switch off-car battery will provide DC power but run down quickly

Engine off-Battery switch on-2 house batteries and car battery?

Main question:On the DC setting, do I need to turn on the battery switch when I drive to power the fridge or should it be off?

Thanks in advance.

[booster]

Normally, if driving with frig on DC, you would need the 12v power switch on. You would then be running the frig and everything else in the coach of the alternator, plus you will be charging all the batteries. If the 12v powre switch is off, the frig won't usually run on DC if the engine is on or off.

It is pretty common that the frigs work better on gas an AC than DC,

You don't ever really want run the frig on DC without the engine on, for more than a few minutes as it pulls a lot of amps. Batteries and two panels won't be enough to carry it long periods. Put it on gas whenever you are not driving or on shore power.

[ManWonder]

I'm still kinda new to this but in my 2004 Roadtrek 190 Popular, I have found that running the fridge on batteries is sort of running it in "maintenance mode" and I only use it when driving long distances or when parked in the sun (I've got a 160w solar panel). My understanding is that while on battery, the thermostat is overridden and the thing runs at optimum cooling level which is another reason why the batteries take such a hit and can be quickly drained under many conditions.

[jmai]

Originally Posted by ManWonder

I'm still kinda new to this but in my 2004 Roadtrek 190 Popular, I have found that running the fridge on batteries is sort of running it in "maintenance mode" and I only use it when driving long distances or when parked in the sun (I've got a 160w solar panel). My understanding is that while on battery, the thermostat is overridden and the thing runs at optimum cooling level which is another reason why the batteries take such a hit and can be quickly drained under many conditions.

This is exactly what I do also.

Over the weekend, I got the refrigerator cold with the AC and then went for a one hour drive with the refrigerator on DC. It was not cooling and the temperature went down quickly.

I came home and cleaned the ground terminal and connector on the black wire. I then turned on the engine, and put the refrigerator on DC and checked for 12V on the red wire and ground and got 12+ volts.

Two questions:

1. Just because I have 12 volts, does that mean the unit is good or do I have to check the ohm value?

2. When checking the ohm value, can I just disconnect the car battery and then do a test with a multimeter?

(In order to totally disconnect the red positive wire, I have to pull the refrigerator. I certainly don't want to do that unless I can definitely confirm the heating element is bad.)

[jmai]

After reading the Dometic troubleshooting manual, I found the following formula for calculating ohm values.

volts divided by (watts divided by volts) equals ohms


I did some testing today and disconnected my car battery and measured the ohm value of the 12V heating element. The original unit was rated at 125 watts which would be 1.15 ohms at 12 volts. Ohm values are plus or minus 10%.

My reading was 1.6 to 1.7 ohms.

But with the engine running, the actual voltage is approximately 14.77 volts. If I use that voltage and assume I have the original unit, 125 watts, then the value should be 1.7 ohms. So it appears that the 12V heating element is functioning at the actual voltage being put out by the alternator.

My next step will be to get it cold on the gas or AC setting, then take a drive with the refrigerator on DC and see if it stays cold.

Perhaps, just cleaning the ground spade and connecting lug may have solved the problem. We will see.

[jrobe]

The best long term option is to just replace that 3 way refrigerator with a new compressor refrigerator that is designed to run efficiently on 12 volt power. They aren't that expensive and you won't have to deal with propane for the refrigerator anymore.

[BBQ]

Originally Posted by jrobe

The best long term option is to just replace that 3 way refrigerator with a new compressor refrigerator that is designed to run efficiently on 12 volt power. They aren't that expensive and you won't have to deal with propane for the refrigerator anymore.

+1

[mkguitar]

Think reading through the manual is a great step- and doing some testing.

and esp on an older rig, brightening electrical connections can really help.


like others, I have found that propane ( which also runs my water heater, furnace and burners) will cool best, followed by AC.
I can dependably get my fridge to 60 or 65º below ambient temps on these, esp if the van is parked in the shade.

and usually start the fridge a day or 2 before rolling- esp if it's 115º out

we have a indoor outdoor wireless thermometer, with the "outdoor" sensor in the fridge - this allows us to monitor temps

The dc can really only maintain temps when rolling and if we stop for more than say 30 minutes I switch to propane.

test the door seals with a dollar bill

I have a small fan internal to the fridge- you can get a camco which runs off batteries- I wired a fan into the 12 volt after buying the camco on amazon and seeing how well it worked

I also have 3 fans on the external fins- one was part of a kit with a temp sensor the previous owner had on there, I added 2 more on a switch.

we never have trouble making ice- freezing.
we don;t use the freezer much for food. I have a bunch of the blue freeze packs which I rotate from the freezer to the fridge- this helps stabilize temps.

and we are conscious of asking the other if they need anything before opening the door.


over the past couple of years we have gone from "fridge trouble" to pretty good function.

a comp fridge would be nice, but our electrical capacity isn;t sufficient.
right now we know we can go 5 or 6 days off grid with our old tech

mike

[Ron J. Moore]

Mike, thanks for the post, seems I learn something every time I read through these inputs. You mention about wiring an internal fan to the 12V - can you talk more about it - sounds like a great way to improve the cooling. Ron

[BBQ]

Xplorer Steve

Cool RV 3 way Refrigerator mods and maintenance

http://www.youtube.com/watch?v=fEQwReqJcMU

[mkguitar]

with my internal thermometer i could the variance between top shelf and bottom could easily be 15 or 20º

the proof of concept was the camco I bought on amazon- the camco ran through batteries and was kinda bulky.
it's in a drawer someplace.

the 12 vdc fan I scavenging from an old DVR...it is about 1.5" by 1.5" square and is zip tied in front of the internal fins....it is a gentle waft.

I pushed the wiring out to the back alongside the condensate drain hose, and wired into 12 volt with fuse and switch.

if I am smart I will wire to a door switch so it isn;t pushing cold air out when the door opens ( will likely wire up a 2 pole momentaryswitch , NO side to fridge led lighting, NC side to the fan


I don;t have pic handy

the fans I have on the external fils are low power and came off ebay...I think 6 for $15...



I also find when camped that IF it is dry, I get better cooling with the top vent cover off - as shown- the heat escapes more quickly and i may not even need to run the fans.

this is a PW so my galley window is right above this- opening the window pulls the heat into the van...so we have to keep window closed except for when using gas burners

Mike

[cruising7388]

Originally Posted by jmai

After reading the Dometic troubleshooting manual, I found the following formula for calculating ohm values.

volts divided by (watts divided by volts) equals ohms


I did some testing today and disconnected my car battery and measured the ohm value of the 12V heating element. The original unit was rated at 125 watts which would be 1.15 ohms at 12 volts. Ohm values are plus or minus 10%.

My reading was 1.6 to 1.7 ohms.

But with the engine running, the actual voltage is approximately 14.77 volts. If I use that voltage and assume I have the original unit, 125 watts, then the value should be 1.7 ohms. So it appears that the 12V heating element is functioning at the actual voltage being put out by the alternator.

My next step will be to get it cold on the gas or AC setting, then take a drive with the refrigerator on DC and see if it stays cold.

Perhaps, just cleaning the ground spade and connecting lug may have solved the problem. We will see.

Typically, the AC heater is around 350 watts and the DC heater is around 250 watts. The DC function serves primarily to hold the temp of an already cooled unit. Because of the substantial battery draw, on some units, DC cooling is prevented unless the engine is running or at least until the ignition is on. While a 125 heater will decrease amperage draw, I don't think it will provide sufficient cooling for holding the temperature.

The propane mode canl provide good cooling while underway.

BTW, unless you are dealing with very low temperatures, sustained 14.77 volts isn't good for the batteries.

[jmai]

Originally Posted by jrobe

The best long term option is to just replace that 3 way refrigerator with a new compressor refrigerator that is designed to run efficiently on 12 volt power. They aren't that expensive and you won't have to deal with propane for the refrigerator anymore.

Long term, that is a good solution. For the amount of time I do multi-week trips, its just not in the budget.

Originally Posted by mkguitar

Think reading through the manual is a great step- and doing some testing.

and esp on an older rig, brightening electrical connections can really help.


like others, I have found that propane ( which also runs my water heater, furnace and burners) will cool best, followed by AC.
I can dependably get my fridge to 60 or 65º below ambient temps on these, esp if the van is parked in the shade.

and usually start the fridge a day or 2 before rolling- esp if it's 115º out

we have a indoor outdoor wireless thermometer, with the "outdoor" sensor in the fridge - this allows us to monitor temps

The dc can really only maintain temps when rolling and if we stop for more than say 30 minutes I switch to propane.

test the door seals with a dollar bill

I have a small fan internal to the fridge- you can get a camco which runs off batteries- I wired a fan into the 12 volt after buying the camco on amazon and seeing how well it worked

I also have 3 fans on the external fins- one was part of a kit with a temp sensor the previous owner had on there, I added 2 more on a switch.

we never have trouble making ice- freezing.
we don;t use the freezer much for food. I have a bunch of the blue freeze packs which I rotate from the freezer to the fridge- this helps stabilize temps.

and we are conscious of asking the other if they need anything before opening the door.


over the past couple of years we have gone from "fridge trouble" to pretty good function.

a comp fridge would be nice, but our electrical capacity isn;t sufficient.
right now we know we can go 5 or 6 days off grid with our old tech

mike

+1 about how to use the various three functions.

I just want to maintain the temp on DC as I go from campground to campground and would prefer to not have the propane on as I am driving, although I have done it once or twice.

I have seen the modifications for fans behind the fridge, but I assume you have to take the fridge out to put them in. My 2001 RoadTrek 190 Popular on a Dodge chassis is great except for the rear refrigerator access. The door is too small-it should extend about 4" more towards the rear to allow full access to the gas igniter (for cleaning) and for heat element replacement. Also the upper hot air vent is part of the window frame and can only be taken off by removing the whole window. Otherwise to access the back of the refrigerator involves removing the refrigerator.

Originally Posted by cruising7388

Typically, the AC heater is around 350 watts and the DC heater is around 250 watts. The DC function serves primarily to hold the temp of an already cooled unit. Because of the substantial battery draw, on some units, DC cooling is prevented unless the engine is running or at least until the ignition is on. While a 125 heater will decrease amperage draw, I don't think it will provide sufficient cooling for holding the temperature.

The propane mode canl provide good cooling while underway.

BTW, unless you are dealing with very low temperatures, sustained 14.77 volts isn't good for the batteries.

My refrigerator is now 15 years old and the 125 watt heater was standard. The replacement none now has 150 watts, but it costs $125.00.

My fridge works great on propane and AC. It just bothers me when all options don't work, but I am not going to "take a chance" on installing a new DC heating terminal when it costs $125 and I have to remove the fridge. I'll stick with option 1 and 2-propane and AC.

I checked my voltage today and at the terminal block behind the refrigerator it was 13.58 volts. Not quite sure why it was a whole volt higher yesterday.

Thanks for all of the responses and good info on the fan install.

[mkguitar]

hmm little dvr fan was a little noisy- I swapped in a larger fan, so here is a pic of positioning- the white thing is my thermometer sensor:








here is the display for the thermometer- about $20 at discount store:



Mike

[mkguitar]

hmm- photobucket has decided they don;t like me sharing...sorry

mike

[Davydd]

Originally Posted by mkguitar

hmm- photobucket has decided they don;t like me sharing...sorry

mike

I got an email this morning from Photobucket. I wonder if my past photos are being interrupted like that. If so, so long Photobucket.

[mkguitar]

test:

working with posting from google photos...also posted in the photobucket thread

do the copy image address- replace url with IMG at the beginning and end of the link





unfortunately this forum isn;t set up to allow full editing of posts, or I would go back and clean things up

[jmai]

No luck on DC.

I finally tested my fridge on DC after cleaning the ground terminal and lug. The fridge cooled down in 5 hours on AC with no problem. I then switched to DC and took a 30 minute drive and the freezer went from -6 to 5 degrees. A difference of 11 degrees in 30 minutes is not good! When I stopped, I also felt the metal tube surrounding the heating elements and it was not hot, especially when compared to how hot it got on AC power.

The electrical testing seem to indicate that the heating element is working, but I don't know if it slowly looses efficiency or just immediately quits. The other possibility is that it may be an intermittent loose wire (red power wire) that goes into the heating element and is making it start and stop when going over the rough roads.

I'm not sure I want to spend $125 for a new DC heating element and have to pull the fridge to put it in due to the the lack of clearance from the access door. I can see the parts, but getting them out is another matter.

I will probably just use those blue freezer blocks and freeze them at night and then put them in during the day. Once I camp, I'll use AC and if I have to I'll use propane when stopped for lunch.

[Bud]

Originally Posted by jmai

No luck on DC.

I finally tested my fridge on DC after cleaning the ground terminal and lug. The fridge cooled down in 5 hours on AC with no problem. I then switched to DC and took a 30 minute drive and the freezer went from -6 to 5 degrees. A difference of 11 degrees in 30 minutes is not good! When I stopped, I also felt the metal tube surrounding the heating elements and it was not hot, especially when compared to how hot it got on AC power.

The electrical testing seem to indicate that the heating element is working, but I don't know if it slowly looses efficiency or just immediately quits. The other possibility is that it may be an intermittent loose wire (red power wire) that goes into the heating element and is making it start and stop when going over the rough roads.

I'm not sure I want to spend $125 for a new DC heating element and have to pull the fridge to put it in due to the the lack of clearance from the access door. I can see the parts, but getting them out is another matter.

I will probably just use those blue freezer blocks and freeze them at night and then put them in during the day. Once I camp, I'll use AC and if I have to I'll use propane when stopped for lunch.

Hi jami,

My 05/04 Roadtrek 190 fridge has Not worked on dc for the last 2 years. I drive on ac from the inverter. Occasionally, I drive on propane at slower speeds. If shore-power is available, I use ac shore-power, Not the inverter. I plug and unplug from inverter to shorepower in seconds from inside the b.

The refer stayed cold during my last one month outing driving or not.

While driving in warmer weather, I use two computer fans on the outside of the b, also for the last 2 years.

Bud

[markopolo]

The power consumption specs for my 20+ year old - manual control - Dometic RM2410 are listed as:

DC Heating Element: 125W
AC Heating Element: 160W

I don't think the DC wire has ever been connected. It is still neatly coiled up as if new. I guess the previous owner either didn't run it while driving or used it in gas mode.

Like Bud, I run it on AC while driving using an inverter. My setup has an added $50 (when I bought it 5 years ago) Xantrex Pro-watt automatic transfer switch so no plugging/unplugging needed.

It is easy to turn the fridge off by turning the inverter off as the inverter switch is easily reachable from the drivers seat.