Normal voltage drop when on battery power w/refrigerator on - Fiberglass RV
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Old 05-31-2017, 06:12 PM   #1
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Name: Bill
Trailer: Scamp 13 Std.
Minnesota
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Normal voltage drop when on battery power w/refrigerator on

I'm trying to troubleshoot an electrical problem with my 2017 Scamp. I've only been on Scamp battery power since I've had my new trailer for a few hours, never more than an hour and a half at a time. The only thing that was on, other than the CO detector was the refrigerator with only the 12V switch on. The hour and a half occasion was today and when I checked the battery voltage at an interior 12V socket it was 11.9v. I confirmed this measurement at the battery itself.

I'm getting good charging voltages when hooked up to 120V indicated at the battery and confirmed at the interior 12V receptacle.

After a half an hour back on shore power, the battery is again indicating a good charge 13.9V when I removed the 120V and went back to 12V.

I'm a little suspicious of the refrigerator's draw on the battery when I'm off of shore power. I show an immediate drop of 0.8V when toggling the 12V refrigerator switch on and off.

The refrigerator works fine on 120V, but shows a very peculiar ability to lower the refrigerator to below freezing when on 12V Scamp battery alone, as well as when hooked up through the 7-pin connecter while towing, even at very low settings, like "1", and it gets to that point fairly rapidly from 60 to 70 degree ambient outside temps. (When running on 120V, I get 35-38 degrees with a normal thermostat setting of 4 or 5.)

I'm looking for ideas and advice on this.


Thanks!

Bill
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Old 05-31-2017, 06:39 PM   #2
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Running your refrigerator off your Scamp's single 24 F battery will discharge your battery down to 50% in 2 or 3 hours.
On 12 VDC the refrigerator runs constantly and is not thermostatically controlled.
Trying to run your refrigerator on 12 VDC is a losing proposition.
I run my refrigerator on 120 VAC or propane never on 12 VDC.
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Old 05-31-2017, 06:53 PM   #3
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Thanks, Steve!

I'm running a 27F and the refrigerator was only on for about an hour and a half on 12V. Could the battery deplete to 11.9V in that time, assuming it was 100% charged at the start?

Also, I understand what you're saying about the thermostat not controlling the refrigerator when on 12V, that it is simply on. But almost everything I've read about RV refrigerators when they're on 12V is they have difficulty maintaining the temp, that it quickly gets warmer in the refrigerator and unacceptably so.

The reason I was testing it at 12V was something froze in the refrigerator after a three hour or so drive. I just can't have that, it ruined something valuable that requires refrigeration. So what am I to do while driving and on 12V to maintain an acceptable temp?

Thanks from a newbie.

Bill
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Old 05-31-2017, 06:54 PM   #4
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12V use of fridge will wipe out your battery VERY quick. I have a 2015 F150 and learned that the charge wire from Ford is very small - too small to charge the battery and run the fridge. After 2 hours or so of driving I got a message on the dash saying the trailer was disconnected. The trailer battery was fully charged when leaving and on 12V I thought it would be OK. NOT! The reason the dashboard light came on was because it cannot send enough current through the little wire to keep up with the fridge. The fridge then depleted the house battery quickly and since it was dead it did not send the confirmation signal back to the truck (it sends a pulse every 20 seconds or so to the trailer to confirm it is still attached). REMEMBER the HOUSE battery is what operates your TRAILER BRAKES if it gets disconnected. I had to turn the fridge off and in a few minutes the truck dash light confirmed trailer was again ok.
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Old 05-31-2017, 06:56 PM   #5
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Consider yourself one of the lucky ones - your fridge actually works too good - lots of people would love that problem. You could run on propane in motion but would need a shield installed to keep the flame from blowing out. Remember to cut off the fridge before going to a gas station or through some tunnels or bridges.
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Old 05-31-2017, 06:58 PM   #6
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You can also control the fridge temperature by changing the position of the thermistor - the slide thing on the fridge cooler fins in the back of the interior of the fridge - up for hotter and down for cooler if I remember.
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Old 05-31-2017, 07:00 PM   #7
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Propane operation will maintain a set temperature as the fridge will cut off the flame as needed and then back on again as needed depending on the setting and the temperature outside.
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Old 05-31-2017, 07:25 PM   #8
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Thanks for the suggest, bsedwebt, but I think I have to look for another solution for my refrigerator that becomes a freezer when towing on 12V.

I simply won't run on propane while towing.
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Old 05-31-2017, 07:31 PM   #9
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Quote:
Originally Posted by Bill MN View Post
....
The reason I was testing it at 12V was something froze in the refrigerator after a three hour or so drive. I just can't have that, it ruined something valuable that requires refrigeration. ...
If you are talking about Insulin, then we should have a discussion about the pros and (especially) the cons of absorption refrigerators.

If you are talking about a nice t-bone steak, then the discussion is much less important.

Temperature regulation with a absorption refrigerator is always going to be a challenge. While many people will tell you that it could be, or is, dangerous to run a absorption refrigerator on propane when on the road, it might work better for you. But the temp will always vary more than it does with your home fridge. If temperature is critical, a different type of fridge might be called for (danfoss type for example).

PS.. I am confused about the reason for your post.. the title refers to voltage drop but the text seems to be concerned about the freezing. The replies (so far) have focused on the latter, but if voltage drop is your concern then we can talk about that.
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Old 05-31-2017, 07:42 PM   #10
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Thanks, Gordon, I'll consider carefully your suggestions regarding a different refrigerator.
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Old 05-31-2017, 08:05 PM   #11
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As has been pointed out above the fridge draws enough current to run your battery down in short order.
As for the fridge freezing before the battery runs out when running battery there NOT any temperature adjustment for battery operation.

I strongly suggest that you read the complete manual for fridge and other appliances supplied when you bought the trailer. If you don't have them the appliance manufacturer will probably have manuals for down loading. I know Dometic and Suburban does. They will guide you through proper operation.
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Old 05-31-2017, 08:23 PM   #12
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Thanks, Byron, very wise advice. I did read the manuals when I first got the trailer, but obviously not well enough. I think I probably "yah-da, yah-da, . . ." through the important part about the thermostat not being operative in 12V operation. That part is certainly there, I just read it again.

I guess I was also thrown a bit off by the refrigerator freezing while on 12V while everything else I've ever read indicated that folks were having trouble keeping things cool enough while on 12V.

So my ill-fated experiment today was to determine whether I could increase the temperature while trying to turn down the thermostat. In retrospect this turned about to be both foolish and futile.

Now, I'm trying to figure out if I ruined my battery by getting it down to 11.9V, even for a relatively short time. Sometimes learning is an expensive proposition!

Bill
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Old 06-01-2017, 12:17 PM   #13
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a few more thoughts....

all 2 or 3 way fridges use "some" 12V power to run the control board (a small amount)...some fridges (mine) have a switch labeled "climate control switch" located inside the top jamb of door opening...according to my manual this should be turned on to prevent condensation in very hot/humid conditions...this is a significant 12V draw.....I know because my fridge is 2 way (AC and prop. only) and I chased for quite a while for a "phantom draw" before finding this one....

Travel: starting with a cold fridge and cold contents you can turn your frige off an go.....as long as you don't open the door the temp in your fridge will stay penty cold enough for steaks or anything else all day (they are insulated, remeber?)...the fuller the fridge the better in that respect

the only way to measure your battery level using voltage is after the battery has been at rest for 30 to 60 minutes with no load on.....the voltage you read when you turn an appliance on will only give you an idea, a vague one to boot, about how much juice that appliance is drawing(amps).....if the voltage drops below 12.2 when you do this is nothing to worry about....the important part is the voltage when you do a "proper" voltage check

12.65+ full battery
12.2.... 50% battery and the level you should not let the battery get below....

additionally, if you can make it happen, battery manufacturers state that batteries that can stay at 12.4 or above have the greatest chance of acheiving their maximum number of charge/discharge cycles (life expectancy)

I have a 4 digit panel meter and I am VERY happy to have it....instead of just 5 relevant numbers to work with (12.6 to 12.2) to monitor my use/battery condition....I have FIFTY....It gives me a surprising amount of information I did not have previously with only 3 digits
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Old 06-01-2017, 01:04 PM   #14
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Thanks for all that additional info, Franswa!
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Old 06-01-2017, 02:29 PM   #15
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Quote:
Originally Posted by Franswa View Post


12.65+ full battery
12.2.... 50% battery and the level you should not let the battery get below....
Please note: 1) not all batteries are created equal.
2) Voltage measurements are at the battery not at the other end of the trailer when can be drop of a volt or 2.
3) Check the specifications of YOUR battery not listen to somebody else's idea of their specifications.
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Old 06-01-2017, 02:38 PM   #16
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We found putting some of those blue ice packs or cold packs for sprains (or back aches) in the freezer helped keep it cold while unpowered during a days travel.


Our freezer was just an aluminum compartment with the cooling coils wrapped around it. Some have separate compartments for freezer and refrigeration and I don't think they would work the same.


I never really counted on freezer keeping stuff frozen so didn't treat it as a freezer, having the space filled by the ice packs was an advantage. Otherwise there would have just been some meat in there that could thaw a bit without harm as long as it stayed cold.
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Old 06-01-2017, 02:39 PM   #17
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To keep stable temperature in the fridge do not allow it to run empty. If you have free space in the fridge, fill a plastic container with water and put it to the fridge. You will be surprised with the result. Cans of beer or bottles of vodka work nice too :-)
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Old 06-01-2017, 08:11 PM   #18
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I pull my Scamp 13 to Utah twice a year from Illinois with my Jeep Wrangler (e-trailer 7 -pin wiring harness) and it will run my refrigerator and charge my battery. To prevent things freezing I alternate turning the refrigerator off and on when I stop for gas. Works great. BTW, we had to spend a couple of days in western Kansas to see relatives; the trailer was disconnected with the refrigerator off for 40 hours and when we hooked back up the refrigerator temp was 50-degrees (We did not open the door while parked).
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Old 06-01-2017, 08:27 PM   #19
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Thanks for all of the suggestions, they are very much appreciated.
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Old 06-01-2017, 08:34 PM   #20
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Quote:
Originally Posted by Franswa View Post
all 2 or 3 way fridges use "some" 12V power to run the control board (a small amount)....
Wrong.

Not all need electric. Some (and years ago, probably most) will run happily on only propane. In fact my pop-up had a three way absorption fridge and I never even put a battery in the camper. The fridge ran fine while boondocking.
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