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Old 08-20-2019, 07:10 AM   #1
P&DZ
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Battery Question

Just returning from our last camping adventure, boondocking in the Colorado Rockies with no hookups. Our solar system charged the batteries to approx 12.6 to 12.7 by night fall each day. Each morning I checked the batteries and they read between 12.25 and 12.30, that being 65 to 70%. So they were losing approx 30% or more overnight. The only draw overnight was the frig fan, the little annoying blue light on the stereo and the little indicator light on gas detector. The frig was running on propane and we did not use any other lights or the water pump. I would not expect to lose 30% just overnight. Is it time for new batteries or should I be looking for some other issues?

I do have an un-matched 12v battery set as follows:
- Interstate SRM-24 Marine/RV Approximately 3 years old
- Maxx 24DC 92 amp hours Approximately 5 years old
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Old 08-20-2019, 07:23 AM   #2
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Quote:
Originally Posted by P&DZ View Post
Just returning from our last camping adventure, boondocking in the Colorado Rockies with no hookups. Our solar system charged the batteries to approx 12.6 to 12.7 by night fall each day. Each morning I checked the batteries and they read between 12.25 and 12.30, that being 65 to 70%. So they were losing approx 30% or more overnight. The only draw overnight was the frig fan, the little annoying blue light on the stereo and the little indicator light on gas detector. The frig was running on propane and we did not use any other lights or the water pump. I would not expect to lose 30% just overnight. Is it time for new batteries or should I be looking for some other issues?

I do have an un-matched 12v battery set as follows:
- Interstate SRM-24 Marine/RV Approximately 3 years old
- Maxx 24DC 92 amp hours Approximately 5 years old
A 5 year old RV battery matched to a newer battery is most likely the problem! Actually both are about done for, 3 to 5 years is about max for this type of battery.. especially if the water levels haven't been maintained & continuously drained below 50% boondocking.
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Old 08-20-2019, 07:32 AM   #3
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How much solar do you have? With those batteries and the draw at night you could be using 10-15% of capacity. Since they are old it doesn't sound unreasonable for a 30% drop overnight.

And if they're not getting a full charge during the day you will slowly lose ground over a few days.
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Old 08-20-2019, 07:42 AM   #4
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All of the above. But in addition to the refrigerator fan, the refrigerator (at least if it's a Dometic) also draws battery power for heaters in the doors, designed to prevent condensation on the seals. From what I've read these heaters draw from .25 to .8 amps per hour, depending on the size of the refrigerator. 24/7.
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Old 08-20-2019, 11:58 AM   #5
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Thanks Guys!
Sounds like it is time to invest in new batteries, which I thought might be the case. Now I just need to re-visit the various posts on the forum to decide 12v or 6v and best make/model. There does not seem to be a unanimous choice among the members.

That is a very interesting reply by compeakw regarding the heaters in the frig doors. i would hve never guessed that.
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Old 08-20-2019, 01:35 PM   #6
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I was in the same boat as you the first summer I had my new Bullet. I was boondocking full time and I couldn't figure out where my battery was going. Except, I had a pair of new matched batteries.

After I heard about the door heaters in the refrigerator I contacted Dometic. They confirmed that there used to be a switch for the door heaters so the user could turn them on or off, but they removed it several years before because "no one used it". It's not permanently wired with the refrigerator light, except it's on all the time. You can pull the J2 pin in the back of the refrigerator, but you will also lose the light. The alternative is to install a toggle switch in the back or near the light. There are videos on Google for both I think.
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Old 08-20-2019, 01:44 PM   #7
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Most Keystone "low and middle range" trailers that have a Dometic refrigerator will have either the DM2652 (6cuft) or the DM2852 (8cuft). On that model series there is no switch for the door heater circuit. It's on "24/7" as long as the refrigerator is on.

On the DM2662 and DM2862 (upgrade model) that's found in more expensive trailers, there is a door heater circuit switch located on the underside of the eyebrow panel at the top of the refrigerator.

There is a "do it yourself" mod that many of us have done to install a switch to turn off the door heater circuit. On the halogen interior light assembly, there are two red wires. One provides power to the halogen lamp and the other is routed up through the refrigerator side panel and provides power to the door heater circuit. All you need to do is install a small switch on the wire (in or just above) the halogen interior light assembly. Then you can control the power drain from the door heater circuit by turning that switch off when dry camping.

It's not a difficult mod, and depending on your battery bank and how much power you use for other things, that switch can mean the difference between getting 2 days before recharging or getting 3 or 4 days before cranking up the generator.

In your Dometic refrigerator manual is a schematic of the refrigerator electrical system. The door heater is listed as item "K" and is named "heater cable". Don't confuse it with the "12 volt heater" which is the "chimney heater" in a "3 way refrigerator" (propane, AC and DC powered)
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Old 08-20-2019, 05:12 PM   #8
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Thanks for the info on the heater. My old fridge had the switch but my new one doesn't and I've not taken the time to check into it. I've got the 2852 model and I'm boondocking right now. It's using about .5 - .6 amps when it's running so I'll play around with it tomorrow and see what disconnecting the heater will save me.
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Old 08-20-2019, 06:07 PM   #9
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When you pull the interior light cover and the bulb (don't get oil from your fingers on the halogen bulb) you'll see two red and two black wires. One is +12VDC from the control board to the light fixture, the other is the wiring harness for the door heater. Same with the -12VDC black wires. Which is which? That's where you have to "make a 50/50 guess" <pun intended>...
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Old 08-21-2019, 12:11 PM   #10
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I put the switch outside. I have my total trailer drawing only .5 amps.
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Old 08-21-2019, 12:32 PM   #11
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Thanks for the instructions! The TT is in storage so I have not had the opportunity to check the model and if it has the door heaters. If it does I am definitely going to do the modification.
Question: How important is the door heater? If I simply cut the red wire to the door heater harness and don't take the 50/50 chance on the black wire will it make a difference? I would just cap off the end of the red wire and be done. That would disable the door heater permanently.
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Old 08-21-2019, 07:12 PM   #12
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John,

I found this video on installing a toggle switch inside a Dometic refrigerator to control the door heaters as you outlined: https://youtu.be/rgZdZO2tWAE

The poster states one of the black wires is a thicker gauge than the other and that that is the negative wire for the for heaters. I verified that it is true that one black wire is thicker than the other in my refrigerator, the red wires seem to be the same gauge. Does that solve the 50/50 dilemma? Is there any reason to prefer installing the switch in the red positive wire instead of the black negative wire? Thanks.

Keith
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Old 08-21-2019, 07:50 PM   #13
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Keith,

Thanks for that info. It'll sure help someone with the "guessing which wire" is for the heater circuit.

As for which is "best" to install the switch, the red wire or the black wire. I'd suppose that goes along with the "never ending argument, "Which cable to install a battery cutoff switch" Is it the pos or the neg cable??? I don't suppose we'll ever get a "100% consensus" on that topic and now I can see the same "illogic logic" being applied to which color wire to install the switch.

Theoretically, as long as the switch interrupts the circuit to stop electron flow, the controlled item (in this case, the heater) will stop functioning... To me, that's the reason for installing the switch, so as long as it performs the function..... Now, if this were a "rocket ship" (rocket science) it might affect other functions or other components, but in the Dometic realm of sophistication, as long as both the light works and the heater circuit doesn't (with the switch in the off position) then "all is good".....
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Old 08-21-2019, 07:55 PM   #14
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Thanks John. That was my general thinking, but you have more thorough professional knowledge of the individual components than I do.
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Old 08-21-2019, 11:28 PM   #15
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Get 2 new batteries. The old battery is pulling down the newer battery
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Old 08-24-2019, 11:49 AM   #16
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Quote:
Originally Posted by JRTJH View Post
When you pull the interior light cover and the bulb (don't get oil from your fingers on the halogen bulb) you'll see two red and two black wires. One is +12VDC from the control board to the light fixture, the other is the wiring harness for the door heater. Same with the -12VDC black wires. Which is which? That's where you have to "make a 50/50 guess" <pun intended>...
I checked this out today. It looks like the heater draws about .4 amps so that's almost 10 amp hours a day. I didn't have a switch laying around so I just put a (red neck switch) disconnect in that's easy enough to plug or unplug as needed. Probably not going to worry much about it as I have plenty of solar when the sun shines. But this past week I was dry camping and in a very shaded spot, with a lot of cloudy hours and running two fans at night because it was so warm and muggy. After three days I needed a little boost from the generator. So I probably could have made it another day if I had the heater disconnected.
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Old 08-29-2019, 07:21 AM   #17
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Sorry, I am not familiar with your batteries. Are they real deep cycle or just marine batteries? A 24v deep cycle should weigh over 150 pounds.
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Old 08-29-2019, 08:29 AM   #18
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There's a few more power vampires that nobody's mentioned.
The circuit board for the fridge also uses some 12V current.
If your TV is 12V, it's drawing some too.

I would go with 2 6 volt GC2 batteries. In my truck camper I had 2 12V batteries, and with the wife's CPAP going all night, had a similar drop. Just got a new Hideout 5'er, and with the 2 6V I lose almost nothing to the vampires. It's been unplugged now for 3 days (no CPAP running though) and still has 12.7V.
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Old 08-29-2019, 09:59 AM   #19
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Stereo drain and battery issues

Your stereo also has a significant full time draw. Check the connections in the back. There should be 2 wires from the stereo attached to the 12 volt feed. One should be labeled "+12" the other labeled "ignition". If you put an easily accessible switch in the "ignition" lead you can reduce the draw and douse the panel light, but keeps all the settings when you are not using the stereo. That puts it into a reduced power mode like turning off your TV ignition switch does for the radio.

Batteries: others on here will tell you that the batteries you currently have are "Starting/Deep Cycle", have thinner plates for the starting amperage draw and are not optimum for RVs without motors. Get a couple of 6 volt golf cart batteries and wire them in series as a cheap alternative or get true Deep Cycle batteries (no CCA or cranking specification) which can run to significant money. Both alternatives will last longer and provide more energy storage.
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Old 08-29-2019, 04:40 PM   #20
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For some inexpensive good batteries, try these. I have 4 and they seem to be holding up well a year and a half later.

Duracell Ultra 6V Deep Cycle Golf Cart Battery
SLIGC115

If possible to purchase online and pickup, you’ll get a 10% discount while ordering.

Whatever brand you choose, the 6v batteries will far exceed your power needs over what you have now or with new equivalent 12v’s.
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