Dometic 2354 doesn't cool on 12V DC

[GallenH]

That's interesting. Looks like they're now recommending a higher wattage element than they used to put in. When I was writing my last reply the thought that RT-NY had passed my mind as well. I have a separate line running from the battery to the fridge. It doesn't go through the converter where the 12v fuses are. Instead there's a 15A breaker on that line. My 125w element draws a little over 10A. If the (A = W/V) formula is correct, that draw makes sense. A 170w element would draw c.14A, still under the breaker rating. My guess is that a 135w, drawing 11.25A, wouldn't tax the circuit much more than the original 125w. But I'm not a wiring expert by any means.

[avanti]

The 125 watt units were no doubt designed back when most rigs had a single lead-acid battery and vehicle electrical systems were less robust than today's norm. The new recommendation looks like a rational response to a changing market.

If it were me, I would go with the 175w replacement, unless I was particularly power-poor.

[RT-NY]

Originally Posted by GallenH

...there's a 15A breaker on that line. My 125w element draws a little over 10A. If the (A = W/V) formula is correct, that draw makes sense. A 170w element would draw c.14A, still under the breaker rating. My guess is that a 135w, drawing 11.25A, wouldn't tax the circuit much more than the original 125w.

Originally Posted by avanti

If it were me, I would go with the 175w replacement, unless I was particularly power-poor.

I just double-checked my dometic three-way--which also draws around 10 amps on 12 volts--and it is also a 15amp fuse. I think that that 135 watt would be fine, but I would be concerned running 14+amps for the 175watt through the existing 12volt wiring. The rule of thumb I have heard is that you should try to stay below 80% of rated capacity. But, my rig is a 1999 Dodge - perhaps the OPs 2015 Chevy has more robust wiring?

[Bryan JR]

I just emailed Dometic confirm the 170 watt is ok with my original setup. It would be comparable to AC heater. Are all of these heater units the same diameter? The original is 7/16" diameter.

[GallenH]

I think that's not exactly the issue. The greater wattage AC element doesn't make use of the 12v wiring. It uses the existing 120v wiring. The question worth asking is if the existing 12v wiring is sufficient gauge to support the greater draw of a 170w element.

[GallenH]

Note that while Dometic is good with a larger wattage element, the question still is did PW put in sufficient wiring to support it. Dometic wouldn't know that.

[Bryan JR]

I went ahead and ordered a 135 watt heater for now.

[avanti]

Have you looked at the wires involved? 170w would require 14AWG.

[booster]

Do any of the wattage specs say what voltage they are rating at? Voltage will have a quite large effect on running wattage.



My guess is that they are rated at 12v nominal, which sounds good for a camper running on batteries, but absorption frigs are rarely run on batteries, I think, as they kill batteries to quickly.


When running down the road on the alternator, they will likely see substantially higher than 12v, depending on the alternator voltage and wiring. Probably could vary from 12.5 to near 15v from vehicle to vehicle.


The AC ratings are probably at a more similar to actual voltage so wouldn't change as much, I think.


The difference between 12 and 14.3 volts would be 170watts vs 202w.


The 135 watt would turn into 160 watts and moving closer to the AC heater rating.


If you also add in a factor for the current increasing with the higher voltage (it may or may not be exact because the resistance can change with temperature and the element will not always be at the same temp), then that 170 watt element could be as high as 240 watts and and current into the 12ga range at nearly 17 amps.


Of course, without knowing the rating point, the only way to know is to test at different voltages.

[avanti]

Most wires and cables have identifiers printed on the insulation. You need good eyes or the 'microscope' app on your phone.

[booster]

Originally Posted by avanti

Most wires and cables have identifiers printed on the insulation. You need good eyes or the 'microscope' app on your phone.

And, as always, buy name brand wire. I have seen lots, and I mean lots, of import inexpensive wire that was severely undersized for gauge like 18ga rated as 16 or 14ga. Also the heat rating where 105*C wire insulation melts off from shrinking heat tubing.

[ChicagoTom]

I'm not replying to start the great run or don't run while driving debate, but mine is running on propane while driving. The 12V is useless and can cause more harm than good. It won't auto switch off of the 12V and if you forget to shut it off, you will quickly kill your battery and possibly damage it. If you don't want to run on propane while driving, you can either run the generator for about 15-20 minutes every couple of hours and it'll have the same effect, or you can simply flip it on propane when stopping for lunch etc. It'll also have the same effect. I replaced my 2354 a couple of years ago with the same model. The first thing I did was disconnect the useless, IMO, 12v. I gutted my old one for spare parts, but can't recall if the 12 and 110 elements could have been removed without removing the fridge. Mine was already out. BTW, if my 110 element went out, I would simply run on propane 100% of the time. You can run a fridge 24/7 for about 30 cents a day. Ex HVAC tech for what it's worth...

[peteco]

Originally Posted by ChicagoTom

I'm not replying to start the great run or don't run while driving debate, but mine is running on propane while driving. The 12V is useless and can cause more harm than good. It won't auto switch off of the 12V and if you forget to shut it off, you will quickly kill your battery and possibly damage it. If you don't want to run on propane while driving, you can either run the generator for about 15-20 minutes every couple of hours and it'll have the same effect, or you can simply flip it on propane when stopping for lunch etc. It'll also have the same effect. I replaced my 2354 a couple of years ago with the same model. The first thing I did was disconnect the useless, IMO, 12v. I gutted my old one for spare parts, but can't recall if the 12 and 110 elements could have been removed without removing the fridge. Mine was already out. BTW, if my 110 element went out, I would simply run on propane 100% of the time. You can run a fridge 24/7 for about 30 cents a day. Ex HVAC tech for what it's worth...

For some reason the 12v works for some people and not others. 12v will generally hold my 5 cu ft RM2554 fridge temps while driving. That's all I use it for. And yes, I do need to make sure I switch to gas or 110 when I stop driving. It is safer to drive with the fridge on 12v, though sometimes I run with propane for convenience. Need to cut off propane when fueling or going through tunnels.

[Bryan JR]

The 12V worked for me. After leveling, I keep engine idling until I turn on gas at site and switch over fridge. Ice cubes frozen on last outbound trip at destination site, but were melted about halfway home.

[GallenH]

You can, but I'm not sure it's that necessary. As I pointed out earlier, my 125w element draws about 10 amps. It's my understanding that the fridge left on for one hour then would draw 10AH. When the engine is off, it's going to draw that power soley from my house battery. But that means that for every minute you are drawing only (10AH/60 =) 0.17AH. IMO not very much.

I believe, however, if your fridge automatically senses source and "knows" which one is currently available, you should read what the mfg has to say about that type of switch-over. It might be exactly what you're doing.

[GallenH]

Re LP or 12v when driving. I've done both and likewise have no interest in re-energizing any debate on this issue. My fridge is older than most on this list: a RM2310 dating from the 90s. The original install/operation manual does recommend that if you have a model with 12v, you should install an ignition activated relay to the 12v source line that would automatically turn off the 12v heating element when the motor is switched off. PleasureWay didn't and I haven't. Just that Dometic did see it as an issue.

I once forgot it on 12v when I went into a visitor center and proceeded on a tour of the park (in their shuttle). Rookie error. Although we were ok all the way to bed time, we were awoken in the middle of the night to beeping from the LP and CO detectors signalling their power was too low to operate. Had to run the engine for a bit.

[OldPilot]

Well, I do have a question about LP on the road. It seems to me that the flame may be getting "blown out". No way to really tell. It's just that everytime I go, it seems the fridge ends up being warmer. The bottom on my RT, rear of fridge has a screen opening. You can see the ground. Do you think there could be too much air flow from there?

Oops. Sorry. Maybe wrong forum. I'll check one for refrigerator.

[JohnnyFry]

I use Propane on the road and have not experienced this problem. OTOH: my RM2554 is auto ignition so it could blow out and be reignited automatically. I suggest that you take a close look at the baffling on the boiler unit as this could be a problem. Regarding the power draw of the electric element, my 12 volt draws 14 amps indicating a wattage of 175 Watts at 12.5 volts. Even at that it is not terribly effective. The 120 volt draws 2.2 amps giving 264 watts and it works much better. I replaced my fridge about 7 years ago so that the manufacturer may have been suppling heavier elemants by that time.