Powering Dometic fridge through 7 pin trailer connector

[Eugene the Jeep]

I’m looking to provide safe power to my Dometic fridge which will be in my Offroad trailer. I wired up a 7 pin connector on my Jeep that includes a 10 gauge aux power post in the trailer junction box. This wire goes directly to the starting battery and has a 40 amp circuit breaker.

From the 7 pin junction box on the trailer tongue I plan on wiring up dometic’s HWK-DC which is a wiring kit with two 12 volt outlets. The kits included wiring is also 10 gauge and has an in line 15 amp fuse. So from the fridge, to the junction box, through the 7 pin trailer plug in, to the Jeep starting battery is not more than 30 ft. of 10 gauge wire. I think the Dometic wiring kit came with 25 ft of 10 gauge wire.

So my questions are thus:
1. Is it safe to run power for a fridge through a 7 pin trailer connector?
2. Where should I put the in line 15 amp fuse? Can I put it near the junction box on the trailer tongue or should I remove the 40 amp breaker near the battery and put it there? This would make the aux power pin on the 7 way dedicated to the trailer, correct?

In the future I plan to install a solar/battery setup so the trailer can be totally independent from the Jeep.

All comments and suggestions are greatly appreciated.

 

[Deleted member 9101]

I'd put a fuse at each end.

 

[jonyjoe101]

As long as the 7 pin connector can supply at least 7 amps it should work. Most 12 volt fridge peak at about 7 amps during startup then settle at around 4 amps. But some 12 volt fridges require very stable power to run, too much voltage drop during startup and the compressor will cutout.
I was having problems over the summer with my 26 liter 12 volt fridge and the compressor cutting out when the battery voltage drop below 13 volts (lifepo4 system) .

I fixed the problem by using a boost/buck converter, the boost converter raises the voltage to 18 volts then the buck converter drops it to 13.4 volts. I been running it 24/7 for the past 3 months, fridge compressor hasn't cut out once from low power and the Li-ion battery bank I have been using lately has gone down to as low as 10 volts. The voltage on the converter is extremely stable, it only drops .2 volts when compressor is running.

If you run into any problems I recommend to use a boost/buck converter, it will cost maybe 20 dollars to build one. I prefer to build one, then to use a voltage stabilizer which output voltage might not be high enough. I tried 12.6 volts on my boost/buck converter but the compressor would cutoff from time to time. 13.4 volts was where it perform the best. It would definitely help with the 25 foot wire run, on mine I had a run of 10 feet. I was using mostly 12 gauge but changed that to 10 gauge and that didn't help. Only the the boost/buck converter helped me.

 

[Eugene the Jeep]

As long as the 7 pin connector can supply at least 7 amps it should work. Most 12 volt fridge peak at about 7 amps during startup then settle at around 4 amps. But some 12 volt fridges require very stable power to run, too much voltage drop during startup and the compressor will cutout.
I was having problems over the summer with my 26 liter 12 volt fridge and the compressor cutting out when the battery voltage drop below 13 volts (lifepo4 system) .

I fixed the problem by using a boost/buck converter, the boost converter raises the voltage to 18 volts then the buck converter drops it to 13.4 volts. I been running it 24/7 for the past 3 months, fridge compressor hasn't cut out once from low power and the Li-ion battery bank I have been using lately has gone down to as low as 10 volts. The voltage on the converter is extremely stable, it only drops .2 volts when compressor is running.

If you run into any problems I recommend to use a boost/buck converter, it will cost maybe 20 dollars to build one. I prefer to build one, then to use a voltage stabilizer which output voltage might not be high enough. I tried 12.6 volts on my boost/buck converter but the compressor would cutoff from time to time. 13.4 volts was where it perform the best. It would definitely help with the 25 foot wire run, on mine I had a run of 10 feet. I was using mostly 12 gauge but changed that to 10 gauge and that didn't help. Only the the boost/buck converter helped me.
View attachment 636496

Good to know. I'll only be powering the fridge this way while driving so it'll have the extra voltage from the alternator. Hopefully the voltage drop over the distance won't be significant enough to require a boost/buck converter.

When I wired the 7 pin on the Jeep side the instructions stated to put a 40 amp circuit breaker on the aux 12v power line so it seems that a fridge that draws 7 amps would be just fine. I guess it's the voltage drop over the 30 feet of wire that I'll look out for.

As for fusing, I like the idea of fusing on both sides. I'll use the existing 15 amp fuse that is in line on the dometic wiring kit next to the trailer junction box. Any suggestions for the best type of fuse to use next to the battery or does it matter? Would a 15 amp circuit breaker work? It would be very easy to swap a 15 amp breaker with the 40 amp.

 

[Ngneer]

As long as the 7 pin connector can supply at least 7 amps it should work. Most 12 volt fridge peak at about 7 amps during startup then settle at around 4 amps. But some 12 volt fridges require very stable power to run, too much voltage drop during startup and the compressor will cutout.
I was having problems over the summer with my 26 liter 12 volt fridge and the compressor cutting out when the battery voltage drop below 13 volts (lifepo4 system) .

I fixed the problem by using a boost/buck converter, the boost converter raises the voltage to 18 volts then the buck converter drops it to 13.4 volts. I been running it 24/7 for the past 3 months, fridge compressor hasn't cut out once from low power and the Li-ion battery bank I have been using lately has gone down to as low as 10 volts. The voltage on the converter is extremely stable, it only drops .2 volts when compressor is running.

If you run into any problems I recommend to use a boost/buck converter, it will cost maybe 20 dollars to build one. I prefer to build one, then to use a voltage stabilizer which output voltage might not be high enough. I tried 12.6 volts on my boost/buck converter but the compressor would cutoff from time to time. 13.4 volts was where it perform the best. It would definitely help with the 25 foot wire run, on mine I had a run of 10 feet. I was using mostly 12 gauge but changed that to 10 gauge and that didn't help. Only the the boost/buck converter helped me.
View attachment 636496

Sorry to butt in gotta say thank you for some valuable info right there Sir, please carry on.

 

[broncobowsher]

7 amp start and 4 amp run? That is a huge power sucking fridge. My Engle/ARB is a fraction of that. Before going of generalities get a meter and measure what you actually use.

My normal rig has solar. Just a little 70W panel. Not even a fancy charge controller, just a solid PWM version. I've run the fridge on straight solar (no battery at all) in an early morning in the winter with some tree shade as well. Good stuff does exist.

As for where to put a 15A fuse on that charge circuit. Put it where the wire gauge steps down. 40A to protect the 10 AWG. When you branch off that to power the fridge with 16 AWG (wait this is the internet, must oversize the wire, 14 AWG) that is where to but the 15A protection.

Are you running a seperate battery on the trailer? If so I would change the direct to starting battery and change that to a relay to isolate the trailer when parked. Relay powered when engine is running (charging system running) No seperate battery, be careful to not run down the starting battery while parked. Very easy to do.

 

[Eugene the Jeep]

7 amp start and 4 amp run? That is a huge power sucking fridge. My Engle/ARB is a fraction of that. Before going of generalities get a meter and measure what you actually use.

My normal rig has solar. Just a little 70W panel. Not even a fancy charge controller, just a solid PWM version. I've run the fridge on straight solar (no battery at all) in an early morning in the winter with some tree shade as well. Good stuff does exist.

As for where to put a 15A fuse on that charge circuit. Put it where the wire gauge steps down. 40A to protect the 10 AWG. When you branch off that to power the fridge with 16 AWG (wait this is the internet, must oversize the wire, 14 AWG) that is where to but the 15A protection.

Are you running a seperate battery on the trailer? If so I would change the direct to starting battery and change that to a relay to isolate the trailer when parked. Relay powered when engine is running (charging system running) No seperate battery, be careful to not run down the starting battery while parked. Very easy to do.

Hey thanks for the response. I’m not sure how many amps my Dometic uses but they’re suppose to be pretty dang efficient. My entire run of wire from the jeep starting battery through the 7pin, through a junction box is 10 gauge. Well I suppose the actual power cord for the fridge (the supplied 6ft? 12v style cord) is a smaller gauge. I did not think about this, but that is where the bottleneck occurs and it is at the furthest point away from the battery. So a 15 amp fuse there, closest to the fridge. And I was thinking another fuse next to the battery. Wouldn’t it be safest to do another 15 amp next to the battery as opposed to a 40 amp? I can’t think of anything else that I will be running off that aux power wire in the junction box.

The trailer does not have a battery yet. My plan is to hard wire a solar setup on my trailer with a couple golf cart batteries in the tongue box. I want to keep this setup independent of the Jeep. But until then I was hoping to power the fridge from the Jeep while driving and then plug the fridge into a portable lithium battery/solar Jackery branded unit.

 

[john61ct]

Amps ratings are pretty meaningless wrt energy efficiency.

The duty cycle is the key, and that depends on lots of variables, biggest factor is the contents being already pre-chilled

and the delta between your thermostat setpoint and ambient temps.

The vital benchmark to measure is Ah @12V consumed per 24hrs.

Best I've seen is 15Ah just drinks in moderate weather

up to 75Ah per day keeping ice cream rock hard in extreme heat.

As I said, the difference is not that much between the different DC compressor fridges

but more according to the use case.

That said, Engel and ARB are both efficient and long lasting in harsh conditions.