Powering a 12 Volt refrigerator via USB port

Rob Culver · 01-16-2024, 12:07 PM

Hello all,
I've got a 2023 2720 QS Trailmanor. I was considering getting a small, perhaps 3 cubic foot 12 Volt compression refrigerator. Something which could run on less that 100 Watts or 8 Amps at 12 volts DC.

Does anyone have information about what type of USB ports my model of trailmanor has and what they are capable of as far as supplying 12 volt DC power?

Looking at the attached picture, I believe that the 4 ports are of type A which supports a square shaped connector. It says Charging Only printed on the outlet. I had no trouble charging a cell phone with one. But is it 12 volt power being supplied and with how many amps maximum?

Does anyone have experience powering a small 12 volt refrigerator or any other appliance via one of these ports? Thanks in advance.

Shane826 · 01-16-2024, 01:00 PM

If that is off the old 12V receptacle wiring, it’s like a 7.5A fuse… So I wouldn’t count on it powering that cooler.

Rob Culver · 01-16-2024, 01:55 PM

Quote:

Originally Posted by Shane826

If that is off the old 12V receptacle wiring, it’s like a 7.5A fuse… So I wouldn’t count on it powering that cooler.

Hi Shane. I don't know if it's the same as earlier years. Mine was built in 2022 but it's technically a 2023. Would each port have it's own 7.5 amp fuse? If so, I suppose two ports could be combined potentially in a custom connector.

My experience with residential compressor AC refrigerators in RV's running through an inverter still only drew about 5-6 amps from the battery on average. But the peak draw could still go over 7.5.

**Bill** · 01-16-2024, 03:59 PM

A USB port produces 5 VDC, not 12 VDC. Most USB ports can provide a max of an amp or two. This, of course, is nowhere near what you need.

Trail Manors used to have a cigarette lighter outlet similar to the one in the picture. This is what Shane was referring to. It could supply 12 VDC at about 8 amps max. If you had one of these outlets, you could plug the small DC compressor refrig you mention into it, but the outlet is on the edge of being inadequate for an 8-amp load. The other downside of these things is that they tended to overheat when run near their max rating. Bad idea.

If you buy a refrigerator that will operate on 12 volts DC, you could have it hard-wired into the TM electrical system. Not a big deal, since the required connections are in the back of the refrigerator cubby.

If you buy a refrigerator that will operate on 120 VAC (house power), you could plug it into a normal household outlet when AC power is available at your campsite - again not a big deal since there is an AC socket in the refrigerator cubby. Or you could buy a small inverter (maybe 200 watts) and use it to run the refrig on 12VDC when AC power is not available.

But USB is not an answer.

Bill

Rob Culver · 01-16-2024, 04:55 PM

Thanks Bill for all that great info. You say there are 12 volt connections in back of the refrigerator cubby. Makes sense since the 3 way fridge already there can run on DC. So presumably you'd have to remove the refrigerator to get at that 12 volt? Sounds fairly straight forward but still a project.

Another possibility would be to get a portable power station. Basicly just lithium batteries with a built in inverter. And then the fridge could run off of an AC outlet on the power station. My Truck has 400 watt AC outlets to keep it charged when driving.

Just as a long shot question, can you think of any easy spots to pick up 12 volts towards the right side of the TM, that would involve only very minimal work to get at?

Thanks again!

Shane826 · 01-16-2024, 05:24 PM

You wouldn’t have to remove the fridge, just the outside vent cover behind the fridge. Is it a 3-way fridge (gas, electric, battery)? If so, the fridge and fan probably pull a solid 14-16 amps going down the road and they are on the same 20 amp fuse. If you added your mini fridge and had it cooling while going down the road, you’re likely to blow the fuse (not to mention kill the battery quick).

Maybe go a little further and tap into the 12V circuit coming off the water heater ignition? That’s a 20A fuse, and it’s shared with the CO/LP detector and the radio antenna (power is killed to both while going down the road) along with the storage lights under the bed. Those are all pretty low draw devices.

Is there an empty fuse slot? If so and you’re really feeling adventurous, run a dedicated power supply. Folks have managed to fish a wire under the bathroom floor from the power center to underneath the cabinets.

Here’s a pic of the 12VDC side of the schematic.

Rob Culver · 01-17-2024, 10:34 AM

Thanks for that Shane. Yes I have the 3 way fridge and with my battery monitor I noticed that it pulls a ridiculous 14 amps in DC mode with the fan on. I doubt I'll ever use it in that mode because of that.

I found the outside Dometic Vent you mentioned as shown in my attached picture. How is that removed? I tried making those black tabs at the bottom horizontal and then trying to pull the vent off but that didn't work. Is there a trick to getting that vent off?

Shane826 · 01-17-2024, 11:29 AM

Regarding the cover… See the slots on the knobs on the four corners? Stick a coin into the slots and turn them 90° and the covers come right off.

The DC mode is to keep the fridge cool during travel. You really shouldn’t use propane since the vents are covered. But it is a ridiculous draw and unfortunately most vehicles 12V+ charge circuit on the Bargman 7-pin can’t keep up. Mine will run a 2-3 hours while towing and then the battery is completely flat. I’m installing a dorm fridge and inverter. Cooling while towing is a big part of the reasons why.

Rob Culver · 01-17-2024, 12:30 PM

Thanks Shane,
I tried turning those knobs vertical before but I was afraid to use enough force to pull out the vent for fear of breaking something. But it worked!

That's quite a close quarters bundle of wires and electrical components under there. Would help to have tiny hands to to work there.. lol. I can see though that it would be easy to come out the side of the cubby, cutting a hole near the cable outlet plug and bringing the 12 volt out that way. Not sure if I'll do that but it's certainly an option. Thanks!

**Bill** · 01-17-2024, 02:00 PM

Just FYI, I find that some of those corner knobs have to be turned to vertical to come off, and some have to be turned horizontal. Annoying, isn't it? I end up turning one button at time, 90* from wherever it starts, and pulling gently on the corner of the panel to see if it is loose.

I'm not sure if cutting a hole in the side of the cubby, and bringing wires to the under-sink area, will help you a lot. You still have to connect your new wires to something, and the under-sink area has poorer access and smaller wires than behind the refrig.

Another idea. I rely on our 3-way frig, but I don't power it up on the road. It is actually a pretty good cooler. Assuming it is nice and cold in the morning, I just turn it off while I travel, and food is still cold/frozen after several hours. In your case, the advantage of doing that would be that you could connect new wires (for the compressor refrig) directly to the existing connections on the back of the 3 way frig. Access to those connections is easy. My Dometic 2354 is shown below, and you can see the arrow for the 12-volt terminal block at bottom center. If you have a Norcold, 3-way refrig, it is similar.

Of course, once you are in a campground, you will want to run both refrigerators, and as Shane suggested earlier, the 12-volt fuse may not carry as many amps as you need. The answer would be to run the 3-way frig on either 120VAC if you have it, or propane.

Bill