The Mystery of the Rotting Bacon: 12V weirdness

[Peony]

I don’t know why this would be happening, but to me, it sounds like you may have a voltage drop when the compressor kicks in. Can you hear the compressor start up when you first connect the fridge? Do you know if the fridges holds the temperature and runs fine for a while, and fails later?

Ideally, connect a volt meter as close as you can to the fridge and see if you see a voltage drop when the compressor kicks in. Even if you have a 10 ga wire, you can have a poor connection somewhere on the way to the fridge.

Alternatively, and this will be a bit destructive and maybe not something you feel comfortable doing, remove the cigarette connector from the fridge cable, optionally (but highly recommended) connect it to a 12v inline wire fuse, and then DIRECTLY hardware it to the battery, and see if that works. That’ll bypass any poor connections in your trailer wiring system. If it works now, you know it’s a wiring issue inside the trailer.

 

[medora]

Thanks Peony. The primary 12v outlet has an inline fuse and is hardwired directly into the battery. That’s ultimately what you’re suggesting right?

Per voltmeter - the dometics show the voltage when running and it always is within a reasonable range 12.9-13.2). Yet another reason why this baffles me.

 

[Peony]

Thanks Peony. The primary 12v outlet has an inline fuse and is hardwired directly into the battery. That’s ultimately what you’re suggesting right?

Per voltmeter - the dometics show the voltage when running and it always is within a reasonable range 12.9-13.2). Yet another reason why this baffles me.

No, that’s not quite what I meant.

If you pardon the crude drawing (that looks at this at the system level and ignores some electrical technicalities), your system looks like the attached diagram (the black lines).

When you connect to the 110V system it works, when you use the 12V system, it doesn’t work.

The most likely explanation is a voltage drop when the compressor starts. You’re probably fine when it’s running, the amps drawn then isn’t huge compared to the moment when it starts. It’s getting the compressor started that’s the issue for most 12V systems. The voltage drop you’d be able to see is probably just for a fraction of a second, but if it happens and is severe, your compressor won’t start and your fridge turn off. I’d use a multimeter or even better a high resolution voltage data logger, and not trust the instrument on the Dometic.

If the battery is fine, then the likely culprit for the voltage drop is either the wiring inside your trailer (could be either the positive or negative side) OR the 12V cable to your fridge. Since it’s happening on both fridges, it’s more likely to be on the trailer side.

So I’m proposing the temporary wiring in the green. If you remove the cigarette plug from the cable (there’s usually one screw holding it together, and then one each for the two wires — note which is positive and negative before taking it apart!), you can (again, ideally via a new not previously used in this system inline fuse) connect these two wires directly to the battery, totally bypassing the wiring inside your trailer, on BOTH the positive and negative side. If the fridge now runs well, you know where the problem is.

 

[Peony]

And if you feel uncomfortable doing this type of electrical work, stay away from it — make sure you don’t short circuit the battery (you may start a fire and/or hurt yourself) - or accidentally flip the positive and negative on those wires (you may damage your fridge).

 

[Ron in BC]

Thanks for letting me know about success with the Bodega - curious if you know which model?

Looked it up on Amazon and didn't see the same 2 lid model. Seems like most are now the wifi enabled types. I'll look at the real one later.

Ron

 

[Ron in BC]

N

If the battery is fine, then the likely culprit for the voltage drop is either the wiring inside your trailer (could be either the positive or negative side) OR the 12V cable to your fridge. Since it’s happening on both fridges, it’s more likely to be on the trailer side.

I think we're on the same page. That's why I previously made the comment that I'd like to see one of the fridges run off some other outlet independent of the trailer one.

Or the trailer battery with a cigarette lighter outlet connected directly to it. They do make cigarette outlets with alligator clips.

Ron

 

[medora]

Ron, Perry, I can try this but I’m still not sure how it’s different from having a 12v outlet with 10 ga wire connected directly to the battery’s positive and negative?

Would the initial V draw on 12v be mitigated by the Ecoflow/ac plugs?

Ron, I’ll test to see exactly when the fluctuations are. Guests in town this weekend so might not be until next week.

 

[Ron in BC]

The fact that there's a 10ga. wire from the battery to the plug makes it seem like there couldn't possibly be a problem in that area. It's easy to overlook that you also have an ETI installed outlet that the fridges have the same problem with.

I don't know how ETI has wired in their outlet and how they've hooked it up.

Looking at anything both situations have in common the only thing that I know for sure is that they both use a negative ground. So maybe taking a really good look, even removing and checking for corrosion might be worthwhile.

Ron

 

[Mike G]

Do you know the rated wattage draw of each cooler? Maybe they are trying to draw more watts than what the outlets can provide, whereas the EcoFlow could provide the watts for a short burst (and then ran out of juice).

 

[vermilye]

Ron, Perry, I can try this but I’m still not sure how it’s different from having a 12v outlet with 10 ga wire connected directly to the battery’s positive and negative?

Would the initial V draw on 12v be mitigated by the Ecoflow/ac plugs?

Ron, I’ll test to see exactly when the fluctuations are. Guests in town this weekend so might not be until next week.

While the wire gauge is adequate, many of the 12V receptacles are not good for more than 5-7 amps. I've had 12V cigarette connectors to small inverters & my 90 watt MacBookPro 12V power supply overheat & fail. The tip often got so hot it burned if you touched it.

It may not be a 12V problem; just a connector problem. I prefer Anderson connectors to either SAE connectors or 12v "cigarette" type.

 

[DragonDM]

Hmm.. I have a factory installed 12v compressor fridge in my 21C, and it works quite well.



I have used a 12v chest fridge/freezer in a previous RV, and it worked fine as well (wasn't a Dometic) I had the 12v cord for that one wired to the 12v fusebox with screw terminals.



I've found the cigarette-lighter style plugs to be a bit unreliable for anything high-current. I would suspect it to be the 12v cord/plug for your coolers. If there's any extra resistance in the 12v plug or cord, it will cause the voltage to drop when the compressor kicks in and starts drawing current. If that drops below the low voltage cutoff, the compressor will stop.

 

[JaneNScott]

We have used this Bodega 12v cooler on and off for years (often for a couple months at a time).

https://a.co/d/7RLSeRj

Plugged into 12v most times it was used.
Worked great but it did get pulled out of a 12v outlet once.

We have a temperature sensor inside (Bluetooth) to double check temps as the ones on the Bodega (cooler and app) seem to be the air and not necessarily the items in it.

We have used it only as a freezer, temp’s can vary (eg add new cooled but not frozen items and it raises 10-15 degrees but still frozen food as it is typically -5 to 5 degrees F).

It takes 1-2 days to freeze solid new raw meat from the grocery store.

We have not used it as a refrigerator, just a freezer choosing the lowest temp’s possibly.
Overall we are very happy with it.

 

[CE Vogel]

My trailer is equipped with a 12V compressor refrigerator, and I have a Camco portable 12V compressor cooler plugged into a cigarette socket. Both work very well. There are two areas I suspect you may have problems. First, as others have said, the cigarette socket. Does the plug get warm while using? Is the plug easily jiggled when plugged in? If either is true, try replacing the plugs on your coolers with a different brand. Also, these coolers have low voltage shutoff settings. Try changing these to the lowest voltage and see if that helps. The low voltage shutoffs are not active when running on AC, which may explain why they work well on your EcoFlow power bank.