CFX3 fridge issue: Lower volt readout on primary battery—but Jeep shows higher volts on display. Won’t keep cooler cold.

[Jems007]

my fridge won’t stay cold when hooked direct to battery, but works when I connect to a real 12v system off the Jeep. I’ve tried it direct to battery and also off the 15a and 40a aux switch. I’m using 14 ga cable so that shouldn’t be an issue either.

On Jeep, My CFX is showing about .5 to 1 volt lower than the battery reading inside the Jeep, for example, the fridge shows 12v and the Jeep shows 13v on the battery display. This somehow isn’t letting my cooler to get below 45 or 50 degrees—so I have to bring my spare 12v in the meantime.

is this because the two battery system isn’t equalizing the voltage between the starting battery and the aux battery? Do I need to run a jumper to the N1 and hook my coolers hot wire up to that?

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[Mr._Bill]

If you have not modified the electrical system, everything runs off the primary battery. The auxiliary (ESS) battery is primarily for keeping all the computer systems stable during an ESS event.

 

[Mr._Bill]

14 gauge seems a little thin for a fridge, I would try 10 gauge. If you plan to have the fridge in the truck on a regular basis, you would be a good candidate for a Genesis dual battery setup.

 

[jebiruph]

my fridge won’t stay cold when hooked direct to battery, but works when I connect to a real 12v system off the Jeep. I’ve tried it direct to battery and also off the 15a and 40a aux switch. I’m using 14 ga cable so that shouldn’t be an issue either.

On Jeep, My CFX is showing about .5 to 1 volt lower than the battery reading inside the Jeep, for example, the fridge shows 12v and the Jeep shows 13v on the battery display. This somehow isn’t letting my cooler to get below 45 or 50 degrees—so I have to bring my spare 12v in the meantime.

is this because the two battery system isn’t equalizing the voltage between the starting battery and the aux battery? Do I need to run a jumper to the N1 and hook my coolers hot wire up to that?

On a working system, the batteries are always in parallel (equalized) except when auto stopped. You're probably seeing the voltage drop due to the resistance of the wire, thicker wire will have less resistance and less voltage drop.

 

[Forum Crawler]

my fridge won’t stay cold when hooked direct to battery, but works when I connect to a real 12v system off the Jeep. I’ve tried it direct to battery and also off the 15a and 40a aux switch. I’m using 14 ga cable so that shouldn’t be an issue either.

I use 10 ga for a fridge.

 

[Jems007]

Fine, I’ll rerun some 10ga.
I kinda figured but was hoping that wasn’t the answer. I should have just busted out my volt meter prior to bothering you all ?

 

[CrazyCooter]

14ga wire is plenty for the 3Amp load! I'm running two ARBs in my back seat off of the constant 12v power in the aux switch bundle. My coolers do read much lower than actual voltage, so I run the battery protect one setting less than normal.

FYI, I also see consistently lower voltage when using the cooler in my YJ with its dedicated spare battery and 10ga wire.

 

[Jems007]

even when battery protect is on low I can’t get to the temps below 40 that I need. Works fine plugged into my 115 inverter and on my RV 12v. I’m probably running about 15’ of 14g to the bed outlet. Tomorrow I’ll put a multimeter on the batter to ensure it matches what the system says.

Worst case, can I increase wire size further back or do I need to re run bigger wire all the way?

 

[j.o.y.ride]

even when battery protect is on low I can’t get to the temps below 40 that I need. Works fine plugged into my 115 inverter and on my RV 12v. I’m probably running about 15’ of 14g to the bed outlet. Tomorrow I’ll put a multimeter on the batter to ensure it matches what the system says.

Worst case, can I increase wire size further back or do I need to re run bigger wire all the way?

If wire gauge is your problem then replace the whole thing.

 

[just_another_guy]

Is your fridge shutting off when the truck isn't running? That would make sense because the voltage drop from your small gauge wire could trigger the undervoltage protection in the fridge.

When you say the truck's battery is at 13v, it makes it sound like the engine is running.

 

[Jems007]

Is your fridge shutting off when the truck isn't running? That would make sense because the voltage drop from your small gauge wire could trigger the undervoltage protection in the fridge.

When you say the truck's battery is at 13v, it makes it sound like the engine is running.

It never shuts off it just doesn’t get below 45 or 59 degrees. Even when driving on highway. But it does if I hook to another 12v.

 

[just_another_guy]

It never shuts off it just doesn’t get below 45 or 59 degrees. Even when driving on highway. But it does if I hook to another 12v.

That's pretty strange because the fridge should be working at any voltage above the shut down threshold. This is sounding more like a fridge problem if it's failing to cool down without shutting off.

And the fridge works fine if it's hooked to a 12v battery that's not even connected to the charging system?

 

[Jems007]

That's pretty strange because the fridge should be working at any voltage above the shut down threshold. This is sounding more like a fridge problem if it's failing to cool down without shutting off.

And the fridge works fine if it's hooked to a 12v battery that's not even connected to the charging system?

Yes. So I usually connect via 12v to my RV batteries and it gets to 30 degrees FAST. Same with the 115v in the Jeep. It’s just when I connect it directly to the battery. I thought maybe a ground issue but now I’ve routed it directly to the negative terminal as well. I ran the wires from battery, down the frame, to the bed to my 12v marine outlet.

It’s only when connected to the truck battery 12v that it can’t get cold fast enough. I was driving an hour and it wasn’t even to 50 degrees. As soon as I swapped the 12v to my RV it was down to 30 within 30 min or so.

 

[Rokon]

Try connecting to your RV battery with 20’ of 14g wire....

 

[just_another_guy]

Yes. So I usually connect via 12v to my RV batteries and it gets to 30 degrees FAST. Same with the 115v in the Jeep. It’s just when I connect it directly to the battery. I thought maybe a ground issue but now I’ve routed it directly to the negative terminal as well. I ran the wires from battery, down the frame, to the bed to my 12v marine outlet.

It’s only when connected to the truck battery 12v that it can’t get cold fast enough. I was driving an hour and it wasn’t even to 50 degrees. As soon as I swapped the 12v to my RV it was down to 30 within 30 min or so.

Was the compressor in the fridge running when you measured that 0.5-1v drop? And do you know if your fridge will kick back on when the voltage raises after a low voltage shutoff event?

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