Refrigerator Battery Protection

AnOldUR

We switched to a 12V chest refrigerator on a slide that has battery protection. The problem is that it relies on a voltage reading taken at the fridge. When the fridge is running there is a significant drop in the reading that does not reflect the actual voltage of the battery. It's been brought up here many time that you can't determine a batteries state of charge when under load or charging. The 54qt chest fridge that replaced the original works fine because the protection level is adjustable, but we purchased a 21qt for additional space that is permanently set to fault out at 11.3V. It's been a challenge to keep it running.

This post is mainly to vent and let you know that if you get one of these 12V chest refrigerators, be sure the battery protection is adjustable.

Sharon_is_SAM

@AnOldUR - good to know.  Our ARB has the adjustable voltage cut off. 

 What about beefing up the wiring to the 21 qt?  Less voltage drop sensed?

AnOldUR

Hi @Sharon_is_SAM. We just got home from our trip that included uCamp. We actually purchased this 21qt while at uCamp and had it drop shipped to the Sugarcreek Post Office. I also was thinking voltage drop as contributing to the problem. The length of the wiring to the cigarette lighter outlet along with the 12' x 16 ga power cord can't be helping. I found a 6' cord for an ARB that works. I'm also going to add a cigarette lighter outlet to our tongue box with a short run directly to the battery. Not sure if this will be enough to help.

Sharon_is_SAM

Yes, I think decreasing the power cord and length and gauge should help.  With the 12V outlet in the tub, a short run will help.  Are you limited in wire size with the 12V outlet?  

Grumpy_G

Do you still have a 12V socket/plug connection going to the fridge ? Depending on design/quality these can add quite a bit of voltage drop. A couple of years ago I helped a friend that had replaced the 3 way with a 12V cooler style compressor fridge and it had the same issue until we hard wired it. 

AnOldUR

The lighter outlet coming has 3' of 12AWG wire. The little compressor fridge only draws between 2-3 amps. We have two 12V AGM batteries in parallel with all the loads attached to the positive on one and the negative on the other. I'm wondering if attaching the leads for the cigarette port to the opposite posts of each battery will isolate it from draws from other devices?

AnOldUR

Interesting @Grumpy_G. Both fridges are using cigarette lighter plugs. The one used to power my larger 12V fridge could be hard wired and that might improve the voltage drop I'm seeing. I'd like to keep the plug on the smaller fridge because we use it in different vehicles while traveling along with outside the trailer when camping.

AndreO

Hi @AnOldUr, Not saying it's convenient however the purpose of the voltage restriction at the cooler end is to protect its components from low voltage damage. It can't be adjustable for that reason.

The 2-way fridges also have the same protection. On my 2018 400, the compressor won't run below a specified voltage to protect itself however the fan will, hence no cooling. Infact the running fan fooled me into thinking everything was fine when in fact it actually caused an extremely high battery drain as the compressor kept recycling in an attempt to cool the fridge.

The only thing you can do is improve the voltage provided to the cooler. This could take one or more steps to rectify depending on your battery, cabling and extentions guages, connections and charging situation.

Hope this helps!

Sharon_is_SAM

AnOldUR said:

The lighter outlet coming has 3' of 12AWG wire. The little compressor fridge only draws between 2-3 amps. We have two 12V AGM batteries in parallel with all the loads attached to the positive on one and the negative on the other. I'm wondering if attaching the leads for the cigarette port to the opposite posts of each battery will isolate it from draws from other devices?

@AnOldUR - most owners with dual battery setups are using 6 volts in series, so I am not sure how your idea would effect voltage vacillations.  Good question for our forum electrical gurus.

AnOldUR

Fingers crossed, but I may have a working solution. Finished rewiring and began running a test. I installed a dual plug outlet on the front of our tongue box. One side is a 12V cigarette outlet. The other is USB with a voltage display (since there was no voltage display on the smaller fridge). The voltage display on the large fridge is reading 11.1V with it running. The display on the new outlet reads 12.5V even with the small fridge running. That matches the reading on the Victron app.

The new wiring is now going to the terminal blocks with the rest of the loads, but if any of the electrical gurus that @Sharon_is_SAM mentioned read this, I'm still curious if there would have been any advantage to connecting to the other posts?

Still need to clean up the spaghetti wiring and run the battery down enough to confirm the results.

Denny16

No, you get the same voltage and amps. The best practice is what you are doing, this way both batteries stay balanced, and discharge at the same rate.
 Cheers 

Sharon_is_SAM

@AnOldUR - so why the difference in the voltage at the large frig?  What do you have for wiring?

AnOldUR

@Sharon_is_SAM when I pulled out the 3-way fridge I used the 12V wire that fed it to power the new chest fridge. On my 2020 320S the fridge was on its own circuit (F4) with a 20 amp fuse. My guess is that the lower voltage reading when the fridge is running is because of the length of the run from the fridge to the panel and then to the battery. I wouldn't think that the 2.5 amp draw would cause that, but I have no other explanation.

subkron

Assuming you have decent guage wire (10,12AWG), 1.4V drop for 2.5A is a lot for just wire. For example, if it is 12 awg it is about 1.6 millohms per foot, so with 2.5A you drop about .008V per foot (since you drop on + and - wires). But you willl have drops at each connection point and across the fuse, the sum of all still seems like it should not be 1.4V. You may want to check each connection point to make sure they are solid.

AnOldUR

@subkron I haven't checked to see what gauge wire nuCamp runs from the fridge to the panel, but the drop may have been in the connections or maybe the small fuse in the plug. At @Grumpy_G 's suggestion above, I removed the cigarette plug and hardwired our larger fridge. Doing this also eliminated about 8' of 16 gauge wire. Now I'm only seeing about half a volt of drop according to the readout on the fridge. At my current state of charge, it reads 12.3V until the compressor kicks on, then it drops to about 11.9V while a reading directly at the battery remains close to 12.3V.

Thanks for the help everyone! It looks like the new wiring will reduce the risk of the small fridge shutting down due to low voltage and I have the additional bonus of having improved the efficiency of the main fridge.