12v Fridge Compressor Won't Kick On Even With Full Batteries

wegotchiu

New member
Hi all.

I'm running a Whynter FM-45G fridge connected to 200ah of house batteries and 200w of solar. During the day, when I'm getting sun and the batteries are running a surface charge of 13.0v or more, the fridge works great. When the batteries come down to what I understand is an actual full charge of around 12.7 or so, the compressor in the fridge tries to come on, but it initially takes the voltage draw down below what it is perceiving to be <10.0v on it's LCD display (even tho my MPPT charge controller is reading no actual drop), and since it has a setting to keep from running your batteries down that cuts out at 10.0v, the compressor won't come on. When it's actually running, it shows on the display that it's about 2.5v or so less than what the charge controller is saying.

I've considered that maybe I'm running it too far a distance to my batteries and getting a voltage drop, but other than that I'm stumped (and that would be a very difficult problem to solve, as the fridge is near the rear driver wheel well and the batteries are under the passenger seat, with wiring running first to the switch panel by sliding door).

Any help would be much appreciated, thank you!

Link to fridge model: https://www.whynter.com/product/fm-45cam-whynter-45-qt-portable-fridgefreezer-camouflage-edition/

Consumption chart: https://1e18z23t25kn1a9twkg87cma-wp...ontent/uploads/FM-45G-Comsumption-Chart-1.pdf
 

danpaul000

A man, a van, no plan
Sounds like you have a big voltage drop over your wire run. What is the length of the wire and its Gage? The fridge should specify what the startup current of the compressor is. With these the numbers you can calculate using online tools what you drop will be at this point. You can also do a test with some heavier gauge wire and just run this from your fuse block to the fridge with putting it behind the walls until you are sure this is the issue.

Dan

Sent from my moto x4 using Tapatalk
 

john61ct

New member
Yes check for voltage drop, too thin a gauge wiring or poor quality connections. Measure both ends with a decent DMM.

Also your battery bank may not be healthy, or large enough AH capacity.
 

HarryN

Active member
Sorry to say it is a typical problem.

More or less need the battery to be very fully charged and a short 10 awg run right from the battery to the fridge - nothing else in between.

If your charge controller is stopping at 13 volts it is the wrong type.
 
Last edited:

john61ct

New member
Any charge source out of the box is 99% sure to undercharge.

Should not be dropping from Absorb to Float until trailing amps drops to say .005C, or half an amp per 100AH bank size.

Full user adjustability is the key.

A PSOC abused battery won't last long.

Distance between the bank and fridge is NBD as long as the wiring is good quality and robust, heavy enough gauge to minimize voltage drop and well-crimped terminators.

I would not bother with less than 200AH, 2x 6V GCs for best value.
 

wegotchiu

New member
The wiring is all 12awg but it does go through a switch panel. Going to go check all connections and do the test run direct from fridge to fuse block as well. Will report back, thank you!
 

Midwestdrifter

Engineer In Residence
A single loose spade terminal, or weak/cheap fuse can drop a volt or more at 4A. I had some trouble with my fridge due to a spade connector that got tweaked on install.

FYI an easy way to probe voltage at the fridge when running (on danfoss/secop units) is to measure the voltage at the fan. The fan should see battery voltage when running.
 

HarryN

Active member
The wiring is all 12awg but it does go through a switch panel. Going to go check all connections and do the test run direct from fridge to fuse block as well. Will report back, thank you!
Perhaps test what happens by using a direct 10 awg connection - nothing at all in between. If it works then it is wiring - otherwise it is just too weak of battery setup. A blue sea fuse block can have a lot of loss.
 

john61ct

New member
Yes rewire from a big load buss near your battery directly to the fridge, no intermediary connections.

If the overall actual wire path distance is more than 10' go up to 10 AWG or fatter. A fuse should be very near the source end sized to protect the wire, for #10 say 40A.

Make sure all terminations are good quality and properly crimped.
 

ddunaway

Member
You can also adjust cut out voltages on this model but larger pipe as suggested is better........
 

wegotchiu

New member
Re ran the wiring to bypass the switch panel and took about 5ft of run length off as well...and it's working great! Much appreciated!
 

Wildebus

New member
This chart might illustrate why thicker cable then one might expect is needed ...
Every time the compressor kicks in, there is an in-rush which lasts just a few seconds.
I sample the data every minute, so this momentary in-rush is not always captured (but does always happen)

Fridge Spike
by David, on Flickr
Fridge usually draws 35W when compressor on - spike increases that massively.

Not sure if US and UK standard are same (same electricity so should be, but different bodies see things differently), but a 12AWG cable is referred to as a 4mm cable in UK and has a rating of 41A in free space on minimal run.
This is the current draw on the spike above

Fridge Spike Amps
by David, on Flickr
And actually should add 16.4A (coming from Solar) onto that 47.1A draw - so that would be like 63.5A being pulled from the battery during the night - 95% of it due to the fridge.

So 10AWG would be a better cable option for anyone doing a new install unless you are nice and close to the house batteries (or even 8AWG if a distance).
(I am running an AC compressor fridge so via a 400W inverter (which does 900W peak so is ok on rush-in spike) and I am running 6AWG Cable for around 15 inches from battery posts to inverter inputs)
 

john61ct

New member
Most efficient DC compressor fridges burn 4A or less while cycling, and many electronics now include soft start features to reduce the startup surge.
 

Top Bottom