Dometic CFX 65W 12V Electric Powered Portable Cooler (Fridge Freezer)... Trouble.

[Richard Kollmann]

If you have confirmed that at Low battery protection there is still a compressor restart up problem 40% of the time it is the wiring between refrigerator and battery. I get this same complaint emails 3 to 5 times a month. I recommend troubleshooting to bypass all the the boats wiring, Switches, Circuit breaker, and wire connections with fused jumper large wire cables direct from unit to Battery

Very few technicians understand or have experience with small brush-less DC motor low voltage spikes. Very short duration spikes that you cannot see cause the electronic controllers to abort a compressor restart. There is no way to alter the design of a refrigeration unit to permanently resolve voltage spikes in boat”s power grid wiring. Attempts to lower starting amperage of a compressor known as Soft Starting will also not fix a low voltage spike problem. The only way is to isolate where the problem is by isolating it and replace the faulty item.

Most techs believe it is the module and and they send them to me to load test. In the last two years I must have tested around 100 Danfoss control modules finding 60% perfectly normal. When you get voltages before compressor start below 12.5 it is not the refrigeration units fault.

[roland stockham]

The issue hear is start-up power. fridges are notorious for it. When a motor is running it generates a voltage of its own, much like an alternator. As the speed increases the back voltage also increases until it all balances out giving the motor self regulation. If this did not happen motors would just keep acceleration to the point of self destruction under no load conditions. When the compressor motor connects but the coil is not turning there is no back voltage so the only resistance is the coil itself ie very low!! Fridges typically draw more than 3x there rated current at startup so that 8a is 24a for a moment. Lighter sockets are only rated 10a and even at that get pretty hot! for the fridge you need a good solid plug and socket rated to at least 20a or hard wire.
With a 10ft cable run and 10g wire if you have 12v at the battery you will be down to 11.5v at the fridge assuming no connection losses. At this sort of power I would not be surprised to loose a further 1v in the lighter plug & socket taking you down to 10.5 even with a well charged battery. ie it ain't gonna work!!!
To be sure you need to measure your cable run and calculate the voltage drop to keep it above the cutout settings.

[PetePetePete]

Ok. So... I just spent some quality time with this thing. And here's where we are.

I removed it from the boat.

I took the cigar plug off and fabricated a fused direct link to a battery. Placing a DMM in-line.

For the first test, I used a battery that was NOT FULLY CHARGED it was at 11.62v via DMM -- the meter showed 11.6v. When the freezer was off the voltage at the top of the app showed 11.4v. So that's off by .2v -- which is likely of little consequence.

When I run the unit, the DMM drops to 11.3v and the app drops to 10.5v That is .8v -- which is interesting.

I am going to put the battery on a slow-charge/tender and get it up to spec and then measure differences.

This is the exact same result I was getting on the boat. I also tested it with the "nipple" of the cigar lighter in place and, again, the same results. So this tells me that there is nothing wrong with the boat wiring or the cigar lighter - female or male end.

I am hesitant to pass judgement, but as of right now, I think that whatever circuitry is in this thing that "tells" it the current voltage is simply not calibrated correctly. From what I remember, when the battery is was fully charged, there was a MUCH larger difference between the voltage shown on the app (reading from unit) v. the DMM.

I will update once I have a fully charged battery and I can make a proper chart showing the differences, etc.

Thanks for all the terrific help with this. This particular unit is an integral part of our cruising -- we use it to freeze water bottles which we then transfer to coolers for refrigeration. I know it's not fancy, but we're able to stay out weeks at a time and never buy a single cube of ice on a pretty small boat with a family of four.

[PetePetePete]

Originally Posted by roland stockham

The issue hear is start-up power. fridges are notorious for it. When a motor is running it generates a voltage of its own, much like an alternator. As the speed increases the back voltage also increases until it all balances out giving the motor self regulation. If this did not happen motors would just keep acceleration to the point of self destruction under no load conditions. When the compressor motor connects but the coil is not turning there is no back voltage so the only resistance is the coil itself ie very low!! Fridges typically draw more than 3x there rated current at startup so that 8a is 24a for a moment. Lighter sockets are only rated 10a and even at that get pretty hot! for the fridge you need a good solid plug and socket rated to at least 20a or hard wire.
With a 10ft cable run and 10g wire if you have 12v at the battery you will be down to 11.5v at the fridge assuming no connection losses. At this sort of power I would not be surprised to loose a further 1v in the lighter plug & socket taking you down to 10.5 even with a well charged battery. ie it ain't gonna work!!!
To be sure you need to measure your cable run and calculate the voltage drop to keep it above the cutout settings.

See my most recent post. The cigar lighter has been taken out of the equation and the only wire run is the actual cord-set included with the unit. The voltage numbers are unchanged from the those taken on the boat. I tend to think that cigar plug being the culprit has been debunked -- but I shall continue to test different scenarios.

Additionally, there is .02v loss from the battery terminal to the point of plug in at the unit... so that is not of any consequence either.

I will report back once the same tests are conducted on a fully charged battery. I just wanted to use a depleted battery as to have varying data.

[roland stockham]

Yes it is sounding like a faulty unit. Not sure what you mean when you refer to a DMM unit in the previous post but to measure start up current you need a meter that will record peak volt/current spikes of around 1/100sec. Usually done with an oscilloscope I believe.

[PetePetePete]

Sorry... DMM = Digital Multi Meter... (A previous forum member used it so I used it too Hehe).

[OzePete]

Originally Posted by Richard Kollmann

If you have confirmed that at Low battery protection there is still a compressor restart up problem 40% of the time it is the wiring between refrigerator and battery. I get this same complaint emails 3 to 5 times a month. I recommend troubleshooting to bypass all the the boats wiring, Switches, Circuit breaker, and wire connections with fused jumper large wire cables direct from unit to Battery

Have to agree that most of these compressor start failures are as a result of a poor power supply. (Voltage drop on start up... not low voltage spikes!!!)

Very few technicians understand or have experience with small brush-less DC motor low voltage spikes. These are NOT "small brush-less DC motors" they are three phase AC motors!.Very short duration spikes that you cannot see cause the electronic controllers to abort a compressor restart. They are not 'low voltage spikes', the start failure is due to voltage drop as load is applied. See: Video tests and Data record. | Ozefridge

There is no way to alter the design of a refrigeration unit to permanently resolve voltage spikes in boat”s power grid wiring. Adding a spike arrestor AKA Zorb or Transient voltage clamp across the DC supply, will prevent near all high voltage spikes... they only cost a few cents but can prevent lots of damage.

Attempts to lower starting amperage of a compressor known as Soft Starting will also not fix a low voltage spike problem. Soft start modules have greatly reduced the type of start problems and module failures that were common to the old DOL modules. It is obvious that start up without the usual whack of start current is beneficial.. Soft Start compressor Motor Drive Modules | Ozefridge

The only way is to isolate where the problem is by isolating it and replace the faulty item.

Most techs believe it is the module and and they send them to me to load test. In the last two years I must have tested around 100 Danfoss control modules finding 60% perfectly normal. When you get voltages before compressor start below 12.5 it is not the refrigeration units fault.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

[Maka]

I am contemplating doing the exact same thing...making ice to go in my refrigerator/ now ice box with a Portable Cooler (Fridge Freezer).

Interested to see how this evolves.

[PetePetePete]

Originally Posted by Maka

I am contemplating doing the exact same thing...making ice to go in my refrigerator/ now ice box with a Portable Cooler (Fridge Freezer).

Interested to see how this evolves.

Hi Maka,

So... we've done this for several trips and it works flawlessly! The key is to not get lazy. Cycle the bottles. Don't wait for them to totally thaw. We use the 500ml Fiji water bottles with a "gel" additive (which I'm not sure if it's snake oil or not). The bottles are square so they use less space. We were using an Engel along with 2 110 liter rotomolded coolers. 2 Adults, 2 Children, and we always had plenty of cold drinks and had room in the freezer for stuff we wanted to keep frozen.

Again, the single biggest variable is to ensure that you do not get lazy with cycling the bottles. Keep a rotating stash of frozen bottles and the coolers stay safe-level cold.

Toward the end of the trip we generally drop it down to to one cooler and use the other cooler for storage.

Hope this helps...

[PetePetePete]

Originally Posted by OzePete

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

Oze... I think the biggest variable that I'm trying to gather more information on is the voltage reading at the top of the Dometic app. According to tech support, this reading is being taken off the board inside the unit (which seems obviously correct)... the issue I have is how can it read 10.x on the app and read 12.x at the power source which is about 6 feet away... with no noticeable loss due to the power run.

The battery is just about charged up - I'm letting it trickle. Once the trickle is 100% complete I'll take some readings and post up.

It will be very interesting to see what the app shows the voltage at when the cooler is off (yes, even when the cooler is off it shows the voltage via the app)... and then what it looks like at startup, etc. I will try and capture video of the app in action and then post on YouTube or something -- perhaps that will give better insight into what is happening.

It's a brand new freezer... It's frustrating to be dealing with all this, but if it's on me, then I want to know -- if it's on Dometic, then I trust they'll take care of the issue.

[Maka]

PetePetePete


Thanks
Very helpful information and advice.

What about using those frozen gel packs ( about 6"x 6" square, 1" thick ) instead of water bottles?
I'm assuming they are more efficient than water?

[PetePetePete]

Originally Posted by Maka

PetePetePete


Thanks
Very helpful information and advice.

What about using those frozen gel packs ( about 6"x 6" square, 1" thick ) instead of water bottles?
I'm assuming they are more efficient than water?

I used this stuff:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Added to the Fiji bottles (you'll want to remove some water for expansion).

The 6x6x1 sound interesting, my concern is that at only 1" thick they won't "hold" as long as I would like -- although they would freeze quickly. In my case the Fiji bottles fit perfectly in my rotomolded coolers. So the system, in my case works. The sticking point is a reliable freezer.

[Maka]

Makes sense
Thats the same stuff in the gel packs I'm sure,,and the added volume of your Fiji bottle will certainly make them last longer. Quart or 1/2 gallon milk containers would last even longer.



I get your point and frustration w the reliable Freezer comment.


Perhaps it would help your cause if they knew you were posting here publicly about your / their problem.

[PetePetePete]

Originally Posted by Maka

Makes sense
Thats the same stuff in the gel packs I'm sure,,and the added volume of your Fiji bottle will certainly make them last longer. Quart or 1/2 gallon milk containers would last even longer.



I get your point and frustration w the reliable Freezer comment.


Perhaps it would help your cause if they knew you were posting here publicly about your / their problem.

I'm not going to get all cranky until I know for certain if it's on my end or not. Right now, I'm assuming it is a "me" issue and not a "them" issue.

[Richard Kollmann]

OzePete, Pete, You, must agree the same unnecessary pointless foolish arguing does not alter the facts as you seem to infer. These Direct Current compressors do not have brushes whether armature excitation is with two field coils or three. Electrical pulse current direction within module eliminate the need for armature brushes. The electronic control module’s electronics are different but both versions of boot up voltage and amperage protection functions are much the same. Both the three and four pin Danfoss BD compressor modules convert 12 or 24 volt DC to pulsating low voltage AC current.

Without an oscilloscope to see the same low voltage spike that control module sees and terminates compressor start up you will not see with a voltmeter. I find that a person looking for Low voltage spikes is better off isolating away the cause and leave the voltmeter in the tool book.

If you ask a owner technicians like at technautics or Cold Ed Marine they will confirm that a voltmeter will detect voltage drop but not a low voltage spike that is the number one cause of Danfoss BD compressor restart problems. Number two is a faulty fan.

Hopefully PetePetePete will advise the forum when problem is located and corrected is without modification or replacement.