Swap 12v for 120v Fridge Element? UPDATE 2

[BFL13]

EDIT--it turned out you can't swap them--they are not the same and it would fry things if you applied 120v to the 12v element
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UPDATE 25 Jan--12v is cooling down the freezer.
UPDATE 2, 26Jan

I found my 120v heating element that was not working to be rusty and it and the 12v element beside it are both rusted to the coil pipe (or whatever the assembly is supposed to be like ????)

I was poking with a screwdriver and it cracked open or made? a fault in the 120v heating element pipe that is rusty dark. the 12v element beside it looks identical but is shiny--maybe never used.

It would be easy to swap the wiring so that the 12v element's two wires went to the terminals on the board that the 120v element's wires go to now. Only thing would be to eliminate the 20 amp fuse on one of the 12v elements wires.

But--are these two elements the same so I can do that?

Photo shows the 120v on the left of the 12v element which is the shiny one to the right of the photo.

[BFL13]

Gjac wrote:
BFL, it will come out but it takes a lot of work. Using long needle nose pliers and a pry bar tool I made to go underneath the element and a lot of PB blaster or Kroil oil it took me several hours to work the element back and forth(only about a 1/16 of an in at a time) while prying up on the bottom of the element with the bar. There is not a straight shot at the bottom so I had to bend a steel rod to the right angle to get in there.

Good to know, thanks. I am afraid to try all that in case I break the cooling (whatever it is called) pipe that goes by there, which would mean no operation on gas or electric.

I think I have solved the problem for now, so no need to risk it.

[Gjac]

BFL, it will come out but it takes a lot of work. Using long needle nose pliers and a pry bar tool I made to go underneath the element and a lot of PB blaster or Kroil oil it took me several hours to work the element back and forth(only about a 1/16 of an in at a time) while prying up on the bottom of the element with the bar. There is not a straight shot at the bottom so I had to bend a steel rod to the right angle to get in there.

[BFL13]

I like that relay idea.

This morning freezer temp is in the cold zone where it is supposed to be at -20ish C and under 0F. Fridge is also where it belongs just above freezing. (But so is ambient)

The element is on (212 watts) so can't tell if it is cycling from that spot check just now. Later observations for that.

Anyway, there it is -- the 12v initial "pull-down", which is not supposed to work according to the owner's manual.

Looking good for replacing my irreparable 120v setting with the 12v set up using the second converter with 120v input. (I cannot swap the 12v element out either --it is stuck in there despite spraying)

EDIT--it has been a few hours and no change in temperatures except fridge is now at 3C, which is below ambient. It has bottomed out for sure at the proper temps. However, I have not caught it with the element off. It is about 8C/45F out where the element is in back of the fridge, so maybe it has to stay on instead of cycle--not a clue. Was 203 watts

[CapnCampn]

Would it be worth it to use a relay to switch power to the element? Use the power from the board to turn the relay on utilizing the thermostat controls, then use the relay to run power direct from the converter to the element. Seem like that would bypass the voltage drop in the board, and get you the higher voltage (whatever you dial in) to the element.

CC

[BFL13]

So far after 10 hours on 12v, freezer temp down to -13C and fridge temp not budged--still at 6C ambient. We'll see in the morning whether this works at all. I know it usually takes a day, even on 120v. Only takes a few hours on gas though.

[BFL13]

Update 2

Second converter on fridge "terminal block" instead of the regular wires from the house battery bank. This was the easiest connection.

Started with converter set to 15v. 193 watts warmed up. Very slow to get the freezer to cool down any. Checked the voltage at the element pigtails 14.3v. So that is 0.7 drop across the terminal block and PC Board. About 13.5 DC amps draw (using AC watts and DC v)

Cranked the converter to 15.3 (under the 15.4 limit) and pigtails now 14.6, 202 watts warmed up. Freezer coming down in temp much better now. Acts like there is a threshold to get it really going.

Anyway, next thing is to wait for it to bottom out and cycle before declaring victory. Not there yet.

If this works I then need to find a place to mount the second converter (under the fridge has a place) and pass wires up through I hole I need to drill. Should be ok.

[BFL13]

pianotuna wrote:
Hi BFL13,

Be careful. My board is rated at 15.4 volts--but I don't want you letting out the magic blue smoke.

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Terminology Note: This owner's manual uses "PC Board (lower)" "PC Board" and "Power Supply Module" to mean the same thing at the back of the fridge. It also uses "PC Board" to mean the eyebrow controls inside on the fridge you use to operate the fridge. I have been using "PC Board" to mean the power supply module at the back of the fridge. It gets its 12v from the "Terminal Block" at the back of the fridge where 12v wires come in from the house battery. I have voltage drop at that terminal block and also in the power supply module. I can by-pass the terminal block for when on second converter if necessary.
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Same with my board at 15.4 (which was also the 5er's Norcold limit)

I need to disconnect the "fridge" 12v from house batts when powering the board from the second converter and that converter is on inverter. I have realized that puts the second converter on the house batteries, and don't want that loop. Also don't want the house batts floating at 15v.

Means an extra step going from 12v to gas, but no big deal. Have to do some wiring and rig second converter so it won't fall out onto the road. Leave the Kill-a-Watt in the mix too, so I can tell from the watts if the 12v element is on.

[pianotuna]

Hi BFL13,

Be careful. My board is rated at 15.4 volts--but I don't want you letting out the magic blue smoke.

[BFL13]

MrWizard wrote:
unless you need a new control board

at least it keeps you busy and out from being in DWs way

The control board seems to work properly on gas. I did have to replace the DC fuse on it when I fumbled something the other day.

If I get the converter to supply the board, I will have to parallel it with the regular connections from that 12v connections thing where there is some voltage drop. That way I can still run the fridge on gas when not doing any converter 12v mode. Voltage drop is not a problem in gas mode.

If I ever get this 12v mode working right, I may never use it, but at least I will have the option.

Ha--the secret is to have vital work to do in the RV so you can't get to the honey-do work just at the moment 🙂

EDIT-- no 120v mode means you can't run the fridge off inverter and make it up with solar to save propane. If I get this 12v mode working via second converter, I could run that converter (since not connected to house batts) on inverter and make up with solar as an option in some scenarios.

[MrWizard]

unless you need a new control board

at least it keeps you busy and out from being in DWs way

[BFL13]

MrWizard wrote:
I think you love doing tests and recording data

you would make a good 'laborant' aka Lab worker Ant

I had quit, until some slave-driver told me to get back to work on this! 🙂

After 3 1/2 hours, still at 196w and freezer now down to -10C.

So whoever said you can't cool-down with 12v didn't try it with my set up! Ha. Looking good so far, but the proof is after it gets cold , will it cycle properly? We'll see.

OOPs!!! How can it cycle when the power to the element is not connected to the PC Board???? So I better shut it off for overnight.

EDIT--so my next trick (for tomorrow) is to feed the PC board from the converter with the element attached to the board. I can crank up the converter voltage to beat the PC board's voltage loss and get under 15 to the element, and it will be under cycle control (I think!)

[MrWizard]

I think you love doing tests and recording data

you would make a good 'laborant' aka Lab worker Ant

[BFL13]

Well, well --after 2 1/2 hours, freezer temp has dropped from 3C (ambient) to -5C and element watts at 14.6v are about 196w (started at 202w) with the warming of the element.

This suggests I could do a "cool-down" on 12v. Hmmmm. I will leave it on overnight and see what happens. IMO it should reach bottom and cycle to hold it there, but who knows?

[BFL13]

Oh very well! 🙂 More measurements: (I found a way to get at it with the meter)

RV on battery only- fridge on 12v, no previous cool down on gas.
Battery voltage 12.8 Tri says 9.6 amps draw
Fridge connector voltage behind fridge- 12.3 (battery 12.8)
12v element pigtails- 11.9v !!!

So that is a lot of voltage drop for a mere 9.6 amps! (Small wires go from 12v connector behind fridge to PC Board. The pigtails go on board's blade terminals)

Disconnected the two pigtail wires from the PC Board, into my spare converter, into the Kill-A-Watt, into the fridge's 120v outlet.

Converter at 13.5v---175 watts
Converter at 14.6v---202 watts (should go down a bit as it warms up I think)

Settled at 199w. Flue too hot to touch. Left the fridge on 12v setting in case it needs that to be on for controls or whatever.

Left it running like that with thermometer in freezer at 3C (about 36F) and we'll see if this time it does anything. 200w is not 350w like with 120v, but it ought to do something IMO.

Those 16AWG aluminum wires on the element come with it AFAIK--looks like it on the parts list drawing, and they come out of the element so no way to attach them yourself.

I would cut them short and go #8 copper from there to spare converter if I get serious about 12v. Did that with my solar panel aluminum pigtails.