JC Refrig DC Conversion Help

[Moira]

Is there anyone out there with a DC conversion compressor unit for the Norcold by JC Refrigeration? I am seriously considering the DC unit.

I am trying to decide on either a AC conversion or a DC conversion. It would be great if I can get real DC amps per day for each model.

Any insight as to why you got one or the other would be extremely helpful. My appointment is Monday.

There are a lot of comments on the AC unit but not much at all on the DC unit.

We like to boondock when we can. I wish there were dedicated threads for each of these units. I have been googling and reading for days.

This is my current setup:

four 6V 220ah AGM batteries, 2500w psw inverter/charger that I would rather not use, 500w of solar but my controller is limited to 600w at the moment, trimetric battery monitor, 12.5 kw genset that we use 2x a day, no biggie,
We have LEDs throughout, at night we just have the TV on and a laptop. That's it I think.

Thank you so much

[MikeandRuth]

I got in here to look for exactly the same answer! I have been in contact with them earlier this week about the same product for my Dometic 1292. I want the DC unit because inverting 12 volts to 120 is an inefficient process. The batteries will run the fridge and the genset will keep them charged as necessary with less amps consumed and needing replacement when you charge. Do you have a clearance issue behind your fridge for the extra space the compressor needs? I need about another 1 1/2 inches. I am going to picture frame the fridge and pull it out to obtain the necessary clearance.

[Moira]

I don't think I have a clearance issue. When is your appointment?

[jddangelo]

Just installed the DC unit and couldnt be happier.

Cools my norcold 1200 down better than ammonia ever did.

Not sure on current draw but I can say its protected by an 8a fuse so must draw less than 8a @ 12V

[Moira]

Well that's great JD, was there a reason you decided on it and not the AC unit?

[jddangelo]

Driving down the road did not want the inefficiencies of inverting 12V to 120V and when on shorepower or genset power the convertor is making 12V regardsless

[Moira]

Can you tell me a little bit about the DC conversion. I understand they are using a danfoss DC compressor. Do you know what model it is. Do they put any extra insulation around the norcold? Did they have any problems changing out your wiring for DC?
There is very little information at all about these DC conversions. Do you know if this compressor has an internal inverter? Thank you in advance

[jddangelo]

- not sure on model of compressor

- no extra insulation required

- I installed myself very good instruction video no issues with wiring

- compressor is 12V driven by house battery bank @ 12V so no inverter req’d

- cools empty fridge down in cpl hours vs cpl days

- watch Mortons on the Move youtube channel they installed and did 6 month update

https://m.youtube.com/watch?v=Yte1V3CkDrw

https://m.youtube.com/watch?v=FeKtqqleMdM

[Moira]

I just lost this entire post because my token expired. Ok I'll try to retype it but it won't be the same.

Thank you JD. I didn't know the Morton's on the move uploaded an update. There is nothing like real life performance. This is exactly the information I was looking for.

The Morton's reported that they were using 400 to 800 watt hours per day and 1200 watt hours per day when the temperatures were over 90*. I use amp hours because that is what my battery uses. So what does this mean?

400watt hours / 12V = 33 amp hours
800watt hours/ 12V = 66 amp hours
1200watt hours/12V = 100 amp hours

The Mortons did not specify if these readings were taken before they installed the fans to defrost their completely iced over fins or after they tweaked the motor to run faster to keep up with the hot weather.

This is what I came up with:
JC Refrigeration uses 5.5 amp hours for their DC conversion frig. I am using a 50% compressor duty cycle. 12 hours on, 12 hours off. And 220ah available from my battery bank (50%). My batteries are wired in series-parallel to give me a total of 440ah and 12v. This is what I calculated:

DC conversion refrigeration
5.5 amps per hour x 12 hours duty cycle = 66 ah (the Mortons got this too)
220ah / 66ah = 3.3 days
but I will be running other things besides the frig. So using half of the available power for the frig, it would be:
110 ah / 66ah = 1.6 days

66ah is 30% of my available AHs.
I would like at least 2 days of power for everything before I am completely out without running the generator. That will give me enough time to fix whatever is wrong with charging my batteries back up without throwing away food.

comparing that to the AC compressor conversion frig:

using my big inverter
5 amps DC x 24 hours = 120 ah
8 amps DC x 12 hours duty cycle = 96 ah (.8 amps AC = 8 amps DC) Thank you twinboat
120 ah + 96ah = 216 amp hours per day.
There is no way I could handle that with my current 220ah available. I have seen my big inverter go from using 5 amps to 10 amps with nothing on, and I don't know why. That would use all 4 of my house batteries a day just for the AC frig.. I don't have room to add a lot of batteries.

using a smaller dedicated inverter for just the AC frig:
.5 amp DC x 24 hours = 12 amps
8 amps DC x 12 hours duty cycle = 96 amps
12 ah + 96 ah = 108 amps per day.
This is doable. The smaller inverter uses a lot less power and would be free of all the parasite loads that are on the big inverter. This uses 20% more power than the DC conversion and it is 50% of my available power. It is also close to what the Mortons used in their DC frig when temperatures were very high.

if JC Refrigeration installed the small inverter, I may have been persuaded to get the AC unit. But they don't do anything like that.

The only time I need my big inverter is when I use the convection oven, turn on the air conditioning or I am charging my batteries. The rest of the time I think I could use a small inverter.

Some people shut off their inverters at night. This raises the temperature in the frig about 5* by morning. I don't want to do that. I may end up doing that but it kinda defeats the purpose of getting rid of the absorption frig.

I almost made a mistake using the .8 AC amps that JC Refrigeration advertises for their AC conversion in my calculations. Compare apples to apples. They should probably advertise DC draw because that is what we need to know. If you are plugged in, you have an endless supply of AC.

Also be sure to use at least 60% of your battery power when you do your calculation. When the compressor kicks on it draws down your batteries. In my case we had 12.2V (60%) when the compressor kicked on for the first time. It drew my batteries down to 10.7V. The compressor shuts down to protect the batteries at 10.4V. So you can't go much lower than 60% battery power before you run the risk of your refrigerator shutting down. The compressor kicks in for just a few seconds. The shut down voltage is set at the factory.

Don't use 100% of your battery power (440ah) to find how long your frig will run. Only lithium batteries can be run down to zero practically. And I don't know what would happen to your voltage. Most people are going to run something in addition to a frig.

more to come

if I forgot to add something, I'll get it in the next post.

[PaulMears]

I love the numbers, but don't for get the start surge on electric motors. Could be 10 times run demand.

[twinboat]

Originally Posted by PaulMears

I love the numbers, but don't for get the start surge on electric motors. Could be 10 times run demand.

It could be, but in my case, with a residental fridge, it was only a bit more then 3 times.

My 120 volt fridge, running on my inverter, had a 10 amp draw @ 12 volts DC.

It failed last year. When it tried to start the seized compressor, It would draw 35 amps @ 12 volts DC for a few seconds, before the thermal switch shut it down. This was seen thru my battery monitor.

So I think, at least in the case of refrigerators, drawing 10 times more when starting up may not be the case.

There may actually be a locked rotor amp rating in the specs.