Electric Cooler Wiring

dlochner · Dec 31, 2020

Go with B. The charger won't mind. Boats with refrigeration stay plugged into shore power all the time. The refrigeration is 12v so the charger will cycle on and off. The Dometic is pretty well insulated, so I doubt it will cycle on that often unless it is sitting in the sun or someone is opening and closing frequently.

dlochner · Dec 31, 2020

Once you are spending time on the boat, the charger will be running a lot to make up for the energy used by lighting, stereo, water pumps, and other devices. What will happen, and it happens on my boat, is the charger will shift from providing a low float current to a current high enough to power the refrigerator and then back down again.

dlochner · Dec 31, 2020

ontherocks83 said:
That's how mine works too,I just didn't know if it ramping up and down constantly all week for the whole summer would shorten its life span at all.

Oh, it might, but that will be the next owner's problem.

Davidasailor26 · Dec 31, 2020

Our built-in freezer/fridge is wired as option 2, and it does lead to that type of spin up/down for the charger. The first charger lasted 6 years before capacitors failed, which I don’t blame on the fridge, and from what I’ve read is about all I could expect from a Xantrex charger.

Captain Larry-DH · Dec 31, 2020

ontherocks83 said:
I just didn't know if it ramping up and down constantly all week for the whole summer would shorten its life span at all.

It won't. It's designed for that.

ontherocks83 said:
It does have a low voltage limit that if the batteries get to a certain point it will shut off, so I'm not worried about flattening my batteries if I lose shore power while I am away.

About that low voltage shut-off: I checked the manual out of curiosity, and it lets you choose the cut-off voltage. It lets you choose Low/Medium/High which correspond to 10.1/11.2/11.8 Volts. DO NOT CHOOSE LOW or MEDIUM.
10.1V is a dead-flat battery. 11.2 is less than 10% state of charge! 11.8 is as low as you want to go without damaging your batteries. (On my boat the Low Voltage Disconnect is set for 11.9v).
Simplified chart does not take temperature into account:

Davidasailor26 · Dec 31, 2020

Captain Larry-DH said:
Simplified chart does not take temperature into account:

The only trick with that chart is that it also doesn’t take into account load. Under the ~5 amp load from a fridge, potentially plus other house loads, 11.75 might happen at a much higher SOC than the chart suggests. High still sounds like a reasonable cutoff to me, especially for when you’re away from the boat and there are no other house loads.

Project_Mayhem · Dec 31, 2020

If the charger can't keep up with the load or you are concerned with it switching on and off you could wire up a multipole 120v relay with the coil connected to shore power inlet so it automatically switches when you plug in

Benny17441 · Jan 1, 2021

I have heard reports from RVers that if the 12V outlet is not wired with properly sized wiring for the refrigerator load that the refrigerator will not perform as desired. This particular person went to the 120V converter and ran it through an inverter and indicated that the refrigerator/freezer was cooling faster and to a lower temperature. I recently acquired a 37 Quarts Refrigerator/freezer and will be conducting a comparison test to see if our 12V outlet is adequate. I guess rewiring the plug or repositioning a new one closer to the batteries might be another solution in case there is a problem.

dlochner · Jan 2, 2021

Benny17441 said:
I have heard reports from RVers that if the 12V outlet is not wired with properly sized wiring for the refrigerator load that the refrigerator will not perform as desired. This particular person went to the 120V converter and ran it through an inverter and indicated that the refrigerator/freezer was cooling faster and to a lower temperature. I recently acquired a 37 Quarts Refrigerator/freezer and will be conducting a comparison test to see if our 12V outlet is adequate. I guess rewiring the plug or repositioning a new one closer to the batteries might be another solution in case there is a problem.

This is an issue that is easily resolved, just make certain the wiring and fusing is correct for the load and distance from the power source. Relying on 12v plug outlets for high loads is risky. These sockets are no all that robust and are prone to corrosion and poor connections. They work for small draws, like recharging a phone, but for higher current draws for longer periods of time they are not the best choice. A better choice are Anderson Plugs or hardwiring the device to a 12v circuit.

Running 12v appliances on a converter is very inefficient and waste energy. There is a current loss in the conversion from 12v to 120v AC and then again when the 120v is converted to 12v at the appliance.

Scott T-Bird · Jan 2, 2021

My first thought is that the charger is less expensive to replace than the cooler, so I would not be concerned about cycling the charger. Besides, I'd think that cycling the charger a bit more often won't make any difference to the charger. My second choice would be to make a conscious decision to simply never have both sources plugged in at the same time. How often would it be that you forget to change plugs when you arrive at the boat when it becomes part of your routine?

captbob47 · Jan 2, 2021

I have the same cooler and leave it plugged into the ac while at dock. When away from the dock I use the 12 volt cigarette plug. It takes less than a min. to switch and all works well. I sail 5-6 times/wk an this has worked for the last 6 years.

Ward H · Jan 2, 2021

For the cost of the cooler you could install an Isotherm 2010-SX cold plate in the ice box. I did this last spring and am very happy with it.
I found it to be very efficient despite the poor insulation around the box. I thought about a powered cooler but thought this install would be more efficient. Money well worth spending.

All U Get · Jan 3, 2021

Ward H said:
For the cost of the cooler you could install an Isotherm 2010-SX cold plate in the ice box. I did this last spring and am very happy with it.
I found it to be very efficient despite the poor insulation around the box. I thought about a powered cooler but thought this install would be more efficient. Money well worth spending.

We looked at the cold plate when we owned our Catalina 30, and found a mod for insulating the ice box. I used the expandable foam between the box and hull, and glued rigid foam around the rest. Our box would hold ice for a week.
We had a 12v Coleman cooler with the heat pump to keep drinks cool, but eventually had issues with the real estate it took up. It was nice having the extra cooling space though.

bawlmer · Jan 3, 2021

I would go with option B. I have a 12 volt fridge (Isotherm 2010SX). I have been running it constantly since since 2018, shutting it off only for winter. The first thing you will notice is how little electricity it uses. I have spent overnights at anchor and the power draw from the fridge has never been detectable. As for the charger it will do what it is supposed to do and that is not an issue either. As far as safety goes it is far safer to run the fridge on 12 volts constantly than to have it run directly on shore power for any length of time due to possibility of surges, etc. As stated previously, a charger is cheaper and far easier to replace than a refrigeration unit.

Ward H · Jan 3, 2021

ontherocks83 said:
I plan on installing one as well, we just like having two "refrigerators", the Dometic for food and the Ice chest for drinks.

Good plan. Now you got me thinking about the Dometic.

Scott T-Bird · Jan 3, 2021

Does it have very good capacity as a freezer? I'd love to have ice cream on the boat every once in a while!