My daughter's 12 volt/120 volt refrigerator has quit working and is 20 years on her Wellcraft Gran Sport. I am switching her over to a 120 volt Kenmore fridge and Tripp Lite inverter. I could not find any small refrigerators where the cooling coils were on the back of the fridge. Now, they put the heat exchanger coils just under the outer skin of the refrigerator sides and top. So, they are no longer recommended for under counter use. They are supposed to be free standing installations only.

Well, it is going under the counter, and I am going to add two 12 volt fans to circulate air around the sides and top when they get warm. To keep the fans from running all the time and further draining the batteries, I ordered some temperature snap action switches that can be glued to the top of the refrigerator. These switches will turn the fans on at 45C (about 113F) to help get rid of the heat. I had to buy 12 of these switches, so I will have a few extras if you need one.

I also measured the amperage draw of the refrigerator before installation. On cold start, the draw is almost 5 amps at 120 volts -- about 600 watts. It quickly drops to 1.2 amps (144 watts) until the pressures in the system normalize, then the draw drops to 0.75 amps (90 watts). The Norcolds draw about 45 watts. So, on a 12 volt inverter, it will draw about 7.5 amps plus 1 amp efficiency loss, or 8.5 amps when it is running. We are installing a 700 watt inverter with surge capabilities to 1400 watts.

This new fridge is so, so much quiter than the old Norcold. I will let you know how it works after it is installed this weekend.

Paul

When I replaced my old 12/120 a few years ago, I stayed with the new dual voltage fridge. The coil issue is almost universal, with all of the new energy codes. Luckily, the new fridge is not as tall as the old one.

I built up a channel below it, allowing air to flow under and back up behind the unit. I'm sure the addition of a 12V fan helped with the air flow, but natural convection is probably even more beneficial. Cool air near the floor is drawn under and up toward the warmer fridge and bulkhead. To make sure I had actual air movement, I cut a couple round grommets in the shelf above the microwave just in case.

Paul:
The refridgerator frame or case might be grounded. If the plug is a 3 conductor grounded plug, they usually are. If so, bolting the fridge in place to the aluminum floor or any part of the hull would defeat the floating ground and bring the hull into the AC circuit by bonding it with the neutral conductor.

Don't forget to install a 250 to 400 amp fuse in the DC wiring on that inverter. (West Marine sells the fuses and holders.) My first inverter shorted out inside and fried the fuse, and boy am I glad it was there!


Jeff

While I was nosing around in the inverter, I noticed that the white 120 volt ground wire was tied directly to the 120 volt green ground wire. I was a little concerned that this defeats the green separate from white ground wire design. But, I guess it will only bridge the white and green for whatever is plugged into the inverter, not the rest of the boat. I just want to make sure that there is no chance of electrifying the water through the green ground bonding system on the through hull fittings.

White is not a ground wire, it is neutral. Green - ground must be continuous back to shore, never tied to white. There's often confusion because of our panel boxes at home, where both the green - ground buss and the white - neutral buss are both in direct contact with the metal box, therefore with each other.

For sake of argument, let's call our home panel box "shore". We never interconnect green and white throughout the house, they are separated until everything returns to that big, safe panel box. The green is there to return a short back to the box, not to carry power to our lights and appliances.

I called the inverter manufacturer (Tripp Lite) and asked to have their electrical engineer who manages these inverter deisgns to call me. My biggest concern is that the refrigerator starts delivering the 120 vac to the green ground that is bonded to all the through hull fittings. If you are swimming in the water, is there ac present?

Paul

If your thruhull fittings are original bronze, as mine are, they are insulated from the hull to prevent forming a battery from the bronze-water-aluminum mixture. Those fittings should not, as far as I know, be attached to the green ground. If they are, then current can flow between the bronze and the aluminum (because the green ground goes back to the hull) and the aluminum will be the loser.

If your thruhull fittings have been replaced with something like Marelon, then there are no worries.

The question I would ask the Triplite engineer is whether the ac output is isolated from the dc input, or whether the dc return (negative) is connected to the output green ground. I suspect that the latter is the case.

If the ac output is actually isolated, the connect the green ground to hull and the frame of your reefer, hook up the black and white, and you are all set.

If the ac output is tied to the dc input (connected from dc black to ac green) then your green is already tied to the hull. Just run green to the frame of your reefer, and hook up the black and white. If the frame of your reefer is already connected to hull through a reliable connection such as bolts or screws, then you do not need the green ground at all, it is already connected. Best marine practice calls for isolating the frame from the hull, and using the green ground.

Roger,
I was thinking of leaving the green ground disconnected too, but the installation instructions strongly warn against this. Still waiting for Tripp Lite to call.

Paul

Remember that your green wire is connected to your galvanic isolator. That prevents DC current leakage.

NEVER DISONNECT THE GREEN GROUND WIRE!!

Now the best and safest approach/test is to isnure that your AC input is a GFIC curcit. If your boat does not have them put them in. If there is any (approx. .006 amps) not returning throuh the white wire the curcuit will trip assuming there is an AC leak throuh the ground /green wire. One of first retros I did on mine was replace outlets curcuits with GFCI. My dock is electrified through a 240 volt 30 amp GFCI main breaker also to protect the dock curcuits. The 240 breakers are expensive costly approx. 125 bucks a breaker. They will not fit in our Big M panels.

Check these GFCI outlets at least monthly they are inexpensive and often go bad in our environment.

Save boating,
dave

Well, after waitng a couple weeks for the electrical engineer at Tripp Lite to get in touch with me, I made another call to technical support. It turns out they had no record of my original call. I explained my concern to the tech support person who did not really understand what the issue was. I asked if I could speak with an electrical engineer or manager in charge of the product line. The answer - no, our engineers do not talk with customers. So, I asked for the corporate officer in charge of electrical design. She gave me his name, so I am going to send him a letter with a diagram and let him address the question.

In the meantime, I looked at the wiring and operation of some other marine inverters. These inverters couple the green and white wire while the inverter is turned on, but have a circuit to uncouple the green and white when the system is returned to shore power. So, when the inverter is running, the green and white are the same potential. When it is turned off, the system returns to at least 25,000 ohms resistance between the green and white.

In the case of the refrigerator, it is the only appliance plugged into the inverter, and the refrigerator is isolated from ground - no screws mounting it to a metal frame. So, I am going to ground the inverter case directly to the battery ground terminal, which ultimately returns to the hull.

Paul