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Old 02-05-2004, 09:43 AM   #1
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switch for 12v supply to refrigerator

When carrying out maintenance on our Dometic 3-way refrigerator I wish to disconnect the 12v supply wires. This is desireable when cleaning the flue and gas jet, or when replacing a thermocouple or igniter board. I don't wish to unscrew the wires from the connector block and cap them each time, so I am looking for a 12v, 35amp capacity surface mount double pole switch (or pair of single pole switches) , or plug and receptacle, or fuse box with removeable fuses. I have tried car accessory stores, marine stores, etc, without success so far. Has anyone found a suitable device? Thanks. Nick.
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Old 02-05-2004, 09:53 AM   #2
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Switch

Grainger sells many two pole multi position switches.



Catalog no. 392 page 569
www.grainger.com

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Old 02-05-2004, 03:32 PM   #3
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I would recommend just removing the positive wire off the battery.

If the battery is too difficuilt to I would add a relay and small size switch to turn the relay on and off.

If you use the normally closed contacts of the relay, it would not normally draw power unless you were servicing the fridge. The switch would put power to the relay to turn to power off to the fridge.

This way you would have a wider selection of switches. Just get a relay big enough to do the job. Most electronic shops would have the parts.
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Old 02-05-2004, 08:12 PM   #4
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Simplicity

I agree that removing battery lead is very simple and effective.

But installing switch to operate contactor or relay?

if you are going to install switch, why install a relay? Relays are typical for different voltage applications or multiple phases of power.

example, a 12 volt relay that opens a set of 120 volt contacts.

Simply allows you to use a lower voltage to operate a high voltage contactor. Used in timers on appliances all the time or stadium lighting where you are going to operate very high voltage lights. You would not want to be in proximity of opening and closing high voltage circuits.

The subject application is for 12 volts. Why use 12 volt control to open and close 12 volt supply?

A 8 dollar two pole switch will be more than sufficient for this application.

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Old 02-05-2004, 08:30 PM   #5
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Need for a relay

Swiching between different voltages is not the only reason to use a relay.

In this instance it is because of the high current involved. He is talking about 35 amps.

That means big wires to a big switch. Which may be difficult to find and costly.

A $10 relay could be added at the location where the load (fridge) is, so no extra length is needed. Then a simple, small toggle swich is used with smaller wires located where ever he needs to switch the relay.

Just an idea....

The battery terminal removal is the best, cheapest and trouble free solution.
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Old 02-05-2004, 08:50 PM   #6
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Conductor and amperages

I would not want to doubt his calculations but I too have a three way fridge, The conductors are no more than 12 AWG if not smaller. I question the 35 amp draw on the fridge.

A relay would be ideal but I wonder if that is a little over kill.

If I were to install a relay, I believe I would place it at the 120/12 volt converter, and Open all of the twelve volt supply, (battery lead removal).

A good example of a high load on a typical two pole switch would be the switch on the electric jack. Only difference is that the jack switch is momentary contact. I assure the load on the jack is a little higher than the load on the fridge. The jack has #12 or #10 AWG conductors.

as far as I know, there are no relays anywhere on an AS trailer for opening and closing 12 volt circuits.

There may be some relays in the sensor panels and I think there may be some on MH 's that have a tank fill feature from the city water connection.

I could be wrong.

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Old 02-05-2004, 09:35 PM   #7
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Switch

Nick,

I've never met a 35a. DC switch that I would trust unless it was UL listed for DC service. I would avoid 250VAC switches, they are not able to withstand the DC inrush current. They'll work OK for awhile, but sooner or later the blades will start to decay due to arcing.

You don't say that this circuit is protected by a circuit breaker or fuse. I assume it is. If it doesn't have a fuse you should put one in and make that your disconnect.
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Old 02-06-2004, 06:41 AM   #8
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Switch lifetime

Maybe true but I know this.

the switch in the jack of my 1979 has lasted ummm (counting fingers and toes)

25 years I think.

Matter of fact almost all electrical components in 1979 trailer have lasted that long. I wonder if those switches are UL DC rated?

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Old 02-06-2004, 09:51 AM   #9
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Switch

Sorry, didn't know we were talking about rocker switches on power jacks.

Maybe you could check and see if your switches are rated?
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Old 02-06-2004, 10:10 AM   #10
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Many thanks for your replies. The current draw for the 12v system is given in the Dometic literature as 20 amps, but the wiring is protected by a 35 amp fuse in the Dinosaur circuit board. I thought it wise to use a switch, plug and receptacle, or fuse box with at least the capacity of the fuse. I don't wish to disconnect the battery as we are full-timing, and I don't wish to interrupt the other systems on the trailer, or feel I have to rush the maintenance job. I'm happy with using 12v to switch a 12v relay with heavy contacts, and my truck is stuffed with similar relay systems. However, I'm always reluctant to add complexity, and hence reliability, into any system as complex as a 3-way refrigerator. I'm leaning towards a fuse box, and thank you, Smily for the link to Grainger. I can't see an ideal switch on a first ten minute look, but there is an interesting 30 amp fuse block , Bussmann # BM6032PQ. This, fitted with a pair of covers, would seem to be a possibility. The refrigerator would be off when the fuses are removed, so there would only be the tiny current to the eyebrow board to break. Arcing when removing and replacing the fuses should not be an issue. The circuit is also protected by a thermal breaker in the Airstream 12v distribution panel, but no one breaker is dedicated to the refrigerator. I'll do some more thinking. Thanks again, you're a great help.
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Old 02-09-2004, 03:16 PM   #11
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Yesterday I found my solution to the isolation of the high amperage refrigerator lines. I purchased two in-line fuses, sold as "30 amp Watertite fuse holders", marketed by Seachoice Products, Pompano Beach, FL 33064, part #12741, or 12721 with a spare fuse in a waterproof holder. They were about $4 each from Sea Hag Marine at Steinhatchee, FL. The fuses pull apart, and are encased in rubber housings. Perfect for my purpose. Nick.
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Old 02-09-2004, 03:33 PM   #12
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Refrigerator switch

Nick,

Looks like a good solution!

Thanks for the link to lots of good 12V. electrical gear.

12V electical stuff
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