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Old 05-18-2010, 08:00 PM   #1
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Bear Family: 12 Volt DC Contactor

Problem has been bugging me for over a year. 2008 Monaco Diplomat 40SKQ. In the battery compartment on the back wall is a is what I believe to be a "Contactor" as shown above. My question is regarding this and is it supposed to be very warm (hot) to the touch? I called the company that makes them and was told this was normal when hooked up to show power - I am guessing it is related to the charging system for the batteries. When disconnecting one of the small wires you can hear the unit open and then click close when reattaching the wire. Can't find anything in any of the books regarding this part - any one have any ideas?

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Old 05-18-2010, 08:17 PM   #2
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That may be your battery disconnect, turn off the battery switch and see if that contactor clicks.
The warmth would be caused by current, either from the converter charging the batteries or the coil. When you disconnect a wire you remove power to the coil that activates the plunger (holding the contacts) and shut it off.
I guess the best test would be to disconnect the batteries and check if it cools down.

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Old 05-18-2010, 08:31 PM   #3
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The Trombetta contacor is the device that is used to connect house and chassis batteries together under the following circumstances:

1. When using the battery boost switch.
2. If a BIRD system is installed, connects the two sets of batteries to for charging purposes either when connected to shore power or when the coach is being driven.

From your description of the contactor feeling hot, it seems that you have the BIRD system installed. Quite often, the contacts in this unit will become coated with verdigris (green corrosion) and will cease to operate.

To check whether or not the contacts are functional, you can do the following.
The contactor needs to be energized, use the battery boost switch if not connected to shore power. Using a DC voltmeter, place the negative test lead on the ground connection (or negative battery post), then place the positive lead in turn on each of the contactor main power terminals. The voltage readings should be virtually identical if the contacts are in good condition.

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Old 05-18-2010, 08:43 PM   #4
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If you have a digital voltmeter, place the leads one each on the large terminals on top of the contactor. Record the reading, then de-energize & re-energize the solenoid and repeat maybe 5 times. If the readings are more than 0.2V at any time, you have burnt metal particles )from the arcing that takes place on contact/de-contact) interfering w/solid and reliable passing of charge voltage. This will get worse at an accelerating rate, and you should have a spare solenoid ready to replace the original. Solenoids wear out in this manner.

The heat is from the coil current and is normal. Using an infrared temp gauge, you should be seeing less than 150 degrees, probably around 135 as a steady state (assumes it is located where airflow will cool it properly. If you are over 150, you may be getting extra heat from corroded contacts causing excess resistance.
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