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    David Pratt
    The discussion about the Big Boy Solenoid and its proper operation comes up quite often on the Monacoers Group  Forum
    There is a lot of mis-information about the operation of the Bog Boy Solenoid and the Bird Relay. With the help of Intelitec I have researched the operation of the Big Boy and the Bird Relay and the following information should help those understand the operation of the Big Boy Solenoid and Bird Relay and help in trouble shooting the system if a problem occurs.  

    The Big Boy System was installed By Monaco in most all of the Patriots, Marquis, Navigators, Executives, Dynasty, Signatures and like Monaco branded coaches. Both the BB Solenoid and the Bird Rely Circuit board are located in the Rear Run Bay. The BB Solenoid is big and mounted almost center in the RRB and the Bird Relay Circuit Board is mounted on the right side about midway on the board will have a Green LED on when it is operating.

     Here is the info for the Big Boy System that might be helpful.

    The Big Boy Relay is controlled by Bird Relay which is located in the RRB. It is located on the right side and is the third circuit board from the top. There is a Green LED-(ISO Relay On)-third from the top on the board that should be Illuminated and the Big Boy Relay should have a low hum and be hot to touch when working properly.

    When you disconnect from shore power and the generator is not running, the Green LED should be out. The Big Boy Relay will drop out of the circuit when the dc voltage drops to 12.5 to 12.8 vdc when measured at the Battery side of the Big Boy Relay.

    When connected to shore power or when the generator is running you should have power to the #2 pin on the eight pin connector on the right side of the board. The #1 pin is ground and the #3 pin is powered on when you turn on the Ignition Switch. Pin #4 is from the battery boost circuit, Pin #5 is the Domestic power circuit. Pins #6 & #7 are blank. Pin #8 is a ground circuit.

    The six pin connector on the top of the board powers up the relays. The left pin is Pin #1 and is ground, Pin #2 powers up the Big Boy Relay, Pins #3-4-5-6 power up the two Domestic Relays to the right of the Big Boy Relay. When working properly you should measure about + or - 4.6vdc on Pin #1 when the Board is powered up and the Big Boy Relay is working.

    If the BB is powered up and running correctly, you should have around 4.5 to 4.8 vdc on pin 1 of the 6 pin connector. You should also have that same voltage on pins 1, 4, 5 & 8 on the 8 pin connector.

    On the BB Solenoid you should be seeing 12.8+ vdc on the chassis side battery post-(left side) and 13.0+ vdc on the house battery side post-(right side). A differential of .3 to .6 vdc between these two posts is normal.

    If your Inverter is set up correctly and the Bird relay is working-(green light on) the Inverter through the BIRD Relay and the BB will charge the Coach Batteries first and then the Chassis batteries and when all the Batteries are fully charged the Inverter will go into float charge. When plugged into Shore Power or with the Genset running the Green LED will be Lit on the BIRD Relay Circuit Board, If not I would venture to guess that the circuit board is failing or has failed. The relay above the eight pin connector on the BIRD circuit board controls the Big Boy Relay, it could be failing.


    Edited by David Pratt

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    Can you disconnect the wire going to the #2 pin (shore or generator power) and the pin 4, ignition wire leaving just the battery boost function in tact for emergency use?  I ask as when switching the House batteries to Lithium, the BB relay is supposed to be disabled since we typically use lead acid for starter batteries...

    Or is there another better way to provide boost for emergency use only with the currently installed system?

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    If you disconnect pin #2, house battery input, the big boy will NOT engage when on generator or shore power to charge the chassis batteries.  When the ignition is turned ON, and the engine is running, big boy will engage thinking that the house batteries are completely dead. 

    If pin #3, ignition input is disconnected, big boy will engage on shore or generator power thinking that the chassis batteries are dead.  But the big boy will not engage when the engine is running.  However, if the generator is running, big boy will engage and alternator voltage will feed the house batteries.

    Battery boost would still work if pin #2 OR pin #3 were disconnected.  If BOTH were disconnected battery boost would NOT work.

    If pin #8 battery disconnect switch input is disconnected, big boy would be disabled and never engage under any scenario.

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