Big Boy Isolator Relay. 07 Patriot

[Bob Reeves]

How how should the Big Boy relay be when connected to shore power?  Just replaced the old one, looking inside the old one  the terminals were really corroded.  Mine runs very hot to the touch when charging both House and chassis batteries.

[Joel Ashley]

It’s a heavy duty relay and I’d expect it to be warm during initial charge-up cycles, especially if the batteries have been deeply discharged requiring an extended Bulk Charge phase.  If the BIRD is operating correctly, the charge sequence off park or genset power should be house first and then chassis, but not both at once.  It’s not a situation I’ve heard of or know if it’s even possible, but if so both at once I’d expect to abuse the Big Boy solenoid. 

Was the “corrosion” on the large points/contacts a lot of burn evidence or actually white acidic deterioration?

Joel

[Gerald Farris]

Bob,
The Big Boy solenoid will heat up some because there is a constant current flow through the windings to keep it engaged, but it is at a reduced voltage to prevent premature failure because the Big Boy solenoid is not designed to be a constant duty solenoid. The "BIRD" system control module sends a 12 volt current to the Big Boy to engage it when either battery bank reaches the set charging voltage, and then it reduces the voltage to the Big Boy and only uses enough voltage to keep the solenoid engaged so that both battery banks receive equal charging voltage.

Gerald

[Bob Reeves]

Thanks to Joel and Gerald.
I just spoke to a "Guru" that has worked with Beaver/Monaco coaches.  He said it is normal for the Big Boy Isolator Relay to run very hot.  It does not matter whether it is on shore power or being charged by the generator or the alternator when the engine is running.
Thanks for your inputl.