Big Boy Issue

[Richard Dangel]

Hi All,
It's been a while since I posted but I read the Forum regularly.  This post is over another Big Boy issue. 
I have replaced the Big Boy four times in five years.  Forum research shows that someone recommended a marine-type alternative (posted 2012).  Is there anything new on this front?  I don't like forking out $260 almost yearly for a new one.
Please note that I am not an electrical engineer so I need a simple solution or a recommendation for someone who could perform this modification.  My motorhome is a 2009 Beaver Marquis.  Any help would be greatly appreciated.

[Eric Maclean Co-Admin]

Richard
Could you tell us what your previous big boys died of ( was it the solenoid winding that failed or the contacts)
The reason I ask his that the big boy is a continuous duty solenoid and as such is intended to be powered for long periods of time with no I'll effects. If the windings are failing I'd check the voltage applied to the big boy windings when it's energized to see if for some reason it is too low or too high damaging them over time.

If on the other hand the contacts are failing this is a more common problem .
The big boy can be dismantled and the contacts can be cleaned to restore proper operation .
There is a post in the coach assist section that covers the cleaning repair of the contacts under common problems.

Hope this helps
Eric

[Bryan Beamon]

Richard , Eric knows alot more than I, but have you researched your Bi- directional isolator relay or BIRD. I made an assumption my Big Boy was not functioning as our chassis batteries were not charging when plugged in to shore power when in fact it was a faulty Bird relay , just a thought

[Joel Ashley]

Our coach is 17 years old and never needed a new big boy, Richard.  There is some reason for such frequent failures;  either there's such a thing as "knock off" Big Boys or some other component is negatively affecting yours, as Bryan alludes to.  Until you or a savvy tech ferrets that cause out, as Eric notes -and going by past Forum posts over the years- many here have resurrected their Big Boys without too much trouble.

Joel

[Richard Dangel]

Sorry this post is so late in being returned. We have been traveling and putting out fires. I attempted to rebuild the last one that failed but on disassembly found the bakelite was fried and cracked. Contacts were slightly pitted and could have been smoothed out. The smaller relay in the run box (bird relay?) has been replaced only twice by me. They are a lot cheaper so I am not complaining. I took some voltage readings at the Big Boy and a temperature reading when the engine was cold.
13.24 volts on chassis battery side
13.24 volts on house battery side 
4.78 volts on rear-most terminal facing front
13.15 volts on right terminal facing front
164 degrees max temperature of Big Boy
I will continue to check the voltages and temperature as we proceed on our trip.
I was really hoping that someone had come up with something electronic and less mechanical to replace this system.
I will persevere and order another Big Boy for next time.
Thank you all for your help and insight.

[David T. Richelderfer]

RVs that don't have a Big Boy/BIRD charging system usually have an Echo Charger.  You might take a look at that as an alternative.

[Steve Huber]

Richard,
164 seems high with the engine off assuming you did not have a high current draw when you measured it. Was it the temp on the Big Boy or just in the bay? The "cooked" bakalite indicates high temps are present. Suggest you monitor temps at the Big Boy and inside the bay. If you have a current meter check to see how many amps are being drawn by house and chassis at the BB. Should be same as shown on the charger monitor. If the Bird was malfunctioning and allowing the BB to remain closed while charging highly discharged batteries (>12v), it could lead to the high temps and BB failures you reported.
Steve

[Fred Brooks]

    Richard,
Steve raises a good point. If your house batteries are old and starting to sulfate, The kind of inverter/converter you have on board will try to overpower the resistance in the batteries. This results in excessive amperage going through the big boy solenoid. The evidence you are indicating suggests that there is too much heat being generated. Fred

[Eric Maclean Co-Admin]

Richard
It's been my experience that a big boy that is powered up or turned on ( closed contacts ) for a long period of time the coil windings get fairly hot to the touch likely in the 165* range this is normal when the coach is plugged in to shore power and the bird has both battery banks combined .
How ever that temperature is no where near the amount of heat required to cook the  bakelite ( plastic housing)
It's my guess the cooked section is where the bolt studs where the battery cables connect to the solenoid, if so this indicated the contacts inside the solenoid are dirty causing high resistance and  arcing under heavy loads ( charging low batteries when first plugged in) and a large amount of heat to be generated which heats up the studs and cooks the housing around those studs.
This can be tested by testing the voltage on both sides of the solenoid while the charger is charging the outage should be the same on both sides of there is a volt drop across the solenoid under charge conditions this indicates a resistance at the contacts ( dirty contacts ) inside the solenoid.
The key is to catch it early and disassemble the big boy and clean the contacts.


Hope this helps
Eric