Selinoid

enblethen wrote:
The Big Boy uses a momentary voltage input to latch or unlatch the relay. Voltage is not required to be present at all times.
The contacts are rated 200 amp continuous duty. The Trombetta is only rated 150 amps.
The Big Boy is a latching relay where as the Trombella is an electrical held relay. The preform a completely different purpose.

That sounds good but then why is it only rated for intermittent duty?

The Big Boy uses a momentary voltage input to latch or unlatch the relay. Voltage is not required to be present at all times.
The contacts are rated 200 amp continuous duty. The Trombetta is only rated 150 amps.
The Big Boy is a latching relay where as the Trombella is an electrical held relay. The preform a completely different purpose.

enblethen wrote:
This is the common battery disconnect relay
Intellitec Big Boy

The fact that is has intermittant duty printed on the label concerns me since it is probably being used for continuous duty. Regardless, it will get hot if it is kept on very long. I would replace it with the Trombetta if it were mine but that doesn't seem to be the problem anyway. I am still wanting clarification of what the actual problem is and why the other relay repeatedly fails. I suspect that it is even less durable than the Big Boy and is also improperly used for continuous duty.

I do know some basics about electricity and can read the labels but I am not an electrician. On that note I have heard that most solenoids take more power to energize that is required to maintain the energized state and that a good controller will reduce the power after an initial surge. This will help reduce lost power and prolong the life of the solenoid. I have never witnessed this and wondered if it is actually a common practice.

I just had something pop into my head why relays can get hot and fail.
Power to control of relay is not correct. Being a large MH, it is possible that relays are receiving 24 volts instead of 12 volts.

This is the common battery disconnect relay
Intellitec Big Boy

I am guessing that by "big boy" your are referring to a Trombetta relay like the one below that is used to connect the house battery pack to the engine battery pack so that both packs can be charged from a single outside source. It may be energized whenever there is a sufficiently high voltage applied to either battery pack to indicate that charging is available.

Trombetta relay

My Trombetta did get very hot to the touch while the coach was plugged in and failed twice. I disconnect the trigger from the house battery pack and put a battery maintainer on the engine battery pack. Now my Trombetta lasts much longer. The link I shared has by far the best price that I have ever seen on a Trombetta.

I am guessing that the relay that keeps failing was not meant for continuous use, most starter relays are not. Either that or you passing too much power through it. I would try to figure out its function and whether the trigger is stuck on improperly if you have the wrong relay or maybe just and undersized one.

It could be a relay for power to the house. My coach has a button that remotely kills all 12v power to the house for storage or whatever other reason comes up. That would definitely require a continuous duty relay.

What are the symptoms when it fails?

The Big Boy is normally hot to the touch, but certainly not hot enough to ruin another solenoid. There is some other problem, and you still haven't said what solenoid??

Have you had a chance to look into problem?
Here is a thought.
Check to see what system the Big Boy latching relay disconnects. Then identify the other relay that keeps failing. Larger 50 amp rigs commonly have 200 amp relays where smaller rigs utilize 100 amp. Installing the wrong amperage can cause premature failure.
Locate the starter, trace the large battery cable back to it's source.
Trace the small wire from starter back toward the front of the rig.

Maybe the "ignition solenoid" is the starter relay and the starter is not disengaging.
Might have to trace some wires or get the wiring diagram for the rig.

farmingdad wrote:
I’m try to help a friend work on his. The big boy in the rear run box stays hot all time to touch and the ignition selonond beside it keeps going bad

If the person has the rv plugged in or plenty of solar that solenoid can run very hot to the touch.

The amount of heat given off should not certainly harm another solenoid nearby.

The person needs a voltmeter to diagnose.