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Old 11-17-2018, 10:06 AM   #1
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Is Big boy solenoid supposed to hum?

I'm hearing a high-pitched hum coming from the Big Boy solenoid located in the rear electrical/battery box. Engine not running, plugged into shore power (20A).

Is that normal?
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Old 11-17-2018, 11:12 AM   #2
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No, it is not normal. Humming indicates the relay inside the Big Boy is stuck closed, potentially draining your batteries. Try unplugging shore power, then plugging back in. Sometimes this will release the relay.

I replaced mine last year. The original lasted 8 years.
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Old 11-17-2018, 11:25 AM   #3
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big boy

Yes it is normal on some coaches. Some Monaco products. It ties house and chassis batteries together for charging purposes. That is the way it is set up on mine, 05 signature.
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Old 11-17-2018, 11:27 AM   #4
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It may hum. Theres a DC, electromagnetic coil in it to energize and hold it connected. You may be getting a bit of AC leakage thru your converter.

If your on shore power, it will be closed so it charges the chassis battery. It will also be closed when the chassis charging system is working. That's what it does.

As a test, pull the shore plug and it should open and not hum.
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Old 11-17-2018, 11:54 AM   #5
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Surprised that the relay used isn't a continuous duty solenoid. Which typically means the coil pushes the contacts to one side, and when the voltage to the coil is removed, the contacts stay connected. And visa versa to disengage the contacts.
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Old 11-17-2018, 12:08 PM   #6
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I believe the high pitched noise you hear is due to the "bird" providing pulsed power to the "big boy" to keep the solenoid energized but not overheated. This occurs whenever the coach batteries are at about 13 volts or so.

Under normal operation the big boy should generate little to no heat when being pulsed.
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Old 11-17-2018, 12:56 PM   #7
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Mine failed early but didn't hum just failed to connect. Found the best price for the exact Trombetta on Ebay in case you need to replace it.
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Old 11-17-2018, 01:16 PM   #8
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Many were operated with a pulsing lower voltage to keep them energized after the initial engagement.

That is to say. A full battery voltage is supplied to slam the solenoid closed and then a lower pulsing voltage is used to keep it closed/ engaged.

Yes this is likely a normal thing. I suspect your wife can hear it better than you. Women usually can hear the higher pitches better. Just a fact I learned from ladies complaining about the high voltage transformers in televisions a few years ago. Ok a lot of years ago when I was just 18.

This complaint has come up over the years and I suspect a search will come up with more comments.
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Old 11-17-2018, 01:18 PM   #9
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https://www.google.com/search?q=big+...earch=irv2.com

It may be normal on yours.
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Old 11-17-2018, 01:31 PM   #10
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A factory electrician helped me diagnose my aux start not operating last year. He explained to me the Big Boy should be engaged only while the engine is running. This allows both house and chassis batteries to charge via the alternator. When engine is off, the Big Boy should be disengaged. When the engine is off and the aux switch on the dash is depressed, the Big Boy should click, tying the chassis and house batteries together, jumping so either the engine or generator can be started. 10.5 volts is the magic number to allow operation. That's why it states in the owners manual to hold the aux start switch for 30 seconds when jumping the generator. Guess it gives the generator time to get up to speed and allows the transfer switch to work.

Sorry for the length of this post. My initial post only answered part of the question.
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Old 11-17-2018, 01:44 PM   #11
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Quote:
Originally Posted by Dav L View Post
Surprised that the relay used isn't a continuous duty solenoid. Which typically means the coil pushes the contacts to one side, and when the voltage to the coil is removed, the contacts stay connected. And visa versa to disengage the contacts.
What your discribing is a" Latching Relay " ( solenoid ).
They need a pulse of power to latch or unlatch and are used for battery disconnect .

An isolation/boost solenoid ( Big Boy ) is controlled by a voltage sensing control and only connects the batteries when the set charging voltage is reached.
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Old 11-17-2018, 01:50 PM   #12
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Originally Posted by AE Wanderer View Post
A factory electrician helped me diagnose my aux start not operating last year. He explained to me the Big Boy should be engaged only while the engine is running. This allows both house and chassis batteries to charge via the alternator. When engine is off, the Big Boy should be disengaged. When the engine is off and the aux switch on the dash is depressed, the Big Boy should click, tying the chassis and house batteries together, jumping so either the engine or generator can be started. 10.5 volts is the magic number to allow operation. That's why it states in the owners manual to hold the aux start switch for 30 seconds when jumping the generator. Guess it gives the generator time to get up to speed and allows the transfer switch to work.

Sorry for the length of this post. My initial post only answered part of the question.
If yours is working as you stated, then you don't have bi-directional charging thru it. You may have some other device to maintain your chassis battery while on shore power.

Many voltage sensing devices sense charging from either source and close the solenoid.
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Old 11-17-2018, 02:26 PM   #13
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Excellent answer... "I believe the high pitched noise you hear is due to the "bird" providing pulsed power to the "big boy" to keep the solenoid energized but not overheated. This occurs whenever the coach batteries are at about 13 volts or so"

OP, have someone else push the boost switch while you listen to the BigBoy... giving it the full 12V. If the humming stops I'd say it's normal as you must have good high pitch hearing.

"He explained to me the Big Boy should be engaged only while the engine is running"...he does not know what he's talking about.

"it states in the owners manual to hold the aux start switch for 30 seconds when jumping the generator" The 30 seconds is before you try and start...giving the good batteries 30 seconds to charge the weak batteries.

I've locked the boost switch on for half an hour when the BIRD stopped working without burning it up.

Most common problem when a BigBoy does not work is the contacts inside get dirty/corroded...cleaning them is fairly easy and cost nothing.
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Old 11-17-2018, 06:08 PM   #14
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There are dozens of variations of these battery interconnecting systems.

IRD, BIRD, Diode isolators for example. In the little green google box above put the BIRD into the search and you will be reading for days.

Some charge both ways. Some charge when the alternator is running.

Many rv's did not charge the engine batteries when on shore power which led to many bad batteries and dead ones at least.

The humming noise is a known issue and it not usually a failure. I can't say I ever heard a solenoid hum when pure 12 volt was applied and I worked with tens of thousands of them in 50 years in the public safety installation service.

Do some reading and try to come up with the actual setup in your rv. That is, was it ever supposed to charge the engine batteries etc. Knowing how it is supposed to work makes it easier to diagnose when they fail. And they do fail.
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