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Cleaning Big Boy & Storage Modification


Frank McElroy
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It turns out that about every 6 years, I need to clean the contacts inside big boy.  The problem starts when I notice that either the chassis batteries aren't being charged when on shore power or the house batteries aren't being charged from the engine alternator.  Cycling the battery switch a few times will clear the problem for the short term but the real solution is to clean the internal contacts.

The procedure is already well documented in the download file.

What I found interesting is the very small contact area on the studs and the edge of the ring making contact.  Over time, the hardened carbonized dielectric grease is acting like an insulator preventing good electrical contact.

Typically, the coach is plugged into shore power when stored in the garage.  Instead of leaving big boy constantly engaged, this year I added a copper plate across the big boy battery posts and unplugged the circuit board. 

This modification will keep both house and chassis batteries charged without wasting energy keeping big boy energized.  When I get back on the road it's easy to remove the copper plate and reconnect the control board.

Pictures are always worth a thousand words.

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Frank,

If chassis batteries seem to charge on shore power intermittently do you believe that the Big Boy is the usual culprit? I am a bit confused as I thought that was only to tie the chassis to the house batteries for jump starting. This may be my phantom culprit. 

 

Thanks,

Ken

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Yes, likely your Big Boy needs to be cleaned.

There is a circuit that controls when big boy is engaged to connect house and chassis batteries together.

When running the engine and the chassis batteries get above about 13.1 volts, big boy will engage and the alternator will charge both the chassis and house batteries.

When on generator or shore power, and your magnum battery charger is turned on, big boy will engage once the house batteries get above about 13.1 volts to also charge the chassis batteries.

When the engine is off and you are not on generator or shore power, big boy will drop out once battery voltage gets below about 12.8 volts to isolate the chassis from house batteries.  If big boy is not engaged and you need extra battery power to start the engine you can use the dash battery boost switch to engage big boy.

That's the big picture without getting into more details on time delays.

Bottom line - if big boy is humming and hot and your house and chassis batteries are not at the same voltage, it's time to clean the big boy contacts.

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Dielectric grease is non-conductive and shouldn't be used on contacts or connections. It is meant to be used on things like rubber boots or, in the olden days, the rubbing block for the points in ignition distributors. What you should use on contacts is Deoxit D5 contact cleaner followed by Deoxit Shield S5. Product descriptions:

The DeoxIT contact cleaner is a fast-acting deoxidizing solution. This D5S6 contact cleaner spray was designed for use as a general treatment for connectors, contacts, and other metal surfaces. More than just any contact cleaner, DeoxIT chemically improves electrical connections to ensure clean and clear sounds. The D5S6 DeoxIT is an essential accessory every musician must have!

CAIG S5S-6 DeoxIT Shield S-Series S5 Spray. Contact lubricant and protectant for metal surfaces. Oxidation and corrosion deterent. Improves conductivity maintains optimum signal quality. DeoxIT? Shield also reduces wear and abrasion arcing RFI and intermittent connections and improves connector performance/reliability. Ideal for severe environments. On oxidized surfaces pre-treat with DeoxIT? D-Series contact cleaner. Temperature range: -34 C to +210 C.

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Frank,

Thank you for the clarification. My rig is connected always to 50 amp shore power and randomly I go out and the chassis batteries are weak and the engine does not want to start without using the batt boost. When fully charged (and I do disconnect to test) the chassis batteries pass load tests with flying colors. The alternator passes all tests also. Most always after a long drive and hooking up to shore power the charger (mine is an older Trace 3000 watt) comes on full charge for quite some time before it goes to float. Perhaps it isn't charging while driving either. I've never known if that is normal behavior of the charging system or not. So anyway I suspect my randomness of symptoms is related to the Big Boy which is the original from 2003. I printed out your cleaning instructions and will attempt that. I can't go wrong the BB is still available to purchase but at $175 dollars for a new one I think I will give the cleaning a go. 

Thanks again,

Ken

 

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You're welcome Ken.  My coach also spends a lot of time in storage lately.  That's why I decided to bypass the big boy relay while in storage.  Saving about $10/month in wasted electric adds up after a few months.

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11 hours ago, Bill Morgan said:

Dielectric grease is non-conductive and shouldn't be used on contacts or connections. It is meant to be used on things like rubber boots or, in the olden days, the rubbing block for the points in ignition distributors. What you should use on contacts is Deoxit D5 contact cleaner followed by Deoxit Shield S5. Product descriptions:

The DeoxIT contact cleaner is a fast-acting deoxidizing solution. This D5S6 contact cleaner spray was designed for use as a general treatment for connectors, contacts, and other metal surfaces. More than just any contact cleaner, DeoxIT chemically improves electrical connections to ensure clean and clear sounds. The D5S6 DeoxIT is an essential accessory every musician must have!

CAIG S5S-6 DeoxIT Shield S-Series S5 Spray. Contact lubricant and protectant for metal surfaces. Oxidation and corrosion deterent. Improves conductivity maintains optimum signal quality. DeoxIT? Shield also reduces wear and abrasion arcing RFI and intermittent connections and improves connector performance/reliability. Ideal for severe environments. On oxidized surfaces pre-treat with DeoxIT? D-Series contact cleaner. Temperature range: -34 C to +210 C.

Bill, I think we will respectfully agree to disagree. 

In contacts inside Big Boy, the only grease you want to use is a dielectric grease.  Having an electrical conducting grease is the last thing you want to use.  There is a debate that will rage on the term dielectric grease.  But, silicon based greases and those petroleum based greases without metal additives (like the one you referenced) are inherently dielectric greases.  There was so much confusion that many manufacturers removed the name dielectric because it was so confusing to people who thought why use a dielectric grease on electrical contacts - that doesn't make sense.

The only real purpose of this grease is to inhibit corrosion, and not to conduct current especially when contacts are being made and broken.  When contact is made, the grease is pushed aside and you actually have direct contact between the copper studs and the round copper disk.  So that's why you use a dielectric grease.

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Bob, you are very observant.  After I took the picture I got to thinking that it actually made more sense to just unplug the control board.  My thinking is why leave that board powered up when I'm not using it anyway.  So I put the wire back on the big boy relay and below is a picture of the rear run bay board #6 unplugged.

One other piece of information that most folks might not know is that those two small yellow colored push buttons perform the same function as the battery boost and salesman switches do up front.  They can come in handy if you need battery boost when starting the engine from the rear.

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