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Topic: A Lesson in 12 volt electrical systems (Read 1087 times) previous topic - next topic

A Lesson in 12 volt electrical systems

 :o I purchased my 1994 40' U300 in December of 2007 from a consignment lot in Jacksonville, FL. Drove it on home to Charlotte Harbor, FL. and started learning the various systems. We took a few short two/three day trips to get the feel of our new to us coach, even though we have had two other coaches, an Airstream and a Bluebird. This one was everything we were looking for in a affordable motor home. When we arrived back home from one of the first shake down trips I had to replace one of the two 8D house batteries, cleaned the terminals and sealed everything with battery terminal spray. From that time on I started having problems with the charger/inverter system. It would work intermittently sometimes it would charge the batteries some times it would not. Finally one day I had a lot of smoke coming from the compartment next to the stairwell. The inverter/charger had burnt out, melted down, became junk. I thought that maybe it had been going bad so I replaced it with a new 2,500 watt inverter. Well, about a week later the new inverter started acting just like the old one, and not wanting to burn up the new one I started looking for a cause. I found that the house battery terminals were very secure to the battery posts, however these terminals have a combining bolt on the rear of the terminal that holds one (1) to four (4) cables that unite the batteries and feed various systems on the coach; the Inverter, the Generator set, the Boost switch and the Isolator. All of the combining bolts were loose, the two positives and the two negatives. So, I got my wrenches out and tightened them up, No more problems, for the next two years. Everything is working like a champion, then I started to notice that the generator glow plugs did not seam to heat up as they use to, the generator became hard to start. Then it would only start with the Boost switch engaged, Finally it started to shut down as I was driving down the road as if it had run out of fuel. The Boost switch did not seam to allow both sets of batteries to charge nor did the Isolator. The batteries would not charge from the generator or from the engine alternator (it would keep the engine batteries charged). I started looking for a bad relay, solenoid, checked the isolator, nothing wrong. So I started at the house batteries, load test, terminals cleaned post checked for tight cables, everything looked good. I decided to inspect the combining connection on the rear of the battery terminals, there is where my problems all originated. Although these connections were tight and appeared to have continuity, upon disassembly I found a crust build-up between each of the cable ends, they were not corroded but more like heated and some type of hard non-conductive substance had coated each terminal end. So I cleaned up at least 10 cable end down to the bare copper re-dressed the back of the lead terminal connector put star washer in between each cable end, re assembled and my problem has been curred. Any place where cable ends are stacked could cause current flow problems. also, check any grounding cables for integrity and proper bonding to ground.    Hope this helps if anyone is experiencing freak electrical problems.  :)   

 
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Gerry & Brenda
CHARLOTTE HARBOR, FL
1994 Grand Villa - # 4466
U300 Unihome - 6V92 Detroit
4 speed Allison - Jake Brake

Re: A Lesson in 12 volt electrical systems

Reply #1 –
Gerry,

Thank you for your dissertation.  I've taught electrical troubleshooting for years and tell people to do the easy and cheap things first.  Cleaning connections fixes 90% of electrical problems.  Also, the owner gets to fondle his second love and learn intimate things about her.
Great post!
Michael Baldacchino
'97 40' U320

Re: A Lesson in 12 volt electrical systems

Reply #2 –
Gerry, I have had problems with the kind of hard black substance on terminals.  I wish I knew what it is and how to prevent it.  The only cure is to do as you have, scrape them clean, coat them and hope for the best.

Re: A Lesson in 12 volt electrical systems

Reply #3 –
Gary,

Does the hard black substance reappear after cleaning or only before you cleaned them?  If it was only before then it might have been something like Glyptal, an insulating varnish.
John Cooper
'91 GV 36'
Oshkosh chassis
Cat 3208T 300HP

Re: A Lesson in 12 volt electrical systems

Reply #4 –
Quote
Does the hard black substance reappear after cleaning or only before you cleaned them?  If it was only before then it might have been something like Glyptal, an insulating varnish.
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John Cooper
John, It apparently apperas only after a long period.  A fellow owner could not start and we found this hard black substance on Start battery posts, I then found it on my start batteries even tho they Had been cleaned recently. Later when I checked again I found it again after 5 to 6 months. I am inclined to think that it forms in areas of high humidity and while in storage when battery is dormant.  I have not had the experience with house batteries even tho they are exposed to the same elements.  Its a mystery.

Re: A Lesson in 12 volt electrical systems

Reply #5 –
Is there any chance that dielectric grease may turn into this black substance over time?
Peter & Beth Martin
No Forrest? What have you done?
MC# 15890 until Dec 2016; FMCA #F329677
Cincinnati, OH

Re: A Lesson in 12 volt electrical systems

Reply #6 –
In my case it was only on the combining terminals of the house batteries. I do believe it is caused by the Heat produced when the connections are not properly cleaned and tightened. Could be melted lead or some sort of chemical reaction caused by the heating and cooling of a loose connection. Although even after I tightened my connections the process continued to deteriorate the connection. I have also had this same build-up on other vehicles between the battery terminal and the battery cable connector.
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Gerry & Brenda
CHARLOTTE HARBOR, FL
1994 Grand Villa - # 4466
U300 Unihome - 6V92 Detroit
4 speed Allison - Jake Brake

Re: A Lesson in 12 volt electrical systems

Reply #7 –
Quote
Is there any chance that dielectric grease may turn into this black substance over time?
Peter, I don't believe that dielectric Grease had been used in either case that I am familiar with.

Re: A Lesson in 12 volt electrical systems

Reply #8 –
Quote
hard black substance on terminals
I would guess it's acid migration from inside the battery (even with Gels and AGMs).  Every post will have some kind of seal with the battery case and like everything some will be better than others.  I would think use of dielectric grease would help maintain the connection by inhibiting the migration (if this theory is correct).  If the battery (or just the terminal) ever became very hot the seal might be degraded significantly.  Just my guess though.
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: A Lesson in 12 volt electrical systems

Reply #9 –
This is a very confusing substance.  The reaction of lead and sulfuric (battery) acid yields lead sulfate, PbSo4, a white powder.  Galena, lead sulfide, PbS, is a black mineral but I don't think it would form on battery posts.

I'll ask a friend of mine, a chemistry professor at Rice University.
John Cooper
'91 GV 36'
Oshkosh chassis
Cat 3208T 300HP