G Scale Model Train Forum banner
1 - 16 of 16 Posts

·
Premium Member
Joined
·
965 Posts
Discussion Starter · #1 ·
I have just found the third axle [from two cars] on my Bachmann 3-bay coal hoppers that was shorted across from wheel to wheel. The first one I found had some trackside wood bark smoldering, melted the truck journals, and tripped the circuit breaker on my power supply. Since then, I have found two axles on a second car that were shorted. When the offending wheel is removed from the axle and a battery and voltmeter test is done , there is voltage transfered between the outside of the wheel and inside of the plastic bushing at the center, to the axle. I guess the entire set of hoppers will have to be checked for conductivity across the axle and wheels.

Note melted journal and pitted wheel:


Ordinarily, this would not be a problem for me running track power. However, one of my lines is track power capable for visitors. This is when the short happened.

I contacted Bachmann 2-1/2 weeks ago [ 9 days before Marty's] and got a less than satisfactory response. First there was an attempt to blame my MRC power supply. When I refuted that idea, I was told to send in the offending parts and if they agree, a replacement would be returned in about four weeks from date of receipt of my parts. The fact that I wanted to take these cars with me to Marty's, was of absolutely no consequence. As example of better customer service, another company making Garden Train products has even given overnight delivery of replacements when there were exceptional circumstances.

To those of you that run track power, I suggest that you check any of these cars you have to make sure "magic smoke" doesn't show up on your layout.

Has any one had a similiar problem?

JimC.
 

·
Registered
Joined
·
1,167 Posts
The best they would do is replace the wheel sets. One look at the rusty screws and cobwebs on the bottom and I doubt they would even do that. Why go through all that hassle and instead upgrade to better wheels like Aristos or Al Kramer's?
Did you use any type of grease or oil on axle tips that might be conductive?

-Brian
 

·
Premium Member
Joined
·
965 Posts
Discussion Starter · #3 ·
Brian,
Thanks for the suggestions and considerations. I ultimately didn't send them to Bachmann for exactly the thoughts you expressed.

The axle tips were lubed with graphite. I have already replaced the axles in the first car with other Bachmann axles/wheels I had on hand. Although I had some, I didn't use San Val axles because they are smaller diameter than the original Bachmanns and it would affect coupler height. Before I could put in the new axles/wheels, the melted flashing on the truck journal had to be cut away and the holes redrilled.

The real point of this thread is to warn other track power operators of a potential [short/fire] problem that could be caused by defective parts.

Jim C.
 

·
Premium Member
Joined
·
1,868 Posts
Jim,
Very strange. I don't use Bachmann wheels but this just got my curiosity up. In order to be a short there would have to be continuity from one rail to the other. Do Bachmann wheel sets have bushings on both ends or just one end? Are they even a solid metal axle all the way across ? Did you take apart an offending axle to see what was in there?
 

·
Registered
Joined
·
1,167 Posts
There is a solid axle all the way through covered by two sections of of plastic cylinders which the wheels are fitted onto. Not sure how both wheels would lose the bushing separation but strange things happen.

-Brian
 

·
Registered
Joined
·
350 Posts
Graphite is conductive. It is vry "slippery" and if used as a powder can migrate to where one doesn't want it.
 

·
Registered
Joined
·
318 Posts
Jim

I have used these wheels on a large number of my cars for years with no problems. Between the wheels and the axles are a think plastic bushing. If for some reason the plastic bushing were damaged the wheel would wobble a great deal.

The side frames are also plastic so you can not get any electrical contact there.

The only way you could get a short is if the plastic bushing on both wheels were shorted.

I can not see how thic could happen as a defect.


I believe that the graphite you added has made an electrical connection from the wheel to the axle. Since the graphic is on each end it is possible that the short occurred on each end

To determine is this is true you might want to clean up one of the shorted wheels with alcohol to remove the graphic and then try an ohm meter.

Hope that helps

Stan
 

·
Premium Member
Joined
·
501 Posts
I see by your photo alot of greasy black gunk around the journal. If you have used graphite it has collected enough to make a connection between the axel and wheel and vola! A BIG short. Back in my HO and On3 days some of used graphite ONCE because it didn't take long to fry a fuse on a transformer. Graphite in aeas where insulation is required is s a big no no Jim. Clean up your wheel sets with a little soap and water, alcohol or other degreaser and you will have solved your problem. Throw a volt/ohm meter across one axel end on one side and the wheel rim on the opposite side before and after cleaning and I think you will be suprised.
Noel
 

·
Premium Member
Joined
·
965 Posts
Discussion Starter · #9 ·
Noel,
The black "gunky" stuff you see around the journal/axle in the picture is melted plastic from the truck.

It seems to be the consensus that the graphite is the cause of the short. I will indeed use some alcohol or soap/water on all cars that the graphite was applied to.
As for this particular truck, the wheels/axles were removed, melted plastic trimmed off, new axle hole redrilled, and new wheels/ axles fitted.

Further explanation of potential problem with cars left outside:
There is a dead short from one wheel, through the axle, to the other wheel. I know some might think that is impossible since there is a plastic [non-rotating] bushing between the metal wheels and the metal axle. After discussion, it seems likely that a conductive trail of the [dry] graphite lube I used on the journals must have formed between axle and wheels [cars were outside]. Although it baffles the mind that this could independantly occur on both wheels on the axle, apparantly that has happened on at least three axles.
I started using the graphite to avoid dust collection when oil or greese is used to lube the journals. "My Bad!"
Another picture of a dissassembled wheel/axle that is shorted will be taken and posted.


JimC.
 

·
Super Modulator
Joined
·
21,372 Posts
Well, I'll go against the flow here. While graphite is somewhat conductive, it's not very conductive as a powder. If you ran enough current through some graphite on the axle to wheel spot to melt plastic, then I will tell you that the graphite would have vaporized first.

Try it... Take a 10 amp transformer, connect the power to each wheel, and then put graphite on it and try to create a short. I think that you will not be able to do it with a thin coat of graphite.

OK, everyone getting mad because "graphite is conductive", I know that, but running a lot of current through a thin coating will just vaporize the thin coating.

I don't think graphite mixed with grease will be conductive enough either. Again, rather than get in an argument, try the experiment.

You can use your melted axles for the experiment.

I believe the results will prove out what I say. It is VERY hard to find a powder that can conduct large amounts of current. Remember, the "theory" is that the graphite passed enough current to melt the plastic. The "theory" is that the graphite "started" the problem.

I believe the cause is elsewhere.

Regards, Greg
 

·
Premium Member
Joined
·
5,629 Posts
As these cars had been left out in the weather I would tend to suspect that rusting at the insulated wheels could have managed to flow to the axles and caused shorting. Later RJD
 

·
Old Senior Member
Joined
·
1,456 Posts
Jim.. At the beginning I used Graphite and had that problem when moister got on wheels and the graphite would run across the plastic insulator on the axle. I have a few melted/ slanted wheel laying around the layout for conversation pieces. Now use only white grease on all car wheels.
Just about half of my rolling stock is bachmann wheels with no problems other than have to gage them when I put them on.
I do use WD 40 some times on my track cleaner car to keep the wheels from rusting.. All of our wheel look good and were track power for 7 yrs now. So it must work in our area. But then we don't leave any rolling stock out side after runs.
We use USA wheel grease on all of our power axles tho.
Hope this helps in your area.........Noel
 

·
Premium Member
Joined
·
377 Posts
Greg
You may be right but I have found that at least some plastics become conductors if charred. So in vaporizing, the graphite might well have
changed the insulating bushing. Mind you, I've only met this problem in 110 volt systems.

Harvey C.
 

·
Premium Member
Joined
·
965 Posts
Discussion Starter · #14 ·


Here is the promised picture of the wheel/axle. A power source was attached to the wheel. The probe of a voltmeter [in series] was placed in the center of the wheel bushing while in place. Battery voltage was shown in the meter. That voltage was then transfered to the axle, which in turn, transfered the voltage to the other wheel [around the bushing].

Jim C.
 

·
Super Modulator
Joined
·
21,372 Posts
Harvey, I agree with you. I believe that it could be a problem, especially if charred, melted, damaged, but I find it hard to believe that a thin film of graphite powder could conduct enough current to melt the plastic bushing.

If you think about it, the short has to be THROUGH the plastic or very near it to melt the plastic. If there was a separate conductive path, then then heat would be THERE, not in the bushing.

Something still does not ring true as graphite being the culprit. N.B. I am not saying that you could not have some conductivity, just that enough to make enough heat to melt plastic could not have been supported by a thin film of graphite.

I hope someone tries the experiment I suggested.

Regards, Greg
 

·
Premium Member
Joined
·
965 Posts
Discussion Starter · #16 ·
The graphite could have gotten wet. The cars were outside for a prolonged period of time.
JimC.
 
1 - 16 of 16 Posts
Top