Horn internal wiring question

mothy

mothy

Junior Member
My EA Labs horn only seems to want to run at 12 volts. Applying 6 volts merely makes it warm. Having read in another post about starter motors being converted from 6v to 12v operation by changing the field coils from parallel to series made me wonder if my klaxon motor is wired correctly.

At the moment power comes into one field coil, then to brush, through armature to other brush and then through other field coil. So I would say the field coils are wired in series through the armature.

Is this correct? If not how should it all be connected together?
I have looked in the Les Andrews and Service Bulletins but don't see an answer there.

Thanks

Roly
 
I don't have an EA Labs horn, but all my other horns are wired in series as you just described.

Could your adjustment screw be too tight? I oil the bushings and put a dab of grease on the wavy wheel that makes the sound. The adjustment should be such that the wavy wheel barely touches the chisel point on the diaphram.
 
Having the field coils wired in series with the armature is common in dc motors, i don't have any EA horns, but the spartons I have are wired that way.

how easy does the arm turn?, sometimes the spring in by the diaphram is too tight, or the thrust area is worn causing too much drag, the alignment of the field frame can be off creating a binding condition in the "bearings"

Oil soaked brushes, dirty commutator also

on a sparton the brushes are compressed copper screen, some repros are carbon, i like using as many original parts, have soaked the oil soaked brushes in solvent to clean them, also use a small pointed stick to clean between commutator bars
 
I have the adjustment screw backed right off.
I am testing directly off a battery not through the horn button.
It spins freely.
Commutator is clean. level and the segments are nicely undercut using a wooden cocktail stick.
I have rewound the field coils as per Les Andrews and the behaviour is the same.
The readings across the commutator are the same for each segment.

However the brushes are carbon replacements, not compressed copper screen which I have to admit I have not heard off.

The carbon brushes have pigtails which I have soldered to the brush holder to give best possible chance of conductivity through the motor.

I do not know when the horn last worked well. When I bought the car I investigated why the horn did not work and found that one of the brush holders was shorted to earth.

So maybe I should look to replacing the brushes with original design ones?

Thanks for the input.

Roly
 
Yes, the original ones will carry more current with less voltage drop than carbon. As Kurt mentioned be sure to spray gas or brake cleaner on the original ones to remove oil and dirt. I helped a friend with a slow turning horn by just holding fine sandpaper on the commutator and he held the horn button down. After a few seconds the speed started to pick up and after about 30 seconds of light sanding it was like a new horn. His commutator didn't look too bad either, but the sanding fixed it up.
 
I have ordered replacement brushes and brush holders, and will report back when they are fitted.

Thanks everyone

Roly
 
if the brushes are new they may need to be "broken in" by running it for a few minutes. I had the same problem with the horn I was working on. After 4- 5 minutes of running (30 secs or so at a time) the motor sped up and then the final minute of two was at 6 volts. The horn runs and sounds good now.
 
WardAZ said:
I just had to re-wind one, it was not shorted to ground, but the coating on the windings was bad and the windings were "shorted" against each other. The motor ran sluggish until the armature was re-wound.
Click to expand...

Did you do the rewind yourself? If so, any tips?

Roly
 
Kurt in NJ said:
on a sparton the brushes are compressed copper screen, some repros are carbon, i like using as many original parts,
Click to expand...

Kurt is right on the mark!

I replaced the brushes with new ones from O'Neil Ford (in the UK), they are labelled as from Snyder. These brushes do have a copperish hue to them. I also replaced the brush holders while I was at it.

Horn worked resoundedly well!
icon7.gif


I completed the rebuild by putting a 6v relay inside the horn to ensure as much current as possible gets to the motor.

Thanks to all.

Roly
 
You must log in or register to reply here.
Back
Top