# ohm readings on arms



## leonus (Dec 17, 2013)

Recently I finally dug my multi tester out of the shed, to help find trouble spots on my track. After finally successfully wiring in some jumpers, I decided to try and ohm out some arms.

In particular, I wanted to test one that was a poor performer, an old mean green (copper wire green tip) from an afx non mag.

I was surprised to see 8.3,8.3,17.8
I suppose that's why the old dog won't go fast..

I was just wondering, what might be the cause of the one pole being so different??


----------



## LDThomas (Nov 30, 1999)

Broken wire...


----------



## leonus (Dec 17, 2013)

Ok then, so I suppose it's not feasible to fix?


----------



## slotcardan (Jun 9, 2012)

........


----------



## slotking (May 27, 2008)

> really measuring the coils for balance requires a very sensitive Ohm meter that is calibrated with a card stating the ohm gain from the probes themselves


it nice,,but but not needed,
I hae used bith crap meters and TOL meters and the readings are always close.

it is just that you may have to do some math!
ie.. touch the probes and get a reading. if it say 2 then subtract 2 from the arm reading. if it says 5, then subtract 5.

never had an issue with this method.


----------



## Rich Dumas (Sep 3, 2008)

If an armature is not defective the three poles will be wired in series. Presuming that all three coils are actually the same, the reading for any coil will be 2/3rds the value of one coil taken out of the circuit. For an armature that reads 6 ohms each pole is actually 9 ohms. See the circuit diagram below.










It looks like the arm has a bad solder joint. If a pole was completely open the readings across the good ones would be higher. If there was a dead short (unlikely) across one pole the readings would be lower.


----------



## Bill Hall (Jan 6, 2007)

Unless your going to investigate re-winding yourself. Do your part to perpetuate the species. Save your cores until you get a pile; then send them to Srigs @ Yellowjacket.


----------



## slotking (May 27, 2008)

just an fyi, a broken wire can increase the ohms.
the wire can still touch but the impedance will increase giving a higher reading.
to much distance and you get an open.


----------



## leonus (Dec 17, 2013)

Thanks for all the info gents.

As far as rewinding, not interested really, but I may try re soldering the ends, just for grins, since the solder was kinda peeling.

Will let you know what happens.

P.s.
I love this forum. To have learned so much for free is great. Thanks again&#55357;&#56841;


----------



## rholmesr (Oct 8, 2010)

If it's a mean green, it should ohm around 5.5 to 6 ohms per pole. If one pole is open (broken wire) and it would otherwise have been a 5.6/5.6/5.6 ohm arm then you would get readings of about 8.4/8.4/16.8. Seems close to what you are seeing. If the break is near the solder joint on or near the finish turn, then you can often fix it by finding the break, dewinding the winding by one turn back from the break and resoldering the wire to the correct pole connection. I have also at least a couple of times found a break a bit farther back, and just dewound both sides of break back one turn and then twisted the wire ends together and soldered them together and superglued the wire to surface of arm and that worked too. May or may not be worth the time. Good luck!


----------



## leonus (Dec 17, 2013)

rholmesr said:


> If it's a mean green, it should ohm around 5.5 to 6 ohms per pole. If one pole is open (broken wire) and it would otherwise have been a 5.6/5.6/5.6 ohm arm then you would get readings of about 8.4/8.4/16.8. Seems close to what you are seeing. If the break is near the solder joint on or near the finish turn, then you can often fix it by finding the break, dewinding the winding by one turn back from the break and resoldering the wire to the correct pole connection. I have also at least a couple of times found a break a bit farther back, and just dewound both sides of break back one turn and then twisted the wire ends together and soldered them together and superglued the wire to surface of arm and that worked too. May or may not be worth the time. Good luck!


That's exactly what I did, right before I read this post!
Now its 6.5, 6.5, 6.5
Gonna put her in a chassis and see what happens&#55357;&#56833;

Upon donning my magnifying glasses and looking closely, I saw that the last winding on one coil was burnt through, so I unwound each side around to the back, carefully twisted them together, wrapped the twistie around the end and resoldered.


----------



## leonus (Dec 17, 2013)

Put her in a heretofore underperforming chassis, and she COOKS!

Love it when a plan comes together &#55357;&#56833;

Thanks all.


----------



## Dslot (Sep 2, 2007)

> Love it when a plan comes together.












... and not only for Leonus' armature-fix, but for the *forum*. 
Seven people instantly pitching in with specialized knowledge to help a buddy have fun with HO slots. 
That's what it's _*about*_.

-- D :hat::thumbsup::hat:


----------



## rholmesr (Oct 8, 2010)

Yay!!!


----------



## LDThomas (Nov 30, 1999)

Good Job!


----------



## leonus (Dec 17, 2013)

Thanks again.

It really is more fun when everyone plays together&#55357;&#56841;


----------

