# Inductance and resistance meter



## Hornet (Dec 1, 2005)

Greg at Gravitas Tech,has asked me if there would be any interest in an inductance and resistance meter to test armatures with.

Resistance is an easy check for most guys,but inductance testing is a bit more involved.

So i'm putting feelers out for him to see if it's worth while for him to develop such a meter.

You can either post here or contact him at " [email protected] " if you're interested in such a meter.

Rick


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## tossedman (Mar 19, 2006)

So what does measuring inductance and resistance tell a fellow about the condition of armature Rick? Is this going to cost me more money?

Todd


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## Hornet (Dec 1, 2005)

If it's good,lol:thumbsup:

Basically any time you pass a electric current through a coil it generates a reverse current when the power is shut off,called back EMF,an inductance meter,is a meter that can measure the arms ability to create back emf .
High levels of back emf generally lead to hotter running motors


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## tossedman (Mar 19, 2006)

Oh, you mean that stuff that Oliver Heaviside coined in February 1886? Uses the symbol L for inductance, in honour of the physicist Heinrich Lenz while the unit of inductance is the henry, named in honor of the scientist who discovered inductance, Joseph Henry?

That inductance? Is that the one? Why didn't you say so? And don't forget about Oersted's law that states that a steady current creates a steady magnetic field and Faraday's law of induction that says a time-varying magnetic field induces a voltage in a nearby conductor. And Lenz's law too! In an electric circuit, a changing electric current through a circuit that has inductance induces a proportional voltage which opposes the change in current (self inductance). The varying field in this circuit may also induce an e.m.f. in a neighbouring circuit (mutual inductance). 

Ah, physics... Nothing like it eh?

Todd

Sorry for being a smart a$$, just can't help myself somedays...


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## alpink (Aug 22, 2010)

inductance, like a flow of electrons in one conductive line affecting a parallel but not attached conductive line?


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## Hornet (Dec 1, 2005)

LOL,you guys got it:thumbsup:

I try to keep my answers fairly simple,as i find it's easier for most guys to grasp things.
Todd's got the more detailed answer,lol:wave:


Rick


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## Boosted-Z71 (Nov 26, 2007)

You guys are too funny!

Boosted


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## jobobvideo (Jan 8, 2010)

glad somebody splained it to me...


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## slotking (May 27, 2008)

my take on.
after years of checking arms for ohms & balance I found it just better to put in the car and see.

I have arms would ohm 6.2 6.4 6.7 that were out of balance that would fly!
I have arms that were 6.2 6.2 6.2 and where naturally balanced that were dogs.

after we started using hot stock arms, I have still had screaming arms with wacked ohm readings!

so now, for t-jets to inlines, I just put them in the car


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## Hornet (Dec 1, 2005)

About the only guys who'd really benefit are real hard core T-Jet and SS racers,and motor re-winders/rebuilders.

The guys who go through a case of arms looking for the best arms to start with, probably should use one,but for the average guy,it's probably not a highly needed tool.

Greg hasn't set a price yet as far as i know,but if they aren't overally expensive,i'll pick one up if he goes into production on them:thumbsup:
Rick


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## dtomol (Mar 30, 2005)

*Aramature Info*

I Think you might find this interesting:wave:

Good Afternoon Everyone,

I finally got a bit of time to play with slot cars again and decided to do a refresher experiment on the magnetic field strength that is produced when a pole of an armature is energized. As you know, the armature pole is energized with an electrical current running through ( technically, on the surface of ) the wire wrapped around a material that is magnetizable, creating a magnetic field that is opposite to that of the permanent magnet the armature is rotating towards. These two opposite magnetic fields attract causing the armature to accelerate until it reaches it’s maximum rpm.

What I wanted to do was to measure the strength of the magnetic field produced by various types; inline and pancake, and different winds; stock, Super II, and rewind. Following is the setup:

WrightWay 1/24th Power Supply, 0v to 11.75v DC, 0 to 10 amps

WrightWay ( Acello ) Gauss Meter, -1999g to 1999g, 

All arms tested at 0.99 vDC. Reading in gauss for one pole.

All Electronics $0.50 slot car motor: 30 gauss ( This is a Mabuchi HT-50 type Can Motor )

Tomy Super G+ Armature: 62 gauss

Auto World T-Jet 500 Armature: 52 gauss

Aurora Blue Tip Drag Armature: 91 gauss

Aurora Super II Armature: 128 gauss

Own Rewind, 9.5 feet of 36 on a 2 lam Armature: 141 gauss

Some information for those of you who are thinking about rewinds. I know that the question was asked about the difference between the same ohm armatures but having different wire sizes. It’s all about which can carry the most current the most efficiently; the larger the wire the greater the current capacity the more work it can do. Maybe not in the way you want it to, but, that is where all the other factors of slot car racing come into play.

I needed to do this experiment to help me design a 12 ohm can motor for BRASCAR and scratchbuilding applications without needing to turn down the volts. Hopefully, in a few weeks I’ll have something to share.

Here’s a photo of some arms done back in the 70’s, the two on the right by me, the two on the left by Merril Rowe.

QLamarms.jpg

Be Good,

Keith VanAtta


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## tossedman (Mar 19, 2006)

Hornet said:


> About the only guys who'd really benefit are real hard core T-Jet and SS racers,and motor re-winders/rebuilders.
> 
> The guys who go through a case of arms looking for the best arms to start with, probably should use one,but for the average guy,it's probably not a highly needed tool.
> 
> ...


Oh thank goodness. Thought I'd have to spend a pile more money that could have been spent on cars, or a track or a new Skinkansen or a subway or something else like that.

Todd


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## Hornet (Dec 1, 2005)

Keith i'm curious about the 0.99 volt used for the test,is that a standardized testing voltage,or an arbitary test voltage.

That's quite a spread in guass readings from arm to arm .

Wouldn't motor mag gap affect some of these readings.
Tightening up the gap should change the readings if i'm getting the test sorta right.
I'm trying to mentally see how your doing the test,pic's would help:thumbsup:

Greg mentioned being contacted by a motor guy,now i'm thinking i know who,lol:wave:
Rick


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