[Boatanchors] Milliammeter shunt resistance wire > sources?

[Paul Kraemer]

My first meter shunt from back in 8th grade was made from a ball point pen 
spring! All pretty and coily and it had the correct resistance to make my 
plate meter in a 100w linear read correctly. Trial and error I kept trimming 
off turns til I had it right.
Yes, they had ball point pens "back then"
I figured somebody would have that comment
Paul K0UYA
----- Original Message ----- 
From: "Drew P." <drewrailleur807 at yahoo.com>
To: <boatanchors at mailman.qth.net>
Sent: Sunday, May 30, 2010 4:02 PM
Subject: Re: [Boatanchors] Milliammeter shunt resistance wire > sources?


> On making shunts for milliammeters, Roger wrote
>
> "You might try a length of light bulb filament wire. You are not heating 
> it to light hot so it will last as a resistor in free air."
>
> I unsuccessfully tried soldering to a piece of tungsten (light bulb 
> filament wire) back in my much younger years and haven't tried since. A 
> problem with tungsten as a shunt is that heating caused by current flow 
> causes large (as compared to copper or nichrome) resistance changes.  Your 
> meter scale would need to be compressed at one end.
>
> Fine enamelled copper wire wound on the body of a resistor works 
> reasonably well as a shunt in this application.  The resistor is being 
> used as a form only and the resistance of the shunt will be low in any 
> case so a resistor of, say, 100 ohms or higher would be suitable. I did 
> this many years ago using a 2 watt resistor and wire from a deflection 
> yoke, both salvaged from the same junk TV set (definitely the right 
> price).
>
> Another approach is to use a standard resistor value as the current 
> sampling (shunt) resistor.  The value is chosen to be somewhat higher than 
> actually required (the required value is likely not standard). The 
> resultant excessive sensitivity is then adjusted downward by use of 
> another resistor in series with the milliammeter.
>
> Yet another scheme is to use a parallel combination of standard values as 
> a shunt resistor.
>
> Drew
>
>
>
>
>
> ______________________________________________________________
> Boatanchors mailing list
> Home: http://mailman.qth.net/mailman/listinfo/boatanchors
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Boatanchors at mailman.qth.net
>
> List Administrator: Duane Fischer, W8DBF
> ** For Assistance: dfischer at usol.com **
>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>