Magneto Coil Resistance
David McC
What resistance value should a good working magneto coil achieve on the
primary and secondary ?
Also, what value can you expect on a mag that is failing or already not
working ?
This has been mentioned before on the NG, except this time I will pay
attention !!
Thanks
David
--
David McCreath
Stationary Engines Scotland
http://stationaryengines.users.btopenworld.com
campingstoveman
therefore you would get no reading at all or if you place one lead of the
meter on the iron core and the other on one end of the coil a dead short
should will show if the insulation has broken down.
Martin P
David McC wrote:
> This is a common question but I am not too sure of the answer !...
>
> What resistance value should a good working magneto coil achieve on
> the primary and secondary ?
>
> Also, what value can you expect on a mag that is failing or already
> not working ?
>
> This has been mentioned before on the NG, except this time I will pay
> attention !!
>
> Thanks
> David
--
please replace email with martin...@btopenworld.com.
May the force be with you, because if she isn't you're on a hiding to
nothing.
Dave Croft
> If the coils are not working then the likely hood is that it has a break
> therefore you would get no reading at all or if you place one lead of the
> meter on the iron core and the other on one end of the coil a dead short
> should will show if the insulation has broken down.
>
> Martin P
> David McC wrote:
> > This is a common question but I am not too sure of the answer !...
> > What resistance value should a good working magneto coil achieve on
> > the primary and secondary ?
> > Also, what value can you expect on a mag that is failing or already
> > not working ?
> > This has been mentioned before on the NG, except this time I will pay
> > attention !!
> > Thanks
> > David
The most common cause of failure is the high tension coil going open circuit .
This still works for a while as the spark jumps the gap but it rapidly deteriates.
--
Dave Croft
Warrington
England
http://www.oldengine.org/members/croft/homepage/
http://community.webshots.com/user/crftdv
Peter A Forbes
<stationa...@NOSPAMbtinternet.com> wrote:
>This is a common question but I am not too sure of the answer !...
>
>What resistance value should a good working magneto coil achieve on the
>primary and secondary ?
>
>Also, what value can you expect on a mag that is failing or already not
>working ?
>
>This has been mentioned before on the NG, except this time I will pay
>attention !!
>
>Thanks
>David
David:
Depends on the coil types and wire sizes, but very approximately:
Primary coil 20 to 100 ohms
Secondary 2000 to 8000 ohms
The values will be consistent within magnetos from the same maker and of the
same type.
A broken down secondary winding will not show a steady resistance and the
resistance will be 30,000 ohms to 250,000 ohms or more.
A broken primary winding will not normally show any resistance as there is no
spark to form a track across the insulation.
A good capacitor will show a low resistance rapidly increasing as the capacitor
charges up from the voltmeter internal battery. A bad capacitor will either show
a short circuit or a high resistance from the start.
Peter
--
Peter & Rita Forbes
die...@easynet.co.uk
Engine pages for preservation info:
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Jack Watson
> >What resistance value should a good working magneto coil achieve on the
> >primary and secondary ?
************>
Peter wrote:
> David:
> Depends on the coil types and wire sizes, but very approximately:
> Primary coil 20 to 100 ohms
> Secondary 2000 to 8000 ohms
> The values will be consistent within magnetos from the same maker and of
the
> same type.
> A broken down secondary winding will not show a steady resistance and the
> resistance will be 30,000 ohms to 250,000 ohms or more.
> A broken primary winding will not normally show any resistance as there is
no
> spark to form a track across the insulation.
> A good capacitor will show a low resistance rapidly increasing as the
capacitor
> charges up from the voltmeter internal battery. A bad capacitor will
either show
> a short circuit or a high resistance from the start.
> Peter
Very true, and to elaborate:
Problem is that a fairly common cause of low HT output is due to shorts
between turns of the HT coil. You will still get a reading in the approx.
range and possibly a weak spark.
Being internal breakdown of insulation within the coil, it is not visually
obvious or easily testable.
Cause may have been operation of the magneto with the HT lead
open-circuited.
Some magys have a spark-gap built in to obviate this.
Only practical test and cure is replacement of the coil, unless you really
are into coil-rewinding and have good eyes as these secondary coils have
millions of turns of spider-web wire!
JW²
**************