OMC Universal Coils and Magnetism

[Buccaneer]

When I tested two nice looking, green, W. Germany coils found in my Johnson TN
project, the first one was normal with the multimeter readings
Primary .3 ish, Secondary 7.4 ish.

The second one I tested was, primary 2.0, and 7.4 on the secondary.

Today I tested them on the Stevens tester, and the one with the higher
primary ohm reading, fired steady at a lower voltage than the one I thought good.
The coil with the normal primary reading, fired steady at 1.35 amps, the
coil with the high primary reading, fired steady at 1.15 amps.
I repeated the test several times on each coil, and came up with the same numbers.

My question is, does the above testing results conflict with any theory
about how easy it is for the flywheel to produce a good spark?
In another words, should the normal coil spark easier with the spin of the flywheel
than the coil with the high primary reading?
The Stevens is showing the coil with the high primary reading is firing steady at
a lower amperage than the normal coil.

Signed, Confused and Stymied.

Prepare to be boarded!

[frankr]

I’m confused too.  But there is another ingredient here that is unknown.  That would be wire diameter and number of turns/length.  Whatever the answer, 2.0 Ohms certainly is unusual.  But all other things being equal, the usual thing affecting transformer output is turns ratio–the number of turns on the primary vs the number of turns on the secondary.

Confused too.

[Buccaneer]

I would think the Germans would have the number of windings down to a science,
but if there was corrosion of the primary circuit, and higher resistance,
you’d think it would take more amps to fire the coil.
Only if the engine runs bad on that cylinder, will we know for sure the
coil is wonky. I may have to haul water into the garage so I can test
run it before spring!

 

 

Prepare to be boarded!

[Hugh Davis]

Hey Bucky,

for what its worth,

I was talking to Glen at Ahlstrand the other day about a coil issue I have with my TN-28 and a problem I am going to have with an OMC4156.  He told me about a guy who knows everything. ( well….. maybe not everything…..)

Standard Magneto Sales Co

212 Ash Ave.

Wood Dale, IL. 60191

800-624-6386

http://www.standardmagneto.com

[crosbyman]

Microsoft Word – Articles-Mohat Part 3 SB review 6-4-18FINAL.doc (wrcoutboards.org)

Joining AOMCI has priviledges 🙂

[Buccaneer]

Thanks for the replies. I’ve read Mr. Mohat’s articles in the past, but
will have to read that one again when all is quiet to see if my answer
therein lies.

Prepare to be boarded!

[Mumbles]

I have two brand new German Prufrex coils here and can test the primaries on them for you  to see what they read.  If I dig out my Merc O Tronic, I will also see what they fire at but I can’t remember if it reads in amps or not like your Stephens unit does.  Time to pull out the manual, which is nearby.

[Buccaneer]

It would be interesting to see what your ohm readings are Mumbles.
I’m guessing yours will be like the coil I deemed to be “normal”.

I guess the real test will be to see how it runs, when that day comes.

Prepare to be boarded!

[crosbyman]

2 cents…

What are ampere-turns (ni)?

The more loops, the more magnetic fields unite and reinforce each other and,  as a result, the total magnetic field becomes stronger. by the wire and the result is called

Ampere-Turns (NI).

your “high resistance  primary” fits in the same  volume (space) size   as the other  coil (lower resistance one)  so what  is the variable…..to cause greater  primary resistance…???    wire size  &  more available turns 

 more wire turns  x amps =  more magnetism  to impart  on the secondary winding !  🙂 .    the fact that it ” fires ” with a lower current  input is compensated by ( or  reflects)   the higher number of  “wire turns” forming the coil primary

see 2 coils   same “pull strenght”   yet  different  amps  are flowing  but the NUMBER of windings  is doubled

 in conclusion I think both of your coils are fine  but built at different periods  by the same company 🙂

Joining AOMCI has priviledges 🙂

[Mumbles]

Me auto-ranger reads 0.9 ohms for the primaries of  both coils.

Have you checked to see what the resistance is of leads you are using?  Subtracting that number from your test results will give a true ohm reading.

 

• This reply was modified 2 years, 10 months ago by Mumbles.
• This reply was modified 2 years, 10 months ago by Mumbles.

[Author]

Posts