Testing a Model A Coil

[BudP]

I am looking for some guidance on testing a 6 volt coil with an analog meter. I presume side post to side post will check the primary windings but what should be the setting on the analog meter and what range of numbers constitute an acceptable reading? Almost the same question with regard to checking the secondary windings. I presume side post to center is proper but which side post and what constitutes an acceptable range? Finally, where should my meter be set for each test. Thanks a lot.

[DaWizard]

Simple, plug it in, see if it fires. If you are taking your VOM to the swap meet and checking as you see them, about the only thing I think you can check is across the poles. That should be 3ohms on the Rx1 scale.

[Mitch]

Bud
i am sure Tom will chime in with the testing info using a meter. Personally i just drive them to test because when they get hot things change internally with the windings. shorts etc.
Keep a spare in your back pocket when doing this

[Tom Wesenberg]

3 ohms would be for a 12 volt coil with internal resistor. The 6 volt Model A coil should be about 1 1/2 ohms, so put the meter on the R x 1 scale, and hope your meter is good enough to read low ohms accurately. I prefer to check them on the battery charger. I use my 6 amp charger set to 6 volts, and look for about a 4 amp draw on the meter.

As far as the secondary, connect to the center and either side and look for over a thousand ohms. I don't recall the spec, but will see if I can find it again.

About 3 to 4 thousand ohms should be good for the secondary. I'll measure my original slant pole coil later and post it here.

[BudP]

Thanks a lot, everyone.

[DaWizard]

Whew, sorry, my bad. 1.5 ohm.

[Mike V. Florida]

This site has info that also includes modern coils.

[BILL WILLIAMSON]

Be SURE to check for cracks/carbon tracking around the tower & terminals!
Bill Short

[Tom Wesenberg]

I just measured the ohms on the original slant pole coil on my 1928 and it has 3,300 ohms.

[BudP]

Thanks, Tom.

[BILL WILLIAMSON]

I just measured the ohms on the original slant pole coil on my 1928 and it has 3,300 ohms.

Tom,
Does that mean the coil's BAD or the meter's BAD???---The reading doesn't sound right???
Bill Confused

[Tom Wesenberg]

Tom,
Does that mean the coil's BAD or the meter's BAD???---The reading doesn't sound right???
Bill Confused

It throws a hot blue spark at least 1/2", so it's good enough for me.
3,300 ohms is factory spec.
6 volts isn't really what fires the coil. 6 volts only builds the magnetic field.
When the magnetic field rapidly collapses, the primary windings get a kick up to 200 to 400 volts, and that's when the secondary fires the plugs.

[BILL WILLIAMSON]

Tom, earlier, you said a 6 volt Model A coil should be 1 1/2 Ohms, I'm confused by the 3,300 Ohms???
Are you measuring from terminal to terminal or terminal to tower?
Bill Confused???

[Tom Wesenberg]

Tom, earlier, you said a 6 volt Model A coil should be 1 1/2 Ohms, I'm confused by the 3,300 Ohms???
Are you measuring from terminal to terminal or terminal to tower?
Bill Confused???

1 1/2 ohms on the primary windings, and 3,300 ohms on the secondary windings.

[BILL WILLIAMSON]

Got it, Tom, I'm SO STUPID!----"Maybe" my too tight skivvies short circuited my "brain"---
Bill Embarrased

[Jwmckenzie]

I am checking the coils I have in my parts bins. Here are the results:

I have a new one marked D-511 D-512 (12V I think) Primary: 1.4 ohm, Secondary 7,610 ohm
Old Delco Remy Primary: 1.2 ohm, Secondary 4,660 ohm
Repro (?) w/ spot welded bracket: Primary 1.1 ohm, Secondary 2,940 ohm

The 6-volt coil offered by Snyders has a note indicating it is marked 12V to be used with external resistor. So assume regardless of 6V or 12V the coil is the same, right?

Which one of these will generate a hotter spark?

[Tom Wesenberg]

I'd think the first one mentioned would be the one with the "hottest spark". Any of the 3 should work fine on 6 volts. Yes, many 12 volt coils which use an external resistor are the same as a 6 volt coil. In a pinch, if your coil goes out while away from home, most any coil will get you going again.

[plyfor]

It seems many folks have issues with coils as they get hot from the engine... Anyone test them in the same position and temps of the running engine?

I don't trust modern oil filled coils quality as tested and posted in other threads, so I position all the oil filled ones with leads on the top. I now use a paste filled junkyard Bosch 12 volt with good 3 ohm reading even with leads on top (with others as spares). Some like the epoxy filled ones while others say they don't dissipate heat very well........