Resistance of 12V Front Mount Coils Available

First time posting to forum, but have been an avid follower for many years now. I've picked up on a lot of great info. Can anyone help me with the resistance of the 12V front mount coils that are on the market today? I purchased a Napa 12V coil and it has 1.4 ohms. I see that Tractor Supply shows a 12V coil that they advertise as 2.5 ohms? Has anyone used/measured this coil? Are there any other 12V front mount coils with greater than 2.5 ohms? Thanks for any insight. Andy
 
(quoted from post at 10:02:38 07/15/15) First time posting to forum, but have been an avid follower for many years now. I've picked up on a lot of great info. Can anyone help me with the resistance of the 12V front mount coils that are on the market today? I purchased a Napa 12V coil and it has 1.4 ohms. I see that Tractor Supply shows a 12V coil that they advertise as 2.5 ohms? Has anyone used/measured this coil? Are there any other 12V front mount coils with greater than 2.5 ohms? Thanks for any insight. Andy
ord specified 0.47 to 0.51 Ohm primary, initially & I have measured 0.5 Ohm on truly original Ford coils. The current day coils from the far east that are available for replacement vary somewhat and the units I have measured (sold as 6v & so marked on box) run 1.6 Ohms. Similarly, the current day coils from the far east that are available for use on 12v systems (sold as 12v & so marked on box) are typically 2.5 Ohms. All these front mount coils need a resistor in the primary circuit, such as to limit steady state on current to about 4 amperes.
 
Thanks JMOR for the reply and info...I did replace the original ballast resistor with a replacement from Napa and have verified that it is indeed working. Tractor running measures 14.5V on battery and one side of the resistor and after warm drops the voltage coming out to around 9.2V. Have checked and have 9.2V on coil. Tractor runs fine but I only ran briefly after figuring amperage...9.2V/1.4ohms=6.57A...too much I think..so that got me looking into a coil with more primary resistance to avoid having to add another resistor. Also, don't want to reduce voltage any more heading up to the coil as this is where I also power the EI that I installed awhile back, and really don't want to add another wire to feed the EI separately if I did have to add another resistor before coil. From what I have researched, the EI requires 8-16V...trying to do it all right as I had a distributor cap and coil fail after not using the ballast resistor the first time. So I think I will get a 2.5 ohm coil...giving me 9.2V/2.5ohm=3.68A...hopefully saving this cap and coil from premature failure...what is interesting is that the Napa coil that I have now states plainly on the package to limit voltage to 13.5V or less....so I guess the coil should be able handle the higher amps they are saying, but I don't think cap/rotor would last very long? Am I thinking correctly on this?
 
Cap and rotor are on secondary, so I call those a non-problem as far as the primary current is concerned. Pertronix instructions always call for EI module to be supplied AHEAD of resistor.
 
Andy........from the values you quote; NAPA did NOT sell you the "infamous" ballast resistor. NAPA is known fer doing this. 2.5-ohms is typical 12-volt square can coil value. The value you quote is typical 12-to-6 volt converting resistor. Cap and rotor has 'nuttin' to do with coil resistance. .........Dell, yer self-appointed sparkie-mister
 
True about cap/rotor on secondary side...I guess I was thinking that way since I had a major cap failure/burning in the cap where the secondary spade mates to the cap...guess that had me thinking to much amperage....the coil I took off measures 0.4 ohms...don't remember what it originally was. And that is correct about Pertronix recommending before the the resistor....I had forgotten that. Not sure if it would matter as long as it remains in the 8-16V range? Thanks for the info. and advice.
 
Dell, the Napa part # for the resistor I got is ICR 40...labeled resistor unit...I think cold it measured like .4-.5 ohm...as I stated earlier...hot it was dropping little over 5V...14.5 to 9.2....it does fit where the original and "infamous" ballast resistor was mounted. And I know cap and rotor has nothing to do with figuring primary resistance, I was thinking about the amperage they would be carrying....because the cap melted down as I described in previous reply...thanks again for the tips and feedback...Andy
 

I wanted to update on what I found with the Tractor Supply Coil in case anyone else was wondering or could use this info now or maybe in the future.
-TSC # 9N12024-12V
-labeled as 12V and 2.5 ohms
-with my Fluke I measured 2.8 ohms across the primary

Hope this may help someone and thanks to those that responded to me!
Andy
 
Not sure where you looked. Their website hasn't seemed to be very accurate. On their website picture I seen showed a distributor gasket set. I will try to attach the pic of the box the coil was in.


Pic is too large and can't get it to attach.
TSC sku# 0238001
Vendor # 9N12024-12V
And like I said, there website/mobile version shows wrong image.
 
When I returned the 12V Napa coil, I asked them what they had in stock as for as front mount coils...they had a 6V and I measured its resistance out of curiosity and if I remember right it was like 0.8 to 0.9 ohms....I too wondered if I had gotten the wrong coil in the package, but after checking their 6V I believe they were labeled right, just variance in resistance from manufacturer to manufacturer.
 
(quoted from post at 09:55:41 07/22/15) When I returned the 12V Napa coil, I asked them what they had in stock as for as front mount coils...they had a 6V and I measured its resistance out of curiosity and if I remember right it was like 0.8 to 0.9 ohms....I too wondered if I had gotten the wrong coil in the package, but after checking their 6V I believe they were labeled right, just variance in resistance from manufacturer to manufacturer.

I've been running the infamous NAPA ballast resistor, 12 volt coil and the IE conversion in my tractor for 2 years with no problem. Never did measure the values. Just installed them and ran it.

Rick
 

I don't have a Sparex to check... I was going to pull a few coils and check'em but but paying customers come first :)

Tisco 6V coil 1.5 ohms
Tisco 12V 2.5 OHMS

Both give are take a tenth if my memory serves me correct...
 
(quoted from post at 21:35:29 07/22/15)
I don't have a Sparex to check... I was going to pull a few coils and check'em but but paying customers come first :)

Tisco 6V coil 1.5 ohms
Tisco 12V 2.5 OHMS

Both give are take a tenth if my memory serves me correct...
ou are right Hobo, it is way off to claim that big a percentage is manufacturing tolerance!
 
(quoted from post at 20:04:15 07/22/15)
(quoted from post at 21:35:29 07/22/15)
I don't have a Sparex to check... I was going to pull a few coils and check'em but but paying customers come first :)

Tisco 6V coil 1.5 ohms
Tisco 12V 2.5 OHMS

Both give are take a tenth if my memory serves me correct...
ou are right Hobo, it is way off to claim that big a percentage is manufacturing tolerance!

Not sure how else to explain it guys? I now measured what Napa has labeled as 6V and 12V and they both definitely didn't measure close to the Tisco values posted above. The 12V Tractor Supply coil did indeed measure close to the Tisco value...it was stated as a 2.5 ohms and I measured 2.8 ohms. Definitely some manufacturing/design differences in the coils between the manufacturers. Not just slight tolerances or variances, but major design/component/materials differences therefore causing the resistance value differences.
 
(quoted from post at 11:44:55 07/21/15)
(quoted from post at 12:52:02 07/15/15) Andy........from the values you quote; NAPA did NOT sell you the "infamous" ballast resistor. NAPA is known fer doing this.

Sure looks like a ballast resistor.

Jim, I just reread this post and realized that you were talking about the resistor I had bought. I missed where you had quoted Dell's earlier comment. I jumped the gun and thought you were talking about the Tractor Supply coil that I had given the part # for, since I also found that their website images for parts has been incorrect on some products, including this coil. Sorry for the confusion as like I said at the top, I'm new to posting to the forum, just been a long time reader. Take care, Andy
 
(quoted from post at 09:38:54 07/23/15)
(quoted from post at 20:04:15 07/22/15)
(quoted from post at 21:35:29 07/22/15)
I don't have a Sparex to check... I was going to pull a few coils and check'em but but paying customers come first :)

Tisco 6V coil 1.5 ohms
Tisco 12V 2.5 OHMS

Both give are take a tenth if my memory serves me correct...
ou are right Hobo, it is way off to claim that big a percentage is manufacturing tolerance!

Not sure how else to explain it guys? I now measured what Napa has labeled as 6V and 12V and they both definitely didn't measure close to the Tisco values posted above. The 12V Tractor Supply coil did indeed measure close to the Tisco value...it was stated as a 2.5 ohms and I measured 2.8 ohms. Definitely some manufacturing/design differences in the coils between the manufacturers. Not just slight tolerances or variances, but major design/component/materials differences therefore causing the resistance value differences.
obo's explanation seems like the obvious one to me. Somebody at NAPA simply put wrong coil in wrong box. Box was labeled, coil was not. Simple.
 
(quoted from post at 06:45:36 07/23/15)
(quoted from post at 09:38:54 07/23/15)
(quoted from post at 20:04:15 07/22/15)
(quoted from post at 21:35:29 07/22/15)
I don't have a Sparex to check... I was going to pull a few coils and check'em but but paying customers come first :)

Tisco 6V coil 1.5 ohms
Tisco 12V 2.5 OHMS

Both give are take a tenth if my memory serves me correct...
ou are right Hobo, it is way off to claim that big a percentage is manufacturing tolerance!

Not sure how else to explain it guys? I now measured what Napa has labeled as 6V and 12V and they both definitely didn't measure close to the Tisco values posted above. The 12V Tractor Supply coil did indeed measure close to the Tisco value...it was stated as a 2.5 ohms and I measured 2.8 ohms. Definitely some manufacturing/design differences in the coils between the manufacturers. Not just slight tolerances or variances, but major design/component/materials differences therefore causing the resistance value differences.
obo's explanation seems like the obvious one to me. Somebody at NAPA simply put wrong coil in wrong box. Box was labeled, coil was not. Simple.

I had the 12V coil that I was returning on the counter at Napa along with the 6V coil that they were letting me test. If the 12V "labeled" coil was mistakenly a 6V, wouldn't the values of the then two coils have been closer than what I measured (1.4 ohms on the "labeled" 12V compared to 0.7 ohms on the 6V) that they were letting me test? I think they would have been nearly identical. Maybe someone else can weigh in with what they find concerning the Napa front-mounts in the future. I was looking for a 12V with approx. 2.5 ohms of resistance from Napa, but I couldn't find. I asked to have them also bring me out another 12V to test but salesman I was speaking with at the time wasn't familiar with where they were or how to look them up.
 
(quoted from post at 10:05:44 07/23/15)
(quoted from post at 06:45:36 07/23/15)
(quoted from post at 09:38:54 07/23/15)
(quoted from post at 20:04:15 07/22/15)
(quoted from post at 21:35:29 07/22/15)
I don't have a Sparex to check... I was going to pull a few coils and check'em but but paying customers come first :)

Tisco 6V coil 1.5 ohms
Tisco 12V 2.5 OHMS

Both give are take a tenth if my memory serves me correct...
ou are right Hobo, it is way off to claim that big a percentage is manufacturing tolerance!

Not sure how else to explain it guys? I now measured what Napa has labeled as 6V and 12V and they both definitely didn't measure close to the Tisco values posted above. The 12V Tractor Supply coil did indeed measure close to the Tisco value...it was stated as a 2.5 ohms and I measured 2.8 ohms. Definitely some manufacturing/design differences in the coils between the manufacturers. Not just slight tolerances or variances, but major design/component/materials differences therefore causing the resistance value differences.
obo's explanation seems like the obvious one to me. Somebody at NAPA simply put wrong coil in wrong box. Box was labeled, coil was not. Simple.

I had the 12V coil that I was returning on the counter at Napa along with the 6V coil that they were letting me test. If the 12V "labeled" coil was mistakenly a 6V, wouldn't the values of the then two coils have been closer than what I measured (1.4 ohms on the "labeled" 12V compared to 0.7 ohms on the 6V) that they were letting me test? I think they would have been nearly identical. Maybe someone else can weigh in with what they find concerning the Napa front-mounts in the future. I was looking for a 12V with approx. 2.5 ohms of resistance from Napa, but I couldn't find. I asked to have them also bring me out another 12V to test but salesman I was speaking with at the time wasn't familiar with where they were or how to look them up.
aybe it just comes to any seller can box & label anything in any way he sees fit. Let the buyer beware!
 
I did have a 6V Sparex coil it checked in at 0.57ohms...
Tisco 12V 2.53ohms


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