Correct Ballast Resistor

[JWT]

Ok, sorry......I still need help on this....here is a photo of my new coil.  It shows 9 ohms...so does that mean my ballast Resistor should be 9 ohms?  We tested the current ballast and the numbers bounced around between 2 and 1.9 so I believe it is a 1.8 ohm ballast resistor on there now.  Correct?  The car runs and starts amazing....no issues at all......I just do not want to be burning the points up.......HELP!

 

 

Edited October 15, 2019 by JWT

[JohnS]

JWT, your coil (silver can, green sticker) should be matched to a 0.9 ohm ballast Resistor.  It should say that on the green sticker.  You can get the 0.9 ohm resistor from Bosch or BERU makes one too that's less expensive.  This is where I recently purchased mine frrom:

 

Bosch:

https://www.rmeuropean.com/Products/0001580845-MFG14-V3244.aspx

 

BERU:

https://www.rmeuropean.com/Products/0001580845-MFG47-V3244.aspx

 

0,9 is the way that Europeans write 0.9 or 9/10ths.

Good luck,

John

Edited October 15, 2019 by JohnS

[JWT]

52 minutes ago, JohnS said:

JWT, your coil (silver can, green sticker) should be matched to a 0.9 ohm ballast Resistor.  It should say that on the green sticker.  You can get the 0.9 ohm resistor from Bosch or BERU makes one too that's less expensive.  This is where I recently purchased mine frrom:

 

Bosch:

https://www.rmeuropean.com/Products/0001580845-MFG14-V3244.aspx

 

BERU:

https://www.rmeuropean.com/Products/0001580845-MFG47-V3244.aspx

 

0,9 is the way that Europeans write 0.9 or 9/10ths.

Good luck,

John

Ok, thank you!  I figured as much from the previous reply I got but I did not have the car nearby to see what was on the green label.  Just out of curiosity, if I ran a 1.8ohm ballast with a coil that says .9 ohm is that creating a weaker spark for the system?  I am still on points obviously.  If I go with a .9ohm Ballast with my coil that stipulates it needs a .9 ohm is that optimal for spark I guess?  I am just trying to understand this electrical wizardry somewhat......

[jimk]

53 minutes ago, JWT said:

Just out of curiosity, if I ran a 1.8ohm ballast with a coil that says .9 ohm is that creating a weaker spark for the system?

Yes a weaker spark.

The wizardry is logical  A coil charges when current flows for a given time frame (dwell time) at the specified voltage.  If the supply voltage at the coil terminal is lower (due to the increased ohm resistance of the ballast resistor), and the time is the same, then the coils will not be fully charged.

[JWT]

14 hours ago, jimk said:

Yes a weaker spark.

The wizardry is logical  A coil charges when current flows for a given time frame (dwell time) at the specified voltage.  If the supply voltage at the coil terminal is lower (due to the increased ohm resistance of the ballast resistor), and the time is the same, then the coils will not be fully charged.

 

Ok, got it.  I appreciate all the responses.  I did search and search but what you said above is the easiest to understand!  If I ever ditch this coil for a "blue" one and get rid of the resistor then I will ask how to jump it!!!  hahaha

[JohnS]

On 7/28/2019 at 9:17 AM, Stevenc22 said:

Yeah I switched to a red coil a week ago with no resistor. The 123 is happy with any coil over 1ohm of primary resistance. 

 

 

Did you also bypass the 0.9 ohm resistance wire that's built into the wiring harness on the later square tail regular (non-tii) 2002 cars?  Running a "red" coil without the 1.8 ohm resistor isn't recommended.  You're essentially overloading your coil with more voltage that's it's designed to run with.  This will lead to premature coil failure.  The "red" coil is designed to run continuously with less than 12 volts (hence the resistor).  Does your coil get hot after you drive for a while? 

[jimk]

20 hours ago, JWT said:

Resistor should be 9 ohms?

That's 0.9 ohms.  European nomenclature is where the comma comes from.

[JWT]

5 minutes ago, jimk said:

That's 0.9 ohms.  European nomenclature is where the comma comes from.

Sorry, yes - all clear!

[jp5Touring]

So for grins I check my coil and resistor and find a 1.8 coil and 0.9 resistor. Glad it's an easy swap of the resistor to 1.8.

Oh the details,

[Stevenc22]

On 10/16/2019 at 9:18 AM, JohnS said:

 

Did you also bypass the 0.9 ohm resistance wire that's built into the wiring harness on the later square tail regular (non-tii) 2002 cars?  Running a "red" coil without the 1.8 ohm resistor isn't recommended.  You're essentially overloading your coil with more voltage that's it's designed to run with.  This will lead to premature coil failure.  The "red" coil is designed to run continuously with less than 12 volts (hence the resistor).  Does your coil get hot after you drive for a while? 

John I'm running with no resistor. If you have electronic ignition (123) I not sure you need a resistor. It even says so on the coil.

 

 

[JohnS]

Weird.  The whole idea behind the external resistor is to drop down the voltage for the coil while the car is running.  That way when starting, the ballast gets bypassed and the coil gets boosted with the full 12 volts during starting.  I still contend that the "red" coil is designed to run continuously with less than 12 volts.

 

You've probably already seen this, but...

 

Glad it's working for you without the resistor.  I'll keep the 1.8 resistor with my red coil and Pertronix.  It's been working great for over 20 years now.  Good luck,

John

 

Edited October 18, 2019 by JohnS

[Stevenc22]

John petronix does require 3ohms of resistance so you do need the ballast resistor. The 123 is different. 

 

I also just confirmed with 123 

 

 

 

Edited October 18, 2019 by Stevenc22

[JohnS]

Yes, I understand that the Pertronix requires 3 ohms (or more) resistance and that the 123 doesn't.  But, these coils have been around long before these electronic ignitions/triggers even existed.  They (the coils) are designed to run with less than 12 volts and the resistor had nothing to do with whether or not a given electronic ignition required a certain amount of resistance.  The whole idea was that they could run at a lower voltage and then be boosted with more voltage during the starting cycle.  They didn't have Pertronix or 123 in 1973.  I'm done.  Good luck,

John

Edited October 18, 2019 by JohnS

['76mintgrün'02]

2 minutes ago, JohnS said:

They didn't have Pertonix or 123 in 1973.

 

 

Ahh yes, back in the good old days.

 

(They did have adjustable dwell back then though... at least on Chevys.   )

 

Tom

[JohnS]

The main point I was trying to get across is that the coil is what requires the matching resistor.  Otherwise the coil is receiving more voltage than it's designed to be supplied with.  So you're overloading the coil (boosting it) and therefore "it might" burn out prematurely.  That's all.  I understand that the coil is designed to handle the "boosting" for short periods of time (like during starting), but not ALL the time.  Otherwise, why did BMW include the ballast and circuit to bypass it during starting in their design?  As one of our friends here always says, "but what do I know". ?

 

My red coil is red and Made in Germany, but I'm older than the coil ?

 

Edited October 19, 2019 by JohnS