The Ford Barn

40larry · 08-11-2017, 10:10 AM

Does anyone have a recommendation on what value condenser should be used with the bosch 12 volt blue coil ? This is a 1942 style crab distributor. Is the original 1ga condenser a good choice ? Thanks for any info or first hand experience you may have...........

tubman · 08-11-2017, 10:23 AM

This is what I found when I developed my reproduction "Big Brass Condensers". A "regular" condenser out of my '51 or something similar was .22 to .25 microfarads. An NOS Mallory "trash can" condenser measured out at .36 mf. I believe the condensers "Bubba" recommends are also .36 mf (correct me if I'm wrong). I have what I believe is a Mallory "Super Condenser" (similar in configuration to a "Trash Can" except slightly larger with chrome finish and a red top) the measures out at .40 mf. I have an instruction sheet that came with the NOS brass "Trash Can" that mentions in passing that the "Super Condensers" were useful in trucks and buses. I surmise that the difference in capacitance between the .25 mf and .36 mf units is single vs. dual points. I believe it takes more capacitance to protect two sets of points. Thus, a "Crab" would use a .36 mf unit. We make our standard "BBC"'s with .25 mf. We can make them on special order anywhere from .22 to .55 mf. If the points degrade rapidly, a change in capacitance may be indicated. Up or down would be dictated by which side of the points erode.

flatheadmurre · 08-11-2017, 04:42 PM

It´s not that you have 2 sets of point taking twice to protect...
First there are dualpoints and there are dualpoints...you either have 4 or 8 lobes in your distributor...8 lobes adding a second set of point´s to increase the chargeup time for the coil giving you a hotter spark...4 lobes for giving your points a break from floating while rewing it full out.
So what does that little capacitor do...it has mainly 2 purposes.
1. when the points open and the field of the coil collapses it has to slow down the rise of the voltage enough so the point open faster then the voltage rise or there will be arcing.
2 it´s a part of the LC circuit oscillating giving you a better spark...if you want to fall asleep i can try and give you the long bla blah blah of it.
So what sets the value...it´s a L(inductance)C(capacitance) circuit so coil,dwell and frequency matters(rpm).
So a to small capacitor doesn´t manage to slow voltagerise down enough to keep from arcing...why don´t we go for a real big one then?
What goes up must come down...so we used a big one that nicely charges up saving our points...then the charge needs to go somewhere...and again we get arcing but in the opposite direction.
This is why we can read which way metal has migrated between the points and descide from that if the capacitor is to big or small.
So what we are aiming for is as minimal arcing at both opening and closing of the points.

tubman · 08-11-2017, 05:39 PM

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Uh, yeah Cool Murre, I think that's what I just said. As an answer to the O/P's question, I think that a .36 mf would be correct. I believe that "Bubba" (on here) has a condenser recommendation that will fulfill his needs.

08-11-2017, 10:10 AM	#1
40larry Senior Member Join Date: May 2010 Location: Northridge, CA Posts: 236	What condenser to use with bosch blue coil ? Does anyone have a recommendation on what value condenser should be used with the bosch 12 volt blue coil ? This is a 1942 style crab distributor. Is the original 1ga condenser a good choice ? Thanks for any info or first hand experience you may have...........

08-11-2017, 04:42 PM	#3
flatheadmurre Senior Member Join Date: Apr 2015 Location: Sweden Posts: 3,045	Re: What condenser to use with bosch blue coil ? It´s not that you have 2 sets of point taking twice to protect... First there are dualpoints and there are dualpoints...you either have 4 or 8 lobes in your distributor...8 lobes adding a second set of point´s to increase the chargeup time for the coil giving you a hotter spark...4 lobes for giving your points a break from floating while rewing it full out. So what does that little capacitor do...it has mainly 2 purposes. 1. when the points open and the field of the coil collapses it has to slow down the rise of the voltage enough so the point open faster then the voltage rise or there will be arcing. 2 it´s a part of the LC circuit oscillating giving you a better spark...if you want to fall asleep i can try and give you the long bla blah blah of it. So what sets the value...it´s a L(inductance)C(capacitance) circuit so coil,dwell and frequency matters(rpm). So a to small capacitor doesn´t manage to slow voltagerise down enough to keep from arcing...why don´t we go for a real big one then? What goes up must come down...so we used a big one that nicely charges up saving our points...then the charge needs to go somewhere...and again we get arcing but in the opposite direction. This is why we can read which way metal has migrated between the points and descide from that if the capacitor is to big or small. So what we are aiming for is as minimal arcing at both opening and closing of the points.

08-11-2017, 05:39 PM	#4
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 10,303	Re: What condenser to use with bosch blue coil ? Sponsored Links (Register now to hide all advertisements) Uh, yeah Cool Murre, I think that's what I just said. As an answer to the O/P's question, I think that a .36 mf would be correct. I believe that "Bubba" (on here) has a condenser recommendation that will fulfill his needs. Last edited by tubman; 08-11-2017 at 07:13 PM.