Enough information to determine dwell?

Jon k · Post by **Jon k** » Wed Jun 07, 2006 3:12 pm

I have a friend who contacted Bosch directly. The coil in question is:

Bosch Ignition coil 0 221 504 410

Bosch replied with:

Peak primary current 7.5A
Primary Inductance 3.7mH
Primary resistance 0.5ohm
Secondary Inductance 38H
Seconradary Resistance 13.3 K
Energy 70mJ
Clamping voltage 350
Voltage gradiant 1.1kV/micro sec
We test the coil at 100Hz

Can I determine dwell times with this info?

Bernard Fife · Post by **Bernard Fife** » Wed Jun 07, 2006 4:04 pm

Can I determine dwell times with this info?

Jon,

Yes, see this post: http://www.msefi.com/viewtopic.php?t=7281- use the primary numbers, that is:

L = 3.7 mH
R = 0.5 Ohms
E = 12.0 Volts
I = 7.5 Amps

Lance.

Jon k · Post by **Jon k** » Wed Jun 07, 2006 4:32 pm

Ok - gonna do the math.

I get 2.7 - seem correct?

Bernard Fife · Post by **Bernard Fife** » Wed Jun 07, 2006 4:54 pm

Jon,

I get:

dwell = (-3.7/0.5) * ln(1-[0.5*7.5/12]) = -7.4 * ln(1-[0.3125]) = -7.4 * -0.375
= 2.77 milliseconds

So it looks like you are right!

Lance.

krisr · Post by **krisr** » Wed Jun 07, 2006 5:23 pm

If that equation is correct, the MSD BlasterSS coil would have a dwell time of 4.24ms !?

Primary Inductance: 6mH
Primary Resistance: 0.355ohm

That might explain why I could never get direct coil control to work properly as I had been trying ~2.5-3ms at the time.

Just a quick note, It may be worth while compiling a 'common list of coils' to add into the manual with known dwell times? Also didn't see a thread with that calculation stickied anywhere as it may be worth while stickying it to the top of the ignition forum so guys can calculate their own if it's not listed? Just a thought.

Kris

Edit: I just checked that thread you posted and noticed you had mentioned what I said so just ignore me