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Creating sparks with a mosfet and ignition coil

Started by Unknown May 22, 2014
On Friday, May 23, 2014 4:59:58 AM UTC-7, Bob Masta wrote:
> On Thu, 22 May 2014 09:02:00 -0700 (PDT), > > mrdarrett@gmail.com wrote: > > > > >I would like to generate a series of ~1000 volt sparks continuously, for several hours, using a spare automotive ignition coil I have lying around. > > > > > >I found this 555 circuit online: > > >http://www.sci-experiments.com/HighVoltagePulser/ > > > > > >My questions: > > >(1) Is a 500-volt MOSFET really necessary? Would a 100-volt IRF530 work alright without frying? > > > > Back in the day (late '60s, early '70s) when I worked for > > the auto industry, the voltage across the breaker points in > > the primary of a mechanical-type system could easily go over > > 300V. I don't recall checking the equivalent in the > > electronically-switched types, but they did put out a lot > > more secondary volts. So you probably ought to stick with > > the 500V part. > > > > Best regards, > > > > > > > > Bob Masta
Ok, I will! It's time to place another order with Mouser anyway... Thanks! Michael
On Fri, 23 May 2014 09:10:55 -0700 (PDT), mrdarrett@gmail.com wrote:

>On Friday, May 23, 2014 4:59:58 AM UTC-7, Bob Masta wrote: >> On Thu, 22 May 2014 09:02:00 -0700 (PDT), >> >> mrdarrett@gmail.com wrote: >> >> >> >> >I would like to generate a series of ~1000 volt sparks continuously, for several hours, using a spare automotive ignition coil I have lying around. >> >> > >> >> >I found this 555 circuit online: >> >> >http://www.sci-experiments.com/HighVoltagePulser/ >> >> > >> >> >My questions: >> >> >(1) Is a 500-volt MOSFET really necessary? Would a 100-volt IRF530 work alright without frying? >> >> >> >> Back in the day (late '60s, early '70s) when I worked for >> >> the auto industry, the voltage across the breaker points in >> >> the primary of a mechanical-type system could easily go over >> >> 300V. I don't recall checking the equivalent in the >> >> electronically-switched types, but they did put out a lot >> >> more secondary volts. So you probably ought to stick with >> >> the 500V part. >> >> >> >> Best regards, >> >> >> >> >> >> >> >> Bob Masta > > >Ok, I will! It's time to place another order with Mouser anyway... > >Thanks! > >Michael
The voltage across the points (_and_ the effective spark voltage) is a function of the value of the capacitor across the points. Here's my basic self-inverting CD ignition from the 1968-1973 time frame... <http://www.analog-innovations.com/SED/CD-Ignition-Basic.pdf> <http://www.analog-innovations.com/SED/CDI_Inductor.jpg> when I was designing chips for Ford, GM, Chrysler, and American Motors... you do remember American Motors don't you ?:-} (Mitt Romney's father, George W. Romney.) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Bipolar transistor? Why?
On Sat, 24 May 2014 00:48:18 -0700 (PDT), mrdarrett@gmail.com wrote:

>Bipolar transistor? Why?
Power/DMOS MOSFET's didn't exist in 1970. To further complicate matters, the HV NPN's of the day had lousy beta, as in ~3 at IC=5.5A So the tricky part, not shown, was how I developed a chip to calculate IC from IE measured at ground, to get the current trip point to stay right at 5.5A irrespective of temperature. With today's Power MOSFET's it's a trivial task. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | #BringBackOurBalls
On Friday, May 23, 2014 9:20:43 AM UTC-7, Jim Thompson wrote:
> On Fri, 23 May 2014 09:10:55 -0700 (PDT), mrdarrett@gmail.com wrote: > > > > >On Friday, May 23, 2014 4:59:58 AM UTC-7, Bob Masta wrote: > > >> On Thu, 22 May 2014 09:02:00 -0700 (PDT), > > >> > > >> mrdarrett@gmail.com wrote: > > >> > > >> > > >> > > >> >I would like to generate a series of ~1000 volt sparks continuously, for several hours, using a spare automotive ignition coil I have lying around. > > >> > > >> > > > >> > > >> >I found this 555 circuit online: > > >> > > >> >http://www.sci-experiments.com/HighVoltagePulser/ > > >> > > >> > > > >> > > >> >My questions: > > >> > > >> >(1) Is a 500-volt MOSFET really necessary? Would a 100-volt IRF530 work alright without frying? > > >> > > >> > > >> > > >> Back in the day (late '60s, early '70s) when I worked for > > >> > > >> the auto industry, the voltage across the breaker points in > > >> > > >> the primary of a mechanical-type system could easily go over > > >> > > >> 300V. I don't recall checking the equivalent in the > > >> > > >> electronically-switched types, but they did put out a lot > > >> > > >> more secondary volts. So you probably ought to stick with > > >> > > >> the 500V part. > > >> > > >> > > >> > > >> Best regards, > > >> > > >> > > >> > > >> > > >> > > >> > > >> > > >> Bob Masta > > > > > > > > >Ok, I will! It's time to place another order with Mouser anyway... > > > > > >Thanks! > > > > > >Michael > > > > The voltage across the points (_and_ the effective spark voltage) is a > > function of the value of the capacitor across the points.
I have a dual 60+10 uF, 440V capacitor I salvaged from the AC unit after installing a new cap. Would this work alright? I finally have some spare time and maybe I can build this with parts I have lying around (irf530, dual cap, etc.) Could you give the equations which would dictate the voltage across the spark gap and the voltage across the mosfet, as a function of capacitance? Thanks! Michael
On Fri, 4 Jul 2014 11:02:43 -0700 (PDT), mrdarrett@gmail.com wrote:

>On Friday, May 23, 2014 9:20:43 AM UTC-7, Jim Thompson wrote: >> On Fri, 23 May 2014 09:10:55 -0700 (PDT), mrdarrett@gmail.com wrote: >>
[snip]
>> >> >> The voltage across the points (_and_ the effective spark voltage) is a >> >> function of the value of the capacitor across the points. > > >I have a dual 60+10 uF, 440V capacitor I salvaged from the AC unit after installing a new cap. Would this work alright? > >I finally have some spare time and maybe I can build this with parts I have lying around (irf530, dual cap, etc.) > >Could you give the equations which would dictate the voltage across the spark gap and the voltage across the mosfet, as a function of capacitance? > >Thanks! > >Michael
For a typical automotive coil (from a point type ignition), ~1uF is the proper value... NON-electrolytic. L*I^2 = C*V^2 dominates until the secondary "sparks" And you need to time shut-off based on coil current. I ought to write that up one of these days ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Friday, July 4, 2014 11:13:54 AM UTC-7, Jim Thompson wrote:
> On Fri, 4 Jul 2014 11:02:43 -0700 (PDT), mrdarrett@gmail.com wrote: > > > > >On Friday, May 23, 2014 9:20:43 AM UTC-7, Jim Thompson wrote: > > >> On Fri, 23 May 2014 09:10:55 -0700 (PDT), mrdarrett@gmail.com wrote: > > >> > > [snip] > > >> > > >> > > >> The voltage across the points (_and_ the effective spark voltage) is a > > >> > > >> function of the value of the capacitor across the points. > > > > > > > > >I have a dual 60+10 uF, 440V capacitor I salvaged from the AC unit after installing a new cap. Would this work alright? > > > > > >I finally have some spare time and maybe I can build this with parts I have lying around (irf530, dual cap, etc.) > > > > > >Could you give the equations which would dictate the voltage across the spark gap and the voltage across the mosfet, as a function of capacitance? > > > > > >Thanks! > > > > > >Michael > > > > For a typical automotive coil (from a point type ignition), ~1uF is > > the proper value... NON-electrolytic. > > > > L*I^2 = C*V^2 dominates until the secondary "sparks" > > > > And you need to time shut-off based on coil current. > > > > I ought to write that up one of these days ;-) > > > > ...Jim Thompson
L*I^2 = C*V^2... V is Vds across the mosfet, right? So, the greater the C, the lower the V (which keeps my mosfet from frying), right?
On Fri, 4 Jul 2014 11:35:01 -0700 (PDT), mrdarrett@gmail.com wrote:

>On Friday, July 4, 2014 11:13:54 AM UTC-7, Jim Thompson wrote: >> On Fri, 4 Jul 2014 11:02:43 -0700 (PDT), mrdarrett@gmail.com wrote: >> >> >> >> >On Friday, May 23, 2014 9:20:43 AM UTC-7, Jim Thompson wrote: >> >> >> On Fri, 23 May 2014 09:10:55 -0700 (PDT), mrdarrett@gmail.com wrote: >> >> >> >> >> [snip] >> >> >> >> >> >> >> >> >> The voltage across the points (_and_ the effective spark voltage) is a >> >> >> >> >> >> function of the value of the capacitor across the points. >> >> > >> >> > >> >> >I have a dual 60+10 uF, 440V capacitor I salvaged from the AC unit after installing a new cap. Would this work alright? >> >> > >> >> >I finally have some spare time and maybe I can build this with parts I have lying around (irf530, dual cap, etc.) >> >> > >> >> >Could you give the equations which would dictate the voltage across the spark gap and the voltage across the mosfet, as a function of capacitance? >> >> > >> >> >Thanks! >> >> > >> >> >Michael >> >> >> >> For a typical automotive coil (from a point type ignition), ~1uF is >> >> the proper value... NON-electrolytic. >> >> >> >> L*I^2 = C*V^2 dominates until the secondary "sparks" >> >> >> >> And you need to time shut-off based on coil current. >> >> >> >> I ought to write that up one of these days ;-) >> >> >> >> ...Jim Thompson > > >L*I^2 = C*V^2... V is Vds across the mosfet, right? So, the greater the C, the lower the V (which keeps my mosfet from frying), right?
Correct, And also limits the spark voltage. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On Friday, July 4, 2014 11:46:32 AM UTC-7, Jim Thompson wrote:
> On Fri, 4 Jul 2014 11:35:01 -0700 (PDT), mrdarrett@gmail.com wrote: > > > > >On Friday, July 4, 2014 11:13:54 AM UTC-7, Jim Thompson wrote: > > >> On Fri, 4 Jul 2014 11:02:43 -0700 (PDT), mrdarrett@gmail.com wrote: > > >> > > >> > > >> > > >> >On Friday, May 23, 2014 9:20:43 AM UTC-7, Jim Thompson wrote: > > >> > > >> >> On Fri, 23 May 2014 09:10:55 -0700 (PDT), mrdarrett@gmail.com wrote: > > >> > > >> >> > > >> > > >> [snip] > > >> > > >> >> > > >> > > >> >> > > >> > > >> >> The voltage across the points (_and_ the effective spark voltage) is a > > >> > > >> >> > > >> > > >> >> function of the value of the capacitor across the points. > > >> > > >> > > > >> > > >> > > > >> > > >> >I have a dual 60+10 uF, 440V capacitor I salvaged from the AC unit after installing a new cap. Would this work alright? > > >> > > >> > > > >> > > >> >I finally have some spare time and maybe I can build this with parts I have lying around (irf530, dual cap, etc.) > > >> > > >> > > > >> > > >> >Could you give the equations which would dictate the voltage across the spark gap and the voltage across the mosfet, as a function of capacitance? > > >> > > >> > > > >> > > >> >Thanks! > > >> > > >> > > > >> > > >> >Michael > > >> > > >> > > >> > > >> For a typical automotive coil (from a point type ignition), ~1uF is > > >> > > >> the proper value... NON-electrolytic. > > >> > > >> > > >> > > >> L*I^2 = C*V^2 dominates until the secondary "sparks" > > >> > > >> > > >> > > >> And you need to time shut-off based on coil current. > > >> > > >> > > >> > > >> I ought to write that up one of these days ;-) > > >> > > >> > > >> > > >> ...Jim Thompson > > > > > > > > >L*I^2 = C*V^2... V is Vds across the mosfet, right? So, the greater the C, the lower the V (which keeps my mosfet from frying), right? > > > > Correct, And also limits the spark voltage. > > > > ...Jim Thompson
What is the governing equation for the spark voltage as a function of capacitor value?
On Mon, 7 Jul 2014 18:27:24 -0700 (PDT), mrdarrett@gmail.com wrote:

>On Friday, July 4, 2014 11:46:32 AM UTC-7, Jim Thompson wrote: >> On Fri, 4 Jul 2014 11:35:01 -0700 (PDT), mrdarrett@gmail.com wrote: >> >> >> >> >On Friday, July 4, 2014 11:13:54 AM UTC-7, Jim Thompson wrote: >> >> >> On Fri, 4 Jul 2014 11:02:43 -0700 (PDT), mrdarrett@gmail.com wrote: >> >> >> >> >> >> >> >> >> >> >> >> >On Friday, May 23, 2014 9:20:43 AM UTC-7, Jim Thompson wrote: >> >> >> >> >> >> >> On Fri, 23 May 2014 09:10:55 -0700 (PDT), mrdarrett@gmail.com wrote: >> >> >> >> >> >> >> >> >> >> >> >> >> [snip] >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> The voltage across the points (_and_ the effective spark voltage) is a >> >> >> >> >> >> >> >> >> >> >> >> >> >> function of the value of the capacitor across the points. >> >> >> >> >> >> > >> >> >> >> >> >> > >> >> >> >> >> >> >I have a dual 60+10 uF, 440V capacitor I salvaged from the AC unit after installing a new cap. Would this work alright? >> >> >> >> >> >> > >> >> >> >> >> >> >I finally have some spare time and maybe I can build this with parts I have lying around (irf530, dual cap, etc.) >> >> >> >> >> >> > >> >> >> >> >> >> >Could you give the equations which would dictate the voltage across the spark gap and the voltage across the mosfet, as a function of capacitance? >> >> >> >> >> >> > >> >> >> >> >> >> >Thanks! >> >> >> >> >> >> > >> >> >> >> >> >> >Michael >> >> >> >> >> >> >> >> >> >> >> >> For a typical automotive coil (from a point type ignition), ~1uF is >> >> >> >> >> >> the proper value... NON-electrolytic. >> >> >> >> >> >> >> >> >> >> >> >> L*I^2 = C*V^2 dominates until the secondary "sparks" >> >> >> >> >> >> >> >> >> >> >> >> And you need to time shut-off based on coil current. >> >> >> >> >> >> >> >> >> >> >> >> I ought to write that up one of these days ;-) >> >> >> >> >> >> >> >> >> >> >> >> ...Jim Thompson >> >> > >> >> > >> >> >L*I^2 = C*V^2... V is Vds across the mosfet, right? So, the greater the C, the lower the V (which keeps my mosfet from frying), right? >> >> >> >> Correct, And also limits the spark voltage. >> >> >> >> ...Jim Thompson > > > >What is the governing equation for the spark voltage as a function of capacitor value?
It's a function of primary/secondary/mutual inductance. Can someone provide modern data? Everything I have dates to 1973 when I last designed ignition systems for the automobile industry. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.