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Re: Sam Barros' 5000Watts Car Ignition coil driver: Which coil is best?



    Thanks a lot for the reply, guys!


>Without overstressing the coil most are rated in the range of 130-150
mJ at
>a working potential of 50 kV.


 Drag racing coils use multiple spark ignition systems that supply up
to 320mJ to the coil. The voltage output ranges from 42 - 55kV, with
anything from 300V to 550V on the primary.


  We use the Accel Supercoil for most HV pulse
>triggering applications (our Marx generators).


 I tried triggering a sparkgap (the gap was 1cm wide, and I was trying
to trigger a 2uF, 4kV cap) with my coildriver...
 Didn't work. How do you it?
  So, would you recommend it for such a demanding application as
2500Watts runs? I am very concerned that a full minute run might start
boiling the oil inside my coil. If it were to explode, it would be
devastating: The steel case will with certainly stand several hundred
PSI!
 I put down my current options in the end of this post. Please tell me
what you think.


  We use a standard doubler on
>the AC power line to run 339 VDC peak and fire at 15 pps.  They will
last a
>long time at this rating.  You could probably increase the energy to
250-300
>mJ if the duty cycle is shorter -- 3-5 pps.


 How long sparks do you get with this system? I suppose it doesn't arc
at 15PPS, right? May I ask what it is based on? 555? SCR?
 Ummm... I also think you are being a little conservative there: I
have discharged a 1050uF Pulse-rated flash electrolytic on my coils at
about 310V: About 50Joules energy. The coils make a hammering noise,
and a large, very fat and bright spark. If you consider the amount of
wire in a coil, and its resistance, you will see that it would take a
few hundred joules impulse to rise the temperature of the windings to
the point of damaging the insulation.
 My driver pulses roughly 1000mJ, at several thousand PPS: The coils
take it, but not for long...


>Regards,
>
>Dr.Resonance-at-next-wave-dot-net


 Thank you for sharing your expertise!



 From Scott Stephens:



>>I would consider the total resistance of the wire, core loss and
thermal
>>effects. I measured these for my car coils (search the archive for
my data
>&
>>comments) by measuring the 3db tuning bandwidth, from which I
derived the
>>coil's Q, and from measuring reactance of the coil at the frequency in
>>question, using signal generator and scope, I found the effective
>resistance
>>(both AC and DC resistance) of which the AC was significantly greater,
>>probably due to the skin and magnetic parallel effects.


  Yes, I saw your data and measurements: Excellent work! Wish I had
the equipment to do that:-( Well, unfortunately it seems that my coils
are somewhat different than the ones you measured...


>>After you know the resistance, you figure the average power
dissapation. I
>>then tried a crude thermal analysis. Using values of thermal
conductivity &
>>dissapation for paper, oil & epoxy I estimated the power to create
around a
>>200 degree C thermal gradient in the center of my car coil immersed in
>>flowing oil (driven by a CPU cooling fan). The coil has a laminated
paper
>or
>>epoxy - copper structure, so I could just SWAG or guestimate.
>>
>>I was dissapointed to calculate my coil couldn't handle over a few
hundred
>>watts dissapation without burning. That means if I couple the coil
to a
>>constant load, I could let the coil dissapate 200 Watts in heat
while the
>>load gets 600 watts. I could probably push the power to 1000 watts
for 5 -
>>10 second runs, then let it cool down for a while.


 I am still trying to do my thermal analysis. Anyone know the specific
heat capacity for transformer oil at the 20 - 120C range?
 But, nevertheless, I have ran my driver for one minute non-stop, at
5000Watts (2500W) per coil. External temperature was about 70 - 80C. I
suppose the core must have reached 100C.
 I think the main reason why my coils can run such high powers is that
they are oil cooled. If you look at my diagrams you'll see that the
actual windings are relatively small and surrounded by large amounts
of fine insulating oil. There is plenty of space for the oil to
circulate and keep it cool. Epoxy is almost as good a thermal
insulator as it is an electric one. Running an epoxy cased coil at
multi-kilowatt levels will cause the heat in the windings to rise very
quickly and be concentrated in the core, where it would destroy the
insulation.


>>I figured it would be good to somehow measure the resistance of the
copper
>>coil, using it as a thermistor, to let me know when I'd pushed it as
far as
>>I could go. I planned to run without a core, letting the car coil
feed a
>>capacitor, resonating around 8KHz. Search the archive for the rest.
The
>>core, being a solenoid, will saturate gradualy, and eat half of you
power.


 Ummm.. Someone on the Tesla-2 list said you couldn't saturate the
core because it was a solenoid and therefore had a huge air gap... I
insisted it was possible, specially when you are pumping 2500W on a
core that has 1Cm diameter... Who is right?


>>You need to know Q (AC losses) core losses (which will depend on
your power
>>levels)


 How would I calculate that? Wire resistance??
 Also, how important is the inductance of such a coil in coildriver
applications?


>>You must be using the new file naming convention, it left blanks in
the
>file
>>name which irritated me when I had to use Microsh*t's Windowz
Explorer to
>>rename & view.


 Ummm... Strange... I didn't get any complaints on that... Well glad
you managed to view the files at least... My homepage effort is still
going... I hope to have them online some day...


>>My 2 cents is the best coil will have the best thermal dissapation
>>character. My TC efforts have stalled presently, when I was
conteplating my
>>own induction coil based on an Allied Metglass core, with teflon
insulated
>>windings, with forced convection oil immersed cooling. Being SCR
pumped, Fo
>>around 4KHz, and 100KV + output voltage.


  Whoa you got me drooling there... You are planning to wind such a
coil? I actually considered winding my own too... But I calculated the
secondary to have approximately 20 000 turns... So I changed my mind:-)
 Better off with the very best high-performance coil in the market.


>>How practical capacitors and spark gaps will be at 100KV +
potentials I
>hope
>>to find out.


 I won't even try... Charging 2 plastic bottle caps to 120kV makes
such a monstrous amount of corona that the caps emit light, and sound
like a rocket engine. The ozone is a big problem too. I actually plan
on parallel connecting 2 or 3 of those coils and running them at >20kV
for Tesla-Coil applications. Initial tests proved very successful. The
arc produced was hot enough that it melted the wires and set the
insulation on fire!
 Note that some coils are rated for as much as 48kV, 1200MA!!! I
suppose that is pulsed power, but average (continuous) power can be
higher than any Neon transformer one can buy, and the insulation is
surpassed only by pigs: My cheap coils can be pulsed at output
voltages of 120kV and beyond (20Cm+ sparks from each, with 1kV or so
at the primary)!!!


 I did some more searching around for the best coil there is... Have a
look at what I came up with:

 At http://www.mrgasket-dot-com/accelnew.htm

 ACCEL DRAG RACE COIL II
48KV, rated output of over 1,200 mA
170 micro-second spark duration

At http://www.msdignition-dot-com/1msdcoil.htm

 MSD PRO POWER COIL (also Drag racing)

Primary: 0.03ohms resistance
 Output voltage: 55,000 volts!
Secondary Resistance:  1000 Ohms 
1:100 turns ratio

 MSD PRO POWER HVC Coil

Primary Resistance: .04 ohms
Peak Current: 1100mA
Maximum Voltage: 45,000 volts
Secondary Resistance: 86 ohms
Spark Duration: 150uS
Primary Inductance: 1mH
Turns Ratio: 85:1


 http://www.centuryperformance-dot-com/mallory2.htm#PROMASTER®

 Mallory MAL 28880 
 Dragster coil, up to 12000RPM


 I Can't help wondering why the call the 12V coils if the ignition
systems deliver voltages of up to 550V to the primary! Anyone care to
take a guess?
 Also, the drag racing coils are obviously the best in power output,
but they are specifically designed for low duration applications. They
can't be used on a street car because they would melt down. So,
Perhaps it would be better to use a really good street performance
coil, like the pro power HVC coil??? I need help on this one... I
can't afford to have 200 dollars in coils shipped from America and
have it not work.



 Thanks for your interest.

 Sam Barros.
==
 Sam Barros,
sambarros-at-yahoo-dot-com
ICQ#:15156975

 "The Less You Know, The Better You Sleep"...
 "Evolution Stops When Stupidity Is No Longer Fatal"
 "If At First You Don't Suceed, Increase The Amperage"
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