lawn mower IGN coils

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Robert Reed
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Re: lawn mower IGN coils

Post by Robert Reed »

As to ignition coils - The max output voltage read is not a practical test. First off, if unloaded, they may quite possibbly arc over and break down internally from abnormally hi voltage. One of the funniest kicks I get is to see JC Whitney, e.g. advertising 40 + KV coils. A normal spark plug will limit the coils out put voltage to 5 KV at which point it arcs over (0.030" gap) and slightly higher for later models that use 0.060" gap. I would suspect most sparkplug wire assemblys that have been in use for a few years would break down at 20 KV. This fact along with the proper firing voltage of a good plug in a gas/air environment renders those HV coil claims as utterly useless (good specs for bragging rights only). The plug to block test as has been mentioned is my favorite - quick,simple and reliable!

As to CRTs- I agree with others here that the overall pix quality is the best. Phosphor?- I have never heard of it failing other than burn traces from idle sweep dwell (days on end to do this).
Electron guns - yes they have a limited life as any vaccuum tube does. Back in the 60's there was a CRT rebuilder in every corner of the city as Crt life seemed to be less than 6-7 years. Today you can hardly find a rebuilder as for some reason CRTs last much longer ( also reduced need for them due to LCD screens in use). Case in point: My 18 year old 26" hitachi has every bit as good a picture as when I bought it new and it sees regular use. Even more amazing is my 9" RCA TV in the kitchen.This was purchased 16 years ago and is on from morning to night. It is used more like the way we used to use a table radio than a TV. This set was purchased 16 years ago and the CRT pix is as good as new.I could go on with other TVs in my family and same story.
Why is this? I have absolute no clue and am blown away by the astounding turnaround from CRTs of the past. Could it be partially from the lower temperature environment of solid state TVs as opposed to the older tube type "ovens" of the past?
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dacflyer
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Re: lawn mower IGN coils

Post by dacflyer »

i guess it all depends on the tube material.. when i was working on video games
( arcade versions ), there was a time for a while that we had several monitors with RCA brand tubes,, they sucked ass a light bulb lasted longer than they did..on average a tube might last a year or so being on 24/7
other games that had different tubes lasted for years, except for slight screen burn
pacman i think was the worst games for making screen burn, bu tthe monitors / tubes lasted forever. bear in mind they came out in the 80's, other than a cap kit or other slight repair to the board, the monitors were work horses.
CRT rules anyday in my book.. even here where i work now, we have a wall of monitors for traffic observation, started out with all tube sets, now a few have been replaced with led/lcd whichever. and you can see a difference with them, one annoying things is fine lines appear to have a rainbow effect, a line / contrast around a object will strobe R.B.G. colors, but not so with the crt, Hmmm
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Janitor Tzap
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Re: lawn mower IGN coils

Post by Janitor Tzap »

dacflyer wrote:i guess it all depends on the tube material.. when i was working on video games
( arcade versions ), there was a time for a while that we had several monitors with RCA brand tubes,, they sucked ass a light bulb lasted longer than they did..on average a tube might last a year or so being on 24/7
other games that had different tubes lasted for years, except for slight screen burn
pacman i think was the worst games for making screen burn, but the monitors / tubes lasted forever. bear in mind they came out in the 80's, other than a cap kit or other slight repair to the board, the monitors were work horses.
Wow, you saw those bad RCA CRT's as well.
I must of run through 20 of these 19" RCA set's that were from the local VA hospital.
Had to trash 5 of them because the CRT's had gotten gasy. :lol:
I also did work on their CCTV Monitors.
Two 3X5" Sanyo's CCTV units.
I really liked those Sanyo units.
Easy to work on, and the picture was good and sharp.
Last I heard, they were still going strong.
{That was in 2003, and they were already 15 years old when I worked on them in 1996.} :lol:
CRT rules anyday in my book.. even here where i work now, we have a wall of monitors for traffic observation, started out with all tube sets, now a few have been replaced with led/lcd whichever. and you can see a difference with them, one annoying things is fine lines appear to have a rainbow effect, a line / contrast around a object will strobe R.B.G. colors, but not so with the crt, Hmmm
Part of the problem is the LCD doesn't have the pixel resolution that a CRT has.
The Rainbow effect, or strobing is a problem with refresh rates.
The on/off rate of the LCD is slower than on a Television CRT.
Kind of like a the green screen monitors, or oscilloscope screens.
Where the electron beam energizes the screen phosphor, but the phosphor slowly dims.
Well....
It will probably take some 50 years for the LCD's to get as good as the CRT's of today. :wink:


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jimmy101
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Re: lawn mower IGN coils

Post by jimmy101 »

Robert Reed wrote:As to ignition coils - The max output voltage read is not a practical test. First off, if unloaded, they may quite possibbly arc over and break down internally from abnormally hi voltage. One of the funniest kicks I get is to see JC Whitney, e.g. advertising 40 + KV coils. A normal spark plug will limit the coils out put voltage to 5 KV at which point it arcs over (0.030" gap) and slightly higher for later models that use 0.060" gap.
That isn't quite right. The breakdown voltage in air at 1 ATM pressure is about 1KV/mm between sharp points and about 3KV/mm between blunt points.

But, that's at 1 ATM pressure. Car cylinders aren't sparked when they are at 1 ATM pressure. They are sparked when they are at about 10 ATM pressure. Pressure has a very large affect on the breakdown voltage of air. Roughy the breakdown voltage increases in proportion to the pressure. So an 0.03" gap, between fairly blunt electrodes (so the 1 ATM breakdown voltage is perhaps 2KV/mm) at a pressure of 10 ATM will breakdown at about
(0.03")(25.4mm/")(2KV/mm)(10) = 15KV. At 1 ATM pressure the same gap sparks at 1.5KV.

An 0.06" gap at 10 ATM would require 30KV to spark. An 0.06" gap on a high compression engine (say 12:1) would need 36KV.

To make sure the cylinder actually fires exactly when it should, particularly at idle speeds, the coil needs to be able to supply significantly higher voltages than the calculated breakdown voltage.

The insulation on spark plug wires is really just there for show. (not really, but almost :razz:) The real insulation is the air gap between the wire's insulation and all things conductive. A 1" gap will provide insulation for voltages up to 25KV to 75KV depending on how sharp a point the spark has to jump to/from. That air gap is much more effective as insulation than the rubber.

Most modern cars use a mugh higher energy ignition system (higher in both voltage and current) than cars did decades ago. A '60's era engine typically will perform better if the stock coil is replaced by a high energy "performance" coil. Indeed that is one of the cheapest and most cost effective way to boost the performance of old stock engines. You'll get a lot more bang for your buck than you will with changing the manifolds or carb.
Robert Reed
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Re: lawn mower IGN coils

Post by Robert Reed »

Jimmy
I like your calculations, but my info was printed in the SAE engineers manual years ago and from my experience as a home garage mechanic the arc over voltages have been pretty much in the ballpark as to the manual. All most all of my tuneups were done with 0.03" gapped plugs. Since they came out with newer systems and 0.06" gaps - tuneups are a thing of the past in those regards (100K miles +). Nowadays I rarely lift the hood only to fill the window washer fluid.
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