Dwell angle

[John L]

I wanted to get a better understanding of this item as I sure there are many people on here who can throw light on this.

My understanding is that the dwell is the time/angle that the points are closed. And this will be constant as long as the points heel doesn't wear, or the cam wears, and so will change the dwell angle.

 

The bit I don't understand is that there is an new electric box call Stealth, supplied by Accuspark, that you can program the advance curve, I understand this bit, but they now also program the Dwell angle at different speeds, why would need to change the dwell angle, surely this will detract the performance of the coil, or does this actually improve it?

 

I'm intrigued to know what benefit it has.

 

John

[TriumphV8]

Quite easy to understand:

 

A coil physically builds up a magnetic field as soon as power is applied.

As long as the field is built up the resistance of the coil is high.

When the magnetic field is on top the resistance drops to the advertised resistance

typically 3 ohm at a normal 12 Volts coil.

The coil than is waiting to fire and heated up meanwhile with no sense.

The coil is fired by removing the power what makes the magnetic field collapse.

 

That means if you continously would apply 12 Volt you would fry the coil with 36 watts

in the example or much more when high power coil is used. So what the coil can deliver is limited

by the situation that the engine might stand with ignition on and points closed.

That must be possible without causing a explosion of the coil after a time.

 

At the distributor we deal with dwell and an angle, where points are closed.

The last means that in former times without electronics the distributor had a cam

that opens and closes the points. At low revs the points are closed for a long time,

at high revs for a short time.

 

The result is that at idle the coil gets warm and at high revs the time is too short

to load the coil fully. One has to find the medium that the coil is not fried at idle

and at high revs preformance does not suffer too much.

 

Modern electronics charges the coil for a dwell time of maybe 2 milliseconds

both at idle and at high revs.

Before the situation rises up, that the magnetic field is fully built up

and resistance drops the charging stops and no heat is generated.

That enforces that the electronic knows after what time the spark is required

and starts charging the coil 2 milliseconds earlier.

 

A coil can be employed that would surely fry at idle in a conventional system

with the advantage that the coil is powerfull at high revs.

 

So the Stealth takes the signal from the points and modifies it depending

charging time and gives it the preprogrammed delay.

[pfenlon]

That was as good an explanation that I have ever read. Brilliant.

[TriumphV8]

Thanks Pete and it is a good chance to improve my English because I can not use hands & feet to expalin!

Very good that there is Google translator to help me to find some words!

 

Cheers

Andreas

[cooper1970]

Quite easy to understand:

 

A coil physically builds up a magnetic field as soon as power is applied.

As long as the field is built up the resistance of the coil is high.

When the magnetic field is on top the resistance drops to the advertised resistance

typically 3 ohm at a normal 12 Volts coil.

The coil than is waiting to fire and heated up meanwhile with no sense.

The coil is fired by removing the power what makes the magnetic field collapse.

 

That means if you continously would apply 12 Volt you would fry the coil with 36 watts

in the example or much more when high power coil is used. So what the coil can deliver is limited

by the situation that the engine might stand with ignition on and points closed.

That must be possible without causing a explosion of the coil after a time.

 

At the distributor we deal with dwell and an angle, where points are closed.

The last means that in former times without electronics the distributor had a cam

that opens and closes the points. At low revs the points are closed for a long time,

at high revs for a short time.

 

The result is that at idle the coil gets warm and at high revs the time is too short

to load the coil fully. One has to find the medium that the coil is not fried at idle

and at high revs preformance does not suffer too much.

 

Modern electronics charges the coil for a dwell time of maybe 2 milliseconds

both at idle and at high revs.

Before the situation rises up, that the magnetic field is fully built up

and resistance drops the charging stops and no heat is generated.

That enforces that the electronic knows after what time the spark is required

and starts charging the coil 2 milliseconds earlier.

 

A coil can be employed that would surely fry at idle in a conventional system

with the advantage that the coil is powerfull at high revs.

 

So the Stealth takes the signal from the points and modifies it depending

charging time and gives it the preprogrammed delay.

Anyone tried a Powerspark electronic ignition kit?