OK, at higher revs the average current through the points is likely to be
less, but this is not so relevent. What causes points to fail is the arcing
across the points as they open.
The points open approximately 6000 times per mile (based on 20mph per 1000
rpm). This is independent of speed but the actual amount of arc current may
be slighly dependent upon revs and loading (high load =wide open throttle =
higher arc currents = shorter points life). Note, slightly!
At higher revs, both the average and peak currents through a normal points
setup will be lower, but this is not relevent to points failure. I don't
propose to explain the physics of this here. Please accept it from a former
designer of electronic ignition systems for Lucas (me).
Overall, I don't think points life is significantly related to driving style.
Incidentally, some Alfa Romeos had a points setup where the relative
position of the points was changed by the vacuum advance. Thus tending to
improve points life.
On a final note. Standing current could be zero, if the engine comes to
rest with the points open. Probably this does not normally happen.
Regards,
Simon
At 06:52 PM 11/13/97 +0000, Robert Allen wrote:
>Barney Gaylord wrote:
>>
>> <snip the part where he calls me a smart-ass>
>>
>> <When I said...>
>> Or maybe the load on the primary side of the ignition is lessoned the
>> higher the revs? I think current requirements for points-type ignitions
>> lessen the higher the RPM. I don't figure you've spent a heck of a lot of
>> those 90,000 miles in stop-and-go traffic.
>>
>> <and Barney said...>
>> The dwell is fairly constant regardless of engine speed, so the points
>> are spending the same total amount of time (per minute) closed and
>> drawing current. That's one of the advantages of the dual points setup,
>> keeping the contacts closed long enough at higher speeds so the dwell
>> doesn't change.
>
>Sorry for letting the thread get stale but it took awhile to find the
>reference.
>
>In the 'C' shop manual it says the standard dizzy consumes 3.9 amps
>"Ignition On: Standing" and 1.4 amps at 2,000 rpm. So I was figuring
>that there would be less of a current load on the points at higher rpm.
>
>So ya don't think so? Is 'standing' when the motor ain't turnin' and the
>other 2.5 amps is used to heat the coil? I _know_ the coil can get
>pretty hot if you leave the ignition on without starting the car...
>
>My only training in this area is the ability to read.
>--
>Bob Allen, Kansas City, '69CGT, '75TR6, '61Elva(?)
>"The biggest thing that happened to the six-cylinder engine in 20 years
>was the seven main-bearing crank" -- John Z. DeLorean, Car Life, 1966
>
>
---
Simon Matthews Avant! Corporation
Phone: (510) 413-8820
Fax: (510) 413-8080
E-mail: simon_matthews@avanticorp.com
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