nuckollsr(at)cox.net
Guest
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 Posted: Mon Aug 28, 2006 4:43 am Post subject: Engine Kick-Back IO-360 |
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| Quote: |
>
>
> I did not break a starter but the inrush current to the
> permanent magnet starter I had dropped my voltage low enough that it
> was
> below the compliance voltage for the electronic ignition. I changed
> it
> out for a wound field starter and the problem was solved.
> If you want to know brand names etc. email me off list.
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| Quote: |
Now here is a problem I've never heard of before.
Does anyone else have this problem and can it be
resolved without changing out starters ?
Larry Mac Donald
lm4(at)juno.com
Rochester N.Y.
Do not achcive
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This "problem" and "solution" has been around for
a long time. When the volumes of rare-earth magnet
motors was taking off in the market place (and prices
coming down) we (at B&C) considered a change-over
to the burgeoning technology.
The change was rejected for several reasons but
prominent among them was the extra-ordinary "locked-
rotor" current characteristics of the PM motor.
This did not present a systems issue with respect
to getting the engine running but we were already aware
of problems that some companies had with respect to
momentary "brownouts" during the first phases of
engine cranking. A typical system voltage transient
during first closure of starter contactor may be
seen at:
http://www.aeroelectric.com/Pictures/Curves/95_GMC_Safari_1.gif
http://www.aeroelectric.com/Pictures/Curves/95_GMC_Safari_3.gif
http://www.aeroelectric.com/Pictures/Curves/99_Saturn_SL1.jpg
http://www.aeroelectric.com/Pictures/Curves/99_Saturn_SL1_2.gif
These are battery terminal voltages taken from
our cars. The batteries are in excellent health. Note in
particular, the last curve where the battery voltage
stays below 9.0 volts (DO-160 recommended, "stay awake"
voltage level) for about 50 mS. If the ignition system
(or any other accessory) shared any supply current
paths with the starter the voltage drops on wires would
exacerbate the brown out conditions illustrated.
Unfortunately, many folks who would sell to either the
TC or OBAM aviation worlds do not take the DO-160 recommendations
to heart and ignore the realities of cranking systems operation,
they allow their products loose in the wild with unhappy
vulnerabilities to such transients.
Sometimes it's an extended reboot interval for a computer based
accessory, or timing for an ignition system wherein
the system delivers spark at the wrong times.
One of several reasons B&C elected to stay with
wound fields was to reduce probability that their product
would be cited as "root cause" of problems with other
systems. Contrary to popular myth, starters are NEVER
root cause for misbehavior of another system, only
a piece of a puzzle at best . . . for issues that
would not have arisen had manufacturers of the "victimized"
systems done their homework.
Bob . . .
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