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Why use starter contactor? (good points Bob)

 
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gmcjetpilot(at)yahoo.com
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PostPosted: Sat Apr 08, 2006 10:29 am    Post subject: Why use starter contactor? (good points Bob) Reply with quote

Bob:

Very good points about PM starters spin down and engagement. I
knew this and even SkyTec addresses this in their documentation.
You say 2 to 5 seconds?

Quote:
From http://www.skytecair.com/Troubleshooting.htm

Complaint: After start button is released, the starter stays engaged
for nearly a second before releasing?

Question: Does it stay engaged only for 1/2 to 2 seconds?

Answer: This is NORMAL operation for a permanent magnet
starter (Sky-Tec LS, PM, CST2, & FST1 models). Although
power is removed by releasing the key/start button, a permanent
magnet motor will actually provide power to itself as it winds-
down and will keep the starter drive engaged for about a half-
second until it loses sufficient RPM to fully disengage.


I never thought about it, so good point.


I personally have a SkyTec HT model (wire wound) Hi-torque
starter. It does not have the run-on characteristic or idiosyncrasy
like the PM model. I guess the PM is OK with it, but agree it is
not the way I would prefer, so a FW contactor may be a good
idea for this application.


SkyTec also has a NEW in-line unit which they claim is the #1
selling starter. http://www.skytecair.com/


PM starters have the advantage in lower cost and lower weight. I
had a Skytec PM on my RV-4 for 900 hours before I sold the plane,
however I ran it with a secondary contactor in the firewall, with no
problems. Besides the 1/2 to 1 second run on they use more current
than wire wound starters. The Pro is they are cheaper and lighter.


There are Pros and Cons to everything, however with the point you
make about PM starters, the FW contactor is probably more of a plus.
Also you have piece of mind of not having a big gauge wire HOT
all the time, which is a concern to many.

The Pro of leaving the solenoid off is less weight, wiring and cost,
albeit small. With a wire wound starter the spin down is not an issue.

Nothing works in all situations and there is rarely an absolute
perfect solution. As I said before the FW solenoid works in most
cases and has advantages, however leaving it off is an alternative
option that the individual should explore and consider.


For me with a wire wound starter, the extra PARTS did not make it
into my design, and since my starter is not permanent magnet (PM)
I can GET AWAY with it with little down side. However I do it with
eyes wide open, knowing the Pros and Cons.

Good debate and points. I understand your position Bob.

Cheers George


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