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nuckolls.bob(at)aeroelect
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 Posted: Thu Aug 17, 2017 7:01 am Post subject: Local Automotive Source for Starter Contactor? |
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At 09:23 PM 8/15/2017, you wrote:
| Quote: | | When I attempted to crank my Z13/8 today I got nothing, no click or anything from the starter contactor. It has been working fine for 250 hours with no hints of any trouble. |
Yup . . . things break
| Quote: | First step was to verify with the meter that I am getting 12v at the contactor when I engage the start switch, and that is verified, so I'm thinking the contactor must have gone bad.
One easy option is to order one of these from B&C:
http://www.bandc.aero/intermittentdutystartercontactor.aspx
But he's in Kansas and I'm AOG in North Carolina. I'll call first thing in the morning to see how long it will take for him to ship one to me. |
Go to any local parts store and ask for a Standard
SS598 or it's cross-referenced equivalent.
[img]cid:.0[/img]
| Quote: | | Bob has said in the list archives that the B&C is a part with automotive pedigree. Being that there are 5 different brands of auto parts stores within short driving distance, has anyone found what that automotive pedigree is? Usually around here the folks that work at those places can't operate without a year/make/model to put into their computer. So has anyone found a way to get a similar part from the local chain auto parts store? Like what kind of car it might have once been used in? |
Just about every part that found its way onto
airplanes has roots in grounded vehicles.
Event the vaunted split-rocket switch
customized for aircraft in the early
days of alternators-on-airplanes was
a modified, commercial off the shelf
component with no roots in aviation.
| Quote: | | Looking at ebay item 1639535936 it looks very similar, though I gather that on the ebay option one of the two small terminals needs to be routed to ground, instead of to a starter engaged indicator. The seller lists in his compatibility charts that it fits a huge list of ubiquitous vehicles including the F150, Taurus, etc. If there isn't a closer match to the B&C, is there a good reason why this one wouldn't be a good choice to get back in the air safely? |
Define 'safely'. There is no such thing
as a safe airplane. Airplanes are dangerous as
hell with all manner of hazard when
limits are not identified and accounted
for with training, planning and skilled
execution.
So your contactor failed. Did that create
a high risk condition? In what circumstance
would a contactor failure in flight represent
a more high risk condition?
If you're wanting to get back the air ASAP,
then hit the local autoparts store. There
are few, if any starter contactors offered
there that cannot be adapted to your needs
with immeasurable difference in levels
of risk.
Bob . . .
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nuckolls.bob(at)aeroelect
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| Posted: Fri Aug 18, 2017 7:40 am Post subject: Local Automotive Source for Starter Contactor? |
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At 10:10 AM 8/16/2017, you wrote:
| Quote: | | Numerous Ford vehicles in the 60's through at least the 80's used a similar starter relay. The real problem is getting one that actually works for a decent period of time. I have a 1988 Ford Bronco II that recently needed a new contactor, so I went to my local NAPA to get one. It failed within 2 weeks, and worse yet, it failed by not disengaging! I returned it and asked if they perhaps had a better quality one. Paid a little extra, but same problem within a month. I finally put an old salvaged contactor from a derelict Cessna 150 on my Bronco and it's been fine every since. My take is that it might be difficult to get a quality unit from a chain auto parts store. A contactor that doesn't engage is one thing. It's a lot worse when it won't stop cranking your engine. I still drive around with a handy wrench to disconnect my battery. Fortunately, in your plane you can turn off the master switch. |
Starter contactor sticking is more likely to be
caused by high resistance in the cranking
and/or cranking control circuitry than for
any reasons of quality/design of the contactor.
The 'ford' style contactor has been around for
decades . . . long enough for manufacturers
to figure out how to do it right. The movable
contact looks rather 'flimsy' and indeed it
is flexible.
[img]cid:.0[/img]
When the 'solenoid' winding is energized,
the movable contact is push up against
the stationary contacts . . .
[img]cid:.1[/img]
. . . hopefully with enough force to 'mash' the
contact surfaces together and develop contact
pressure needed for good connection through the
fat wires.
High resistance in the fat wire circuit and/or
the battery itself can manifest in excessive sag
of bus voltage during the starter's inrush transient . . .
just a few tens of milliseconds. That depression
in voltage reduces the closing forces on the
fat wire contacts and increases contact bounce
while increasing contact resistance. This is the
stuff of welded contacts.
The fact that you had a series of failures suggests
a high resistance scenario in some combination of
battery, fat wires, battery contactor, and starter
control wire. You may have noted that my Z-figures
show 20AWG wire to the starter switch . . . 18AWG
wouldn't be overkill. Has nothing to do with
wire 'overheating' and everything to do with minimizing
losses in the system during those first few milliseconds
after you hit the button.
Any 'stick' on the starter contactor, especially
a low time part is cause for close examination of
causes other than quality of the contactor.
Bob . . .
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