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Johann G. Johannsson
Joined: 10 Jan 2006
Posts: 18
Location: Iceland
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 Posted: Tue Jul 07, 2009 1:44 am Post subject: Connection of the starter relay (STARTER SOLENOID 22735) |
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Hello Bob Nuckolls.
I have been having a starter problems on my Rotax 912 lately. The starter
is the original Rotax starter. The starter has always needed more than
normal power to start the aircraft. I have been connecting a booster
battery every time I start the engine cold.
The Regulator/Rectifier from Ducati stopped charging, so I replaced it with
the Schicke GR6. Charged the new battery and still the same heavy load on
the starter. In my search for the problem, I checked all electrical
connection and noticed when looking at a drawing from your site that the
Starter contactor (STARTER SOLENOID 22735 from Aircraft Spruce) is wired
with the diode between the grounding poles, i.e. one to the starter switch,
diode between poles and the other to the ground.
When I connected the contactor at the time of building, I was adviced to
just connect the one pole, i.e. from starter switch to the pole and the
diode directly to ground on the mounting bracket for the contactor. Is this
correct or should I change it to the same as on your drawings?
Could this hook-up be the cause for a bad starter?
I removed the starter yesterday and it has been overheating and a few wires
have soot and melted connections. The engine has 250 hrs. total time on it.
Hope you can help,
Regards,
Johann G.
Iceland.
Zenith 701
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_________________
Johann G.
Iceland.
Flying Zenith 701. |
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nuckollsr
Joined: 24 Mar 2009
Posts: 95
Location: Medicine Lodge, KS
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| Posted: Tue Jul 07, 2009 6:25 am Post subject: Re: Connection of the starter relay (STARTER SOLENOID 22735) |
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Hmmm . . . sounds like more than one problem.
First, you can KNOW if your rectifier/regulator is working properly with an accurate voltmeter. The absolute minimum bus voltage after you've been flying for awhile is 13.8 volts. The best voltage setting for use on airplanes or other low duty-cycle vehicles (a few hours per week) is 14.2 to 14.4 volts.
Your battery should be checked for load-bearing ability. Use a service station style load tester like
http://aeroelectric.com/Pictures/Battery_Testers/HF91129_4.jpg
For a 17 a.h. battery, crank the load current up until the battery voltage as read on the meter is 9 volts. Keep adjusting the current to maintain 9 volt reading for 15 seconds (this particular device has built in timer) and not the current after the time has expired. A healthy 17 a.h. battery will still be putting out 300 plus amps. A 12 a.h. battery will be in the 200 amp range. Test values below these numbers will give rise to suspicions of poor cranking performance due to battery condition.
The fact that you need to jumper the battery for routine starting says the battery is not being properly charged, the batter is going soft, the starter is drawing an inordinate amount of current or some combination of these three. Cooked wires says they're too small or the starter is drawing too much current . . . or some combination of these two. Check your starter current while cranking (use jumpers if necessary) by measuring with . . .
http://www.hoytmeter.com/products/Models_629_Starter_Current_Indicators.html
Compare your readings with another airplane with same engine/starer. But I would suspect that anything over 150 amps is too much and suggests a starter motor problem.
The existence of a diode (or lack thereof) on the starter contactor has no effect on the considerations cited above.
Bob . . .
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