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peter(at)sportingaero.com
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 Posted: Wed May 16, 2007 12:38 pm Post subject: Starter Wiring |
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Dear All,
I am building a One Design and am striving for the lightest possible weight while maintaining acceptable (to me) levels of safety. I have researched the wiring of the starter and admit to a certain amount of confusion as to why a relay is used to switch the current to the starter. I have researched the subject quite extensively and would appreciate your comments on the following.
The goals are light weight, simplicity and reliability (probably means minimum number of components). I am not prepared to fly without a starter. I will be using a starter button and two independent mag switches (both ignition systems on during cranking) and a permanent magnet type starter.
Allow me to summarise what I understand the issues are, and describe what I intend to do. The “conventional” system where a relay on the firewall is used to switch the thick wire to the starter is not too bad a system, but there is a risk that the contacts weld themselves together (and hence the British authorities require the installation of a ‘starter warning light’ – an led on the switched side of the relay). The installation of a diode is recommended (still can’t remember why). There is also the possibility that once the starter button is released the starter motor will become a generator and cause the motor mounted solenoid to remain engaged for a short time – apparently not too good in the long run for the starter. It also seems to me that using a jumper from the starter feed to the solenoid is a bit daft, the starter has to have a solenoid so why not use it?
If the firewall relay is deleted and the starter button is used to actuate the motor mounted solenoid the button is subject to high in-rush currents (~35A) and up to 10A of steady current, values that may require a very heavy duty starter button, or the average starter button may have a rather short life. But this way the starter warning light is not needed – I don’t know exactly what it is, but I really don’t want one of these lights (I never look at the one currently fitted to my current aircraft).
The firewall relay could be retained, and the 4th terminal used to switch the solenoid, but I’m not sure this really buys you very much over the conventional set up.
The final set up is to run the starter feed directly from the master relay (I really don’t think it matters that this wire will be ‘hot’ all the time that the master is on), and to use a relay to switch the solenoid only. As I already have a 200+A rated relay I might as well use that, or I could go to the local auto parts store and get one of those plastic cube relays rated at 40A (assuming one is available). As I’m not switching 200+ amps with the relay I won’t need a starter warning light (hooray), the starter button is only switching a few amps, I’m using the solenoid for what its meant to do, I will only have to terminated the minimum number of thick connections and I won’t need any diodes. Seems to me like a winner – so what have I overlooked?
Comments welcome.
Peter
[quote][b]
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aurbo(at)ak.net
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| Posted: Wed May 16, 2007 1:28 pm Post subject: Starter Wiring |
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Peter,
Check the archives for, contactor, relay or solenoid. I am sure your questions have been answered many times.
Mike
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nuckollsr(at)cox.net
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| Posted: Wed May 16, 2007 6:48 pm Post subject: Starter Wiring |
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At 09:36 PM 5/16/2007 +0100, you wrote:
Allow me to summarise what I understand the issues are, and describe what I
intend to do. The “conventional” system where a relay on the firewall is
used to switch the thick wire to the starter is not too bad a system, but
there is a risk that the contacts weld themselves together (and hence the
British authorities require the installation of a ‘starter warning light’ –
an led on the switched side of the relay).
EVERY contactor, whether built onto the starter or
added piggy-back as shown in the Z-figures is subject
to contact sticking. The warning light is a good
thing to consider no matter which contactor actually
does the task of controlling starter current.
The installation of a diode is recommended (still can’t remember why).
See: http://aeroelectric.com/articles/spikecatcher.pdf
There is also the possibility that once the starter button is released the
starter motor will become a generator and cause the motor mounted solenoid
to remain engaged for a short time – apparently not too good in the long
run for the starter. It also seems to me that using a jumper from the
starter feed to the solenoid is a bit daft, the starter has to have a
solenoid so why not use it?
See: http://www.aeroelectric.com/articles/strtctr.pdf
If the firewall relay is deleted and the starter button is used to actuate
the motor mounted solenoid the button is subject to high in-rush currents
(~35A) and up to 10A of steady current, values that may require a very
heavy duty starter button, or the average starter button may have a rather
short life. But this way the starter warning light is not needed – I don’t
know exactly what it is, but I really don’t want one of these lights (I
never look at the one currently fitted to my current aircraft).
"Need" is a matter of perceptions but no contactor
is immune from sticking. Treat this as you wish for
the decision as to whether or not a starter engaged
warning light is to be a part of your system.
The firewall relay could be retained, and the 4th terminal used to switch
the solenoid, but I’m not sure this really buys you very much over the
conventional set up.
Either works.
The final set up is to run the starter feed directly from the master relay
(I really don’t think it matters that this wire will be ‘hot’ all the time
that the master is on), and to use a relay to switch the solenoid only.
This is illustrated in: Figure Z-22 of
http://aeroelectric.com/articles/Rev11/AppZ_R11J.pdf
As I already have a 200+A rated relay I might as well use that, or I
could go to the local auto parts store and get one of those plastic cube
relays rated at 40A (assuming one is available). As I’m not switching 200+
amps with the relay I won’t need a starter warning light (hooray), the
starter button is only switching a few amps, I’m using the solenoid for
what its meant to do, I will only have to terminated the minimum number of
thick connections and I won’t need any diodes. Seems to me like a winner –
so what have I overlooked?
The diode is always useful. Which ever process by
which you wish to control the starter is fine.
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