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20A should be more than adequate. Only reason for the caution is that some have eliminated the separate contactor, when using a starter that has a built-in solenoid (that can on the side of the starter motor) that both moves the pinion out, and provides the high current connection for the starter. Those can stress a typical 10A switch.
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https://m.grainger.com/mobile/produc...fc=MWP2IDP2PCP I think I might use one of these with the “momentary on” for the starter and the “on” position for the ECU master of the SDS EI. I will have to check if the “on” stays on while the starter is engaged though or that obviously won’t work. |
I wouldn't think the switch in the cockpit would see more than about 4 amps.
Looking at the wiring diagrams, it looks to me like the only current going through the start switch in the cockpit is from the 12vdc from the "Start" circuit breaker, through the switch, then coil of the starter contactor, and then to ground. So, discounting any resistance of the wire, the switch, and the circuit breaker and their connections, the current in the circuit would only be 12vdc divided by the resistance of the coil. I was looking at a popular starter contactor spec sheet today. It listed the coil resistance at ~3.5 ohms. That's less than 4 amps, nominal. |
Keyed OFF/ON L/R
I've had a keyed switch in the -7 and kept it that way after the panel upgrade. I thought about going to a push button but that would have required 2 more switches for the Mags and possibly another solenoid. I'm not sure the "failure rate" on the Keyed Cessna type switches are that bad. The key is also the same key that opens my canopy so there is that. About the only complaint I have is that if you have too much "stuff" on your key ring it will flop around when you do aerobatics, so I do agree with that. I only have the 1 key on mine so it doesn't bother me. I did change the contacts at around 700 hours. I think it comes down to a personal preference again. I think the next plane will have a push button with e-Mag switches.
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Larry |
Is there a circuit diagram that shows how to modify a key-switch system to push button?
Thanks |
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How you do it in your aircraft is going to depend on a couple of different things. If really want some help with it, PM me and I can give you some ideas. |
I've also got the spring loaded toggle switch with red cover protector. I'd go this route again.
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RandyAB,
I used the momentary start push button + keyed ?enable switch? for the reasons someone else explained. It can prevent unauthorized or unintentional starter activation - much the same as a standard aircraft (Cessna) start switch, but at a much less expensive price, and either switch could be bypassed if there was a switch failure and you were stranded somewhere. |
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Switch Rating Question
Just a question for technical types here.... Most switches I've seen are rated for AC (think industrial switches from Allen-Bradley, Cutler Hammer, SquareD, and etc.). When switching DC don't they have to be de-rated somehow? :confused:
Mike |
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I use an "enable" switch with a flip up cover on it and a start button on my stick which pulls a relay closed to power the contactor. The relay coil current is very low so I think the switch should last a long time. If it or the relay were to fail, the enable switch also has a momentary position that bypasses the relay straight to the contactor. Ed Holyoke |
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I agree with Charlie. The fact that the voltage is being reduced by a factor of
10, 120 down to 12, automatically reduces the rating. The switch carries 1/10 of the power (volts times amps). The important thing is for the switch to be snap action so that the arc is broken quickly. A diode should be connected in parallel with a relay coil with the banded end of the diode connected to the positive side. Even a small diode like a 1N4148 will work. |
Randy,
I can send you a pic of my switch installation if you would like. I?ve tried posting pics here on this site, but haven?t been able to (I?ve been trying new ideas for a couple hours now). When I eventually figure it out, the next time I try to post a picture, it doesn?t work anymore, and I have to load some other picture posting ap. This usually takes more time than I?m willing to devote. I?ve probably used maybe 5 picture posting applications for posting pictures here, but they seem to be a temporary solution. Sending you an email with a picture attached is very easy, so send me your email address and I will be happy to send you what I have done, and where my switches are located on my RV8. If you happen to be at Sun N Fun, come and take a close look at JB Aircraft Engines exhibit booth, near building C I think (N60-N61). |
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