Van's Air Force
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Push button starter question
- Thread starter olyolson
- Start date
Scott Hersha
Well Known Member
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.
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.
Where did you put it Scott? I?m trying to be as economical with the panel real estate as possible given what I have planned.
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?
Mike
DC is harder on switches than AC is. A diode on the start contactor helps the switch by absorbing the spike as the magnetic field collapses. A start contactor could pull as much as 5A which can be tough on a lot of switches.
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
rv7charlie
Well Known Member
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?
Mike
According to Nuckolls (Aeroelectric) 12-24v dc is about the same stress as 125vac (much lower ability to drive an arc when the switch opens). That's supported by ratings on switches that do have both ac & dc ratings; they're typically the same current at 12-24vdc & 125vac. Plus, our lifetime cycle count in a/c is about 1% or less of a typical switch's life rating.
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.
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.
Scott Hersha
Well Known Member
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).
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).
