gahorn wrote:If the airplane is original it won't have a starter relay.
lowNslow wrote:gahorn wrote:If the airplane is original it won't have a starter relay.
True, but how many of us have original airplanes.
However, if you do want to stay original, the cessna original relays are available for $400+.
mongo2 wrote:...was just wondering if the
"not for certified aircraft" was anything I should really worry about? Rick
gahorn wrote:It does not state "not for certified aircraft". It says "applicable to all homebuilts". It also states "used on production aircraft".
lowNslow wrote:gahorn wrote:It does not state "not for certified aircraft". It says "applicable to all homebuilts". It also states "used on production aircraft".
Welll....actually it does (large bold print next to the picture). However I think this is a recent change as it did used to say "used on production aircraft" which it is. Many Cessnas use this unit.
mongo2 wrote:Thank you for the clarification. I'm sure it would be ok to use.
gahorn wrote:Yes, that schematic leaves a little to be desired. That diode should probably be put upon every airplane in the fleet regardless of what equipment is/is not aboard. There is another Cessna Service Letter which adddresses that matter, but basically.....
When the master switch is turned off, the electrical "ground" is removed from the battery solenoid/relay, which subsequently relaxes as it's magnetic field collapses. When that occurs it is common for an electrical "spike" to hit the electrical system. That "spike" can be as much as 600 volts!
If the pilot forgets to turn off all his avionics before turning off the master switch then all the avionics receive that "spike" which may cause damage to some solid-state components. Installing a diode across the master (battery solenoid, not the actual cockpit switch) will provide an "escape" for that "spike" back to the battery. The diode does not have to be large, but a 1watt diode will cost you almost a whole dollar at Radio Shack and will do the job just fine. Connect it across the two large terminals of the battery relay with the diode symbol "pointing" towards the battery's connection with the relay. (Installing it incorrectly will let the smoke out of it immediately the next time you turn on your cockpit master. If you let the smoke out of any electrical device they will not properly work ever again. Don't believe? Try it.)
gahorn wrote:Having read thru the link* which Miles posted, I notice that none of their drawings depicts the schematics of our airplanes. Specifically, they do not place their relay-activation switches in the circuit at the same place that our airplanes are wired.
I suggest we should all follow Cessna's suggestion and install the diode as they depict in their later drawings and their Service Bulletin.
Here's the link Miles posted:
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