| Hi Colyn,
The sneak paths that can retract the nose gear occur in the circuitry that activates the up relay. The conventional relay is activated with current (ampere turns) so any sneak path needs to be substantial enough to actually activate the relay. When considering an electronic relay solution one needs to take into account that the electronic relay is voltage activated and requires only a very small amount of sneak current energy for activation. The low energy required to activate the electronic relay opens up the possibilities for additional problem sources (noise, RF transmissions, etc.). In any case just dropping an electronic relay in place of a conventional one should be tested carefully, particularly with aircraft that have modifications to the original Lancair wiring. In the case of the 320/Legacy gear pump, an inadvertent pump activation ruins your whole day as well as draining your bank account so a through test regime is prudent.
I don't see any obvious sneak path problems created by a snap jack across the relay coil. The usual suspects for sneak paths are, but not limited to, added indicators for pump operation, gear in transit circuitry, safety gear interlock circuitry, and such bells and whistles.
For those who venture into the electronic relay world, the typical specs for the transient conditions on the 12 volt main buss are as follows:
Normal operating range. 6 to 18 volts Jump start voltage. 24 volts continuous Load dump 80 volts for 1/2 second (comes from the alternator) Reverse battery 12 volts continuous. Temperature range passenger compartment -40 to +85 centigrade Temperature range engine compartment -55 to +125 centigrade (very location dependent)
The reverse battery requirement can be ignored in aircraft equipped with a reverse protection diode in the master solenoid activation circuitry.
It should be noted that many items in the aircraft that are on the the radio buss won't meet these specs thus underscoring the importance of not activating that buss until the engine is operating smoothly and any jump starting facility is disconnected. Components that only meet the 0 to 70 centigrade industrial temp range should be avoided as temperatures above and particularly below that range are common in various parts of the country and at altitude.
Since the gear pump operating properly is unforgiving in the 320/Legacy set up, I add a particular warning to be very thorough with any changes that one might make to insure new failure modes are not introduced. A failed or continuously operating pump in a IV is really only inconvenient assuming you are checked out on proper usage of the back up hand pump.
I suggest that those interested in further comment on this and the relay snubber issue contact Colin and/or I off line as this is probably of further interest to a very limited audience. I am always happy to trade emails with anyone on LML off line.
Keep that nose gear extended and be safe if you experiment with this.
Jack Morgan
On Nov 26, 2013, at 1:27 PM, Lancair Mailing List wrote: Subject: Re: [LML] A couple Tyco papers on emf reduction in relays
Date: November 26, 2013 9:36:59 AM EST
Changing the title back so people who sort on subject will see it.
Jack, interesting points about the sneak paths. ...I need some education about how a snapjack would cause that.
I updated the links late last night.I think the content of the articles is still valid.
The tyco Kilovac line is NOT an electronic (e.g. solid state ) device. It's an old fashioned coil style relay. Just a well-done one.
I have no objection to mechanical relays. I'm just saying look at the specs. I'm not sure what model number you are talking about when you say the pump relay specification is well out of the usage range. What is the usage range? I think someone published a chart once that showed current draw vs. starting pressure of that pump. It gets pretty high if the pressure is high (and it's working). If it starts to have an internal fault, current will get very high. Then you want to be able to turn it off.
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