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.
On Nov 26, 2013, at 9:15 AM, Jack Morgan wrote: Hi Colyn,
The website has been changed so the links didn't work for me. Please keep in mind that the mass of the relay makes a difference. The longer coil current decay caused by a diode snubber is significant in a lighter weight relay loaded near it's rating as Tyco and others have pointed out. The heavy solenoid armature used to control the hydraulic pump is only slightly impacted if at all. The solenoid is also well away from it's current rating in the pump application. If a diode snubber is used across the solenoid contacts the whole discussion becomes even more moot.
There have been reports of nose gear collapse in the 320/Legacy style set up due to sneak paths related to adding various indicator lights which inadvertently activate the up pump relay. An electronic relay solution might be more prone to this type issue. I am very conservative when it comes to electronic relays since they can easily be misapplied resulting in either failure or sensitivity to other noise sources. Each manufacturer has their own design so each will have different sensitivities to noise, etc. I agree that an electronic relay properly applied is a good solution, but given the variations in the wiring schematics that seem to creep into our experimental world, they could also introduce a failure mode. So if a builder goes the electronic route he/she should be aware that careful testing in all possible voltage, temperature, radio transmitter, equipment on/off conditions for this particular aircraft is important. Especially keep in mind that some FBO's will significantly over voltage 12 volt airplanes with external power sources which needs to be taken into account if "snap jack" and/or electronic relay style solutions are implemented. A common specification for this abuse is twice battery voltage.
The "crappy old mechanical solenoid" also has the advantage that 10's of millions of them have been built over decades which gives them the benefit of many iterations of quality/manufacturing improvements as compared to the recent and unique design of each electronic relay.
Electronic solutions have the potential to introduce all sorts of head scratching behavior so each builder should proceed with caution. The potential reliability improvement may be worth the trip if careful qualification testing is done in each application.
Sorry to be a downer but 50 years of designing electronics into vehicles has left me scarred........ and amazed.
Jack Morgan On Nov 25, 2013, at 10:33 PM, Lancair Mailing List wrote: Subject: A couple Tyco papers on emf reduction in relays
Date: November 25, 2013 9:06:50 PM EST
I just stumbled across these while researching something else.
Recently there have been some reference to how to protect switch circuits connected to relays. Here are two papers done by Tyco which have been corroborated by certain others and are consistent with Eric Jones' recommended use of Snapjacks (bi-directional zener diodes).
Some methods (not recommended here) of protecting the switch contact result in extending the opening time of the relay, which causes arcing, bouncing and degeneration of the relay contacts. (not a good thing for maximizing starter current).
If you are going to do something in this department, I highly recommend reading these. (or just use EV100 relays and be done with it)
Colyn
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