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  #11  
Old 05-17-2018, 01:09 PM
jeffsvan jeffsvan is offline
 
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Location: detroit, michigan
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Not looking to start a laboratory study:

Just to clarify I was looking to just have one part# diode to make life simple and satisfy these items:

Diode for starter,
master,
and aux ground power solenoids/relays.

This 1N5406 seems to have specs that are sufficient. It is a larger diode with thicker leads.

Can I get some agreement?
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  #12  
Old 05-17-2018, 01:35 PM
rv7charlie rv7charlie is online now
 
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I wouldn't hesitate to use it.
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  #13  
Old 05-17-2018, 02:03 PM
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Lenny Iszak Lenny Iszak is offline
 
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I have these on all my relays/contactors, way better than diodes. They protect against spikes in both directions. $0.48 each at Mouser.

P6KE18CA
STMicroelectronics BI-DIRECTIONAL TVS DIODE 18V 600W

https://www.mouser.com/ProductDetail...%2F3pNzg%3D%3D
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  #14  
Old 05-17-2018, 05:28 PM
Mich48041 Mich48041 is offline
 
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Diodes limit inductor induced voltage to about 1 volt.
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  #15  
Old 05-17-2018, 06:08 PM
lrgabriel lrgabriel is offline
 
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So, I'm not much closer to understanding the failure...but I have turned up some interesting info in the meantime. All of this is for the four-post starter solenoid (ACS 11-03162):
Without flyback diode: -510V peak pulse
Current through flyback diode: 6.3A decaying over about 40 ms
Coil inrush current: 7.3A
Coil steady state current: 3.6A
40 ms is an eternity in the world of diodes--a reasonable forward current limit is definitely something to consider.

Interestingly, I have come across datasheets listing different limiting Vr values for peak reverse vs. RMS. Maybe there is something relating Vr with forward voltage (not drop)?

To get back on topic, I'm liking the looks of the 1N5408.

Last edited by lrgabriel : 05-17-2018 at 06:38 PM. Reason: typo
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  #16  
Old 06-11-2018, 11:36 PM
Cumulo Cumulo is offline
 
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Regarding the op's Q, as previously stated , (almost) anything with 2 wires and a part number that starts with 1N*** will work to snub a relay coil in small a/c. I agree that a 3 or 5 amp rated unit with stout leads would be a good choice. In any case, the relay coil energy itself is not likely to damage a small diode like a 1N1*** series.

HOWEVER------

There IS one badass element in most aircraft that is often not snubbed. It is capable of generating a spike of hundreds of volts and hundreds of ampws which translates into thousands of Joules. It has caused electrical mayhem for years. The starter. This starter spike is negative polarity and if not effectively snubbed could easily take out the typical small diode across the starter or master solenoid and possibly other electronic devices $$ as well.

The reason this type of damage is all too common in aircraft and not autos is because aircraft generally have an electrically actuated battery contactor - the master switch. So, if the master releases the battery during cranking, everything else on the bus is alone in a dark alley with Mr. Starter armed with hundreds of amps and looking for trouble.
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  #17  
Old 06-12-2018, 04:45 AM
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maniago maniago is offline
 
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FWIW I just did relays, 3 ColeHersee units (Z14 setup) and I used 1N5408 for all the diodes. Bought 50 for $5 off amazon. Pretty much cant beat that, and Ive used them elsewhere on the plane as well.......
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  #18  
Old 06-12-2018, 04:46 AM
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snopercod snopercod is offline
 
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I installed large MOVs across my starter contacts and - I'll probably be soundly flamed for this - I didn't run my starter solenoid in series with the master relay. It's on it's own separate circuit. The risk I'm taking, of course, is that the starter solenoid contacts weld themselves and the starter keeps cranking until the battery is dead. Since I had protected the contacts with the MOVs, I decided to take that risk. Flame away!
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  #19  
Old 06-12-2018, 05:03 AM
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maniago maniago is offline
 
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Quote:
Originally Posted by snopercod View Post
I installed large MOVs across my starter contacts and - I'll probably be soundly flamed for this - I didn't run my starter solenoid in series with the master relay. It's on it's own separate circuit. The risk I'm taking, of course, is that the starter solenoid contacts weld themselves and the starter keeps cranking until the battery is dead. Since I had protected the contacts with the MOVs, I decided to take that risk. Flame away!
Across the contacts an MOV makes sense to cut out arcing. The diode discusison above is for the coil terminals here to short out the back current from the field collapse.

I'm not great at electronics, and I've not seen MOVs used as you are doing, but I dont see an issue. I also dont see what youre trying to gain since the usual start sequence would be done before any avionics are brought on line....
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Mustang II (FoldingWing) "Firewall Fwd stage.Yea!" IO-360B1E,RSA,C2YR-BF/F7666-2,Superior sump,James; 2xHXr,MiniX,EIS,480,327,240,SL30,(maybe)Echo; SteamAlt,AS,VSI
Don't be a hater; I'm a cousin with thin wings!
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  #20  
Old 06-12-2018, 05:10 AM
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snopercod snopercod is offline
 
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Quote:
Originally Posted by maniago View Post
The diode discusison above is for the coil terminals here to short out the back current from the field collapse.
Yup, I have one of those, too.
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