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Which diode for master contactor?

Desert Rat

Well Known Member
Is there any difference in the two contactor diodes?

Vans shows the blue one for the start relay and the yellow one for the master relay, so presumably they have some differentiator or they wouldn’t be color coded.

Somehow in my giant pile of bits and widgets I’ve ended up with one blue one from vans and a start diode pn 16050-2 from spruce.

Is there any reason I can’t use one of these on the batt relay? Seems like if anything it might be more robust, but mostly I’m just trying to avoid having to order another one
 
Is there any difference in the two contactor diodes?

Vans shows the blue one for the start relay and the yellow one for the master relay, so presumably they have some differentiator or they wouldn’t be color coded.

Somehow in my giant pile of bits and widgets I’ve ended up with one blue one from vans and a start diode pn 16050-2 from spruce.

Is there any reason I can’t use one of these on the batt relay? Seems like if anything it might be more robust, but mostly I’m just trying to avoid having to order another one

I think the two versions from Vans are the same, but have the anode/cathode reversed in the two different versions, relative to their outer markings, so they match their instructions. It is easier for them to give markings and instructions than to write an explanation of how to wire in a diode with a solenoid. If I remember correctly, they also need the smaller ring terminal on different ends for the two versions. You can put a VOM on them to figure out which end is which (band is covered by shrink wrap) and crimp or solder on new ring terminals. Or just cut off the shrink wrap to expose the band.

On the starter, you go from the start term (+) to the ground ear(-). On the master, you go from the Batt term (+) to the switch terminal (-). Arrange diode so it can only flow from - to +.

Larry
 
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Good advice from Larry. I'll add that if you can't see the band, just use an ohm meter. With continuity, your ground lead is connected to the ground end of the diode (cathode). My old Navy-taught mnemonic was "the dead cat is on the ground"). If your meter has a diode checker function, you get a nice tone as well.

I'll add that a slightly better diode for this job is an SR560 (also SB560), which is a Schottky. To the casual observer, they're look about the same and are installed in the same manner. The last time I bought some, they were about 30 pieces for $6 from Amazon.

You can simply crimp terminals onto the diode leads and attach (install heat shrink for additional strain relief and insulation prior to crimping).

There are really good instructions in this document from Vertical Power as well: Contactor wiring
 
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Bob Nuckolls uses 1N5400 diodes on many of his wiring diagrams.
The part number is not important. Just about any diode will suppress high voltage inductive spikes that can damage the controlling switch. What is important is mechanical robustness. Diodes have solid wires. You don't want those wires breaking. Diodes used for arc suppression must have the banded end connected to positive. Diodes connected backwards in this application will result in a short circuit. The diode should be connected directly across the coil. A diode connected in parallel with a switch will NOT protect the switch from arcing.
 
Ugh. Thats what it is. The ring terminals are on backwards with respect to each other depending on whether the heat shrink is blue or yellow.
 
Bob Nuckolls uses 1N5400 diodes on many of his wiring diagrams.
The part number is not important. Just about any diode will suppress high voltage inductive spikes that can damage the controlling switch. What is important is mechanical robustness. Diodes have solid wires. You don't want those wires breaking.

The suppression diode need to be able to dump the energy stored in the coil so the characteristics of the solenoid and the suppression diode need to be matched.
The master solenoid typically has more turns of smaller gage wire so the final static current draw is less than the starter solenoid which may have less turns of larger gage wire and a higher final current and therefore more stored energy to dump. The 1N5000 series of diodes should be good for both applications. There is no particular need for a schottky diode since the forward voltage drop and turn on time are not critical. Attaching the diode body (suitably heatshrink sleeved) to the case of the solenoid with a big glob of RTV takes the strain off the leads.
 
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