Starter contactor question

[AviatorJ]

Wiring up this plane is completely out of my comfort zone. Then again so is everything when I first start. I'm starting out on easy stuff like running power from the battery in the tail to the front of the plane. I think I know the answer to this but want to validate.

Can I connect the wire from the master contactor to either side of the starter contactor as long as I have the lead that goes to the starter on the opposite side? Earlier in the build I enlarge the hole for the battery cable and used the stainless steel fittings. I'm not comfortable with the radius I would have to bend the cable to attach to the port side of the contactor.



My thought is do a more gradual radius to the starboard side of the contactor. I would also attach the Bleads for both alternators to that side as well as run a 6ga back to the VPX pro from that side (Back through the fitting). Then it's essentially a straight shot from the port side of the contactor to the starter.

Any issues with this?


Also I'm not a big fan of open hot contacts. Is there a standard battery boot type thing used in aviation? Otherwise I was just going to grab some from some online electrical supply outlets. They have some that can go up to around 200F. Thanks

[az_gila]

Generic connection diagrams here -

http://www.skytecair.com/wp-content/uploads/80001.pdf

Rubber booties here -

https://www.aircraftspruce.com/catal...s/termnips.php

[Mich48041]

It all depends on how the starter contactor coil is connected. If the contactor has two small coil terminals, then yes, no problem. Connect the large cable terminals either way. If your contactor only has one small terminal that connects to positive through a switch, then still no problem. Connect the large cable terminals either way.
But if the contactor only has one small terminal that gets grounded through a start switch, then no, the large cable terminals can only be connected one way.
In other words, if your contactor is wired internally as in Stein's center picture (that Gil Alexander linked to in the post above), then it can only be wired one way, polarity matters.

[rv7charlie]

Isn't it pretty unlikely that a true starter contactor would use ground side switching, which is more typical for master contactors? I'd certainly avoid using one (middle one in the linked image), because there's no protection on that control feed, and if it goes to ground, you might not be able to stop the starter (depending on how the fat wire gets to the battery).

Also, the OP should be cautious about contactors with 2 small terminals. Not all are set up the way it's shown in that 1st link. In older designs intended for vehicles with Kettering ignitions, one small terminal is the control (expects to see 12V from start switch). It's tied to the 'top' of the coil. The other end of the coil is grounded to the case. The other small terminal, typically labeled 'I', is tied to the load side of the heavy contacts. It's intended to bypass the ignition's ballast resistor during starting. See:
http://studiootb.com/starter-solenoi...ok-electrical/

In those, the fat wire in & out does matter.

edit: An ohm meter, used with the diagrams, will tell which design one has.

Charlie

[AviatorJ]

I guess it's hard to see in the picture, but I have the one from Vans. Mounted with the bracket on the bottom.

https://www.vansaircraft.com/cgi-bin...oduct=start-sw

If I'm interpreting those links correct it appears the starter should be mounted on the outboard side... if it's mounted upside down... the side that is closest to the small terminal with an S.

[Mich48041]

Van's description says, "Needs +12v to energize". That means that the coil is not getting positive 12 volts internally. Therefore it does not matter which large terminal connects to the battery or starter.

[rv7charlie]

Justin,

Does one of the small terminals have an 'I' stamped next to it? If so, take a look at the link in my previous post, because you probably have that type of contactor.

Here's how to check. Disconnect both small wires, to be sure that external 'stuff' isn't affecting your measurements. Use your ohm meter to measure from the 'S' terminal to the metal case of the contactor. If it measures just a few ohms, then the coil of the contactor is wired like the one in my previous link, and like the drawing on the right in the Skytec doc linked earlier. Now, use your ohm meter to measure from the 'S' terminal to the other small terminal. If you show very high resistance, or open circuit, you almost certainly have the one I linked. If that's the case, then you need to determine the destination of the wire hooked to the 'I' terminal. If you have it grounded, you're going to 'let the smoke out' of the wire. The reason is that the 'I' terminal gets 12 V from the big terminals when the start button is pushed. Here's another link to the 'I' terminal type contactors:
http://aeroelectric.com/Mfgr_Data/Co...Contactors.pdf
Scroll down until you find #24103 & #24138. The schematic drawing of the 'guts' is shown to the left of each. Note that the small contact on the right of each drawing connects to an arrow pointing at the big contact bar. That bar will connect the two 'fat' terminals, and also connect the arrow line to the fat terminals, when the contactor is activated.

Hope the above helps...

Charlie

[AviatorJ]

It does have an 'I'. I'll mess with the multimeter when I get back, I'm out of pocket till next week.

[rv7charlie]

If you don't have anything connected to the 'I' terminal, you should be good to go (with fat wires interchangeable, like Joe said). I realized after writing my previous post that you might have your contactor mounted inverted from the way it's shown in Van's product listing.