Question about soloenoid.
 

I've got a solenoid I'd like to use to replace my burnt out relay by way of a push button switch. It has three terminals, one that connected to power, one that connected to the starter, and one that came in from the interior. What I'm double checking is that the metal cylinder on the bottom of the solenoid is needed because it moves up and completes the main circuit, and whether or not the terminal that went to the interior should go to the button which goes to power.

https://www.fuelly.com/attachments/fo...1f0d6988a3.jpg

In other words, I have a switch that's connected to power, and the third terminal. When I hit that switch, it energizes the coils which draw the big cylinder up and connects the other two terminals so the power goes to the glow plugs, correct? :thumbup:

Your explanation is as clear as mud -- Ime lost :D

The two main bolt on terminals are the high current capable swtiched contacts.
One can go to the battery + and the other to your ''glowplugs'' or whatever device you want to turn on and off.

There will most likely be a push on female spade terminal connection in the same area which supplies power to energize the solenoid.
This will have to go to a switch inside the car where 12v + can be switched.

If your going to mount the solenoid in the engine bay I suggest placing it with the plunger at the bottom so that water cant go into the solenoid.
You could also glue a small plastic cup over it to protect it as well ,, but make a tiny drip hole so it cant fill with water.

The plunger will move inward when the solenoid is energized.

That's o.k. I think I understood what you're saying. How about this version?

The female spade will be connected to a switch, which goes to power. When I hit the switch the solenoid is energized, the plunger goes into the solenoid, and the switched high current closes, giving the device however much current it pulls. Right? :D

I don't know what your planning on powering, but it would be a good idea to put a capacitor of some kind across the two contacts on the end of the solenoid. It will keep the solenoid contacts from arcing and welding themselves to the plunger contact. I'd also put one across the switch your going to use to power the solenoid, for the same reason. You can use pretty much anything, like a .01 micro farad or so.

Thanks for the heads up, I'll do that for the switch. Would it be worthwhile to do it for the device itself if I have a 50A fuse in line? The device should pull ~50A for at most 15-20 seconds on start up, which I'm guessing is much less than what was going through it when it was connected to the starter.

Yes. Any time you have a switch, like that, if you don't put a capacitor, or something similar, across the contacts, the contacts will arc when they are being closed and opened. Each time it arc's, it burns the contacts and if it gets hot enough, the contacts can fuse together. If your pulling that much current, you should probably go with a larger capacitor, like 0.1 or so.

I have never seen a cap on the back of any car starter solenoid.

Caps are mostly used to protect the contacts in relays where they are trying for the 10 gazzilion cycles ,, car solenoids do not use silver plating on the switch surfaces and are not intended to last that long.

Even so they will still last 20 years.

Oh yeah , I forgot to add that you must ground the metal body of the solenoid for the 12v (-)
Typically you would use a fusable link and not a regular fuse in this application.

Right.- any problems and message me, i'll draw a wire-up picture for you.

I'm not sure if the dealy in the car was a fuse or fusable link, looks kinda like a little red box with two copper prongs for wiring, so it might be a fusable link. I'll get a few from a VW stealership since I've been told they're handy. I can run a ground off of one of the screws in the assembly that used to hold it to the starter, and just for posterity, here's the old relay... There are a few people who relocated it because they don't like the idea of 50A running through the passenger compartment.
Is it just me or do the contacts not look good?

Thanks for all the help! :D

The difference between fusable links (they look like normal wires ,,usually right off the battery terminal) and fuses is that a fuse will blow fast at the specvified rating , but a link will allow short term high current surges (which happens with glow plugs) but will still blow at the rated amps if held there for some time.


You might have something like this....it is a type of fuseable link....in a box.
https://www.larpro.com.au/larpro/images_prod/1663.jpg
It might be found in your fuse box ,,or if you have a separate relay box under the hood it could be there too.

You cant see the relays switch contacts from that view., they are on the other side.

That relay looks like it has a controller timer built into it.- normal relays dont have those other electronic parts.

50 amps is a lot , but you have nearly that much current anyway passing inside the car anyway when you hit the starter button.
Look on the back of the ignition switch ,, you got some beefy wires on there.

Yup, that's what I have, It screws into the firewall. The glow plugs start out pulling ~14-15A each (four plugs) for a second and settle down to 12A each, which explains why a fusable link is used. One last question about grounding the solenoid, when it's on the starter, it's grounded because the starter is and it's flush with it. W/o a separate ground off the case, the coil wouldn't energize when I hit the switch, would it?

Thats right.
You will have to add a ground to the body work.

It can be either a screwed on support bracket which makes both an electrical connection and holds the solenoid , or a wire from the metal part of the solenoid to the body.(and some other support)
It doesn't need to be a super thick wire ,, just one good enough for about 8 to 10 amps .