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When’s a S25-400 not an S25-400?


Zzap

Question

So I needed a new relay coil for my 1965 bowl-a-strike as a stuck switch had burnt out the old one. As you can see on this pic, it’s a relatively small, solid core relay coil - S25-400. (not the burnt one!)

 

zBLEpLn.jpg

 

Unfortunately I hadn’t learned a lesson previously as this had happened 12 months ago too. Then I tracked one down at Marcos (should have bought two!) This time they were all sold out, so after some Google searching I tracked down some at Bay Area Amusements. The picture looked a little odd on the website as the coils had a yellow paper around them instead of the blue, but they said “similar to pictured” and since the code matched I though it should be right.

 

Anyway, cut forward a week and the parcel arrives, and yep, nowhere near the same! Quite a bit larger, hollow and a brass sleeve.

 

An9wtDa.jpg

 

z1Sio0G.jpg

 

Does anyone know what these yellow ones are from? I can’t seem to find any other references anywhere.

 

It seems that Marcos has gotten more in, or my searching has gotten better :rolleyes I might have been looking for an S25-400 instead of a S-25-400 :huh:

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The yellow one is a Coil & the Blue one is a Relay. The 25 is the wire gauge & the 400 is the number of turns, Not sure what the S is. I went through a similar thing when I was chasing a Relay for my Space Mission needing a M-28-700 same type of thing being a Relay.
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Ah well, lesson learnt! I’ll have a look at deconstructing the old coil to see if there’s enough left there to wind up. I guess winding 400 turns by hand can’t be that bad? :unsure

 

- - - Updated - - -

 

Could have sworn I saw one of these in my stash while looking for Gemini's coil a few weeks back. I'll try and remember to look tonight.

 

Thanks :)

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Check the resistance of the coil. If it's close to what the relay should be, it should be pretty close.

 

I've never done this, but if I were going to move the wire from one spool to another, I'd do it like winding thread onto a bobbin for sewing:

  • Unsolder the outside end of the donor coil
  • Put it on a screwdriver mounted a vice like the thread of a sewing machine
  • Figure out some way to mount receiving spool in the chuck of a drill
  • Solder end to receiving spool
  • Slowly wind from one to the other, guiding the wire back and forth onto the receiver so it sits flat
  • Unsolder from the donor, do the last few wraps and solder to the lug of the receiver

 

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As always pinrepair has this covered http://www.pinrepair.com/em/index3.htm#low (scroll down or search for "Rewinding a Coil")

 

He uses a bolt to secure the receiver for winding:

http://www.pinrepair.com/em/rewind2.jpg

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Make sure if you do decide to unwind the dead relay which way the winding goes, Clockwise or Counter-clockwise.

 

Ah yep, takes me back to some high school physics...

 

- - - Updated - - -

 

Check the resistance of the coil. If it's close to what the relay should be, it should be pretty close

 

Thanks for all the tips, I’ll have to read up on that guide and see if there’s a good way to count turns

 

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Does it make a difference?

 

And wouldn't you use new wire?

As that's the reason your doing the change?

 

If my memory serves correct, using the right hand screw rule, you make a loose fist with your thumb straight out, the direction of winding is with your fingers, the direction of electromagnetic force is with your thumb.

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If my memory serves correct, using the right hand screw rule, you make a loose fist with your thumb straight out, the direction of winding is with your fingers, the direction of electromagnetic force is with your thumb.

 

Flemings?

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Referring to coils in pinball machines (which we are) - it doesn't matter which direction the coil is wound in.

 

It does matter indeed IF you are winding a transformer where two or more separate winding's will interact OR your coil interacts with a permanent magnet.

 

In the case of a simple pinball coil (or coil in almost all relays) the electromagnetic attraction is pulling a shaft/plunger towards the coil and this will happen regardless of the electromagnetic direction.

 

Same goes for most standard relays - the flat plate is pulled towards the coil when it is activated regardless of the polarity of the magnetic field generated.

 

I would strip off the old wire and wind the new wire to the original former - have done similar dozens of times with 100% success. Don't panic about winding it perfectly neat - the only thing that will be affected by not being very neat is that sometimes you won't be able to fit all the winding's you need onto the former.

 

"Lenz's law is based on Faraday's law of induction, so before understanding Lenz's law ; one should know what is Faraday’s law of induction? When a changing magnetic field is linked with a coil, an emf is induced in it. This change in magnetic field may be caused by changing the magnetic field strength by moving a magnet towards or away from the coil, or moving the coil into or out of the magnetic field as desired. Or in simple words, we can say that the magnitude of the emf induced in the circuit is proportional to the rate of change of flux."

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I'd wind a few extra windings on the coil you are making say 420 windings rather than 400. This will increase the resistance and allow the coil to run for longer without burning.

 

As long as the coil can still pull in the relay with the extra windings, (which it should easierly), you will have a better, longer lasting relay.

 

If it doesn't pull in simply shorten the winding turns back to 400.

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Thanks for all the tips, I had a crack at winding the coil myself today!

 

One crunch relay coil:

T1yWnfA.jpg

 

Unwound, nice ball of charred wire :)

kkg33Zv.jpg

 

Cleaned up a bit:

35asifY.jpg

 

Soldered on the new wire ready to wind:

3xICcIl.jpg

 

About 100 winds in...

ZA5bB92.jpg

 

Around 420 winds now, testing the resistance. Was at 2.6 ohms, vs 2.2, I thought I might as well give it a crack as per @Autosteve's advice!

iANAi0E.jpg

 

Finished up, ready to install:

OpVGIpA.jpg

 

Got it installed, and it's working great! I need to make a few leaf adjustments on some of the rollover switches to ensure it doesn't lock on again, but electrically it's back to good :)

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Over the last few days I'd been trying to think how to attach it to a drill to make the winding easier, and thinking of ways to count the turns (opto, arduino etc). In the end the simplest option seemed best - just shove a screwdriver through the donor and mount it in a vice, and then manually turn the other one and count. Was done quicker and with far less effort than I thought. Of course as I got closer to 400 turns I was starting to think of the scenarios of what if I dropped it etc! :o :lol
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