Question about hand winding a relay coil

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Mar 10, 2013
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I have some 33 awg coated wire to replace the wire on this coil. This is for a 12v dc automotive relay. The wire thats on there has a short. I have never done this before so i have a few questions. For starters im going to replicate what is there so it should function the same. What i want to know is do i have to wind the exact length of new wire on or can i just have at least the same amount of new wire as old wire. I assume if i have an extra foot or whatever wrapped around it will just create a stronger magnetic field. Can i have to much wire wrapped around? Also does it matter which way i wrap the coil. Whether it clockwise or counter clockwise? This is 12v dc im working with.
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Whether it clockwise or counter clockwise?
doesn´t matter
how do you know it has short? anything burnt?
a little more wire won´t hurt, it may consume less amps due to resistance.
watch out for scraping varnish or you might get shorts. (before soldering you must scrape it.)
i would grab same awg and fill the space similarly as it was, this way i would skip counting the turns. +- few turns will not get dramatic change.
 
doesn´t matter
how do you know it has short? anything burnt?
a little more wire won´t hurt, it may consume less amps due to resistance.
watch out for scraping varnish or you might get shorts. (before soldering you must scrape it.)
i would grab same awg and fill the space similarly as it was, this way i would skip counting the turns. +- few turns will not get dramatic change.
The coil looks ok but i checked the ohms and it was 23.7 which is pretty low so i assume somewhere in there there might be a short. I’m not sure if the relay is original but it says made in Canada and it’s from a gm vehicle so it has the probability of being original and that would make it 43 years old.
 
1978 ?
that makes it 0,5A to draw. ~6W... you should feel some heat if ran for a while
from datasheets, modern small brick relay consumes like 70ohm) unless really a big one.
https://sk.farnell.com/c/switches-relays/relays/automotive-relays
maybe you can buy new unit , and swap the coils. i am not familiar with old relays.
(maybe the old spring is stronger...that creates new problem)
Yes, i can definitely buy a new relay. This is more of me just tinkering. I get more joy out of fixing than buying.
 
i would wind in the same direction, i know some relays are ok with power applied in either direction. but worst case here, you just swap coil polarity.

I would use same amount of turns. plus minus a bit is ok, but less will draw more current and may not hold the contacts together with enough force. more and it likely won’t fit.

what is the diam of the wire?
 
Look up the rule of thumb for coils. I can’t remember it but always holds true.
smoky
You mean right hand rule? if you wrap your right hand around the coil, in the direction of current, magnetic field will be positive in the direction that your thumb faces.
 
i would wind in the same direction, i know some relays are ok with power applied in either direction. but worst case here, you just swap coil polarity.

I would use same amount of turns. plus minus a bit is ok, but less will draw more current and may not hold the contacts together with enough force. more and it likely won’t fit.

what is the diam of the wire?
33 awg or around .0075"
 
coil polarity is important only in special relays, like those containing magnets.
i presume this is basic type.
Yes it’s very simple. There is a metal plunger that sits in the center of the coil. It is spring loaded and held upwards. When the coil is energized the metal plunger is pulled down into the center of the coil.
 
So the wire came. I rewound the spool and reassembled the relay but it still does not work. 🙁. Its an extremely simple relay. When i plug the relay in i can move the plunger by hand and activate the horn which is what the relay is for. Here are some pictures. Anything i can test for?
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can you measure any ohms?
did you scrape varnish before soldering ?
yes the new ohm rating is 30 ohms. the old was 23.7 but as you can see I got a little carried away with the winding. So considering the low rating of the newly wrapped coil the old coil was probably fine.
 
start pushing iron down by little, you should find when it pulls inside fully, when powered.
perhaps the iron is way too away from coil, and-or the spring is too strong.
you can lube it, let´s hope rust isn´t blocking movement..
 
so the iron and brass shaft are very clean. There is nothing holding it up and i cleaned it when i took it apart. Now im using a 9v battery to power it but that should be more than enough. When i attach the 9v battery i can push the plunger down and it will stay pulled down but after a few seconds the coil wont hold the plunger down until i let the coil sit for a minute. Its like the magnetic field is very weak and gets weaker as power is constantly applied.
 
Good news is the relay works great using the car battery. I assume the 9v battery couldn't supply enough current.
 
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