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View Full Version : Autopsy of a Welded EV200 Contactor



robo
16 April 2013, 1521
Step by step. These things are not easy to take apart in an organized way. It involved a hammer- not a graceful tool. I figured some people might want to see what these contactors look like inside. They're too expensive to do this for fun.

This contactor really was welded. I couldn't pry it apart. I particularly like the copper welding spatter.

Rob

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robo
16 April 2013, 1523
Here is the "economizer" board that reduces the current needed to keep the contactor closed. I still have this board if somebody wants it for any reason. I have no idea if it would work on an LEV200 or not.

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robo
16 April 2013, 1527
The outer casing is pretty hard to get off. I had to use a band saw to score it and then use a hammer and chisel to chip off the rest.

The contactor is essentially in a metal "cup" surrounded by cast plastic.

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robo
16 April 2013, 1530
There is a very small copper tube that is sealed on the top. The bottom of the tube just goes into the body of the contactor. This must be how they manufacture the interior environment using either a vacuum or an inert gas.

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robo
16 April 2013, 1531
After carefully chipping away long enough, I could finally extract the contactor from the surrounding metal cup.

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robo
16 April 2013, 1534
Here you can see the coil and the piston it actuates. The piston actually slides over the shaft and a spring pushes down on the piston. There is a small c-clip on the bottom that the piston "pulls" when the coil is deactivated. This pulls the shaft down to open the contacts. When the coil is activated, the piston and shaft rise and they push the contacts closed.

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robo
16 April 2013, 1538
Two permanent magnets are positioned above the coil around the piston's path of travel. The magnets slide out of two plastic pockets that surround the actual contactor points (we're getting to the contactor points, I promise).

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robo
16 April 2013, 1541
I had to carefully cut around the plastic chamber that surrounds the contactor points. When I finally opened that up, here are the charred and welded remains of welded contactor points. This is what I was curious to see.

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SplinterOz
16 April 2013, 1546
Nice work... man they are seriously welded.

robo
16 April 2013, 1548
Looking more closely, you can see where the molten copper spattered and how the plate sank into the point. This looks like it was a fairly spectacular weld complete with molten copper flying on to the spring. I could not separate the weld.

Anyway, I hope this was useful for people to see how a contactor works...and how contactors can fail with potentially dangerous effects. But when these are installed and used properly, they are a great safety tool.

Rob

p.s. I did not weld this contactor...it was sold to me by accident and it has subsequently been replaced.

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robo
16 April 2013, 1549
Nice work... man they are seriously welded.

That's no joke! I'm going to see what it will take to try to separate the contacts.

Nuts & Volts
16 April 2013, 1754
Great thread. We actually opened one up last week, but we had a much smaller weld point which was easily pulled apart by hand.

EVcycle
16 April 2013, 1756
Any idea what volt/amps caused this?

liveforphysics
16 April 2013, 1805
Any idea what volt/amps caused this?

All it takes is a single botched pre-charge in my experience.

robo
16 April 2013, 1840
I was puzzled that the flat bar only overlaps half of each point. I would have guessed the bar would have covered both points completely to maximize contact area. Not the case.

Doctorbass
16 April 2013, 1947
Great post man!.. Very interesting!!. I have like 5 of these contactors used in various EV project i have and i always thought i would be curious to do the same even if i also have a weld!

My guess about the half area covered by the flat bar is probably due to the arc blow out design that work also with the magnet flux.

Doc

robo
16 April 2013, 2025
Great post man!.. Very interesting!!. I have like 5 of these contactors used in various EV project i have and i always thought i would be curious to do the same even if i also have a weld!

My guess about the half area covered by the flat bar is probably due to the arc blow out design that work also with the magnet flux.

Doc

Doc! I loved your posts on ES about using Mean Wells.

I confess I did not understand magnetic blowouts until now. It is very cool that the magnetic flux of the permanent magnets is used to affect the DC arc to help "blow it out" sooner to reduce damage and to prolong the life of the contacts.

The blowouts didn't quite work in this case though...

ARC EV Racing
16 April 2013, 2224
Excellent thread, thanks for sharing

EVcycle
17 April 2013, 0402
If nothing else this post reminded me that I needed to order a back up one for the track. :O
I have spares for just about everything else including a controller/ motor/ batteries, etc.

The racing rule is that if you have a spare...... you never need it.. :)

robo
15 October 2013, 1606
Had a number of requests (far too long ago) to have these pics visible to non-elmoto.net folks.

They are now available on my build pages in my sig below (see bottom of page).