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Discussion Starter #1
Hi guys, I pulled a few contactors like the one shown in the pic off of an old forklift controller. They're marked "300A" on the side. Coil voltage is 24V, so I'll probably end up rewinding them for 12V.

So- is 300A really the limit for these things? Being the cheapskate that I am, I'd really like to use these in my Tercel (it will probably pull around 600A surge). :rolleyes:

Anybody else use contactors like these in high amp situations? Or am I crazy? :D
 

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Wire two with the contacts in parallel and the coils in series. No wait, that would be for 12 volt coils in a 24 volt system.
Wire the coils in parallel too.

Fatboy
 

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I'm sure these will be fine if the contact surfaces close and open before passing current , In older forklifts these contactors were used to switch large currents with a carbon pile and used very large contact tip areas , with modern PWM these are now much smaller . You may find they will operate at 12volt but close a little slower.Good luck
 

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Discussion Starter #5
Cool, thanks. The contactors won't be opening and closing while under load, except in an emergency (hopefully they'll be able to do it once) so it should work out.

I could also increase the spring tension and rewind them. That way they'd have more power to break a connection and they'd be optimized for 12v.
 

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I think you should be more concerned about the voltage that the contactor has to handle, rather than the current. How many volts was the traction pack in the forklift that it came out of?

Your comment that it will only be used in an emergency and will "hopefully work once" should be a cause for some serious reflection. The higher the voltage, the more air gap is required to stop the flow of current when the contacts are opened with current flowing through them.

The main contactor in my car has two sets of armatures wired in series, four air gaps total. It's hard to tell from the photo, but if I had to guess, I'd say that my contactor has a bit more travel in the armature, giving even more air gap. If you rely upon this single contactor to open the circuit in an emergency, and it arcs, not only will you have the original emergency to worry about, but you'll also have a plasma fire across the contacts of this device. Let me tell you from experience, you do NOT want that! Such a reaction uses whatever is in the vicinity for fuel, and the silver contacts of the contactor will burn just fine under those conditions.

If you insist upon using these contactors, use two of them with the contacts in series and rewind the coils to 12 volts and put them in parallel. Leave the springs alone. At least then you'll have a chance to shut the power off without causing incendiary aftereffects.

Safety equipment is something you do not want to pinch pennies on.
 

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I am using the identical 300a contactor but 48 volt in my electric atv, I pull 500A or so at 48 volts on hard accelleration. I had a problem with the contacts heating so I filed the crown off the contacts to improve surface area and my heat in the contacts went away (moved to other parts,lol).
If switched under load they would probably weld or pit badly.
Previous comments about airgap and operating voltage need to be considered as well, I use a set for directional swiching and a main contactor and don't have any problems.

http://www.austinev.org/evalbum/preview.php?vid=1174
 

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Discussion Starter #8
I think the forklift used a 48v traction pack. This is beginning to sound like it isn't such a brilliant idea. ;)

I also just remembered something (I removed these a few months ago). There was major pitting on the contacts when I removed them, so I filed them flat. This tells me they were a little underdesigned to begin with. Yeah, maybe I should get some better contactors.

And just so you all don't think I'm an idiot, I wasn't planning on relying on these as my sole emergency cutoff. I'm using dual contactors, a 250A delay breaker, and a 400A fuse.

Anybody got a couple SW200s they wanna get rid of? :D
 
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