Our group recently received a crane that came with a total of 4 electro mags. Does anyone have a method to field test these to see if they are any good? We cannot use the crane's generator for this.

TIA

All I ever did on my magnet was to use a meter to see if there was a short to the magnet case or an open circuit in the coil otherwise it was good to go in my experience .

Most scrap metal yards use them. One of those fellows might be able to help.

Please disregard my previous post . After being set straight buy the Union Pacific Railroad's crane expert, Paul ,this is what he had to say. ( Look at the tag on top of the magnet. It will state what it will ohm out at , + or - 2 ohms . If it's in that range, it's good , if not it's junk ). Thank you Paul for informing us of the proper way of testing an electromagnet .

I drove a overhead crane in a scrap yard with a large magnet on it. We never conducted any electrical readings. The best way to test it is to lift something very heavy. Most likely your magnet should lift up to the crane capacity. In our case our crane was rated at 20 tons so if the magnet lifted 18 or 19 tons it was working fine. 95% of the steel you lift however never even reaches a fraction of that capacity. It piles up on the magnet getting weaker as it strings down lower. We used to get huge pieces of solid steel from the newspaper mills sometimes 5 feet thick and 15 feet wide. Magnet would stick to it incredibly well despite the heavy weight.

Be careful using a magnet next to rail cars when picking up steel. If close to the ground the magnet will swing towards the railroad track (as the center of the magnet is strongest). Magnet swung over and punched a hole in one of the air tanks on a gondola when I was doing a clean up. Railroad frogs are usually made out of manganese and the magnet will not pick that up.

"Read the instructions" - sounds like a good start!

Well, the resistance of the coil might be in the specified range, it's the resistance from the hot leads to the case I would be concerned about. Unless you are operating it under 50 volts or so it could have a short to the case which could zap someone standing on the ground. Depending on applied voltage, condition of electrical cable insulation, grounding of the power source, existence of a ground fault relay, etc. it could be a fatal zap.

And I suspect the coil resistance could be out of the specified range and it would still work, maybe a little less "grabby". If a few of the coils shorted internally it would reduce the resistance, but also reduce the number of active coils. Magnet strength is a product of amps times number of "turns" (loops) of wire (Ampere Turns).

If you are working above about 50 volts I would check the coil connections to the magnet case resistance, preferably with a hi-pot tester (a Megger). 50 volts is the National Electric code "cutoff point" for separating "low voltage" (not fatal) from "high voltage" (could be fatal). It gets more involved, but 50 volts AC or DC is a good guideline when considering electrical safety.

And, don't just hook it up to a generator with a "hardware store" on/off switch, the back EMF when you open the switch will destroy the switch in no time. You need something rated for a large inductive load (a "snap switch" which has a big spring to "rip" the contacts apart really quickly and arc chutes to direct the arc away), or at least a hefty "flyback" diode to send the impulse current back into the magnet

And, if you have an old mechanical pocket watch keep it far away from the magnet, the fields can be strong enough to magnetize the innards and it will never turn again, could possibly erase the magnetic stripe on your credit cards if close enough (wow, that could come in handy; Honest Honey, I have no idea why your credit card stopped working, guess the bank just ran out of money....)

And, be cautious about working in front of the "face" of the magnet with ferrous wrenches, hammers in your hands, when the current is turned on it can pull the wrench (with your hand wrapped around it) to the magnet, could hurt a bunch.

They make bronze wrenches, hammers, crowbars for non-sparking work (think oil refinery), but they are also non-magnetic, could be useful if you are planning on a bunch of work around electro-magnets.

"Lectricty, they've been studying it for years and nobody knows how the heck it works"....

Have fun, Kevin BSEE, MSEE.

You can find a training video in "Breaking Bad".

I think if you had any idea what those cost new you would be disabused of the idea of them being junk. They are repairable. What size, type and manufacturer do you have?

As Steven said, read the instructions! Anyone who has had any crane training and/or operated an electromagnet would have seen the safety instructions on the crane and electromagnets stating " Do Not Touch , electrocution/shock hazard " If you don't see a sticker like that you should apply one.

I agree, but my point was, if you are gifted a large electromagnet (or several) with an unknown history of maintenance or safety testing records (and probably missing instructions) the most responsible thing to do is a complete inspection and test of the electrical insulation (magnet and connecting cables) to make sure it is up to the task and safe to use. Simply applying a "This May Kill You" sticker to a magnet with an uncertain history is less than due diligence.

And those things have a whopping amount of copper in them, copper is about 4 dollars a pound and a 20 ton capacity electromagnet probably has 2 tons of copper in it. That's $8000 scrap value for the copper alone. They are rugged as heck, unless they have been in a flood or fire they last forever. And even if they were flooded you can probably disassemble one and clean/dry it out. A fire could possibly warp the magnet and it may need to be scraped (there are soft iron field pieces inside like in a motor, high temps may warp/twist them along with melting the internal insulation).

Have fun, be safe, Kevin.

The magnets are worth as much, if not more than the crane that was donated, in my estimation. The thing to do is pick one to keep, and sell the other three. I found it astounding that the donor wouldn't know their value and keep them!

Magnets are still very much in demand.. just look at the scrap metal industry. They can't live without them.

Long ago, a shop I worked in still had a Bullard vertical boring mill that would turn a 4' diameter piece.
An electric motor repair shop in the area got the job of repairing a defective electromagnet. He got permission from our shop superintendent to use the boring mill to do some work on the working face of the magnet. Flipped it upside down on the table of the machine, secured it nice and level, and proceeded to cut the areas out where the front face was welded to the body, so he could get in there and repair shorted turns.

As far as controls, a local museum was gifted a Burro crane from the UP a number of years ago. The Burro was going to scrap, before that, and had the magnet controls and the 250vdc generator removed. I ended up with the control panel. I've used lots of the switches for projects, but I've still got the Ohmite rheostat and volt and amp gauges.

I've worked on one of the generators for an electromagnet.

It's probably very high DC voltage. Be cautious. There are such things as 24 vdc magnets that work directly off the equipment battery but i suspect they are pretty weak.

The back EMF is brutal. The controls I worked on sent the back EMF to a large power resistor, which quickly gets very hot.

This one also had a reverse 'kick' mode. It briefly reversed the magnet polarity to help kick the metal off faster.

Definitely megger the magnet and wires. A short to the frame will fry the controls.

Interesting conversation so far.

Two are "Ohio". Another says "Type SH" and the other is a Cleveland(?) has a fancy logo cast on the top center, looks like "EL&M".

Thanks for all the input!

Ohio is still around. The SH ( scrap handling) may have been a National Electric Coil, acquired by Magnatek , then Walker Magnetics, And since February, Industrial Magnetics of Boyne City MI. EC&M has been similarly acquired.
The idea of a sticker warning of a shock hazard is ridiculous. You can't even keep a coat of paint on one of these for more than a week or two. Do you have such a sticker on every receptacle in your house? I thought not. The 130 volt AC is much more likely to be fatal that 230-250 V DC of a magnet. There is a reason that electric chairs are AC.
No a "snap switch" will not control such a magnet worth a damn. Maybe a tiny one but real scrap magnets use a Cutler- Hammer or Hubbell controller that would be 3-4 grand for a 72 inch magnet. A proper magnet control has 3 positions, lift, drop, and off. In drop the field is momentarily reversed to repel the load. In off the load just trickles off as the field collapses.
No magnet made in the last 50 years would likely be copper wound. Every lb of magnet is a lb you can't lift in payload. They are all aluminum wound nowadays unless you are made of money and special order. The weight penalty would kill a Burro crane.
Pretty much any magnet manufacturer or well equipped apparatus shop can repair or rewind a magnet with the possible exception of Dings. They don't mention scrap magnets on their site anymore and they did not have separate insulation for their windings. They used anodized conductors instead. They may be orphans.
Magnets are normally either 48-50 volts or 230 volts. The lower voltages were made after WWII when welding machines were dirt cheap and scrap was everywhere. Many startup scrap dealers wanted to use these cheap welding generators and so low voltage magnets were built. That would be a special order today. The standard would be 230 volts, commonly operated at 250 for more lifting power.
I spent 25 years in the scrap business. I've bought entire set ups, had them repaired, and done some repairs in house. Sized for the Burro there might not be a lot of demand but someone out there would love to avoid the new price. They don't eat much so wait for a buyer.