Gantry Crane Magnet

For top performance, I'm thinking the resistance should be around ten ohms or less.

Did any of the newer cranes use DC in the magnet?  The "effective resistance" of the coil would be much lower at DC.

143 ohms seems very high to me, that wouldn't be pulling much current, and of course it also wouldn't be very strong.

 

I'm confused what point you're making Dale.  With DC, the effective resistance is what he measured, it should be pure ohms law to calculate current in the coil.  With AC the effective resistance would be higher due to the inductance of the coil, right?  With a coil resistance of 143 ohms, I can't imagine this thing having much strength.

My crane works well to pick up 2 inch sections of tubular track with a tie.

My amprobe says approximately 1/4 amp ac at 17.25 vac.

So that's about 70 ohms impedance.

The DC resistance is 5.25 ohms.

 

Hmmm...I see a pattern here...

 

John, cjack makes my point.  If a reactance of 70 ohms and 1/4 amp will work with AC, I wouldn't be surprised if half that current would work at DC.

 

The fact that the flux is reversing constantly with AC actually works against the pickup power for any steel that retains any magnetism (significant retentivity.)  With DC you have a continuous unipolar attraction. 

 

And there are no eddy currents which tend to repel, not attract.  (I built a repulsion coil for a science fair in high school, and I remember well how high the aluminum rings would shoot into the air.)

Engineering Open House here used to feature a cannon shooting rings across the EE lawn. And cooling them with liquid nitrogen made for more fun.

I checked again 1439 ohms at 18vac. The clamp measured what I think is .08 amps. Not much current at all. What would this indicate? Too small and too long of a winding? Maybe overheating and fusing in middle of winding. I made the cub scout dc motor with nails and Red coated wire as a kid but that used two electromagnet windings to spin the motor. But this does not look to be rewound or messed with so unless it is a factory dud, I have know idea. Does anyone know what size wire and how many turns would work supposing I decide to tear it apart. Otherwise it is less useful than the original hook. Thanks FMH

Typo. 143.9 ohms FMH

The strength of the magnet is going to be based on ampere turns.  High resistance may just indicate the magnet was made with many turns of a fine wire.  

It is made of very fine wire.what are Ampere turns.

One amp in one coil of the wire is one amp turn.  One amp in one thousand turns of wire is the same magnetic strength as one thousand amps in one turn of wire.

Actually Dale, we're saying the same thing.  My point was that 143 ohms measured would be a much higher impedance.  I agree that DC would give more magnetism, however that coil resistance is much too high for any decent electromagnet.  I believe there's something amiss there with the magnet. 

 

80 ma of AC current is insufficient for the task, and I doubt DC in that coil would be that much better.

The orginal electro magnets that Lionel used were AC

powered. The remakes from MPC had a bridge

rectifier in the crain so the magnet used DC.

 

Which still doesn't explain the high resistance of that coil.

Hi Pa, Just reading your post. Up early and did belt changes on two bucket cranes. Very fast once I figured out how to get the first one opened. Used # 023 o ring from Ace. Much better than the original square profile belt. And I also tested my replacement magnet that Trainz sent no questions asked. Same symptoms as the other one hooked up to new controller. And same resistance. Setting up my cranes to have both magnet and buckets so I was a little disappointed. On a lark, I wired in a bridge rectifier. Sure enough it worked and no hum. Still seems a little weak compared to what I was expecting. But much better than ac. Dismal. So it looks like you are correct. To bad they do not show it in parts diagram. If anyone has a postwar ac one that really grabs metal and they are willing to part with it, let me know how much. Thanks, Fred

If you now have 2 magnets, you might want to tear one down and rewind it using close to original 282 specs.

Great idea. I could do both. Easily enough if I had the specs. Do you have those specs? Wire gauge, number of turns etc. Thanks Otherwise, I would not know how to proceed.

If you put an electrolytic capacitor across the bridge output, you will get more DC current in the coil.  I would start with a 470 uF at 35V.

You can build a powerful magnet by taking a junk or unused(but with good continuity) 6019, 6009, or 6149 uncoupler track section and carefully unwind the magnet wire from it, winding it onto the crane magnet core.

 

You may need to compensate for any difference in power requirements between the crane and the magnet, I have always used a separate, adjustable power supply(currently a little 1010 transformer) for my 282 crane magnet - separate from crane power - for easy control of the voltage and current to the magnet.    You want good power for the magnet, but you don't want to burn it up either.

Hi Dale, By across, do you mean the capacitor goes in parallel with and in front of the magnet coil? If I do this and I am happy with the performance, will there be an issue with the unit becoming magnetized running on Dc and do I need to unsolder bridge and capacitor to DeGauss? Love that word. Not sure if I spelled it correct. Sounds so Mad Scientist. Also, if the Dc is an issue, why did Lionel change from Ac to Dc?

Rob, Thanks for the instructions but I would rather not dismantle what few uncouple tracks I have. The red coated wire is easy to acquire. Are you saying that the Ac Magnet spec is same as the uncouplers. If so, can you just provide me with wire gauge and number of turnings? Save me from reverse engineering. Actually if I had one to reverse engineer, I would not need reverse engineer it. LOL Thanks Fred

I do not believe the uncoupling track has the same specifications as the crane magnet.  The uncoupling track gets hot very quickly and will melt the spool with power for very long, the magnet doesn't have that issue.

 

They're close - which is why you want control of the voltage for the magnet.

 

I'll try it sometime soon.  I do know that the resistance of a good uncoupler winding is 5-7 ohms.

The capacitor can be connected in parallel anywhere from the bridge rectifier's output to the leads of the electromagnet.  The + side of the capacitor must go to the positive voltage, and the - side to the negative voltage.

I experimented a while back with halfwave DC and a flywheel diode across the old AC electromagnet, but I never completed my tests.  I wanted a quieter magnet that didn't buzz so much.

I don't know if the DC will create a problem, but the fact that Lionel used it gives hope.  The biggest problem would be if some of the load you are picking up would retain some residual magnetism and not release from the magnet.

By the way, testing with a rod, rather than something with a flat surface, is a "worst case" test since there is very little actual contact at the tangent point where the rod touches the magnet.

As in all cases with the magnet, check for heat buildup to avoid burning out the coil.

I just checked the resistance of a properly functioning crane magnet(a 182) - 18.4 ohms.  That seems very reasonable from a power requirement perspective.

That sounds more reasonable, a lot less current than the uncoupling track.

Just ordered some caps and also some 6 amp diodes. Since the cranes are already rectified for the Dc drive cans I might as well try to improve the Dc magnet instead of rewinding for Ac. Sounds like the Ac version is pretty annoying and has its own downsides. I am also going to also try the mod to a couple of conventional switchers with the diodes per a previous thread to see if I can improve smoke output and improve slow speed starts. I want to thank all you guys for your patience and feedback with us electronically challenged. I consider myself to be on the higher end when it comes to mechanical aptitude. Will tear down and rebuild/ modify anything without fear or hesitation, whether, pneumatic, hydraulic or internal combustion. And while quite proficient with house wiring , low voltage and mechanical relays, switches, and circuits, but for some reason, I have always shied away from those little things on circuit boards. Doing these little projects is a lot of fun and this forum has been great way to learn. As an older ( 56) single Dad ( long story) with two little kids in 3rd and kindergarten, I do not get much time for myself and trains has been an excellent home based pastime that keeps the kids excited and involved but also can be an intellectually stimulating and creative hobby. And more fun than my executive job. Fred

I think one of the greatest values of this Forum is the mentoring that gives folks the support to try something new.  Get out there and make a few sparks!!  That is how we all learn.

Since you mentioned residual magnetism, I will put in the cure we use in Industrial magnetic brakes.

During annual periodic maintenance we have the user swap the wires to reverse polarity of the magnet.

A year of operation will not build enough residual to matter, and the following year will remove it.

Problem solved for them, you can put it on your annual list or just make a note if it starts to be a problem, swap the wires.

I'm new to the forum so I hope I'm not sticking my foot in my mouth.  One thing you could do is take one of the magnets(hopefully an original 282) and mike the wire diameter.  Take the next smaller size(to allow for the varnish coating) in the awg table and find the resistance per foot.  Someone earlier suggested that a properly functioning magnet was about 17 ohms.  Calculate the number of feet you would need to obtain that resistance.  You could also measure the lenght of the existing wire after removing it from the magnet.  Rewind the magnet using the correct lenght and diameter of wire.  You need to take care to keep the layering smooth or you will not be able to fit the require length on the bobbin.  The reactive part of the equation will not change materially with the new winding.  The downside to using dc is that it will permanently magnetize any iron bearing material it comes in contact with.

I have been running my Magnet Crane on DC for years with no problem, BUT I don't pick up scrap metal or other very light weight objects so any small amount of residual magnetism has no effect.  What I do pick up with the magnet are objects that have upolstery tacks that are attached to their tops.

I have been running my Magnet Crane on DC for years with no problem, BUT I don't pick up scrap metal or other very light weight objects so any small amount of residual magnetism has no effect.  What I do pick up with the magnet are objects that have upolstery tacks that are attached to their tops.

 

Here is a video of my crane in operation.

 

 

Dave

 

Thats really cool, thanks for the video.

 

Dale H

Hi Dave, I  have a PW magnet Assbly from a 282. Give me a call at 740 816 7481.  Stew

For the Intermodal Crane, which I suspect is a similar type of control, I tweaked the resistor values for the DC motors to get everything working at optimum levels with one power supply. 

 

I have the TMCC version of the 282, and the DC magnet will pick up 4oz, but has trouble with 5oz, probably all you can expect.  I'd like to slow the cab rotation down a bit, but other than that, I like the speed it operates at.

 

I haven't taken the covers off to measure the magnet resistance or current yet.

Hi John,

The Interrmodel uses the same motors and gear boxes so I would expect the controller to be similar. So are you saing that you added resisters inline with the diodes?

That seems to be a better solution than my method of rewiring multiple power sources.

 

i was under the belief that the TMCC crane allows you to program  differnt voltages and also set independent speeds fors hoist and rotation. Iam actually thinking of installing a ERR Crane Commander in mine but even though they will sell me the parts, they stopped selling  them because a lot of people had problems  programing.

Fred

 

The Intermodal crane controller has resistors inside the control box.  I changed the values, raising them to slow things down, and lowing them to speed things up.

 

I looked at the crane manual, and you're right, I've never used it with the TMCC yet, just with the control box.  That will make things easier.   I will have to connect it to the TMCC and see how well it functions.

 

I'd love to have TMCC for the Intermodal crane, but with all the functions, I'm not sure I could get them all working and logically with existing products.

 

I'm working on the Ardunio processor decoding TMCC commands, maybe that's the ticket to do some of this fancier stuff with TMCC control.  I could perhaps map the commands to the TMCC crane car commands and have Legacy icons.