Loco Motor Questions

That is the typical symptom of a motor that has lost its magnetism, it can most likely be cured by remagnetising it. There was an article on how to do that in MR in 1972. I could provide a scan if you contact me off list. (Reply won't work get my address from my website).

Could be, they take a lot more current when the magnet is weak, usually they also go faster but with less torque as you observed with the first one. This second one is probably not so far gone.

Keith

Make friends in the hobby. Visit Garratt photos for the big steam lovers.

Check the armature windings. It could be you have one open winding, the remaining windings are enough to make it run under light load, but you need all the windings intact to have real torque. The fact that you have to give it a spin by hand to start it is a hint that one of windings is open. With luck you can spot a broken wire, they often break right near where they solder onto the commutator. Put your ohmeter across the brushes, it should read a ohm or so. Rotate the armature by hand slowly. If you see the resistance go "open" you are missing one winding. It is possible to rewind an armature, assuming some soldering skills on your part. You have to find replacement wire of the same gage. Then it's just a matter of carefully winding the wire neatly onto the armature and getting the same number of turns into each little slot. If the replacement wire is bigger, or your winding technique is less than neat, it may not fit.

Yes, if the permanent magnet looses its strength, the motor looses torque. On the other hand I have never had this particular problem happen to me. You can make a rough check by feeling how hard the magnet tugs at an iron tool. Compare the pull of the suspect motor with the pull on a good motor. If the suspect motor's magnets are weakened enough that you can feel a difference, then you might be onto something. It is possible to "recharge" or remagnetize the older Alnico magnets. In principle this can be done by putting the magnet into a very strong magnetic field, and perhaps tapping the magnet lightly. I've never tried to do this in the basement and I have a feeling that creating the necessary strong magnetic field could be tricky with just homebrew equipment. What's the current draw like? A good open frame motor ought to run unloaded pulling something like .25 amps. Motors try and run at the speed where the back emf of the motor matches the driving source voltage. They pull current as required to get up to that speed. When you load them down, they pull more current to keep their speed up. If the field is weak, it takes more current to create the same torque. You mentioned that this one gets hot, which is a sign of pulling too much current. David J. Starr

Sounds to me like both motors have VERY weak magnets.

It is possible to remagnetize them, find a hobby shop that specializes in slot cars. I recall from years ago remagnmetizing motors was "sop" after rewinding them.

Don

Hi:

Before testing old motors they should be cleaned an lubricated. The commutator plates can be cleaned with a soft eraser, lightly applied. I generally use Labelle 101 on bearings and spacer washers, if no plastic parts are close. A small drop on plates improves brush contact.

Question 1: In many older motors poor solder joints were not uncommon and centrifugal force at high RPM threw wire ends outward, breaking connection.

To determine if there is a open winding on an open frame motor, start motor, then reduce throttle until it stops. Mark the armature with a soft pencil. Repeat several times. If it stops at the same point constantly, a connection is broken. Usually this is at the commutator plate and may show up as arcing in a darkened view. Examination under magnification might reveal the break. Plates are skewed with respect to poles, so the break will not be aligned with mark. The wire end will probably be close to original solder connection on plate.

In most cases, the connection can be resoldered. Since the wire is insulation coated, the end should be carefully scraped to avoid breakage. If too short, a fine wire jumper can be added. I have repaired many this way, especially Revell.

If the stopping point is not consistent, the problem is usually a weakened magnet caused by application of AC or rapid reversal while running. This is indicated by excessive RPM, running with no load and drastic drop in speed under even light loading, accompanied by excessive current. Speed can be detected by ear. Higher pitch equals higher speed. Remagnetizing is possible but dangerous.

The Alnico magnets used do not deteriorate with age unless subjected to high temperatures, strong opposing magnetic fields, interuption of loop path or hard jolts. More recent experiments have revealed methods to replace these magnets with Neodymium types yielding lower RPM and current. These can be removed from pole pieces without deterioration.

Question 2: The AHM FM C-Liners were originally produced by Rivarossi with ballbearing motors, then farmed out to Tempo of Jugoslavia with poorer motors. Some had one carbon brush and one rolled-up copper mesh. These were prone to wear. Lubrication may solve problem. If not, the best solution is to find a replacement, since recharging would be very difficult. Since these locos were very inexpensive and common, they can be easily found.

For details and extensive discussion of problems and solutions, see first site below.

Hope this helps.

Thank you,

Budb

Author of:

MODELRAILROAD TECHNICAL INFORMATION

PROTOTYPE TECHNICAL INFO FOR MODELRAILROADERS

Moderator of:

MR TECHNICAL HELP GROUP

COUPLER HELP GROUP

After much good advice

What do you mean by dangerous? For yourself, for the motor? It might not be too easy to find the kit these days, 30 years since I made a magnetizer following instructions in MR, I no longer have it but it worked a treat.

But older magnets very often did lose strength hence the need for remagnetising, those who want to operate old locos still need to do it.

Keith Make friends in the hobby. Visit Garratt photos for the big steam lovers.

Thank You all for your help and knowledge and the links. Great Help! I will follow up with the information from the web sites.

And even though some of my old models are pretty poor, I am still interested in what they do and why. Get as much satisfaction in fixing up one of these old clunkers and getting it to run as in taking a nice new Proto 2000, etc loco out of the box. No, perhaps even more :0)

Also, some of my neighbors have discovered my hobby and have brought a few old trains around for advice and repairs. So far so good. The latest is a Rivarrossi 2-8-8-2 Pennsy #2197 engine. It's a real beauty. The gentleman actually wanted to give it to me, belonged to his late father in law, and he has no trains. So I told him, just bring it over and let's check it for cleaning and lube, etc. Luckily the motor in this one is fine and it just needed some tlc as above. Pretty dirty and dry after sitting in an attic for years, and now its shiny and proud, running smooth and quiet, pulling a line of coal cars on my layout. It has been here over six months.

I reflect that my first HO model train was a Rivarrossi 0-4-0 B&O dockside that I bought used from a hobby shop for $.50 during the early 60's. It still runs great and is still one of my favorites. And I still have the Lionel 027 trains my Dad bought for me starting when I was born. As well as a few of his Ives trains that he kept.

Thank you all again. I hope to be able to contribute as well to this fine newsgroup.

Very Best Regards,

Robert Arlington VA

Hi:

As explained on my site; first, all motors with Alnico type magnets are magnetized after assembly to retain maximum retentivity with a closed loop flux path. To attain this, the magnet must be driven well past the saturation knee on the hysteresis loop. The main determining factor in providing sufficient coercive force in any solenoid, internal or external, is the ampere-turns product. Size limits the wire gauge and the number of turns. Thus a large current must be applied. This is essentially a short circuit, which generates heat very rapidly , possibly melting insulation and shorting out turns. Commercial units use timers.

WARNING!!!! THE FOLLOWING IS NOT RECOMMENDED!!!!!

In lieu of making a "charger", for casual users a frequently touted method uses a car battery as a high current source. A few loops of wire are fed between the pole pieces and around the magnet. The wires are then rapidly touched to the battery terminals and if you can react in microseconds, the magnet will be charged. But the insulation and possibly the wire may melt. Fire and burns may result. The collateral damage may cost as much as a thousand motors.

If these are not dangerous to the user and possibly the motor, I stand corrected.

Still using in excess of 40 motors, dating back to the 1950's, none have deteriorated retentivity. These include Pittman, KTM, Mantua and some cheap New One Model, Japanese motors. All have been operated at heavy loading, but not abused. Of many hundreds tested over the years for customers, only abused units showed any signs of faults.

For details and extensive discussion of motors and new magnets, see first site below.

Hope this helps.

Thank you,

Budb

Author of:

MODELRAILROAD TECHNICAL INFORMATION

PROTOTYPE TECHNICAL INFO FOR MODELRAILROADERS

Moderator of:

MR TECHNICAL HELP GROUP

COUPLER HELP GROUP

Well, yes but you can make anything dangerous if you use stupid techniques.

The most common cause of loss of magnetism was taking the armature out without shunting the magnetic field. Far from obvious to most people servicing their loco so they only found out when the problems started on re-assembly. And reasonably sensible ways of generating the required field to remagnetise them are not dangerous.

Keith Make friends in the hobby. Visit Garratt photos for the big steam lovers.