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 Posted - March 21 2010 : 09:58:30 AM
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While looking at my broken 5-pole motor casing, I thought Hey, I have a perfectly "good" 3-pole motor in the Dual cab BL-2 project box...wonder if the armature will fit? LETS FIND OUT!
Here's the two units , 3-pole on left, 5 pole on the right. Notice the damaged area which holdes the spring tensioner, the loop is broken and gone :
Here are the two armatures, out from their housings. basically the same size :
And here we have the completed swap, with 5-pole armature in the 3-pole housing :
Now, to make an important note here, I noticed that the little bronze bearing inside the 5-pole housing was SMALLER than the 3-pole unit. One end had some play, and wobbled some. The 3-pole housing provided a tighter fit, due to a longer bearing, and should last longer, with the downside being some added friction due to more bearing surface. But if you don't have enough, the stress from the motor will cause it to wear out sooner. And I think , looking at the bearings in the older 5-pole unit, they are smaller and are more prone to early wear-out. So these 3-pole housings MIGHT be worth saving just to convert the older 5-pole types to a bigger bearing. The swap was easy enough, since the housings and the armatures are the same dimensions, apparently. I'll try to test it today, Sunday, to see how it runs. With a new housing with intact plastic hoop for the spring, I can repair one of my BL-2's back into service again. And it may run better than ever! That's today's Repair Report from the BL-2 Doctor.
Jerry in Virginia, USA
" When life throws you bananas...it's easy to slip up"
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Posted - March 21 2010 : 10:01:32 AM
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Thanks Doc. Enjoyed your Treatise!
-gareth
"A is A"
-Aristotle
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 Posted - March 21 2010 : 11:00:24 AM
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RE: 5-pole motor rebuild with 3-pole housing , update Sunday morning :
Well, I got all the electrical parts re-installed, and I cleaned up the contact areas with a miniature spiral wound wire brush, and hooked it up to my test track transformer. The 5-pole proceeded to give a satisfying whine and ran fairly smooth. I do need to put some oil on the bronze bearings. So it looks like another BL-2 will rejoin the running roster soon. I love successful ( and completed! ) projects! I rarely manage them frequently. LOL.
Jerry
" When life throws you bananas...it's easy to slip up"
Edited by - AMC_Gremlin_GT on March 21 2010 11:02:26 AM
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Posted - March 21 2010 : 1:01:29 PM
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| Sweet...
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Posted - March 21 2010 : 5:45:43 PM
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I've never seen one of these 5 pole motors in an all plastic housing before, Jerry. Maybe there was an in-between period where Mehano was using up 5 pole armatures, or else a previous owner did an armature swap. The only 5 poles I've seen have a brass bottom plate.
One note: when I change these armatures, I pull them out with the magnet and pole pieces still around them so that I don't break the field, and swap the whole assembly. Most open frame motors lose some or most of their magnetism when the armature is removed.
The Tyco Depot
Edited by - NickelPlate759 on March 21 2010 5:46:16 PM
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Posted - March 21 2010 : 9:48:10 PM
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quote:
One note: when I change these armatures, I pull them out with the magnet and pole pieces still around them so that I don't break the field, and swap the whole assembly. Most open frame motors lose some or most of their magnetism when the armature is removed.
Originally posted by NickelPlate759Â -Â March 21 2010Â :Â 5:45:43 PM
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Um, I've never heard of that...there's a reason they're called "permanent" magnets, simply pulling a copper armature out which doesn't contact it much should not have that effect on it, that I know of. If that's the case, then how does the original magnetic charge get applied? It's all from the permanent magnet, so that doesn't change. I can see the metal side plates losing their charge if you pull them away from the magnet, but they should reacquire it from the permanent magnet, and not have any degradation. Now, I can see if you swap the plates, from one side to the other, they may be slightly magnetic from being in use, and then they're applying an opposite charge to the other side of the magnet, er, the same charge ( N-N ) instead of N-S, so it may cause a drop in power. I don't know, I've rebuilt generators before, and worked on slot cars, and never heard of anything about losing charge by pulling out the armature. I believe that isn't quite right, can you find any technical reference to that phenomena ?
Jerry
" When life throws you bananas...it's easy to slip up"
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Posted - March 21 2010 : 10:24:25 PM
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Most open frame motors got an extra shot of magnetism with a big coil once they were assembled, because these older alnico magnets weren't able to hold enough of a charge on their own. When the armature is inside the field, it acts as a keeper, allowing the whole assembly to hold an additional charge that is lost when disassembled. A steel plate across the ends of the pole pieces is usually enough to prevent any loss when removing the armature.
Many motors in early HO locos would gradually lose their magnetism over time, and there used to be articles in the model railroading publications about how to build a charging coil. Newer ceramic magnets don't need an extra shot of magnetism, so that's why you can disassemble slot cars or modern can motors without having to worry. On the other hand, I removed the magnet from a Mantua PM-1 motor thinking it would be okay, and I was left with a paperweight.
It all depends on how much extra charge Mehano gave that motor when it was manufactured. If it still runs fine, they may not have given it any. Fortunately, if there were a problem, now all you have to do is replace the old magnet with some super strong neodymium magnets, and it will run better than new. 
The Tyco Depot
Edited by - NickelPlate759 on March 21 2010 10:25:53 PM
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Posted - March 22 2010 : 07:31:15 AM
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Alnico magnet research - Well, I did google this subject, and found it to be fascinating. While there is a need to use keeper rings on larger magnets, I could find no supporting evidence to suggest that the types used for hobby purposes required it, and most concerns for the Alnico magnetic fields were for long-term storage, and not having N-N and S-S contact , not temporary separation for installation, etc.
To test it conclusively, I finished reassembling the BL-2 chassis, reinstalled all the gears, and put it on the test track. It fired up, and raced around the track with little hesitation. I tried the other BL-2 chassis's,and they were slower by comparison ( of course, I'd cleaned up the contacts and armature contact patches, so the revamped 3-to-5 pole unit had clean and robust electrical connections now ). Bottom line - I don't think it will lose much of it's magnetic force from keeping it separated a few minutes for clean-up and repair. I can see if you leave it apart for months at a time, but for the few minutes it will be separated, the Tempo motor doesn't appear to be affected in the least by it. And again, the magnets themselves are stored in packages in bulk at the supplier, although they do apparently use a keeper bar or plate when in storage ( again, for long-term storage ), so that I can see. But I'm not worried about my BL-2 motors losing power now, they should be fine having them apart just a few minutes if I need to go in and do a full-press clean and grease.
Jerry
" When life throws you bananas...it's easy to slip up"
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Posted - March 23 2010 : 4:14:19 PM
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In the open frame motors I've disassembled that lost magnetism, the loss was instantaneous. It's just something to be aware of.
The Tyco Depot
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