[AMRadio] Dynamotor discoveries

[CL in NC]

I had posted a question about a dynamotor problem I was having and received input vie email from Mark, K3MSB, Harold, W4PQW, and from Meir, WF2U on out local AM net.  Thanks for all the information and, that along with a little internet searching allowed me to sort the thing out.  There is just not alot of info on the actual internal wiring around, and the TI for the BC348 just has circles with wires coming from them showing the dynamotor field coils and armature.

The field windings go to the 24VDC end of the dynamotor, The field coils had been installed backwards in the dynamotor, and from the fact that the field coil screws were still staked in their original position, indicates to me that they were installed that way.  The field coil wires had been routed to the high voltage side of the unit, and wired up.  It will run this way, but not at full speed.  There is no way that somebody could have re-routed the field coil wires to the wrong end with the coils in place, no room to do it, and the attached lugs would have never made it through. 

The armature has 2 copper bands on it that are crimped, then soldered.  One band had a large lump of solder on it.  The armature turned freely by hand, and with low voltage applied, but as it sped up, it acted like it went out of balance.  Apparently the copper band expanded due to centrifugal force, forcing that solder blob to hit the field windings and slow down.  Smoothing the blob flatter with the solder gun fixed that.

Lubrication with wheel bearing grease is not the best route to go either. Ramping up the 4440 rpm dynamotor speed to wheel bearing speeds on an average 15 inch rim  car tire, comes to about 405 MPH.  Mobil SHC 100 is rated for high speed electrical applications, ENCO sells this, but with the cost plus shipping, I looked a little closer to home.  Found Lucas makes a multipurpose grease, Red N'Tacky, high temp, industrial use, for $5 at AutoZone.  Ran the dynamotor for a couple hours, then opened up the ends to look at the grease and it was still fully coating everything, no runoff or slinging.  Saw several posts where folks say to pack the bearing.  The book and the metal motor covers say don't pack the bearings.  I didn't pack them like a wheel bearing, but did get a goodly amount into and around everything.

Considering all the things wrong with the unit, it is amazing it had not been thrown away at some time.

Charlie, W4MEC in NC