Getting Rid Of Ingrained Residual Magnetism From Poles

[Eurybates]

Had a problem with a tiny 20amp DC lucas generator recently. Was actually a foreigner (for my brothers tractor). Rewound the fields and inadvertently transposed them. A lot of times in the past especially with excitation fields of the self excited design you lose residual when you heat (or) do an AC drop test during the testing process. This is not normally a problem as you simply flash it back into life and away you go. BUT no matter how much I flashed this little sucker, it just refused to play ball. I had to pull it down and reverse the field winding for it to start self exciting again. It had me beaten for a long time until an "old timer" came along and told me that it was SO OLD that the laminations had established a memory and essentially turned from it from a temporary magnet into a semi-permanent and that by getting the poles mixed up (regardless of electrical polarity) makes it impossible to flash your old north to south.

 

Anyway..It works now. I just thought I would share this as it may benefit somebody else in the future and it sure had me befuddled for a while. I would also be interested to know if there was an alternative (other than un-screwing pole pieces or reversing field) . Would sending AC at high current through the fields kill the residual thus allowing you to re-magnetize?

 

Eurybates