BuckeyeDennis wroteAs the motor spins faster, the winding-commutation frequency increases proportionally. As that frequency increases, the corresponding eddy-current loop diameter gets smaller. As the eddy-current loop diameter approach the thickness of the laminations in the motor iron, the laminations become much less effective at blocking the eddy currents. So you get little eddy-current loops circulating in the iron, doing nothing useful, but heating the iron.
I'm bringing this thread back because, as a more recent PowerPro convert, I'm trying to decide what, if anything, I should do to improve cooling. There are some great ideas here, and we see some of those ideas implemented in another recent post:
https://www.shopsmith.com/ss_forum/viewtopic.php?p=273588#p273588 My first comment is to expand on Dennis' explanation. I believe that higher speed operations of the headstock also contribute a burden to the motor as the bearings and belts are turning faster. I'd have to find my notes or redo the experiment, but by measuring AC input current while varying speed on a conventional headstock I found input power to have minimal change up until, IIRC, around Saw speed. From that point on current increased rapidly as speed was increased. Assuming I'm correct in attributing this to belts and/or bearings, the impact would be much greater at the higher speeds of the PP.
Second comment - I'd like to know more, if possible, about the impact of belt tightness discussed in an earlier post on this thread:
https://www.shopsmith.com/ss_forum/viewtopic.php?p=251538#p251538 While I agree that 1/4 inch under light pressure was once in the manual, it has been changed and that seems way too loose for the PP. Speed was not specified, unless I missed it, but I've noted that Idler shaft temp elevates quickly at all speeds I use. (Normal, per Jim McCann, but I didn't measure.) Are the temps cited a concern for others? I can't make any obvious correlation with Power Supply over-temperature, but Idler Shaft heating is a secondary concern.
And a question: I went the DIY route, so my motor pan has a number of holes with no obvious utility, other than improved convection cooling. I'm wondering if those holes are present on the 'new headstock' version PPs. Specifically, I'm talking about the motor vent from the AC motor, the motor mounting holes, and the original power cord hole. If some, but not all, are present, please specify. Thanks.
- David
