PowerPro High Inverter Heat Issue

[JPG]

I'm off topic here, but why were you band sawing at that rpm through the speed reducer with the PowerPro? At 7/1 reduction that's a speed of roughly 878 rpm which you could just set the PowerPro to (for that matter a regular headstock will be at that rpm with the speed control set a little past the "B" speed setting).

'Because' of past 'issues' with PP direct drive to the band saw.

[wa2crk]

I may be out of line here and I apologize if I am. It is true that an AC induction type motor will self destruct in a few seconds if stalled with power applied but I believe that (I read this somewhere in the literature) that when the PP controller detects the shaft not rotating the "brain" shuts down current to the motor windings. I may be mistaken. After all; three things happen when you get old. The first is that you lose your memory but I can never remember the other two things!!
Bill V

[JPG]

[quote="wa2crk"]I may be out of line here and I apologize if I am. It is true that an AC induction type motor will self destruct in a few seconds if stalled with power applied but I believe that (I read this somewhere in the literature) that when the PP controller detects the shaft not rotating the "brain" shuts down current to the motor windings. I may be mistaken. After all]

It is true that an AC induction type motor will self destruct in a few seconds if stalled with power applied YES

when the PP controller detects the shaft not rotating the "brain" shuts down current to the motor windings YES

I may be mistaken NOPE


FWIW, A DVR motor will get crispy much much faster if not protected by the controller.

Reason - very low impedance coils which depend upon back emf while induction motor is 'running' or short pulse duration with the DVR to limit current.

FWIW tweaking the control parameters can get you into the crispy mode.

[Barney1]

Got a high heat message while pushing my bandsaw to the limit in a cold (<60deg) garage are all the posts on this forum more than 5 years old? Is anyone out there?

[JPG]

Got a high heat message while pushing my bandsaw to the limit in a cold (<60deg) garage are all the posts on this forum more than 5 years old? Is anyone out there?

Yep there be live bodies present.

Now how on earth did you get temp high enough while bandsawing????

How do you push the bandsaw???

i.e. more details needed

[Tyer]

I just received my PowerPro about a month ago, and haven't used it much. Just experimentally, I wound it up to 10,000 RPM, with no tools attached, and let it run for a few minutes. The first thing I noticed was the smell of belts getting hot, and then it wasn't too long (around a minute) when I noticed the back top area of the headstock getting warm.

I'm an engineer by trade (among other things, I've designed and written firmware for variable frequency motor drives), so I was immediately concerned about how much energy must be being dissipated by something to have heated things up noticeably in such a short time, with no load at all. It didn't seem to bode well for extended use at high speeds (such as shaping, which I intend to do). Reading around the forum some, this does appear to be a problem for this machine.

I hypothesized that the immediate source of inefficiency and heat was neither the motor nor the electronics, but rather the belt drives, based on the location where i could first feel the heat. On my old Mark V headstock, the auxiliary spindle ran at 1.6 times the speed of the main shaft, so on this machine that would be a fairly blazing 16,000 RPM. There aren't many high-horsepower belts that can withstand that kind of speed, especially over small-diameter sheaves. Since I don't really need the auxiliary spindle for anything (most of my machines are on separate stands), I'm considering removing that belt. (I couldn't actually find that ratio documented anywhere for the PowerPro, but looking at the exploded view of the headstock, the size ratio of those two sheaves looked to be about that.)

Incidentally, when reading the "Shopsmith PowerPro Headstock Maintenance and Troubleshooting" manual (all eight pages of it), I found this statement: "...will run smooth, relatively cool and quiet." (emphasis mine). Leaving aside the creeping loss of adverbs in modern English (it should have been "smoothly" and "quietly"), or one's position on the Oxford comma ("...cool, and quiet"), this seems to be a known issue to Shopsmith. On reading the forums, it appears that getting rid of heat on the controller board is also a problem. My immediate idea for a solution would be a fan on the end of the motor shaft, and then external fins on the housing. It's certainly true that the engineers were struggling, and did a remarkably good job of, finding space to mash everything into such a tight enclosure; however, it's definitely not quite a truly "industrial" machine.

I'm still pretty happy with it, though. I'm looking forward to doing more wood-turning with it, where the low speed operation will be really nice.

[sehast]

I have never noticed mine getting warm at the speed you would be running a bandsaw. Even at 10,000 RPM as long as I don't run it continuously for several minutes it is fine. When routing and shaping I usually take a pass or two and have to readjust or do something else so it has not been a problem but if you were in a production mode for 5 minutes or more I could see it getting pretty hot. Hot to the touch does not mean that it is running hotter than designed. My mini mill runs very hot, so hot you can't hold your hand on it, but has never failed in the last 10 years. That said there have been several reports of a cooling problem with the PowerPro and even some have modified theirs with a fan. Do some searching on the forum and I think you will find some relevant discussions. One common problem is not having the belts aligned in the proper spindle grooves. If you are one groove off it makes a big difference.
I would be interested to know if the disabling of the auxiliary spindle by removing a belt is possible and if it is, does it make a difference of how much heat is created.

[Tyer]

@sehast: I agree that running noticeably warm in continuous use could be normal for some types of equipment. For example, an industrial motor running, for example, a pump can comfortably run all day at 150 degrees (F), which is hot enough that you wouldn't want your hand on it for more than a couple of seconds.

However, in this case I'm concerned about two things. First is the source of that heat: if it's due to the belt(s) flexing too much and too fast, that's a recipe for a belt blowing out. It would all be nicely contained in the housing, and would probably just move away from the sheaves and stop, but I'd rather not be replacing them very often.

My second concern is the fact that the electronics are also contained in that enclosure with, as others have pointed out, limited ways to extract the heat regardless of where it's generated. And heat truly is the enemy of electronic longevity; the curves of lifespan versus temperature are truly dramatic for some components in particular (electrolytic capacitors, for example). (If you'd like some light reading, look up "Arrhenius' Law of Chemical Activity" - capacitor life roughly halves for every 20 degree rise in temperature, and the ones in the PowerPro are most probably 2000 hour rated at 25 degrees C [77 F].)

The temperature rise itself probably won't affect the life of my particular unit that much, as I'm just an amateur user (albeit a relatively serious one) so I won't be running it eight hours per day. I just don't feel like replacing that one damn belt very often...

[Tyer]

BTW, regarding a belt being off by one notch, it's possible that this is an issue for mine, but I wouldn't know because I've never opened it up. I purchased the factory-built PowerPro upgrade to my Mark V-500, rather than the rebuild kit for my existing headstock. The amount for which I sold my standard headstock - in very good condition - nearly covered the difference in cost, without adding in the value of my time at all.

It's possible that the unit was incorrectly assembled at the factory - tomorrow I guess I'll open it up and see...

[Tyer]

Well, that was interesting! I wasn't quite ready for bed, so I went out to the garage and took a quick look at the PowerPro. The back cover came off very easily (just two screws, plus the coupling adapters). And sure enough, the upper belt was off by one groove on the upper sheave! I didn't even bother to loosen anything - I just coaxed it into the proper position with a large screwdriver blade while (manually!) rotating the spindle.

I also learned that my idea of taking off the auxiliary spindle belt completely is a non-starter, because the auxiliary spindle actually acts as a jack-shaft between the motor drive pulley and the main spindle sheave. Oh well.

Then, because OSHA rarely looks into my shop, especially at midnight, I spun it up with the guard off. It did sound a little better, but it didn't sound badly before. I let it run for my now-standard 60-second test, and sure enough, the belt smell, although still there, was less. Feeling the belts, they were both definitely heating up a lot, but within reason (sort of - I like things running *way* within their limits if possible). The upper belt was probably about 120 degrees, and the lower about 105 or so. I'm guessing that this is because the upper belt is only about half the length of the lower belt, and also runs over two small sheaves (the motor sheave is much larger - about four inches or so).

So I reassembled the unit - trivial, except that I dropped the @#$% speed nut into the bowels of the powerhead; fortunately, it was pretty easy to find. I then spun it up again, and felt the temperature rise at the same place (on the housing just above the upper pulley). It still warmed up, but probably only half as fast as it did before. The shaft of the auxiliary spindle still gets way too hot to touch after a couple of minutes at 10,000 RPM, which I'm not crazy about, but hopefully that won't hurt anything.

So thank you, @sehast, for the tip about the belt off-by-one-groove issue. I'm still not thrilled about how warm those belts run, but the situation is probably twice as good as it was. Groovy!