PowerPro High Inverter Heat Issue

[rpd]

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.

There has been discussion of heat build up before.
https://www.shopsmith.com/ss_forum/main ... 21659.html
https://www.shopsmith.com/ss_forum/main ... t5183.html
https://www.shopsmith.com/ss_forum/main ... t6406.html

I don't have a PowerPro, but one thing to consider is that the headstock cooling was designed in the early 1950's, for a 3/4 hp motor, and for backward comparability the headstock has changed very little over the years .
There have been PowerPro owners that have added a fan to blow filtered air into the headstock to minimize heat buildup and prevent the ingress of fine sawdust.
This has been done either through the access port on the rear side, or through the vent plate area around the auxiliary shaft.

This one came up recently on the Facebook group

https://www.facebook.com/groups/6844615 ... 183947526/

[Tyer]

So far, I haven't worked the unit hard enough to get either the motor or electronics to heat up excessively; my initial concerns was just for those belts, especially the top one. They're running awfully hot to have a very long lifespan.

When I do start loading it heavily (which may never happen in my use case), and I start running into problems, then I may look into adding some sort of forced cooling.

Update:
I read the posts you pointed to (the ones I hadn't already found), and on page three of one of them I found this: https://www.shopsmith.com/ss_forum/view ... 27#p251427

This gentleman did it right, and used an IR thermometer to get quantitative measurements both before and after re-tensioning the belts. The temperature of the top belt dropped a full 40 degrees. Since I already found that one belt was installed incorrectly, I have no reason to assume that the tension from the factory was correct either, so adjusting that will be my next step.

Thanks for the pointers!

[rpd]

So far, I haven't worked the unit hard enough to get either the motor or electronics to heat up excessively; my initial concerns was just for those belts, especially the top one. They're running awfully hot to have a very long lifespan.

When I do start loading it heavily (which may never happen in my use case), and I start running into problems, then I may look into adding some sort of forced cooling.

If the top belt is running excessively hot I would check the tension, proper adjustment should mitigate.

[sehast]

Ron beat me to it. Tension is the next thing to check and then make sure the tension of the two belts are equalized using the procedure in your maintenance manual.

[reible]

One of my machines behaved differently at first requiring a couple of retention cycles early on. The belt was slipping which was very easy to spot and fix but still seem a bit odd since the other machine was more stable. Now they are both stable but I don't know what the difference would have been. I got both of them as kits and did them myself so????

I have not heard of anyone needing to replace belts, has anyone?

Keep in mind this sort of belt is used in auto engines where the conditions are far worse, hotter, driving more hp, weather including water getting splashed on it etc.

As far as capacitors, that would be my fear as well but we have no idea what temperatures they see and we have no idea of the rating. I know they are oil filled as one let loose on initial power up on one of my units. A cloud of smoke followed the bang. Reminded me of the big power inverters we use to make for RPO disks so they could keep running after being swapped off AC to DC in power failures. Hopefully the heat sink is doing it job and keeping those parts cool enough.

BTW the heat is transferred to the case, so it becomes a dissipation surface which is a good thing.

Another thing to think about is not running at all the way up to the 10K just because you can. Shaping can be done even on the old headstock which is no were near that fast. Perhaps 7000 or 8000 would be more in order to keep things cooler or even if you need 9000. Just staying at a lower rpm will help.

Ed

[garys]

To start with, 90 degrees isn't a temp fit for human or machine to work in. Cool the shop or move north to a more decent temp.

We have always known that heat, cold, water, and dust are all the enemies of electronics. That should tell us to not try to use electronic devices under those conditions.

I bought my current house back in 2003. There was a 2 year old Amana kitchen range in here with fancy electronic controls. It wouldn't function when the oven was turned on and heated up. Amana said they could repair it for the price of a new mechanical range. After that, for $100 a year, they would warranty it and repair it the future times it died from the heat. I junked it and bought a new all mechanical one for repair price of the electronic Amana. The mechanical one works perfectly every time no matter how hot it needs to be to cook.

One simple thing to remember is that it never makes sense to build a complicated device to do a simple job. It never works out. Mechanical is simpler, cheaper, and more reliable than electronic for these simple jobs.

[Tyer]

Ed, your point about the other uses of this type of belt is well taken; the abuse I was seeing in the Shopsmith is nothing compared to the under-hood environment.

I haven't disassembled the unit to the point of being able to see the controller board; I'd be sort of surprised to see oil-filled capacitors there, although it's possible (regular electrolytics blow up just as you described, too). If the heat sink is thermally bonded to the case somehow, that would certainly be a Good Thing.

I found a cut-away view of the headstock, and it sure looks like a fan blowing air down the channel between the motor and the controller board (between the board and motor heat sink fins) would do a great job of removing heat from the system. Perhaps a project for the future...

[reible]

Trust me they are oil filled. Pulled the dripping thing apart and wrapped in two bags to send it back. Big cleanup inside as well. Exciting day that day. If I remember right it was a Friday morning and I had a replacement from shopsmith on Monday.

Ed

[DLB]

One of the most enlightening posts I've read on PowerPro thermal performance was one in which the author had returned his headstock to SS for repairs:
https://www.shopsmith.com/ss_forum/main ... 18352.html
"A note from Jim McCann was included on my shipping document saying, 'Your PowerPro, after repair, ran for 32 minutes at 9500 rpm before "inverter heat" showed on the screen and power dropped, lowering the speed. This is all normal and will protect the electronics in your PowerPro headstock.'"

Unspecified, but I assume this was with no load and in a temperature controlled environment. Personally, I'm troubled by the terms "32 minutes" and "normal."

Anything that makes the air inside your shop and Headstock less dense (higher temp, higher altitude, lower humidity) is going to decrease the time for reaching that 'inverter heat' temperature threshold. Same for running at higher RPM and anything that makes the PP work harder than the test condition. Similarly, how long the PP will run at a given speed is also impacted by how warm it is when you start that operation.

- David

[claimdude]

I have had a DIY PowerPro since not long after they came out. I have never had a heat issue but do not use mine at anything about table speed usually, and then for only short periods. It seems to me that the only change needed by SS is to advertise the potential heat challenge when used at high speeds for extended periods so that buyers are well informed when they decide to buy. The PowerPro was a huge leap for SS and considering the fact they made it fit existing headstocks is pretty amazing. Since the available space is necessarily limited there doesn't seem to be much of a way to change the heat issue short of providing a way to add an exhaust fan. I suspect most users don't need it though. I have an Incra router table with 3hp router so really have no need for the shaper function. Just my 2 cents ;-)

Jacj