DC motor conversion

Moderator: admin

edma194
Platinum Member
Posts: 771
Joined: Fri Jun 19, 2020 4:08 pm

Re: DC motor conversion

Post by edma194 »

The following quote was originally posted in this thread about using a DC motor on an ER10. I'm responding here because of it's relevance to the thread.:
JPG wrote: Thu Sep 16, 2021 3:55 pm FWIW,one of the slow speed SPTs is the band saw which does not require great hp. Neither do the jig/scroll saw. Belt sander may require A bit more. Disc sanding also does not require great hp. The jointer and planer need high rpms. The planer needs great hp in addition.

So As I see it lower power at slow rpm is not a show stopper for SPTs, Turning large stuff is another matter.
You're right. Maybe thick stock on the band saw, especially for plastics where low speed is needed, but otherwise not that big of a deal on the SPTs strictly as a matter of HP.

At any speed heavily loading the motor will have side effects, these are not synchronous motors, they can slow down considerably under load, and speed up again when the load is removed. The slow down is alleviated slightly by a flywheel, but only for a couple of seconds. At lower speeds you won't get good response to increasing voltage to speed up the motor. You can end up in a cycle where you have to start the operation at higher than necessary speed, and even then it could still become necessary to unload the motor and let it regain speed.

Any qualitative measure of performance is in the eye of the beholder. In this thread I'm juggling comparisons to the PowerPro, expected performance from 1-1/8 HP motors in conventional headstocks, and my own desired performance for certain kinds of functions. All sorts of configurations would be possible that would satisfy many Shopsmith owners. Some would consider such a conversion because of improved performance for specific functions.
Ed from Rhode Island

Mark V 510 with PowerPro headstock, Mark V Greenie with 510 headstock, Mark V 500 in progress
Sawsmith 2000 Ultra, 10ER in progress, 10ER undetermined future
edma194
Platinum Member
Posts: 771
Joined: Fri Jun 19, 2020 4:08 pm

Re: DC motor conversion

Post by edma194 »

lahola1 wrote: Thu Sep 16, 2021 8:05 pm The setup I had on the end of my SS is a 3HP, 130v, 2975RPM ,MC2100 PWM control, with 2"/6" pulleys.With that setup I got 188 RPM @15% and 3564RPM @85% speed at the SS quill.
The smaller motors have the mc60; larger motors have the mc2100 control generally.
I don't think your going to get anywhere near what you are looking for out of your mc60 setup but I think you can get close with a larger motor ( I've seen them up to 4.25 hp) and an mc2100.
With a PWM controller even the very common 2.5 HP treadmill motors will probably outperform the 1-1/8 HP AC induction motor in the conventional Shopsmith headstock. To get the same kind of steady speed as the AC motors I'm sure requires motor speed feedback to the controller though. Unlikely to compete with a PowerPro head to head but could be done for very much lower price.

More powerful motors, especially at slower speeds seems like the key to maintaining performance if very low speeds operations are desired. If you're trying to make a milling machine that might do the trick. Maybe you wouldn't need a PWM controller for that, but it would certainly be beneficial. And for the typical Shopsmith range of spindle speeds It would also be a way to maximize performance without keeping the belt and pulley speed changer.

BTW: The frequency generator shown in a photo in one of your linked threads is exactly what I was looking at on Amazon. Curiosity will get to me if I don't get one of those and attempt to PWM control an MC60. I hear they are very sensitive and expect to ruin it.
Ed from Rhode Island

Mark V 510 with PowerPro headstock, Mark V Greenie with 510 headstock, Mark V 500 in progress
Sawsmith 2000 Ultra, 10ER in progress, 10ER undetermined future
lahola1
Gold Member
Posts: 117
Joined: Sun Jul 09, 2017 11:43 pm
Location: Sedona,AZ

Re: DC motor conversion

Post by lahola1 »

edma194 wrote: Thu Sep 16, 2021 3:44 pm

PWM would maintain torque across the speed range. The typical motor runs in excess of 6000RPM and if installed in a Shopsmith has plenty of power at the high end of the speed range. However, even to get to the ordinary low speed of ~700RPM the motor would be running at 50% power or less.
I did a little power test on my Smithy Supershop. This also references my weak MKVII motor thread.
viewtopic.php?p=286682#p286682

My Supershop has a 90V 1.5 HP 2800RPM DC motor controlled with a potentiometer speed control and 3 pulleys for low, medium and hi speed/power.
My test is ripping a 2x4 with my old but resharpened 40 tooth combo blade I used in the referenced, attached thread. Speed was set at 3400RPM on both the mid and high speed pulleys.
The high speed pulley was set at 45% on the POT to get 3400RPM . The motor stalled out in about 10 seconds trying to rip the 2x4.
The middle speed pulley was set at 75% on the POT to get 3400RPM. I had no problem ripping the 2x4 at this setting. I had power to spare to rip several more times.
So edma194, you are correct. The POT controlled DC motor has a lot less power at the lower % speed settings. Thanks for pointing this out. I did not realize this.
SS Mark VII(sn 405025), SSband saw, SS 4" jointer, SS Mark V 1980,
Smithy SuperShop 720, Powerkraft RAS,Craftsman RAS, Ridgid TS2412 Table Saw,
Delta 12" planer
User avatar
JPG
Platinum Member
Posts: 32597
Joined: Wed Dec 10, 2008 7:42 pm
Location: Lexington, Ky (WILDCAT territory)

Re: DC motor conversion

Post by JPG »

lahola1 wrote: Mon Oct 04, 2021 9:47 pm
edma194 wrote: Thu Sep 16, 2021 3:44 pm

PWM would maintain torque across the speed range. The typical motor runs in excess of 6000RPM and if installed in a Shopsmith has plenty of power at the high end of the speed range. However, even to get to the ordinary low speed of ~700RPM the motor would be running at 50% power or less.
I did a little power test on my Smithy Supershop. This also references my weak MKVII motor thread.
viewtopic.php?p=286682#p286682

My Supershop has a 90V 1.5 HP 2800RPM DC motor controlled with a potentiometer speed control and 3 pulleys for low, medium and hi speed/power.
My test is ripping a 2x4 with my old but resharpened 40 tooth combo blade I used in the referenced, attached thread. Speed was set at 3400RPM on both the mid and high speed pulleys.
The high speed pulley was set at 45% on the POT to get 3400RPM . The motor stalled out in about 10 seconds trying to rip the 2x4.
The middle speed pulley was set at 75% on the POT to get 3400RPM. I had no problem ripping the 2x4 at this setting. I had power to spare to rip several more times.
So edma194, you are correct. The POT controlled DC motor has a lot less power at the lower % speed settings. Thanks for pointing this out. I did not realize this.
It is not just the rpm(pot setting) that this illustrates, but the power needed and how the speed reduced setup increases the available torque.
╔═══╗
╟JPG ╢
╚═══╝

Goldie(Bought New SN 377425)/4" jointer/6" beltsander/12" planer/stripsander/bandsaw/powerstation /Scroll saw/Jig saw /Craftsman 10" ras/Craftsman 6" thicknessplaner/ Dayton10"tablesaw(restoredfromneighborstrashpile)/ Mark VII restoration in 'progress'/ 10
E[/size](SN E3779) restoration in progress, a 510 on the back burner and a growing pile of items to be eventually returned to useful life. - aka Red Grange
lahola1
Gold Member
Posts: 117
Joined: Sun Jul 09, 2017 11:43 pm
Location: Sedona,AZ

Re: DC motor conversion

Post by lahola1 »

True. I didn't think of that :rolleyes: .
SS Mark VII(sn 405025), SSband saw, SS 4" jointer, SS Mark V 1980,
Smithy SuperShop 720, Powerkraft RAS,Craftsman RAS, Ridgid TS2412 Table Saw,
Delta 12" planer
edma194
Platinum Member
Posts: 771
Joined: Fri Jun 19, 2020 4:08 pm

Re: DC motor conversion

Post by edma194 »

lahola1 wrote: Mon Oct 04, 2021 9:47 pm
edma194 wrote: Thu Sep 16, 2021 3:44 pm

PWM would maintain torque across the speed range. The typical motor runs in excess of 6000RPM and if installed in a Shopsmith has plenty of power at the high end of the speed range. However, even to get to the ordinary low speed of ~700RPM the motor would be running at 50% power or less.
I did a little power test on my Smithy Supershop. This also references my weak MKVII motor thread.
viewtopic.php?p=286682#p286682

My Supershop has a 90V 1.5 HP 2800RPM DC motor controlled with a potentiometer speed control and 3 pulleys for low, medium and hi speed/power.
My test is ripping a 2x4 with my old but resharpened 40 tooth combo blade I used in the referenced, attached thread. Speed was set at 3400RPM on both the mid and high speed pulleys.
The high speed pulley was set at 45% on the POT to get 3400RPM . The motor stalled out in about 10 seconds trying to rip the 2x4.
The middle speed pulley was set at 75% on the POT to get 3400RPM. I had no problem ripping the 2x4 at this setting. I had power to spare to rip several more times.
So edma194, you are correct. The POT controlled DC motor has a lot less power at the lower % speed settings. Thanks for pointing this out. I did not realize this.
I'm back on my feet and doing stuff now so not spending much time looking into this subject for a while. But as we discuss power and torque and performance I am left wondering how to evaluate power on these simple permanent magnet DC motors with flywheels relative to AC induction motors.

Initially, based on various opinions I had seen, I had the impression the nameplate HP numbers were highly over-rated, if not impossible to achieve with 120V 15A power. I have learned that the flywheel momentum is typically included in the HP figures allowing for greater performance for a short time . In addition those permanent magnets supply additional power to the motor on top of that from the main supply. It's still not clear how to account for loss in power conversion. However, I now have the impression a permanent magnet DC motor rated at 2.5 HP can deliver a substantial portion of that power at full speed and constant voltage max voltage. That would be a relative measure in comparison to an similar AC induction motor. That suggests to me that even running at 50% power it will perform well even in the lower speed range using a simple voltage controller in combination with conventional Shopsmith belt and pulley speed control. It also suggests that a PWM controller will deliver excellent performance over a wider speed range, possibly eliminating the need for the belt and pulley speed control altogether.

So hopefully we'll hear from the intrepid experimenters out there who attempt headstock conversions and will report back on their experiences. I'm back to conventional speed controllers again for a while, although I'm thinking I'll use the motor and speed controller I have to power grinding wheels.
Ed from Rhode Island

Mark V 510 with PowerPro headstock, Mark V Greenie with 510 headstock, Mark V 500 in progress
Sawsmith 2000 Ultra, 10ER in progress, 10ER undetermined future
Post Reply