My mini lathe started out as an HF 7x8 (billed as a 7x10), and I converted it to a 7x14. I never felt the screw that came with the 7X14 bed mated up properly with the grip nut on the carriage, so the other day in frustration I started my ballscrew CNC conversion. I'ld been accumulating misc parts for it for a while. It will still be a while before I have it going, but I do have a larger lathe to use in the mean time.
Anyway, while I was playing and figuring (and cuttign a part) my speed controller quit working. Rather than waste a bunch of time playing with it I checked the obvious. Fuse, power, switches, etc, and jerked it off the machine. I had a part on the lathe, and no way to run the motor. Not even at full speed. I tried running AC straight to the motor and got a beautiful demonstration of the 60 cycle vibration of running a DC motor on an AC power source. LOL. I had already decided the speed controller was going to go bye bye since I would want one I could control with an external pulse source when I proceeded with my CNC conversion so I unsoldered the bridge rectifier from the controller and hooked it directly to the incoming AC and to the motor. The motor spun up to full speed nicely. I finished my part, and then went in search of a new speed controller.
I found one from a Chinese Hong Kong vendor pretty cheap. Claims to be pulse width modulated for speed control and will use either a 100K POT or an external pulse signal at 3-12V. It also appealed to me because the selection seemed to be by way of a jumper. This would easily allow me to switch between manual or machine control of spindle speed. Given that they were cheap, and that replacements might be slow I bought two of them a few weeks ago. They finally arrived last week.
As is often the case with low price Chinese electronics there was no documentation. By putting on a pair of high power reading glasses (2x) I was able to make out power in, and motor out. The POT was already connected to the board. I soldered some jumper leads to the bridge rectifier and hooked it up to my new speed controller. I hooked the motor up to the proper terminals, plugged it in, and turned up the POT. The motor ran beautifully backwards. Not unexpected.
As is often the case with DC motors I found that there was a point near the top of the control were it actually dropped off slightly in speed as I turned up the control. That is unexpected. I have found many DC motors that seem to run better in one direction than in the other. I was curious. The control had claimed in the advertisement to be either AC or DC input and non-polarity. I swapped hte input leads and hte motor still ran backwards. Cool. It truly is nonpolarity for input. I swapped the leads to the motor, and the motor ran perfectly in forward all the way to top speed at the full travel of the POT. When I have some time I may try it on straight AC in and see if its any better, but for now its working fine.
I left it spinning for half an hour at top speed no load and the motor did not get noticeably hotter than it ever did. I pulled the motor cover and I could put my hand on it. Then I let it run for another half hour at a fairly low speed. Maybe 2-300 RPM. I did not get out my optical TACH and check it. I'm not to worried about it though as those little motors don't have much power at that low of a speed. I just set it at the slowest speed that it seemed to run smoothly. Anyway, the motor did get noticeably warmer, but not enough to raise any alarm bells. Also not unexpected with a "cheap" DC motor.
At that point I had it working as well as before, although electrical was all exposed across my work bench in front of the machine. I wanted to "know" how it was supposed to be connected and exactly what the three pin jumper did so I emailed the vendor asking for documentation, and I proceeded to be a search. I found a picture of a similar speed controller with inputs and outputs labeled. The jumper and pot were different, but similar. Yesterday the vendor emailed me the exact same picture. I guess I'll have to try the jumper and see, but it does seem pretty straight forward. Its really only got two positions plus no jumper. The picture showed the motor and power source connections just as I had them hooked up, and it shows the other terminals as the external pulse source, and shows the polarity. Maybe in the next few days I'll take one of my Mach 3 setup computers and try doing external speed control to see if it works as well.
IF (note the big if) everything works as I think, I'll use a relay to reverse polarity to the motor so I can trigger it from MACH for forward or reverse, I'll put in a toggle switch so I can swap jumper positions from manual to machine speed control, and that should be about it. I still need to make bearing mounts for my ball screws, and do a lot of other work, but I thought some other mini lathers might appreciate knowing about a cheap substitute speed control that works.
Here is the link for the Ebay vendor where I bought them. Later when I get out to the shop I'll post a picture of my board(s) and the terminal connection picture I have.
New 5V 110V Max 10A DC Motor Speed Control PWM Mach3 Speed Control | eBay
Anyway, while I was playing and figuring (and cuttign a part) my speed controller quit working. Rather than waste a bunch of time playing with it I checked the obvious. Fuse, power, switches, etc, and jerked it off the machine. I had a part on the lathe, and no way to run the motor. Not even at full speed. I tried running AC straight to the motor and got a beautiful demonstration of the 60 cycle vibration of running a DC motor on an AC power source. LOL. I had already decided the speed controller was going to go bye bye since I would want one I could control with an external pulse source when I proceeded with my CNC conversion so I unsoldered the bridge rectifier from the controller and hooked it directly to the incoming AC and to the motor. The motor spun up to full speed nicely. I finished my part, and then went in search of a new speed controller.
I found one from a Chinese Hong Kong vendor pretty cheap. Claims to be pulse width modulated for speed control and will use either a 100K POT or an external pulse signal at 3-12V. It also appealed to me because the selection seemed to be by way of a jumper. This would easily allow me to switch between manual or machine control of spindle speed. Given that they were cheap, and that replacements might be slow I bought two of them a few weeks ago. They finally arrived last week.
As is often the case with low price Chinese electronics there was no documentation. By putting on a pair of high power reading glasses (2x) I was able to make out power in, and motor out. The POT was already connected to the board. I soldered some jumper leads to the bridge rectifier and hooked it up to my new speed controller. I hooked the motor up to the proper terminals, plugged it in, and turned up the POT. The motor ran beautifully backwards. Not unexpected.
As is often the case with DC motors I found that there was a point near the top of the control were it actually dropped off slightly in speed as I turned up the control. That is unexpected. I have found many DC motors that seem to run better in one direction than in the other. I was curious. The control had claimed in the advertisement to be either AC or DC input and non-polarity. I swapped hte input leads and hte motor still ran backwards. Cool. It truly is nonpolarity for input. I swapped the leads to the motor, and the motor ran perfectly in forward all the way to top speed at the full travel of the POT. When I have some time I may try it on straight AC in and see if its any better, but for now its working fine.
I left it spinning for half an hour at top speed no load and the motor did not get noticeably hotter than it ever did. I pulled the motor cover and I could put my hand on it. Then I let it run for another half hour at a fairly low speed. Maybe 2-300 RPM. I did not get out my optical TACH and check it. I'm not to worried about it though as those little motors don't have much power at that low of a speed. I just set it at the slowest speed that it seemed to run smoothly. Anyway, the motor did get noticeably warmer, but not enough to raise any alarm bells. Also not unexpected with a "cheap" DC motor.
At that point I had it working as well as before, although electrical was all exposed across my work bench in front of the machine. I wanted to "know" how it was supposed to be connected and exactly what the three pin jumper did so I emailed the vendor asking for documentation, and I proceeded to be a search. I found a picture of a similar speed controller with inputs and outputs labeled. The jumper and pot were different, but similar. Yesterday the vendor emailed me the exact same picture. I guess I'll have to try the jumper and see, but it does seem pretty straight forward. Its really only got two positions plus no jumper. The picture showed the motor and power source connections just as I had them hooked up, and it shows the other terminals as the external pulse source, and shows the polarity. Maybe in the next few days I'll take one of my Mach 3 setup computers and try doing external speed control to see if it works as well.
IF (note the big if) everything works as I think, I'll use a relay to reverse polarity to the motor so I can trigger it from MACH for forward or reverse, I'll put in a toggle switch so I can swap jumper positions from manual to machine speed control, and that should be about it. I still need to make bearing mounts for my ball screws, and do a lot of other work, but I thought some other mini lathers might appreciate knowing about a cheap substitute speed control that works.
Here is the link for the Ebay vendor where I bought them. Later when I get out to the shop I'll post a picture of my board(s) and the terminal connection picture I have.
New 5V 110V Max 10A DC Motor Speed Control PWM Mach3 Speed Control | eBay