How to adjust spindle speed of a dc motor?

[HereinCS]

I want to control the speed of my zen motor by changing the dc voltage. Is there a SIMPLE way to vary the dc voltage? Thanks in advance.

[RomanLini]

Have a google for "Benchtop power supply" or "0-15v adjustable benchtop power supply" or similar.

These usually have a voltage adjustment knob and the better ones have voltmeter and ampmeter as well, you just set the voltage to adjust the speed of your little DC motor.

Because they produce a regulated voltage your motor speed will remain quite constant even when loaded.

[Al_The_Man]

I believe the top range of that motor is 48VDC?
Unfortunately without some kind of feedback a DC motor will drop in rpm according to load, Without feedback and regulation the rpm has to drop in order to increase torque.
With a regulated control where the rpm is monitored, the voltage is increased proportionally to maintain torque and rpm.
Al.

[wireb]

The cats meow so to speak for this problem would be a PWM controller that takes in RPM feedback. That said I don't know of any directly off hand. I am going to build one to drive my BLDC motor for my mill once I get to that point. (hopefully next month still welding up the frame at the moment)

[HereinCS]

I found a cheap PWM motor controller on ebay here. No speed feedback, but it's cheap and I figure will be worth a try.

[Al_The_Man]

Originally Posted by wireb The cats meow so to speak for this problem would be a PWM controller that takes in RPM feedback.

If you just want manual control using a pot (analogue), the Advanced Motion range with tach feedback go down to 20vdc.
The are abundant on ebay.
The 12A8 is about the smallest.
Al.

[RomanLini]

Originally Posted by Al_The_Man I believe the top range of that motor is 48VDC? Unfortunately without some kind of feedback a DC motor will drop in rpm according to load, Without feedback and regulation the rpm has to drop in order to increase torque. ...

I don't want to sound argumentative, but I use a simple regulated DC power supply for my PCB drill press that uses one of those small DC motors, and it gives surprisingly good speed regulation and power using it's typical 0.8mm to 2.0mm drill bits. Those are fairly light loads and high-ish RPM, but I figured if HereinCS wasn't needing light loads he probably would have a different motor.

I've also tried a PWM controller on it but it doesn't give speed regulation anywhere near as good as the regulated DC supply.

[HereinCS]

Originally Posted by RomanLini I don't want to sound argumentative, but I use a simple regulated DC power supply for my PCB drill press that uses one of those small DC motors, and it gives surprisingly good speed regulation and power using it's typical 0.8mm to 2.0mm drill bits. Those are fairly light loads and high-ish RPM, but I figured if HereinCS wasn't needing light loads he probably would have a different motor. I've also tried a PWM controller on it but it doesn't give speed regulation anywhere near as good as the regulated DC supply.

Can I ask how you you vary the motor speed with a regulated DC power supply? I'm thinking that if I cut wood, I'd keep things at a good rpm, but for plastic I'd like to slow down a bit so not to melt the material.

[RomanLini]

You just get a variable voltage DC bench supply. It has a knob to vary the voltage, which varies your speed.

It's not perfect speed regulation (as Al_the_man rightly said) but for light cuts, like engraving, small drills, fine endmills etc it works quite ok.

There are a heap on this ebay page;
0-30v DC power supply items - Get great deals on Business Industrial, eBay Motors items on eBay.com!
and they seem a little more expensive than I remember but they also have many other uses including testing things and charging batteries etc.

[HereinCS]

Thanks. That's an interesting idea. I see some of the power supplies have dual output. Can I use one for the drivers and one for the spindle?

[RomanLini]

If they provide sufficient voltage and current for your drivers.

Many PSUs I saw on that ebay page were 0-30v and 3 amps, that should supply your drivers on a small CNC machine but may not be optimal for the very best high speed performance. But then on a small CNC machine you probably don't need very fast movement.

[jyotti]

If you have access (not shunt motor) to both armature, and field separately, you need two supplies. One for the field, and one for the armature.

Many many motors are shunt wound though .. like tyical ac/dc handtools.

IF .. you have four leads .. two for armature, and two for field, then you have something goin' on.

Hold field at nominal .. 90 volts? ... gradually increase armature untill motor turns. Increase armature up to minimum usable speed. Make sure, you have adequate current capacity, for your armature.

You will increase your armature voltage, untill you reach maximum speed, and then ... start Decreasing your field voltage.

That's why, you need to control .. both voltages. You may need only 4 amps for field, and 40 amps, for your armature .. but both need to be continueously variable.

Caveate .. you need to improvise, an overspeed "drop out", so that your motor does not go soo fast as to self-destruct.

As it happens .. I have a 1951 Monarch Speedee-Matic here .. with a 3hp Relaince DC motor, as big as a bread box. While I have retro-fitted the ancient thyratrons long ago with solid state stuff, that's Exactly how it works.

In the olden days ... specs reffered to "base speed" for these types of motors. Typically about 1,000 to 1,200 rpm. PM D.C. motors, won't allow you to decrease the field, as they are fixed .. as intended.

FYI .. the Monarch has incredble torque at 75 rpm .. for large threading, and at 4,000 rpm .. barely vibrates a fingernail. Truly an incredibly design.

Summary: Four wire DC motors, need separate power supplies, and need overspeed protection field excitation circuitry to prevent motor catestropic failure and/or operator injury/death.

sooo ... there ya go ... be safe .. have fun