[G59]

Hello everyone, I'm new here and have learned so much from these forums in the last few months.

Does anybody have a spindle braking circuit example that I can look at?
I have a 10 HP spindle and sometimes at 6000RPM that needs to come to a quick stop if the E-Stop switch is pushed.
I have braking resistors, but how to have them activate only when the monitored voltage of the capacitor is excessive, or at 150V dc?
Can a 150 volt Zener diode with a BJT transistor and a heavy MosFet be used to open the circuit to the braking resistors?
Thanks.

[Al_The_Man]

The 100A40 has an internal 5Ω 180W brake resistor, to replace it with a larger external unit, you need to remove a jumper before connecting the external one.
Al.

[G59]

Ok, I will look into that. By tomorrow, I will have a schematic posted so you can give me your opinion and see if it will be good enough to send the over voltage into the braking resistors.
For now, my 0-10V pwm to dc analog board just gave up so I'm off to see if it's still repairable.
I have the motor tuned(offsets), and if I wasn't looking, I wouldn't know it was turning, as it is so silent.
Also, when the drive is disabled, does that turn it off? Or is it still energized just not outputting current?

[G59]

Here is what I'm thinking of doing as a braking circuit. The Zener should regulate the voltage if it reaches 140 Volts. The values for the Transistor resistor are not completely calculated, but I just want to know if this is feasible or if I'm way off on this one. The MosFet is rated at 250V 49 Amps.

[Al_The_Man]

That is traditionally the way it is done and is similar to the dump circuit units made by A-M-C and sold separately.
Al.

[G59]

Al, thanks for the help. I appreciate your time and value your opinion.
So after simulating my circuit in Proteus, I'm still left with a small detail that's bugging me.
If you take a look at the picture of it running in Proteus, you'll notice the base voltage is at 21.2481 volts. The datasheet says 5V max on the base.
In the pic, you can also see that the base to collector voltage is way under specs and that the base to emitter voltage is also well under critical voltage.
I have included the spec sheet of the Tip47, NPN transistor so maybe you or someone can make more sense of it.
I'm just wondering if this can work?Attachment 246834


Also the arrows are the current path to the resistor bank.
I added many voltmeters along with amp meters so you can all see whats going on.

[Al_The_Man]

Probably because your circuit is + oriented instead of common (-ve). And the load is shown in the source rather than the drain of the mosfet.
I have used this type of circuit but used a LM311 comparator to drive the Gate circuit, I used the zener as one input and a variable input on the other to set the trip point.
Also In my case I used a 2n222 and a 2n2907 in a push-pull to drive the gate of the mosfet.
Al.

[G59]

Hmm never thought of that. I will make some more adjustments and I'll see what Proteus can come up with. I'm familiar with the LM311 but I'm trying to avoid buying and paying the shipping fee from Digikey.

[G59]

Well, today I will try this version.


It simulates well in Proteus. When the capacitors reach 135Vdc, the Zener reverses and applies 5 V on the IRFP260N gate.
I don't encourage anyone without High Voltage experience to do this.
I'm well aware of the potential danger involved. This circuit can kill you if proper precautions aren't followed.

[Al_The_Man]

The voltage to the gate of the mosfets is going to vary quit a bit as the zener conducts up to the maximum voltage detected across R2.
Also those are not logic level mosfets so the required turn on will be higher than 5v.
Some kind of snap over such as a Schmidt trigger or LM comparator would be a little more positive. IMO.
Al.

[G59]

Well, as you might of guessed, it turned out to be another failure(sort of). My last attempt works, but the gate voltage has to be up in the 18V range for it to have any effect. So back to the drawing board. This time, I will spend the money and by a voltage supervisor chip using voltage reference. I wasted so much time(stubborn), trying to use the parts that I have in my parts bin.
On another topic, I fired up the mill today with the 100A40 as the spindle drive. Commanded an m3 s1000 through Mach3 and something is not well.
The spindle spools up as it should, but it seems that the drive has a hard time stabilizing the speed with the tacho, and is overshooting the RPM. Suddenly it has to cut power so that it can bring the RPM back down to 1000, but as soon as it see's it has slowed down too much, it powers the motor again and overshoots the rpm again. It does this about a dozen times until it finally manages to settle the speed to 1000RPM. This is less pronouced if I want 4000RPM but is still there.
Maybe along with the tacho dip switch On, I should also have the Voltage mode selected as well? Possibly I'll have to tune the loop gain?
What do you think?

[Al_The_Man]

What are the dip switches set to?
Al.

[G59]

At the moment, all dips are off, except for SW3 which is on.

[Al_The_Man]

You could try sw3 & sw 1 for voltage mode, also the ref gain may need adjustment.
It took me a while to get one high inertia spindle motor to stabilize.
Al.

[G59]

Setting SW3 and SW1 to ON, eliminated the long RPM settling problem. Thanks Al.
Now after adjusting loop Gain, which I don't think did anything, and adjusting the ref gain to maximum, the spindle runs at half the speed I have typed into Mach3 MDI.
Probably a Mach3 setting. I'll look at pulley settings and do a search on here , I'm sure I'm not the only one that went through this.

[Al_The_Man]

The rpm is set by the ratio of the analogue signal to the tach feedback, once they are equal (via the settings) the unit is at speed.
Al.

[G59]

got it. so i need to add more resistance to my tach lead as the tacho generates 30V per 1k rpm. Am I on the right track?

[G59]

I think this because the 100A40 has a maximum of 60V tach input. So if I can reduce the tach output by 1/3, then I should be able to get an increase of motor RPM as the analogue reference will be the same but the tacho voltage will be less.

[Al_The_Man]

As you can see from the spec's the max tach is 60vdc so you may have to tailor it a bit if the output is very high, the average for a tach is 12v - 20v/1krpm.
At 6krpm that would be 180vdc!!
You may require a pot divider across the tach to tailor it even more than the internal adjust.?
Al.

[G59]

I added a 1watt 60k resistor in series with one of the tach leads. The spindle speed is now within 10RPM at M3 S1000. At 2krpm, it is within 15rpm. I'm satisfied with it so I will leave it as is. Do you see a problem with doing it that way?