[coors]

Hi,

I recently got a Wolfgang Engineering TB-650 spindle and I am looking for a PWM unit to control the speed a little bit better. I got a 12V 20A power supply setup and the missing part is the PWM unit.

The motor used in the spindle is a "Atomik 50T 540 Fireball Rock Crawler Brushed Motor" (see RC Car Motor - 50T 540 Fireball Rock Crawler Brushed Motor | Atomik RC) Richard (the guy who sells these) told me he would use a 12V, 20A supply along with a PWM unit on ebay. That one doesn't work very well and just overheats. I suspect it's because it is not meant for inductive loads and lacks flyback diodes.

Also, the motor description says "Input Volts: 4.8-9.6V" instead of 12V, so I am a little puzzled by that. Anybody here who could recommend a PWM unit that would work with this?

Thanks,
Felix

[yours_prabhat]

PM me your email i will send you a circuit you can make in your shop , just 3-4 components are used for that

[HPB]

PM me your email i will send you a circuit you can make in your shop , just 3-4 components are used for that

Is this PWM circuit of yours patented?. If not why not post it on this fora,
so we all take a look at it.

Regards,
Hanspeter.

[coors]

So, I checked on the circuit and it does have a diode (20A), so that shouldn't be a problem. It still gets too hot, so I mounted a fan to keep it cool. It's working, but it doesn't allow me to control the spindle through Mach3 at the moment.

At least, I want to be able to shut the spindle off remotely if things go bad. After looking around a bit, it seems like higher current PWM is often a bit tricky because the MOSFET can overheat quickly. If anyone has a proven design for a motor like this one, I might go with that instead and just scrap the PWM board I bought.

I am looking into modifying the one I got as well. It uses a pot to control speed, so I am thinking about just replacing that with the PWM output of Mach3 and a lowpass filter. I guess it should work, but I saw that people like to use optoisolator to keep PC and CNC machine separate. Any opinions on this?

Felix

[HPB]

If anyone has a proven design for a motor like this one, I might go with that instead and just scrap the PWM board I bought.

I am looking into modifying the one I got as well. It uses a pot to control speed, so I am thinking about just replacing that with the PWM output of Mach3 and a lowpass filter. I guess it should work, but I saw that people like to use optoisolator to keep PC and CNC machine separate. Any opinions on this?
Felix

Hi Felix,

See this post http://www.cnczone.com/forums/genera...hobby_cnc.html

...and this http://www.cnczone.com/forums/mini_l...troller-2.html

Your Mosfets must be capable of switching three times rated current of
your motor, goes as well for the free-wheeling diode. Remember the Mosfet
carries a snubbing diode this intrinsic in it's design!

Take a look a the Mosfet data-sheet, must have 1. a very low RDS(on),
2. a suitable mosfet driver, the Chinese ones on ebay don't have it, but
you can incorporate a driver and replace/parallel the Mosfet + Diode with a high current, Low RDS(on) ones.

Mosfet's HEATING up is a result of switching slope
on the On & Off edges. You must have a clean vertical ON/OFF switch
transistions including a hight current Schottky diode.

In lay-mans terms, your Mosfets must switch the entire -Ve side of your supply, else Mosfets will act like a voltage divider! instead of switching
like a power relay.

Getting this big a Mosfet rises the question of how one can turn On/Off
the large gate capacitance. This where the mosfet drivers comes into the equation with ferrite a bead on the gate leg/pin.

Cheers,
Hanspeter.

[coors]

Hey HansPeter,

So I read up on it for a little bit. The easiest way out seems to be a relay like this one. Digi-Key Part Search

Then, I can keep using my PWM with the fan for a while and Mach3 is still able to switch the spindle off. In terms of making a PWM circuit for 12V/20A, I think I'll have to play with it a little more. I have only been making little H-Bridge circuits for much smaller DC motors, so I am lacking experience with the high power ones. I am still hoping someone bought the same spindle and has a tested circuit that works with it.

What I have in mind right now is this MOSFET: Digi-Key Part Search
and this Diode: DSS60-0045B IXYS | DSS60-0045B-ND | DigiKey

The circuits look easily, but people still seem to have a lot of problems with them. I'll wait and see if anyone has a good suggestion for this.

Felix

[HPB]

Hi Felix,

The diode is OK, but your link to Mosfet was missing, but check this one from Digi-key IPB80N03S4L-02.

This PWM speed design is not rocket science. If you want a sand-alone PWM driven by NE555 timer with
and option of driving Mosfet output from Mach3. I can post one here.

Cheers,
Hanspeter.

[coors]

Hey Hanspeter,

Posting the circuit would be great. I assume it's something you are using as well, aren't you?

Are you by any chance using a low-cost machine? I am looking to upgrade mine next as the machine body I am using is not treating me very well. I got it from mydiycnc.com and it is really more of a toy than a CNC machine. Now I am looking into the KL3025 from Automation Technologies. Any thoughts on that?

[HPB]

Hey Hanspeter,
Are you by any chance using a low-cost machine? I am looking to upgrade mine next as the machine body I am using is not treating me very well. I got it from mydiycnc.com and it is really more of a toy than a CNC machine. Now I am looking into the KL3025 from Automation Technologies. Any thoughts on that?

Hi Felix,

I use a ZEN Toolworks 12x12 F3 CNC. I did take a look at the site and am seem to be impressed
with the all aluminum structure except the moving gantry. For precision and stability I would prefer a
stationary gantry with moving table, and the ballscrew drive is great for this CNC at automation technologies.

I saw the DC spindle and PWM board, this is the same PWM board I discussed, on other post elsewhere.

I use a similar spindle from Zen toolworks, but the ranout is 38micron = 0.0381mm. Am sure the supplier is same
for both sites, ie Zen & automation technologies. If you consider Kavo spindles going for 1micron Runout! you get
what you pay for. See LPKF site these are the RollsRoyce of PCB milling, these are out of the common mans reach .

Zen spindle has no fan on the top, and recommends a driving voltage of 32. The datasheet max. 48 volts at automation technologies
looks worrying except to hope the fan will compensate for it.

The PWM driver board is going for $15 at ebay and both are exactly same, these PCB's have NE555 timer outputting PWM
without a 'totem-pole' driver as I had pointed out earlier on some forum topics.

If you happen to mill PCB's with this CNC from automation technologies then running the spindle the maximum speed is best.
I only consider the PWM for ramping up the spindle from rest so as not to stress the bearings! this is very important.

Cheers,
Hans.

[neilw20]

Attachment 179739
Switch off of the mosfet can be quite fast.
As flywheel current flows through the diode, you must turn on the mosfet slowly, longer than reverse recovery time of diode, other wise the mosfet is a short across the supply for the duration of reverse recovery. Usually for your current a 150 ohm resistor in series with the gate will slow it enough.
You need a 15v zener between the cathode and the source (anode of diode to left of choke and cathode to the gate).
This is to prevent large transients damaging the mosfet.
For the diode use a schottky diode for best results.
ON Semiconductor MBR4015CTL: 40 A, 15 V Schottky Rectifier
ref:Semiconductor Products
The mosfet needs to be rated at 60A or more.
The gate drive needs to be relative to the source (bottom of mosfet) so quite a bit of other circuitry is required.
I am just showing the principle here. The gate needs to be driven 10-15v above the positive supply.
Done correctly, this will run almost cold.
Search for application notes using google for more details.
You still need a good heatsink for the mosfet and the diode that can disipate around 30-40W at full load.
This will give excellent low speed performance provided the mosfet has a high enough current rating.
This circuit will do a DC transformation to the lower voltage the PWM is commanding.
You can find some sophisticated circuits that can have a controllable current limit too.