Need tiny bit of assistance.

[Ian Rogers]

Normally you don't choose a SMPS for motors, especially motors that need to do some work. Linear power supplies are what is usually best for motor driving. Just a suitable transformer and bridge rectifier, filter cap not really needed.

Before the fall out, do pepeole use SMPS for motors? Yes. Are they ideal? No

One is on the way... MusicManager has one that will suit.. I just need to rework my PWM generator...

 

[Musicmanager]

I knew I'd end up getting the blame !

MM

 

[Ian Rogers]

Ears burning MM... Guilty conscious or what..

 

[Musicmanager]

Well Yes, I'm often both, guilty & conscious .. .. although not necessarily at the same time - it's a matter of what my conscience will allow !

In my defence, Mrs MM says I only have two faults … .. .

.. .. .. .. everything I say & everything I do !

MM

 

[Ian Rogers]

Ditto..

 

[shortbus=]

It's down to appropriate design, rather than the type of PSU.

That's why I added the part about the fall out. But mose every stepper motor driver says or did say not to use a SMPS for stepper power. In your example of the machine your working on, I'll bet you could have used a linear and saved money.

Just like the change to lead free solder, governments are mandating change to SMPS for power factor correction, not for the best suited to the job.

 

[Ian Rogers]

At 24v my hexfet isn't switching clean so it's getting piggin hot.. I have a motor driver coming as well now... It's now working at 24v @ 0.7a PSU with a hexfet on a large LARGE heatsink and is coping quite nicely... I have the speed I need.. So a few more enhancements and I'll put it to use..

 

[gophert]

As an example, the machine I'm working on at present has a 95KW (~ 200A input at 415V) switched-mode regenerative PSU running the drive systems..

what size cables and what kind of connectors do you use for 200A application? (Photos would be very interesting)

 

[gophert]

At 24v my hexfet isn't switching clean so it's getting piggin hot.. I have a motor driver coming as well now... It's now working at 24v @ 0.7a PSU with a hexfet on a large LARGE heatsink and is coping quite nicely... I have the speed I need.. So a few more enhancements and I'll put it to use..

new mosfets are available with R(on) under 5 milliohms so you should see any heat that requires a heat sink until 10 amps - a Mosfet with 2mohms will only need heat sinks at 25A loads. All in e@sy to use TO220 packs or similar.

 

[rjenkinsgb]

In your example of the machine your working on, I'll bet you could have used a linear and saved money.

At 600V, 200 Amps output??
And regenerative, returning power to the mains when the machine motors are braked and the DC bus voltage increases, plus various logic control and safety interlock systems built in:



Even fairly small drive systems (at machine tool scale) used switched mode supplies for the drives, such as the leftmost module in this setup:

 

[Ian Rogers]

Right... A tiny, tiny thing
Here's the turntable working.. I get really low speeds as the mech now has a nylon gear drive.

My math..... 24vac -> 34vdc rectified... Motor takes 0.7A I have used a LM338 to get @ 20v for the motor So.. 34v > 20 is a 14 volt drop at 0.7A , so 10W.. So i have a weird but suitable heatsink on the LM338.. After 20mins running the heatsink is tepid to warm...

Have I the right thoughts? Have you better ones..

 

[JimB]

Junk box engineering, on a plank of wood...

I love it!

JimB

 

[Ian Rogers]

Works.. There is a cover ( just out of shot) that the pot and led connect to..

 

[Ian Rogers]

The reason its on wood is to isolate the 24v from the welder.. Thats why there is a nylon driven gear.

Would have been easier for me to have it all lazered.. But thems the breaks... I may have a frame lazered now and mount all the gubbins on nylon spacers... Prototype..

 

[shortbus=]

Have you better ones..

I'd have used a stepper motor, for the slow speed. But then my junk box has them and the drives for them.

 

[Nigel Goodwin]

I'd have used a stepper motor, for the slow speed. But then my junk box has them and the drives for them.

There's been plenty of scrap printers full of steppers over the years

And drivers are trivial to make.

 

[Ian Rogers]

Well it ran all afternoon and my son welded 20 tubes non stop.. So it's the right tool for the job.. Now I can design the thing properly and get a small PCB made

Incidentally... I noticed a small footnote... On the LM338 if you place a diode from the ADJ pin to the output ( something about a cap discharging ) it runs smoother... Well it certainly worked as the heat sink stayed less than tepid the entire afternoon.. In fact the only thing warm was the huge transformer...

 

[gophert]

Using a voltage regulator to drop the voltage to slow the motor results in a motor with very low torque. PWM let's you slow the motor to very low RPMs wi no stalling. Also, virtually no heat to worry about if you select the right Mosfets.

 

[Ian Rogers]

Also, virtually no heat to worry about if you select the right Mosfets.

Its a max14870 bridge... Good for 1.7A continuous.. The fets on these things are top dog... I've bought from Pololu before.. Never had a duff one..

 

[gophert]

Its a max14870 bridge... Good for 1.7A continuous.. The fets on these things are top dog... I've bought from Pololu before.. Never had a duff one..

then I'm confused why you're using the LM338...?