STMBL (and others) DC Motor Drives Power Supply

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05 Apr 2019 16:23 #130347 by silopolis
Hello friends,

This discussion actually started here , but it was hijacking OP thread, let's carry on here...

Quoting for ease of continuation:

silopolis wrote: What kind of power supply do you use to feed the 155VDC?

tommylight wrote: Usually big transformers with rectifiers and some capacitors to smooth the output voltage.

andypugh wrote: In most applications you can use just a fuse, inrush current limiter [1] and bridge rectifier and rely on the internal caps in the STMBL. You only need external filter caps in high power applications.

[1]That's just an example, you might want to read the data sheets to choose the most suitable.

silopolis wrote: ok, so, seems like I should have bookmarked those DIN modules where it seemed you could just plug those thermistors in !?... Couldn't find ICL boards (if that makes sense), but nevertheless, found "proper" ICL DIN modules.

I know that can get toroidal transformer with the secondary outputs I want. But I'm having much harder times finding rectifying circuit modules in for the high voltages the motors I've seen around ask for (220V, 310V).

In the end, I've found professional PSUs for servo motors, but afraid the bill would be discouraging, and a little too far of what I'm looking for as the ideal option would be an Open Hardware circuit.

Finally, opinions seem controversial about switching power supplies for servo applications (as they are in audiophile ones BTW) so they remain a suspended option to me...

PCW wrote: Normally for large drives the power supply is just:

Linevoltage --> inrush current limiter --> bridge rectifier --> large capacitor

No transformers or switching supplies needed...


Well, doesn't the supplied voltage have to match the motor's rated voltage ? Or does the drive handles the up or down transformation ?

Also, from readings, "linevoltage" extends to "Wall outlet -> Circuit Breaker -> Noise Filter -> Magnetic Contactor"... Am I right ?

andypugh wrote: Rectifiers are easy, you must be looking in the wrong place.

www.ebay.co.uk/itm/273136909974

That sort of thing. Bolt it to the machine case (through the middle) and attach with faston crimps.

If you _need_ it to be DIN-mounted then consider modifying one of these: www.ebay.co.uk/itm/223125816784

(I bought myself dozens as they are so handy for this sort of thing)


Well, that worth actually... It's 'cause I'm ignorant ! ;-/ Seen these many times but could figure how to use them... And couldn't imagine that was that simple. Thank you. Further searches triggered by your answers also finally led me to these cutties: www.poweralia.com/din-rail-rectifiers

andypugh wrote: www.windpowerengineering.com/electrical/...nergy-80-a-currents/ shows an easy way to mount the thermistors, just use one to bridge between two DIN terminal modules. (be sure to keep it clear of other wiring, they get pretty warm)


Nice! Should be able to use jumper posts to keep the input up output down topology...

andypugh wrote: On my machines I tend to take a more active approach to ICL, I use a power resistor initially, then bypass that with an SSR once the bus power is up. This is handled in HAL, and the drives are enabled by the same logic that bypasses the current limiting resistor.


Let me put it with my words to see if I get it: power initially go through a power resistor (making heat waiting for control to wake up), then when (drive ?) control circuits are up the SSR, controled by HAL, switches the power feed from resistor to drive power input... right ?

Questions: about power resistor, how do you spec it ?

andypugh wrote: And for 1kW or so the internal caps in the STMBL are (apparently) OK.

So line voltage -> ICL -> Rectifier -> STMBL

I would probably use an SSR on one of those SSR DIN mounting plates, but with a metal plate sandwiched between the SSR and the mount. Bridge rectifier bolted to one side, power resistor bolted to the other. SSR controlled by HAL.


Well, I think (not completely sure though) I picture this plate setup...

IIUC, you have kind of a start sequence in HAL that pilots power up of important subsystems, is that it ?

andypugh wrote: If several STMBL drives share the same input circuit then their internal capacitors all end up bussed together, which is actually helpful.


Shooting for the best I was more inclined to split power circuit of each motor, but that's another argument for common supply, others being simplicity and cost.

andypugh wrote: The reason I prefer an SSR to an NTC device is just that the NTCs get hot, and that bothers me.


In an enclosure where temperature can be a concern, I'm with you on this.

Thanks a lot
J

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06 Apr 2019 01:42 #130379 by andypugh

silopolis wrote: Let me put it with my words to see if I get it: power initially go through a power resistor (making heat waiting for control to wake up), then when (drive ?) control circuits are up the SSR, controled by HAL, switches the power feed from resistor to drive power input...


Sort-of...

The resistor and the SSR are in parallel to each other. Initially the SSR is off, so all the power flows through the resistor to the rectifier and then to the drive capacitors.
Once things have settled then the SSR is turned on, and all the power flows through the SSR preferentially to the resistor, though the resistor does stay in circuit.


Questions: about power resistor, how do you spec it ?

I aimed for an RC time constant of "a few" seconds. If we say 3 seconds and 4 STMBL drives with 2 x 270uF each then:
3 seconds = .002 * R, so R = 1500 Ohms.
Then power: P = V^2 / R = 38W for a 240V supply. So a 50W 1k5 power resistor sounds about right. (you could actually use a much smaller one, as the duty cycle is tiny)

I think that one of these
uk.rs-online.com/web/p/panel-mount-fixed-resistors/1649052/
bolted to a plate with one of the rectifiers on each side of one of these:
www.amazon.com/Aexit-Control-electrical-...0DA-H/dp/B07MHHBSQD/
Will give you a reasonable (and inexpensive) power supply for STMBL.


Bear in mind that you might not even need inrush limiting. I do because my workshop is at home, and the inrush current is enough to trip the breakers turning the entire house off :-) This might only be a problem with an RCD protected system.

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