Hello all!

I need to controll my stepper motor with FM Stepdrive device. The manual tells that the pulse interface must be supplied with 5V input while the S7-1512C-1 (which I'm using) has only 24V outputs.

Is there any good and tested way to reduce the output voltage of PLC to 5V for this kind of usage? I'm thinking of voltage divider but I'm not sure how to select resistors so that the current isn't exceeded (pulse interface tolerates max 25mA).

I'm grateful for every solution and tip!

Regards, Artur

You should use some special ICs to control in Stepper motors like LM297 and LM298 ,,,you can search on them and download the datasheet from the internet.

you can supply LM298 with 5 V to energized and Lead you stepper.

LM297 is responsible about pulse control of the stepper and direction

for more details read the datasheets

Warm Regards

MAZENJER 

Do I understand properly that these ICs are just for controlling stepper drive, not to reduce voltage? I am using FM Stepdrive module which is a power controller for Siemens motors (in this case, it's SIMOSTEP FL3041). I was told that I only need to connect it with PLC which is responsible for sending control signals to power controller. My only problem is that the signals are supposed to be 5V so I have to reduce the output voltage from PLC.

I found some ideas in the Internet, for example I can use voltage divider (with simple resistors) which would be the best solution for me but I'm wondering if it's safe to use - I don't want to exceed maximum current of the interface and simply fry it. Has anyone ever tried such solution and know if it works properly with PLC?

Hello,

yes that LM is power amplifier. If your idea is create divider, try look at some free circuit simulators on web, there you can see all what you need

Hi!

We use high-speed optocouplers in these cases. They are more expensive but also safer than resistive voltage dividers.

E.g. Phoenix Contact has some with 100kHz switching freq. in the specs.

 Thank you for answers!

Kahl

Hi!

We use high-speed optocouplers in these cases. They are more expensive but also safer than resistive voltage dividers.

E.g. Phoenix Contact has some with 100kHz switching freq. in the specs.

The manual says that the pulse interface already has optocoupler inputs, that's why I think it's not necessary to use it for reducing voltage.I uploaded a screenshot.

I'll check the voltage divider circuit in simulator, as Duris_I suggested and we'll see if the current doesn't overrun permissible value.

artnew

 The manual says that the pulse interface already has optocoupler inputs, that's why I think it's not necessary to use it for reducing voltage.I uploaded a screenshot.

 It is your call. Costs are always important in a project.

However, in my oppinion it is cheaper to destroy a stand-alone optocoupler outside of your drive than the ones inside.

Thanks for your advices!

I created a simple circuit using optocoupler and one NPN transistor (see it in attachment). The 5V voltage supply is provided from extrenal source, in this case from USB port (in final project I will probably use standard phone charger with USB port). Basically, it doesn't reduce voltage from PLC - the 24V output signal only opens transistor so the 5V voltage can float from source to "Output to pulse interface". The circuit works fine, output voltage is a bit more than 4V

FM Stepdrive manual says that the pulse interface can be controlled with signals from 2.5V to 5.25V therefore my output signal should be high enough in this case. Unfortunately it seems that FM Stepdrive doesn't get my signals. When I set the ENABLE input (in pulse interface) for "true", the RDY led doesn't light. However, when I set ENABLE_N (in signal interface) for "true" with standard 24V from PLC, the led lights and the module is in "Ready" state. Sending pulse train to PULSE input doesn't make any effect as well. The motor only gets holding torque when both GATE_N and ENABLE_N in signal interface are supplied.

I need to ask again, do you have any ideas whan can be the problem? It's my first contact with this module, unfortunately I cannot use any positioning module with S7-1500 which, I pressume, would make the whole thing much easier.

Hello,

I think that this is inverter, that signal is always inverted. Check this pls and give info.

aaaaaa understand, what about connect grounds together from this 5V power supply and that FM? Nothing else goes within my head. But pls check again my idea...

Edit: because you're using signal from external power source to another device. Am I right?

I obviously did this, I connected the GND input from pulse interface (on the left side) with the 5V source's ground.

I'm wondering what are the "_N" ended signals on the right side of the interface, I mean "PULSE_N", "DIR_N" and "ENABLE_N". There's nothing about them in the manual. Does anyone know what are they for?

Hello, probably these are Negative signals, I think.

Edit: reverse?

hmmm I'm affraid that if you want drive some servo motor, you can use some SW simulation. Is this your situation?

Edit: with static signals it will work ok I think...

hello,

did you look at this?

https://cache.industry.siemens.com/dl/files/051/1118051/att_23930/v1/FM_Stepdrive_A0101_e.pdf

Page 12.

Update2: also page 13 is important.

What do you mean by SW simulation? Software simulation? I have my stepper motor connected, all signals on the side of PLC work properly, when I turn on online mode in TIA Portal I can see them switching and everything is good. The problem must be located on the side on FM Stepdrive or, possibly, my circuit. The module works properly, possible causes can occur only in pulse interface because other "parts" of module seem to work perfectly.

Edit: I've seen this manual, I connected everything according to the schemes I found there.

I triplicated my circuit (one per every pulse interface input, they only have common 5V supply) and to every one (circuit) I connected one output from PLC. Otput from every circuit is then connected to proper input in pulse interface. I supply ENABLE with static signal, PULSE with 10Hz and DIR is not supplied (so the motor can turn clockwise). I also supply inputs in signal interface - ENABLE_N and GATE_N with 24V. Everything else is connected according to the manual (FM supply with 230V, motor phases connected to U, V, W etc.)

I think it's not the question of bad wiring, I would figure it out on my own. I guess there's the problem with 5V signal because when I supply only ENABLE input (in pulse interface), without ENABLE_N (in signal interface) the RDY led doesn't light. The manual says that it's enough to supply one of them to get the READY signal so it is a proof that my 5V signals are not received by the FM Stepdrive.

Originally the FM device was connected with positioning module e.g. FM353 which controls the pulse interface with 5V signals. It was necessary for older controllers like S7-200 or S7-300. I need to connect the FM device directly to S7-1500 PLC so have to "reduce" the output voltage from PLC to 5V - that's why I'm using that optocoupler circuit.

/Offtopic/

Thnx for perfect explanation. It was very interesting to me from your first post to see, that you need make some own solution to this. Will look to this topic to see conclusion, but will also try discover something helpfull to you. Thnx.

Thank you for your answers and advices! When I finally figure out how to run this motor using FM Stepdrive I will describe it here.

Unfortunately the problem is still not solved. I'm working on it but still look for advices.

Duris_I

Hello, probably these are Negative signals, I think.

Edit: reverse?

 Hi!

In the FM-353 doc these signals are true and negated.

See the attachment from this doc about the wiring.

Thank you Kahl!

I contacted with the German Support and got an information that the inputs require differential signal to control the motor - it's even shown in the file included by Kahl. That explains why my circuit doesn't work in this case.

I have two options then - make another circuit for sending differential signals or simply use one of modules meant to cooperate with FM Stepdrive (FM353 with S7-300 or 1-STEP-DRIVE with ET200S). It's bad solution for me because it increases cost and size of the whole instalation.

Hi!

You could try the third option from fig 4-3.

Excuse me for such a late answer. I tried that circuit and it, unfortunately, didn't work. When I connected the cables from FM Stepdrives to the circuit, it didn't even get the voltage signals (I placed some LEDs there to know when the signal appears). When I disconnected them and was only sending signals from PLC, the LEDs were working so signals appeared.

I kind of gave up in this case and I'm currently trying to commission the motor with 1PULSE 5V/204kHz module for ET 200S, maybe this solution will work.