SLA7051 board - Some questions

[Baganauss]

Hi Phil
Sorry for my english.

first my compliments for the project you describe in your site.

I have check for many days and I have realized that its semplicy is extraordinary.
My only problem is the difficult to find such componets (SLA7051) in Itlay


I am not expertise on powering stepping motor, but I have compared your hookup circuity described in your site whit other similar.

I have 6 stepper motor from Minebea 23LM-C004-51. I know they are UNIPOLAR with 6 wire (2 phase + central).
The characteristics are 6V/Phase - 1.2A/Phase 1.8

[PMinMO]

[quote="Baganauss"]Hi Phil
Sorry for my english.


first my compliments for the project you describe in your site.

I have check for many days and I have realized that its semplicy is extraordinary.
My only problem is the difficult to find such componets (SLA7051) in Itlay


I am not expertise on powering stepping motor, but I have compared your hookup circuity described in your site whit other similar.

I have 6 stepper motor from Minebea 23LM-C004-51. I know they are UNIPOLAR with 6 wire (2 phase + central).
The characteristics are 6V/Phase - 1.2A/Phase 1.8

[Guest]

With either the SLA7051 or L297Uni, you don't need an external power supply, you set the max current via the trimm pot on the board.

Hope this helps.

Hi Phil

Thanks for your porompt reply.
Your answer confirm partial my deductions and calculation, but no answer for the problem related to the Load resistor as asked above.
I do not weel understand the quoted sentence.
You means that is not need the load resistor for the motor.
I figure to connect the motor power supply 24Vcc directly to the board and set the Vref with the trimmer. But, how can I calculate the VREF Value?


Best regards
Marco

[BigBen]

Marco,
I believe the confusion comes from the wording used. A "load" resistor typically refers to a resistor inline with the power supply that allows you to limit the current into the motor whilst still having a high voltage (improves high speed performance of the stepper). For chopped stepper drivers one uses a "sense" resistor that, as the name implies, senses the current flowing through the motor. The value of this resistor is not necessarily determined from the voltage/current specifications of the motor but from the currents you want to run this stepper with.
Generally, a small resistor is better since it will give off less heat and provides a higher gate voltage to the drivers (which make them run cooler). Take your motor for example: Using Ohm's law and a resistor of 0.5ohm, having a current of 1.2A will give you a voltage drop of 0.5*1.2=0.6V over the resistor. If you take a 1 ohm resistor, that goes up to 1.2V etc. Having a higer voltage will allow you to set the reference voltage closer to match your desired current (and will also let the comparator operate a bit better). On the other hand, the 0.5Ohm resistor will create 1.2^2*0.5=0.72W of heat, wheras the 1ohm resistor will create 1.44W. This can be significant, especially for larger currents (power is a function of current squared).
So basically to sumarize, you should pick a (non-inductive, not wirewound) resistor of a value somwhere in the order of 0.5 to 1ohm and set the reference voltage base upon V=I*R...

Hope that helps

BB

P.S. you may want to go with the L297 design since those parts should be more readily available in Europe (i.e. from Digikey europe).

[Guest]

Hi Big

Thanks for your explanation, but...not enought

my questions is related to the scheme here http://pminmo.com/troubleshoot.htm.
This hookup ciscuit is similar to the one know as CNC3AX France made, which use L297/298.

If I am not wrong, near to the "Motor Power supply" in the Unipolar Motor drive Supply, there are 2 resistor (red drawing) connected between the 2 central wire of the motor and +Voltage of supply voltage for the motor.
We are speaking for UNIPOLAR Motor. My motor has 6 wire (4 +2 central)

So, which formula need to be used in order to calculate the value? (previous post)

The "sense" resistor you mean is already placed on the Phil scheme and have also a trim for best regulation to complain motor requirementsd for best performance. Same scheme as Application note where I can find the formula for calculate the sense resistor.

My questions remain usolved.

Is my intention to realize this scheme, Is very simple and is also very very small, so I can hide somewhere in a small box o protection inside the CNC machine. I like the modular aproach used here.

To arrange the components in Europe, I change the optocoupler with similar named TIL192.
For the FET that drive external spindle I change with equivalent like TIP129. SLA7051 is coming from distributor, I have no pay, they are sended as sample free of charge. (6 unit) (2 CNC)
I think at the end, one axis cost me about few Dollars (or Euro) Great!!!!
For these and othe reason I need your tip and trik

Best regards in advance
Marco

[BigBen]

Well, actually it's Ben, but you can call me Big if you like

To be quite honest, I don't have a perfect answer for you. The way I understand Phil's drawing (and I'm sure he'll be the better person to explain just what he meant) the two "boxes" which are probably resistors are there to protect the circuit should the reference voltage be set too high. In other words, they are not required for normal operation, just for troubleshooting. If you want to assume that that is right, you can add any value between R=Vsupply/Imotor and zero. What that basically means is that you can choose it so that for a power supply voltage of 24V and a motor current of 1.2A you would need to pick a 20ohm resistor (30W) in order to be able to safely ignore the chopping action (i.e. if you didn't set the reference voltage or set it too high). Or you could set the reference voltage to 0.5ohm*1.2A=0.6V and hope that everything works...
Personally I always use a regulated power supply where I can regulate both current and voltage. In that way I can start up from a low voltage (i.e. the rated voltage of the motor where I=Irated without any chopping action required) and see what happens as I keep increasing the voltage...
If you don't have that luxury, the approach outlined above usually works quite nicely...

BB

[Guest]

Hi Ben

Your answer is really very apreciate.
This confirm what I am doing.

Thanks again

Ciao
Marco

[Guest]

Hi all
I have some new question.

DRIVER BOARD
The JP1 (5pins) is used only as TEST Point?

LOGIC BOARD
The IC1 for 5Vcc powe supply can be like7805?
What is the use of JP5?
RST is a pusbutton for RESET? Normal Open or Normal Closed?
ESTOP is for Emergency Stop. What kind of switch I need to use? Is request a type with HOLD system?


Does anyone has a sheet with complete hookup connection for all the connector of the sheets. I need to understand all the connection prior to start my construction in order to decide what functions to include and to delete.



Best regards in advance
Marco

[PMinMO]

JP1 is has two functions, easy access for adjusting vref, and setting the direction via hardware.
The interface board A 7805 or any other fixed 3 terminal voltage regulator that is compatable with a 7805. JP5 allows you to disconnect the spindle channel on pin 1 an use it as a logic probe to troubleshoot problems via led 7.

Rst is NO and resets the estop circuit.

Have you looked at this document? http://pminmo.com/4axis/4axisBOBdata.pdf

[Guest]

Hi Phil

your answer is really really apreciate.
I start to study this document. I am shure more answer to my question are inside,
I will back if I have more questions.

Best regards
Marco