where to insert mulitmeter to read stepper current

i'm testing NEMA 14 using L293D, and LM317 voltage regulator providing 2.7V from 5V adapter.

the motor current spec is 1A per coil:

LM317 using 270 + 330 resistors:

when multimeter is inserted between the LM317 output + L93D pin8, the stepper does not function, otherwise it does.

i need to audit circuit load, and don't know what would provide accurate readings.
i have sucessfully read the LM317 output at 2.72V, and also realize that this is probably not the way the finished circuit will be powered -- just beginning testing the motor for my project's (kinetic sculpture) needs.

thanks

That circuit cannot possibly provide the 2 amps needed for the motor (1 amp per winding), if you need reasonable output torque. The L293D driver chip is specified for a minimum motor voltage of 4.5 V (pin 8 ) and the output transistors will insert a voltage drop of around 2-3 volts. So with your 2.7 V power supply you have virtually nothing left for the motor.

You will have MUCH better luck using a modern motor driver chip such as the A4988 or the DRV8825. You can safely use a much higher voltage on the motor supply and get the maximum torque out of the motor. Pololu's driver boards are well engineered and well supported.

@jremington is perfectly right.

You are correct to measure the current in the supply to the driver chip.

Is you meter capable of measuring high currents?

...R

@jremington: i have a lot to learn...the motor runs, meaning it turns on the bench, but i wasn't using it yet to move anything.
the motor specs show its voltage rating at 2.7V. i think that means 'this is the power it needs to operate'.
in measuring the output from the LM317 circuit (with input 5V), i'm getting 2.72V, so i thought that was OK, and that i could expect that it would meet its 'holding torque:20oz-inch' maximum with this.

@Robin2: multimeter can range DC 2V-500V, and DC current 2mA-200mA. i don't know if this is considered 'high'...well i mean, yeah 500V is not something i'm going to be next to ever.

thanks to both of you.

You need to read up about the difference between voltage and current.

You say your meter can only read up to 200mA. If you tried to measure the current going into your motor (apparently 2 amps or 10 times what the meter is capable of) you will probably have blown a fuse in your meter, or otherwise damaged it.

The information in my post #18 in this thread may help Stepper motor power supply - #19 by Robin2 - Motors, Mechanics, Power and CNC - Arduino Forum, as may the rest of the thread

...R

robin, thanks for the link.

i'll study it and learn.

lulu35:
@jremington: i have a lot to learn...the motor runs, meaning it turns on the bench, but i wasn't using it yet to move anything.
the motor specs show its voltage rating at 2.7V. i think that means 'this is the power it needs to operate'.
in measuring the output from the LM317 circuit (with input 5V), i'm getting 2.72V, so i thought that was OK, and that i could expect that it would meet its 'holding torque:20oz-inch' maximum with this.

You were on the right track! If you supply 2.7 volts directly to the motor, then according to its specs each winding will draw 1 ampere of current (2 amperes total) and the motor will give you full rated torque. Unfortunately the LM317 voltage regulator can't pass more than about 1.5 amperes (if on a heat sink) before it starts to overheat and shut off. If not on a heat sink, then expect even less current from the LM317 regulator.

Doubly unfortunately, the motor driver you've chosen won't supply those 2.7 volts to the motor, as the motor driver will consume somewhere between 2 and 3 volts internally. If you wish to continue experimenting with the L293D motor driver, it is pretty safe to use a 5 or 6 volt power supply for the motor, that is to apply 5-6 volts to pin 8 of the driver. Your motor power supply must be capable of supplying about 2 amperes. The ICs will probably get warm, though and may partially shut down if the heat is not removed by a heat sink or fan.

@jremington: thanks for letting me know how i can use what i've got right now to find out somethings about this motor. its actually ok with me if the L293 stops working while i am checking it out because i realize that i will be changing to an optimum future circuit.

i'll be ordering a better motor driver, and thanks to your comments here, and on the link robin2 referenced, i will understand more about how to decide what is needed for my project -- which is evolving as i learn more.

measuring the current at different places will also help me 'get' it. i want to understand more about things.

thanks again.