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Topic: driving 2 12v 2A DC motors with Mega (Read 2464 times) previous topic - next topic

TwinkleToes

Hey everyone,
I am building a controller that needs to drive two 12V dc motors (2A) independently of each other. I am looking for the best Shield/drivers to do this. Are there any suggestions? I am new to this and could really use the help.

groundFungus

#1
Aug 05, 2018, 11:49 pm Last Edit: Aug 05, 2018, 11:52 pm by groundFungus
Is 2A the "running" current or the stall current?  The rated voltage and stall current are specifications that are important when choosing a drivers.

Some Pololu motor drivers.

TwinkleToes

Ok so the two different motors I am attempting to run are linked below. I am new to this and don't know exactly how to tell. I assume it is the running Amps though.

https://www.amazon.com/gp/product/B0791YL351/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

https://www.ebay.com/itm/Dual-Head-BPT-Tube-Lab-Dosing-Micro-Self-priming-Peristaltic-Liquid-Pump/362164888278?ssPageName=STRK%3AMEBIDX%3AIT&var=631375460094&_trksid=p2057872.m2749.l2649


If you could help me I would really appreciate it.

Someone on another forum reccommended this type of driver

https://www.amazon.com/gp/product/B01M29YK5U/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

groundFungus

#3
Aug 06, 2018, 01:17 am Last Edit: Aug 06, 2018, 01:27 am by groundFungus
The L298 motor driver is ancient and inefficient technology.  They drop 2 to 4 volts and dissipate the power as heat.  If your motor supply is 12V, the best that the motor will see is 10V, probably less.  Modern motor drivers use MODFETs on the output and drop very little voltage and therefore waste much less power.

Do the pump motors need to run in reverse or only in one direction?  If they run in one direction the driver is much simpler.   A logic level MOSFET rated for the stall current is a simple driver.   The flyback diode is necessary to protect the MOSFET from high voltage when the motor shuts off.




TwinkleToes


groundFungus

#5
Aug 06, 2018, 01:28 am Last Edit: Aug 06, 2018, 01:31 am by groundFungus
I was working on inserting the driver schematic when you replied.   I asked the seller for the stall current.  Hopefully he knows.  If not, we can estimate the stall (starting) current by measuring the winding resistance.   Do you have the motors?  Do you have a multimeter to measure Ohms?

TwinkleToes

I have a generic voltmeter I could use. And thank you so much for helping! This is looking promising.

groundFungus

#7
Aug 06, 2018, 01:53 am Last Edit: Aug 06, 2018, 01:57 am by groundFungus
Measure the resistance between the positive lead and the negative lead of the motor power.  The stall (starting) current is the rated voltage (12V) divided by the measured resistance.  For instance, if the resistance is 2 Ohms:  12V / 2 Ohms would be 6 Amps.  When measuring low resistance, short the test leads together and measure the test lead resistance.  Then measure the winding resistance and subtract the measured test lead resistance to get a true(er) winding resistance measurement.

TwinkleToes

Ok I will measure it now. I will need to find the meter so I may not reply today.

TwinkleToes

Here is what it says I'm not sure if I did it right though.

jremington

#10
Aug 06, 2018, 02:39 am Last Edit: Aug 06, 2018, 03:25 am by jremington
Put the meter on the X10 scale, and make sure that the meter is properly zeroed (connect the multimeter leads together).

Ohms are read right to left off the green scale.

TwinkleToes

This is what I got after touching leads and having it on X10

groundFungus

#12
Aug 06, 2018, 03:29 pm Last Edit: Aug 06, 2018, 03:31 pm by groundFungus
This takes me back, I haven't used an analog meter for, well, a while.

Quote
This is what I got after touching leads
To zero the meter you hold the leads together and physically adjust the meter to read 0 Ohms.   Carefully adjust the screw in the yellow box till the needle lines up with 0 Ohms.  Then, please post a new reading.




jremington

#13
Aug 06, 2018, 05:43 pm Last Edit: Aug 06, 2018, 06:56 pm by jremington
The zero adjust screw on the front, at the base of the pointer is for zero Volts, not Ohms!

Most meters of that type also have a zero adjust thumb wheel for Ohms, as zero is the other end of the scale. You have to adjust both.

Instructions on meter reading.

groundFungus

#14
Aug 06, 2018, 05:52 pm Last Edit: Aug 06, 2018, 05:53 pm by groundFungus
Sorry, like I said it has been a (long) while since I used an analog meter and I do now remember the Ohms adjust.  



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