I can not understand this that surely is something basic for those who know about electricity but not for me. The thing is that I need to control a motor with a lot of torque. I have taken the motor of an electric screwdriver (6Nm) that works with an 18650 battery of 2000mAh and 3.6v.
I have disassembled it from its board and I have kept the battery, gears and the motor, which I have put in my circuit already created and tested with an L298N board. The motor works perfectly but it doesn't have even half the strength of its original plate.
If I measure the voltage and amperage outputs in both cases, in the L298N circuit they have larger measurements in both cases since I put two batteries to make 7.4v and 2000mAh. It offers the motor more than 5v and it marks around 1200mA, when on its original plate I see that it offers 3.6v and 900mA.... how can it be that in this last case it moves more weight and friction than some wooden gears and in the first case with higher numbers can I stop it with my hand?
I guess it's something basic but I've read and searched and I can't find a solution, unless somehow the intensity in one case stays high for something (even if it's minor) and in the other the L298 plummets right away... isn’t?
If you don't need to turn the motor both ways, then you're much better off with a logic level mosfet instead of an L298 dinosaur. The L298 could loose 4volt. And yes, short/thick/soldered wiring is needed.
Leo..
Sorry I don’t have schematics. This is a image of my circuit, and as I said the motor receives 6-7 v and 1000mAh aprox. The motor start to run with the joystick (BLE between both esp32). If I connect the motor directly to the batteries the motor has enough torque. It seems that the problem is the L298n but I don’t understand why, because the output voltage and current should be sufficient.
The ancient L298 bipolar transistor output stage drops 2V to over 4V and dissipates that power as waste heat. The more current that you pull the more the voltage drops. At 2A draw the motor is getting 4V or more less than the motor supply voltage.
The L298 is only good for 2A, what is the stall current of the motors?
The stall current can be several times the running current. The stall current will be drawn, briefly, every time that the motor is started. The stall current should be listed in the motor data sheet. In the absence of a data sheet, the stall current can be estimated. To estimate the stall current, measure the motor winding resistance. Zero your meter lead resistance before measuring the motor coil resistance. Take several measurements rotating the motor a bit between readings. Use the lowest reading in the calculation. The estimated stall current is the motor supply voltage divided by the measured resistance.
I believe that you would be better off getting a better motor driver. One that can handle the stall current of the motor and has modern MOSFET output stage that is much much more efficient than the piece of crap L298 driver. Pololu has a good line of modern DC brushed motor drivers. Choose the motor driver based on the stall current of the motor and the motor supply voltage.
To find the stall current, disconnect the motor from the circuit and measure the resistance across the motor's terminals, ie the resistance of the windings.
Then Ohms' Law i=v/r with v= whatever the supply voltage is and r just measured will give you i. (V in volts, r in Ohms, i in Amps)
Best to just measure the drop across the L298N - with the motor running controlled by the L298N, measure the actual voltage across the motor - the rest is being wasted in the L298N. Doubling up the driver won't help a lot, though you might eke out enough current, depending on your application. The fundamental problem is the device itself, so it needs to be replaced.
Yes this is I said… I take measures in the running motor and result 5-6v and 1000mAh aprox, more than the motor in the original circuit, but the problem is taht the original move my mechanism but not in this circuit.
Let me try and explain it as you have been told why but still don't seem to get it.
The L298 reduces the voltage you have to drive the motor by at least 4V. That is why you are seeing the motor not produce as much torque as when you connect it directly to your battery.
The solution is to either supply the L298 with a three batteries, or better to not use the L298 in the first place because it is a pile of crap.
If you want to replace the L298 you need to tell us:-
do you need to run the motor in one or two directions
what is the motor's stall current
Then we can make an informed decision about advising you what to do.
Note that 1000mAh, is not a current it is a battery capacity. If you measured the current the motor was taking it would be 1000mA or 1A. You can't measure battery capacity with a meter. While this is the running current it is NOT the stall current.
But no matter how much I lose voltage, it still gives me 5v when it's running... that's more than the 3v I was getting in the original circuit (and more current too).
This is precisely what I don't understand that even if it loses voltage I put more batteries in it and get much more than it already had, but it doesn't move the mechanism. I don't know if I explain myself.
On the other hand, I need two directions and I have measured the resistance of the stopped motor and it gives me 1.1 ohms (I hope I have measured it correctly). How do I need a maximum of 4v in the motor, since I understand that the stall current is 4400??
I have seen this Pololu TB6612FNG, I think it might fit my needs.
Did you remove the Ohmmeter test lead resistance. That can be significant when measuring low resistance like motor windings. To estimate the stall current, measure the motor winding resistance. Zero your meter lead resistance before measuring the motor coil resistance*. Take several measurements rotating the motor a bit between readings. Use the lowest reading in the calculation. The estimated stall current is the motor supply voltage divided by the true coil resistance.
*Touch the Ohmeter leads together and note the lead resistance. Subtract the lead resistance from the measured coil resistances to get true coil resistance.
That makes little sense.what is the circuit you have? It sounds like a big mistake in wiring up or taking the measurements to me.
Have you got diodes to cut off the back EMF like the example in the L298 data sheet?
How are you measuring the current?
You should put the meter into current mode and insert it in series with the motor.
To measure the voltage you should put your meter in voltage mode in parallel across the motor's terminals, no where else in the circuit. Does the voltage change when you turn the motor off?
Have you got any supply decoupling capacitors in the circuit? Lack of decoupling can affect what a meter reads.
Then you need to draw one if we are ever going to spot the mistakes you are making. The photograph of a tangle of wires going from place to place is not going to cut it.
I've repeated the measures and eliminate the usb charger component. The next images are the schematics and photos with measures (the more batteries I put higher values)... please let me know if are not correctly taken.
The current (motor running): --> you can stop the engine by hand
