I know, there are a lot of topics refering the pwm control of a "high" voltage dc motor, but I just want to be sure, that it works what I have in my mind.
So it is a 300W motor powered by 24V dc. This means I have an amperage of 12.5 A
In some forums, I have red that it might be sensefull to use a amperage limiter, but I dont really know why?
Is it necessary because the fast pwm signal might produce amperage peaks? Maybe I should use other capacitors?
Additionally I will implement a fuse in the future.
So what would you say. It would be nice to hear your opinion
So long as you only want to drive it in one direction, that should work well enough. The datasheet for the IRZ34N says that it can handle 30A.
However, that datasheet rating is only for a thousandth of a second. To run continuous current, you need to do some calculations on power dissipation. The headline Rds(on) says 0.035 ohms. But that's with 10V of gate drive. At 5V, the resistance is 0.046 ohms. With 12.5A running through a resistor of 0.046, you will be dissipating about 7 watts of heat. That's a lot for a small device like this. If there was no heatsink then it has a thermal resistance of 62 degrees C per watt. Multiply that out and add room temperature and I get 470 degrees. Hot enough to totally destroy it.
You will need a heatsink with a thermal resistance more like 10 degrees per watt. That's a pretty large heatsink. In fact, I would be worried that the small transistor won't be able to transfer enough heat to the heatsink and it will cook anyway.
You should try this circuit but I expect that you will overheat the transistor until you replace it with something with an Rds more like 0.01 ohms. There are many dedicated motor driver chips which can do this.
Speaking of which, have you calculated the power dissipation for the 7805 voltage regulator? Once again, those things give a large amperage rating in the datasheet which doesn't account for power dissipation.
It looks like the 7805 output is connected to the RAW power pin. That goes through another voltage regulator which has a "dropout voltage", meaning that the Arduino doesn't get to see the full 5V. Your 7805 should be powering the Arduino through the 5V pin.
"A fuse in the future"??? That's a funny place to put a fuse. Normally the fuse is placed in the positive supply line, as close to the source of power as possible. The size of the fuse depends on the size of the wires, not the load that is attached to those wires. Have you selected the wire size yet?
I know, there are a lot of topics refering the pwm control of a "high" voltage dc motor, but I just want to be sure, that it works what I have in my mind.
So it is a 300W motor powered by 24V dc. This means I have an amperage of 12.5 A
Unfortunately its not like that. The stall current of the motor may be more like 100A or more, and
that's the current that will flow initially till the shaft has built up speed. In a running motor the
motional back-EMF nearly completely cancels the applied voltage, but from stationary there is
no cancellation so that the current that flows = V/R where R is the motor's winding resistance.
I suspect your motor will have 0.2 ohms or so of winding resistance, you can measure it if you
want (although its tricky to measure such low resistances with a multimeter).
Thank you very much for your replies!
And sorry I failed translating current and voltage but I think you got what I ment.
so first point I want to regard, is the high current when the motor starts moving.
Something like a Current-Sensing Low-Side MOSFET Driver should be ok, right?
Or as an alternative, a resistor parallel to a RC-Relay which creats a shourt circuit after a second or less to ignore the resistor. But the relay might be to slow, so the first solution should be better.
The next point is the mosfet, which seems to get burned as you say. Its P=(12.5A)^20.046Ohm=7.2W
So maybe the IRLZ44n is the better option. There we have Static Drain-to-Source On-Resistance 0.023Ohm , so we reach P=(12.5A)^20.025Ohm=3.9W, which means we reach a temperature of 242°C (+ambient temperature). This is still very hot and probably destroy the mosfet.
Im not in the topic regarding electric components. Do you have any suggestions for a current sensing mosfet driver and a logic n-channel mosfet?
As I see, it has the following specification:
Heat production: 110 K/W
Drain to Source resistance: 0.004 Ohm
If I regard an ambient temperature of 20°C and a current of 12.5 A, I get 88.75°C as result.
By looking at all the values of the datasheet I m not sure if this mosfet fits to my application but I think so. Can anyone confirm this?
The only red flag I see is the maximum voltage Vdss. That is not far above your supply voltage. Spikes from just plugging it in to the battery could easily exceed that. You already have a flyback diode around the motor, so that removes that major source of spikes.
30V is not a good enough margin above 24V (*), choose a 40 or 50V device. If your
calculations show it will get hotter than 60C, using a heatsink is highly recommended.
Automotive grade MOSFETs are the ones to go for perhaps, they are specifically designed
for 12 and 24V operation in harsh environments.
(*) motors can spray out loads of interference spikes, add that to 24V and you are asking for dramatic
failure of the device under load. Also if the supply is a 24V lead-acid battery, thats about 29V if under
charge at the time...