I need some advise from you guys, Just recently started learning arduino.
I want to build my Own CNC machine in the future and I started by controlling speed of my Spindle Motor.
For Now I have this 12v motor
and a 24 V, 6.5 A Switching powersupply. I know my supply is a lot higher for the motor to take but
i want to try using it,
At first i tried Directly hooking my motor to 24v power supply out of curiosity, the motor runs for 2seconds and the power shuts down and turns on again. On in 2 seconds then off then on again (loop forever). Making the motor on and off also. I think the power supply current is not enough? and the power supply is protected in supplying more than the rated amps?
Because if power supply current is enough it will just burn my motor right?(which i dont like also).
(
Then I tried to Run The motor using PWM in arduino. By using a potentiometer and a Transistor(IRF520).
it makes me happy to see it run but for only a mere 5sec! My transistor is Burnt! haha.
Then I borrowed my friends DC adaptor I think it is for laptop use and rated 12v, 4A but
the motor never turned a bit. well i hear a bit of buzzing sound. I tried to turn it by hand to give it a push but no luck.
Well what im thinking now is to add a Bunk circuit so i could step down my power supply to 12v 6A?
or Maybe you know some transistors that can handle current more than 6-10A?
Considering i dont want to buy a new power supply withouth knowing the exact current my motor taking.
That motor has a 12V stall current listed: "stall more than 5 A, no way to test"
Since the rated current at 12V is 1.8A I'd guess the stall current is anwhere from 8 to 20A,
so hasn't a hope of not reseting a 24V 6A supply brutally every time.
The IRF520 is not logic level and thus will not work from 5V logic at all. Its also extremely
ancient with hopeless specifications for a low voltage high current load.
You will need something more like a 40V <=0.02 ohm logic-level device, not a 100V 0.27 ohm
10V gate device.
You will have a much easier time with a power supply that has current limiting, such as a bench
supply, then it will simply current-limit rather than shutdown on initial powering.
Also with PWM drive you will be able to avoid pulling large stall currents too (but you need
a decent MOSFET, not something from the 1980's!).
sorry need i need more infor. You said:
"The IRF520 is not logic level and thus will not work from 5V logic at all"
IRF520 is a 10v gate is it? if I apply 5v in it using arduino it can still close a bit the transistor but only
with limited(or lower) load current right?
Im really confused. if the load current will be limited should have more advantage correct?
Well i do get the point the the IRF520 have bigger resistance so i will need a transistor with lower so that it will not get burned.
sorry need i need more infor. You said:
"The IRF520 is not logic level and thus will not work from 5V logic at all"
IRF520 is a 10v gate is it? if I apply 5v in it using arduino it can still close a bit the transistor but only
with limited(or lower) load current right?
No, its basically not properly on, if you use a MOSFET as a switch, you want it to be ON or OFF,
not vaguely conducting a little. If its not properly on the drain voltage is too high and the
thing will current limit, be non-linear, heat up, basically be a problem, not a solution to a
problem.
Im really confused. if the load current will be limited should have more advantage correct?
If a power supply cuts out on overload, it will need to handle the full stall current (or maybe
twice that if you reverse the motor at full power), or it will just cut out again and again.
If the power supply current limits, then the motor gets less current/torque while it spins up,
which can be a good thing mechanically as well as electrically.
Well i do get the point the the IRF520 have bigger resistance so i will need a transistor with lower so that it will not get burned.
Thanks!
In the old days MOSFETs weren't as good and usually needed big heatsinks - these days you
can usually avoid that.
MarkT:
No, its basically not properly on, if you use a MOSFET as a switch, you want it to be ON or OFF,
not vaguely conducting a little. If its not properly on the drain voltage is too high and the
thing will current limit, be non-linear, heat up, basically be a problem, not a solution to a
problem.If a power supply cuts out on overload, it will need to handle the full stall current (or maybe
twice that if you reverse the motor at full power), or it will just cut out again and again.
If the power supply current limits, then the motor gets less current/torque while it spins up,
which can be a good thing mechanically as well as electrically.In the old days MOSFETs weren't as good and usually needed big heatsinks - these days you
can usually avoid that.
wooahh..
I learned a lot.
If mosfets these days should be avoided,
I am thinking they have something to replace it?
what can i use if lets say i want to use a transistor.
The key parameter to look for in a MOSFET datasheet is the "Rds(on) = ?? ohms at Vgs = ?? V"
That tells you the on-resistance you will get and the minimum gate voltage to use to turn it on.
If there is a value quoted for Vgs=4.5V or 5V, then its logic level (well 5V logic level). If there's
only a value quoted for 10V then its intended to be driven with 12V.
If you drive the gate below the minimum voltage needed the device may not work properly or at
all - you are creating problems for yourself. If you drive as told to in the datasheet it will work
(unless you've blown it up!).
You also need to ensure the voltage rating is high enough of course for the drain... Given the Rds(on)
you can calculate the heat dissipation and figure out if a heatsink is needed.