Hi,
I am Contolling the speed of the Rc car Dc Brushed Motor with 370 28 turns (max 7.2v, 26A stall current)
I have a Mosfer IRL3705Z whether its capable to my Project?
Arduino (5v) to 100ohm and to Gate of Mosfet. i have a external power supply 6v 1200mah Rechargable Nimh
Hi Aimtohigh
That MOSFET is fine, in fact it will work at quite low Vgs (gate voltage) it's 8 mOhm when 'on' so if you driving 26 amps at a gate voltage of 4.9V then it won't quite turn on hard enough, so the power dissipation will be typically 8 watts(especially if your device is on the wrong side of typical, at 5V Vgs and 30Amps the typical 'ON' restance is 11-12 mOhm) and the power dissipation if fully on will be 5.6 watts. As I suggested earlier use several in parallel (the more the better to reduce power dissipation). If your only using your 1200mA power supply then it will work fine, except the motor won't be very powerful, but once you change to NiMh batteries then you will be wasting a lot of power in heat dissipation in the device.
To get that extra 0.1 volts on the gate use a pullup resistor on the output of the Arduino to 5volts of 5 to 10KOhm should be fine (absolute minimum is 125 Ohms).
I will make a note of this device (IRL3705Z), it looks like a good device to use.
I hope this helps
Dead_Ard
Your FET should work fine. Might want to consider an irl40b209 if your in the market. 1 mOhm on and 2.4 Vgsth. A little more juice to the motor and a cooler running FET.
Dead_Ard:
Hi AimtohighThat MOSFET is fine, in fact it will work at quite low Vgs (gate voltage) it's 8 mOhm when 'on' so if you driving 26 amps at a gate voltage of 4.9V then it won't quite turn on hard enough, so the power dissipation will be typically 8 watts(especially if your device is on the wrong side of typical, at 5V Vgs and 30Amps the typical 'ON' restance is 11-12 mOhm) and the power dissipation if fully on will be 5.6 watts. As I suggested earlier use several in parallel (the more the better to reduce power dissipation). If your only using your 1200mA power supply then it will work fine, except the motor won't be very powerful, but once you change to NiMh batteries then you will be wasting a lot of power in heat dissipation in the device.
To get that extra 0.1 volts on the gate use a pullup resistor on the output of the Arduino to 5volts of 5 to 10KOhm should be fine (absolute minimum is 125 Ohms).I will make a note of this device (IRL3705Z), it looks like a good device to use.
I hope this helps
Dead_Ard
Thanks for your help @dead_ard. I am using 2 MOSFET in parallel with 100ohm and 220oh. Its working fine.
But the problem to my analogewrite pwm lets say start from 100 good, 50 gut , 40 and 30 seems gut. But once when i start the motor as first with 40. Its still lagging with beep sound.
The IRL40B209 looks good as well especially with the 1mOhm fully on resistance. Thanks for that Ray_Beebe,
another FET to take note of.
Aimtohigh. I don't know what you mean by analogewrite pwm of 40. I am new to the Arduino and I have not yet used this function so I don't know what it does. I will probably find out before too long.
What is the beep sound?
Dead_Ard
The irl40b209 can handle a lot of current however look at the gate charge ( 180-270nC!) , this is not a mosfet to PWM with anything more than a few hundred hz without a mosfet driver. Great for an on/off load switch.
I would pick a mosfet like the irlr7843. Logic level, has a decent rdsOn and much better switching times. There are literally thousands that would work. Your mosfet might be just fine for the load that your motor is going to have.
It sounds like friction is keeping you from starting the motor at lower duty cycles so you are just hearing the coils whine at the PWM frequency ( once its started the speed can be reduced ).
Aimtohigh:
Thanks for your help @dead_ard. I am using 2 MOSFET in parallel with 100ohm and 220oh. Its working fine.
What do you mean here , 100 Ohm gate resistors or 220 Ohm? Are you using two different value gate resistors for the mosfets?
@alka : yes two different resistor to gate. Its works Fine.
Due to unavailablity of irf3705z Now i am planning to Change the Mosfet with irl3803pbf. using 3 parallel Mosfet with reapective three 220 Resistor. I hope it will work with this MoSfet. AnySuggestion @alka @dead_ard
220 ohm? No, if you are driving 3 paralleled high power MOSFETs use a MOSFET driver and 10 to 20 ohm
gate resistors, otherwise you'll struggle to do PWM at all. That's 0.42uC of charge to pump into gates in
total, you want a decent amount of current to do that, 0.5A to 1A sounds good to me. The gate resistors
must be matched, and good layout is needed.
If you use a MOSFET driver chip be sure to decouple it well, which means 0.1uF and 1uF ceramic minimum
right on the leads (within mm) - this is vital. My favorite big grunty driver is the MIC4422 which will work
from 4.5V to 18V, can source/sink several amps, is available SMT or through-hole, and can be driven
from 3.3V or 5V logic easily.
@markt; yes, i am struggling. i used 3 Mosfet parallel with 220resistor. i want to control Rc car motor and servo at same time. pwm by motor while running the motor and servo at same time i am facing some issue like my analogewrite above 125 motor spins fast but below 125 it stops completely. This is because i used a Arduino pin 9 to motor and 10 to servo.
Now i overcome with the problem and tried with different pin 11 to motor and 7 to servo. Its works gut at initially and i can control the motor via pwm but after some time motor runs suddenly little faster or some time its competely fast or stopped.. I dont the reason. About my circuit : 3 resistor to gate mosfet, drain to dc (-ve) and source to ground.
for dc motor 6v 1200ma power nimh at positive and negative to drain of mosfet.
Might be the reason of the higher Resistor ? i used 220ohm resistor. did you have any suggesion
Do you have a flyback diode?
Did you try just a single MOSFET and a 150ohm resistor. Three of these MOSFETs have too big of a gate capacitance to switch fast with the small current from the Arduino. Read Marks suggestion carefully or pick a more suitable MOSFET.
It might still work fine with your motor as it probably only draws a few amps running but losses will be very high. It's a bit cumbersome using three outdated MOSFETs and a driver circuit for something that can be done with one.
no i did not connect diode. I think 3 mosfet will equalize the power dissipation but for 1mosfet wit small speed of pwm wil take more heat on Mosfet.
now i tried with 3 mosfet with three 10ohm resistor with a arduino pin 5 to motor and pin 8 to servo . now its works fine but i need to even reduce the speed. it takes at analogewrite 80 speed is okay and 60 some what less and 50 start beep sound - doest start to run the motor due to load torque.
so at 60 speed of motor is not expected as my speed. i need even to reduce the speed. (like a speed of small ship sailing) any suggestion
Aimtohigh:
no i did not connect diode.
Do so! and read about flyback diodes and their purpose.
Aimtohigh:
now i tried with 3 mosfet with three 10ohm resistor with a arduino pin 5 to motor and pin 8 to servo.
10 Ohm gate resistors only makes sense when you couple it with a gate driver that is designed to deliver that current. There is a max current that can be delivered by an arduino pin and you have exceeded it.
Aimtohigh:
like a speed of small ship sailing
I have no idea how to quantify that, but it sounds like you need a gear box.
alka:
Do so! and read about flyback diodes and their purpose. ?
You meant from source to drain as place diode. so in my case 3 diode for 3 mosfet
alka:
10 Ohm gate resistors only makes sense when you couple it with a gate driver that is designed to deliver that current. There is a max current that can be delivered by an arduino pin and you have exceeded it.
ya I had coupled all 3 resistor together to act as pwm pin from arduino and to gate for each mosfet. Is it what you meant.
alka:
I have no idea how to quantify that, but it sounds like you need a gear box.
I am using the motor in rc car. it has a pinion gear from motor and spur gear to shaft.
I don't think it's an FET problem as the frequency of the FET switching can be as high as 500Khz with 100Ohm gate resistors and the Arduino outputs can source and sink a lot more than their rated current for very short periods (like 500nS. Anyone got any different evidence). I think the problem lies in the torque being produced by the motor, it needs a lot of wellie to get it going.
I have a power boat (in the loft) and it had five FETs in parallel to drive a 26 amp motor and they were driven from the PWM output of the receiver with no problems and FETs in those days (20 years ago) were not as good as they are now. (I must get it down and play with it).
The problem with using a single FET is the gate voltage that is required to turn it fully on at high current levels is usually greater than 5 volts
Dead_Ard
Dead_Ard:
I don't think it's an FET problem as the frequency of the FET switching can be as high as 500Khz with 100Ohm gate resistors
No, not true
200kHz using GaNFETs and a following wind is more realistic, for large silicon MOSFETs limit your ambitions to
50kHz or lower for acceptable switching losses(*). The exception to this is a resonant converter where the switching
time can be synchronized with the current zero-crossings, but that's rather more advanced than we are talking
here.
The problem with using a single FET is the gate voltage that is required to turn it fully on at high current levels is usually greater than 5 volts
A logic level MOSFET is fully turned on with 4.5V on the gate, at high current, that's what logic-level means.
(*) Consider a really fast switching MOSFET, 200ns to switch, at 50kHz it spends 2% of the time dissipating a large fraction (25% or so) of the load power. For 100W load thats 2W wasted, pretty good. Switching
at 500kHz would mean 20% losses, 20W extra dissipation in the FET, not acceptable. In practice the switching time is likely to be slower, perhaps 0.5 to 1us, due to stray inductance and wanting to
keep EMI under control.
GaNFETs are the device of choice for faster switching, but are way harder to drive safely and need
special surface mount packaging to tame the stray inductance that allows faster switching.
Aimtohigh:
You meant from source to drain as place diode. so in my case 3 diode for 3 mosfet
No, the diode goes in (reverse) parallel with the motor. Just one diode will do, but it's best to use a high speed "fast recovery" diode of about the motor rated current if you are using PWM. (As opposed to when you are just doing simple start/stop control, in which case you can use a standard rectifier diode at reduced current rating).
I think that your power supply hasn't got enough power to deliver a very high current pulse such as required at low revs high torque. We are talking something like 26 amps here. The other problem could be that your PWM frequency is too low. Can you increase it?. Not too high or your FETs won't be efficient with direct gate drive. Have you got a scope?
Dead_Ard