Hello, I'm currently working on a circuit attempting to drive three DC motors with an Arduino and 3 transistors. I'm currently using three separate batteries and three identical circuits to the one added to the post. I'm using three BD243C transistors and a PEL00883 DC motor.
When using a 150/270 ohm resistor connected to the base of the transistors the DC motor won't start. I'm assuming this is due to the base current being delivered from the Arduino is too low. At these resistor values the transistor gets sort of hot. When reducing the resistor values to 5-10 ohms the motor starts running, but the transistors get extremely warm, and the DC motor is clearly not running at full capacity. I'm wondering what I could do to combat this?
I tried using an IRF520 NMOS transistor instead, but had a similar issue where the transistor overheated, this one also started emitting smoke. However with the NMOS transistor the motor started while using a 270 ohms resistor.
That motor needs 5A or so for nominal max output, and pulls perhaps 20--30A stall,
completely beyond a single BJT to handle.
Also with a BJT driven by an Arduino pin you are limited to 30mA or so from
the Arduino pin, which only allows 0.6A collector current or so as in switch-mode
transistors require the base current to be at least 5% of the collector current
(DC current gain doesn't apply to switch-mode).
0.6A is far below even the no-load current of the motor (1.8A).
very low on-resistance logic-level MOSFET is needed for this motor.
Why not try a FQP30N06L MOSFET. Change your schematic to E=S, C=D, and B=G. Change the 150 ohm to 50 Ohm, remove the diode and it should work just fine. You will probably not need a heat sink. These can be gotten from Adafruit for less then a buck.The MOSFET has an avalanche rating of 32 Amps, much more then you need here.
gilshultz:
Why not try a FQP30N06L MOSFET. Change your schematic to E=S, C=D, and B=G. Change the 150 ohm to 50 Ohm, remove the diode and it should work just fine. You will probably not need a heat sink. These can be gotten from Adafruit for less then a buck.The MOSFET has an avalanche rating of 32 Amps, much more then you need here.
Definitely do not remove the free-wheel diode, its essential to keeping EMI down and reducing
the chance of interference with the low voltage logic circuitry.
[ Its bizarre to assume because the device happens to have an avalanche rating that it will
handle this particular load, or that 60V spikes flying around are anything but a nuisance to
the rest of the system. Yes the FQP device is rated upto 8mJ pulses - but what is the energy
of pulses from that motor? Have you measured it? Know the inductance of that motor? ]
It's a 47W motor (47W/8.4V = 5.6A !) (do the math)
No surprise the BD243C transistor is overheating. It may be rated for 10A but that's with a heatsink.
