# Need help with simple circuit. Stumped!

Discussion in 'The Projects Forum' started by triops124, Mar 21, 2016.

1. ### triops124 Thread Starter New Member

Mar 21, 2016
4
0
Hi all,
I am trying to control a small motor with a TIP32C PNP transistor, both powered by a small Lipo battery from a toy quadcopter. The battery is 30C, 1S, 180Mah, 3.7v. When I try the circuit shown in the attached photo, the transistor heats up burning hot. So then I tried putting a resistor color code brown-black-black-red-red between the switch and the base pin. It no longer overheats, but it still won't spin the motor as fast as it does when the Lipo powers the motor directly. I need the motor to spin at full capacity, not this slow!

2. ### #12 Expert

Nov 30, 2010
16,705
7,358
You need a resistor in the switch line to avoid huge current in the base circuit. Adjust the resistance to allow 1/10th of the amount of the motor current to flow in the emitter to base circuit.

3. ### Dodgydave AAC Fanatic!

Jun 22, 2012
5,172
778
You need a base resistor like this.

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4. ### #12 Expert

Nov 30, 2010
16,705
7,358
and don't forget to add the diode. It will stop the motor from kicking the transistor to death.

5. ### triops124 Thread Starter New Member

Mar 21, 2016
4
0
Ok. Thanks for the quick answers! My multimeter isn't able to measure current, must be a bad fuse. So I'll have to borrow my neighbor's multimeter to calculate the motor current draw, in order to find the correct resistor.

6. ### #12 Expert

Nov 30, 2010
16,705
7,358
OK. Measure the motor current and divide that by ten.
The voltage is 3.7V minus 0.7V for the transistor base.
So R = E/I
Rbase = 3V/(Motor current/10)
Rbase = 30V/motor current

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