Calling Electrical Engineers

[Monel Funkawitz]

My brain hurts right now. I am at work, and I have a red flashing LED. I need to use this flashing LED to turn on a transistor so I can get more output from it to run a small motor. Here are the parts I have.....

1 flashing red LED
2N3906 General Purpose PNP Transistors
2N3391 NPN General Purpose Transistors
Large Resistor Assortment
Large Hammer 😀

I am thinking this.... using a 2N3391. Hook the 9vdc+ power in to the Flashing LED anode (It is current limited) LED cathode gets connected to a 100k ohm resistor. Other end of resistor gets connected to the NPN's base. Emitter gets connected to ground. 9vdc+ goes through the motor, and the other terminal on the motor gets connected to the NPN's collector.

Think it would work?

 

[Demon-Xanth]

Common collector amplifiers work good for increasing current drive capabilities.

 

What is the power consumption in watts of the motor ?

 

[Monel Funkawitz]

Heck if I know Rodger. 😀 Its one of those little Mabuchi motors, you know, one of those little motors that is in damn near everything?

 

[Monel Funkawitz]

Well, my design is useless. Motor comes on when bat is hooked up, and runs all the time. LED don't blink.

 

Do you have a ohm meter handy ?

Please Monel, it's Roger 😉

 

[Monel Funkawitz]

LOL... sorry Roger, it is a habbit. 🙂

I have lots of ohm meters. Everything from a standard Fluke 87 to a Megger, to a Extech Scope meter with trace. Problem is I don't have much experience in designing. I am a schematic rat.

 

Hook up the ohm meter in series and check the the amperage of the motor.

 

[Monel Funkawitz]

Well, with the scope I get 250ma at 3vdc no load. I get 700ma + or - 15% at max efficiency with the very scientific finger powered braking dyno. I'll be overvolting this motor, but it will be in pulses, so it won't hurt it. I'll limit the current to around 700ma later.

 

I believe you are going to need a relay between the emitter and the moter.
I have to go look in my electronics book to make sure though.
Will post when I get the answer.

 

[Monel Funkawitz]

Well, I gotta scrap this idea and go with a different transistor, like a Darlington NPN. This GP trans just doesn't have enough ass. With a darlington I think/know it would work. I can't use a relay for power consumption reasons. My battery life is going to be short enuf anyway.