I'm really new in Arduino and near zero experience in circuits. I really hope experts here can help. Currently my friends and I are trying to use Uno to start up and shut down the motorcycle engine, which is conventionally attached to a 12V battery. Is it possible to do this, just by using 2 2N3704 transistor? Will it blow the transistor and the board? Or shall I use the relay system?
hi lefty! which schematic are you referring to? is the relay connected wrongly?
i guess what we are trying to say is, instead of using a relay to close the motor circuit, can we the uno directly (say, by supplying it with a 12V and digitalWrite(PowerPin, HIGH)). any suggestions?
btw, this is related to the previous question, we are using the hall effect sensor with the uno for cruise control.
Lefty, thanks for the comment. But I found that for 2N3704, Vcbo=50V, Vceo=30V, Vebo=5V. using a 12V battery is supposed to be safe, right? Or is there any suggestion from you to simplify the circuit?
magnethead794, thanks for the suggestion! Will try!
tingyik90:
Lefty, thanks for the comment. But I found that for 2N3704, Vcbo=50V, Vceo=30V, Vebo=5V. using a 12V battery is supposed to be safe, right? Or is there any suggestion from you to simplify the circuit?
magnethead794, thanks for the suggestion! Will try!
As I stated before there is a gross error in that linked schematic, so I'm reluctant to comment much further. What is the purpose of the lower transistor? As shown all it can do as drawn is to turn on and short out the battery and then burn out the lower transistor. That can't be the desired purpose of the lower transistor?
As far as would a 2N3704 work for the upper transistor that is controlling the starter motor on and off? You haven't told us what the peak current demand of the starter motor is. Only then can one select a transistor of an appropriate maximum current rating well above whatever the peak starter motor's demand is. A transistors voltage rating is just one of several specifications that must be matched to the application. Now adays logic level mosfets are a better choice for high current switching applications being driven by arduino type voltages.
We're using Honda EX5 engine. From the site, and from the starter motor, the only info I could get is 12V and 5AH.
Is this the right info?
Not sure if 5AH is correct. AH = amp/hours and that is a specification for batteries not motors. Maybe they mean just 5 amps draw.
Anyway as stated before, I like the newer logic level N-channel mosfet transistors for switching higher current loads. Here is a nice module that has connectors already setup, you need one for each device you want to be able to control with an arduino:
How do you propose to detect that the engine has started so that you can stop cranking the starter motor. I also think you'll find the starter load will be in the many 10s of amps so would suggest you use a correctly rated relay for the main driver contact and use the arduino to control the relay (via a suitable transistor driver)
Inductive loads on say, something like a starter motor would have a serious voltage spike, make sure you're designing in or choosing a transistor with a 'flyback' diode built in. To be honest I would not recommend a transistor at all.
The other thing is on start up your motor is going to take SERIOUS current draw. There are reasons they use relays (starter solenoids) in a circuit like this. A relay isolates your control side from your motor load side. A motor on start up acts like a dead short and kicks back a major voltage spike.
We're talking lethal voltages/current, you need to do your homework on this one if you really want to DIY this right.
