Hope someone can assist me here... I have a 12V DC motor that works fine when connected to a battery source, but when connecting it to a 12V 3A wall adapter, it starts and stops repeatedly.
After a lot a searching online I did figure out its because the "draw current" when starting is too high when starting the motor causing the power supply to cut out. To confirm this I also added another 12v fan in series which causes the motor to work, but of course the 12V is now being split to the motor and fan (also just a motor really) and I both dont want to run both all the time and think it might not be good to run 2 x 12v motors in series with a 12v psu - but I might be wrong - if it is safe and Im happy with the reduced speed can I run it like that?
I also seen it mighty be possible to add one or more resistors (in series) which might also fix the issue, but I have no idea which resistor to use nor how many (Im an out-of-work software developer learning electronics). Should this be the best fix, how do select the right resistors? I have tried a few already but to no avail - I suspect they might not provide enough resistance (could be too much as well - again I have no idea).
Without purchasing an expensive new PSU that can handle the current, is there another solution that someone can possible explain to me please?
By running the two in series you are effectively supplying your 12V motor with only 6V (half the supply voltage). At that lower voltage it takes much less current. If you really don't mind the reduced speed it is safe to run the motor like that. To run at full speed you simply need more total power than your supply can provide and there is no easy way around that.
slipstick:
By running the two in series you are effectively supplying your 12V motor with only 6V (half the supply voltage). At that lower voltage it takes much less current. If you really don't mind the reduced speed it is safe to run the motor like that. To run at full speed you simply need more total power than your supply can provide and there is no easy way around that.
I would really like to be able to get a fix here without spending more money. So thus far running the 2 motors in series is my only option.
I tried (as said in my first post) adding resistors in series as well as a smaller 12V computer fan - in both these cases the 12V motor did not run at all - where it goes on and off connected by itself - and my limited knowledge tells me the smaller pc fan as well as resistors did not add enough resistance to the circuit. Can I add more pc fans (multiple fans connected in parralel, and they then connected in series to original circuit maybe? Or resistor(s) that would work perhaps?
Without any details of any of the motors or fans or the resistors you've tried I'm working blind here which makes it difficult to comment.
Do you have a multimeter to measure the current that the motor takes when it's connected to the 12V battery? Or when it and the fan were running in series. Either would be useful. Or you could measure the voltage across the motor when it and the fan are going.
I'm pretty sure you're wrong about the resistors and small fans. It's almost certain that they add far TOO MUCH resistance to the circuit reducing the current flow so that it's not enough for the main motor.
The catch with adding resistors is that at the current the motor needs the resistors will get hot, probably very hot. What value resistors did you try? You really need low value (low Ohms) but high power (so physically quite large) resistors.
If you are going to control the motor with an Arduino, you'll need a way of amplifying the current. Usually this is done either with a relay, or a (logic level) MOSFET transistor.
If you used a MOSFET, you could try driving the motor with a PWM (pulse-width modulated) output, which A) would give you speed control of the motor, and B) would let you start the motor "gently", ie a soft-start, which would probably overcome the problem of the power supply cutting out on start-up.
Hope someone can assist me here... I have a 12V DC motor that works fine when connected to a battery source, but when connecting it to a 12V 3A wall adapter, it starts and stops repeatedly.
Immediately you can deduce the supply cannot handle the motor's stall current and trips out.
Thus the motor has a stall current > 3A at 12V. From the fact two in series work the stall current
must be < 3A at 6V.
One way to avoid the full stall current is to ramp up the PWM drive to the motor gradually - so
long as the PWM frequency is high enough this will limit the max current during the period the
motor starts to spin up. Once the motor is upto speed the back-EMF will limit the current unless
you actually overload the motor mechanically.
To answer the question about resistors measure the resistance of the motor when it's not powered and try using a resistor of the same value, which will halve the starting current. You can put a switch across the resistor and close it once the motor is spinning.