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Topic: Power supply building technical help required (Read 1 time) previous topic - next topic


Hi friends,

Newbie here for electronics,

I need your help in estimating power supply requirements for my project.
Quick Info:

Project consist of
1 DC motor 30 RPM 12 volts
1 DC motor 60 RPM 12 volts
1 proximity sensor 5 volts
3 standard servos 5 volts

Now what happens is my present power supply 1 amp is not able to fulfill power requirements for above said components(lets say when 2 dc motors starts simultaneously, servo starts flickering)

What I want is even though both motors are moving none of servos should start flickering or loose their arrow.  The following is my power supply..

In this image I am only having single transformer, due to above said problem I added one more transformer for both different extensions.  But it doesn't improve the problem.

So can you give my your advice how to go further?  I am thinking of buying new power supply with 12 volts and (1+1+1+3)X0.5 = 3 amperes is it correct?


I have a motor 12-24 volts, 2amps. My power suplys could only give about an amp, so I used two power suplies.
What is man's best friend? The breadboard!


It's impossible to say what your power requirements are without knowing what current the motors take. However, an ATX computer power supply will probably be sufficient, and gives you both +12V and +5V outputs (and -12V and +3.3V as well). You may need to place a dummy load on the 5V output to get thr voltage about right.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.


To find out the peak current drawn by a motor you can measure it thus:

disconnect motor from the circuit.

Use multimeter on resistance range across the terminals.  Take a few readings, rotating the shaft a little between
each reading.  Discard all but the lowest reading.

Measure the resistance of the multimeter leads by shorting them together, subtract this from the motor reading
to give a best estimate of the winding resistance.

Say this gives 1.6 ohms (for instance).  At 12V the motor can pull 12 / 1.6 = 7.5A.  [ insert your own figures here of course! ]

If your supply cannot supply this current its voltage will dip momentarily as the motors start moving, or if they stall.

[ Adding a large electrolytic cap can reduce the dipping associated with starting ]

If the supply dips then you can't share it with the servos and other parts of the system - it may still be
perfectly adequate for powering the motors under normal load.
[ I won't respond to messages, use the forum please ]


Those little TO-220 linear regulators aren't good for much current.  Even trying to get a full amp out of them requires more effort in effective heat-sinking than it would be to move to switching regulators.  But, the real question is this:  Do your engines even need regulated power?

What's the voltage rating on the transformer?  Maybe you can power the engines straight from the DC rectifier?  (BTW, you do have a rectifier, right?  I don't see any diodes...)  Speaking of the transformer, what's its VA rating?  You may need a bigger one to supply enough current to everything.

Then, the servos... What are their current demands?  You might be able to use one 5v regulator for the servos, and power your control circuitry from another.

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