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I got a old desktop SMPS rated 250watts. In the output panel its written as, it can supply a output of 12v16amp. So my question is, it is possible to supply a steady 12v3amps from a 12v16amp smps. I also checked connecting my motor with the smps but the motor rotated for just 2 seconds and turned off automatically.

Thanks!

The image is just for reference

Dave Tweed
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Pradeep
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    Did you use a multimeter to check what the voltage on the lines is doing while this happened? Having "too much available current" from a power supply is pretty much *never* a problem for devices like motors (LEDs and battery-charging circuits have to control the current....motor drivers can use voltage control). – Robherc KV5ROB Apr 12 '17 at 19:19
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    You say "a steady 12v3amps", but is the motor to be on all the time? Some switching supplies have a minimum current rating. Also, does the desktop supply supply any other voltages (such as 5V)? There may be a minimum current rating on that which might affect overall operation of the supply. – Tut Apr 12 '17 at 19:34
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2 Answers2

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It is indeed possible to supply a steady 12 V at 3 amps from a 12 V 16 amp SMPS.

The thing to watch out for with ye olde PC PSUs is that some of them need some load on other rails to be stable.

I thought, and could well be wrong, that it was the case that a load (e.g. some 12 V fan that is to hand) was required on the 12 V rail for the PSU to stay on, but it could be that you need a small load on the 5 V and/or 3.3 V rails.

Drawing a few hundred milliamps from the other rails at the same time should enable the PSU to stay on.

Andrew Morton
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This sounds like a problem with the motor itself. Or, maybe the power supply is malfunctioning.

Merely having a power supply that is capable of providing more current than is required isn't a problem because the load will determine how much power it draws.

So the answer to your title question is that you can reduce 12V16A to 12V3A by making sure your load doesn't try to draw more than 3A.

Time to break out the multimeter and watch the voltage into the motor and see what is happening. Or try a different motor to try to localize the problem.

If it looks like the problem is the power supply, then you can confirm by using a lab-style bench power supply to run the motor.

SDsolar
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