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atx power supply for robot


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Hello
can anyone help me in selecting an appropriate DC power supply for robot. I had heard it is advantageous if using ATX power supply for robots, but i dont know the basic difference between ATX power supply and simple rectified dc power supply. Is it suitable for continuous operation.

The stepper motors I m using are of different ratings.
as: 12volts/ 3.6volts/ 5 volts/ 24 volts.
please suggest.

The motors are likely to be operated simultaneously, but the overall current requirement will not exceed above 10 amps.

Hw do I select the atx power supply?
please advice.

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Kumar and Ante,
You might use a DC-DC converter chip to turn the 12 VDC to 24 VDC so that you can use the ATX power supply without adding another supply. Here is an example from the ICL7660 data sheet from Intersil.

MP

Thank You Sir
In the last mail You had told about using ICL7660 to boost the voltage to 24 volts from the atx power supply.I have few questions:
1. Can I use the same type of IC to raise the voltage to 36 volts or more?
2. what are the restrictions imposed on this? Is the working principle of ATX power supply is the same as that of SMPS power supply?
3. what should be the power rating of the supply if my current requirement is up to 7 amps. using different voltage levels?
4. Do it support negative voltage levels too?

Thanks in advance.
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Kumar and Ante,
You might use a DC-DC converter chip to turn the 12 VDC to 24 VDC so that you can use the ATX power supply without adding another supply. Here is an example from the ICL7660 data sheet from Intersil.

MP


Hello Sir
The IC for which you are talking about does not tell about the max. output current. Could you make it clear how should I design the subsequent stages ( O/P onwards) of the ATX power supply so that I can have voltages greater than 12 volts. and still satisfying my current requirement, which may vary from 1 amp. to 2amps.
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Kumar,

Yes you can raise the voltage to more than 24 volts but there is a very low current output from the ICL7660/62.
The PC PSU is a SMPS.
7A is not a problem.
Yes negative supply is also available.

Hello Sir
once again! I am being told by the google groups that atx power supplies do not work well for the reactive load(motor) because of back emf. and that they are not designed for the continuous current since they operate on switching. I m in ambiguity.
how can i make sure that none of my ckt element gets damaged. including controller (stepper motor -ucn 5804) and 89c52 mc.Please find the enclosed as such from the google page.

One more thing, I want to use ICL7662, voltage doubler and my current req. is 2 amp max. can I use NPN transistors as darlington pair at the oupput of ICL7662, in this way getting voltage upto 38volt and the req. current to drtive the stepper motor.



google page

If I were you, I'd steer well clear of computer power supplies for anything
except driving a computer.

The big problem with them, other than the fact that they're not adjustable
and lack the useful ammeters and voltmeters you find on a laboratory power
supply, is that they are switch mode supplies. This means that, rather than
using a bog standard isolating transformer, bridge rectifier and some other
simple, rugged components, they use a complex mess of high frequency
circuits and inductors to regulate the output.

The principle is still a bit of a mystery to me, but it's something to do
with applying raw mains (or whatever you're supplying it with) to the
inductor and switching it on and off at the correct rate to produce the
required output. Some models apparently don't even use an isolating
transformer, which means that if they do fail, you might end up with mains
voltage on all the output lines. Definitely not good. Of course, if they
fail, they might also dump mains into all their internal components, and can
sometimes explode quite violently if they go wrong (that's the cheap ones -
better models have safety cut off devices)

Another reason they're useless for robotics applications is that they must
never be used to drive inductive loads, like any kind of motor, including
steppers. This is because the added inductance buggers up the power
supplies' internal inductor, and causes bad things to happen. Shorting them
out has similarly catastrophic effects.

They do have some advantages, though. The best (and one reason I do plan to
use a similar device for some very specialised circuits in my own robot) is
that, because of the charge-pump way the inductor works, they can easily
produce output voltages greater than their input voltage, or with opposite
polarity, and operate with almost any input, ac or dc. There isn't really
any other practical way of doing this. Second, they are very small compared
to conventional power supplies because they don't need a massive transformer
(though, as mentioned above, this can lead to added mains hazards).

The charge-pump effect also means that they could theoretically allow a
battery to continue to supply it's specified potential when the emf of the
cells themselves has dropped much lower than this value, so the system could
run for longer without recharging (though certain types of battery might be
permanently damaged by this).

Finally, on PC switch-mode supplies, there is a signal sent back into the
supply from the motherboard to shut the supply off immediately if it
produces an incorrect output, to prevent damage to the motherboard. If you
still plan to use the supply, you'll need to find a way to provide this
signal.

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They are idiots. I have a CNC drill machine that I built years ago which uses a computer power supply to control 3 steppers. This unit runs for hours at a time. I originally used a linear supply but I did not like the heat it generated or the losses in the conversion. You will not have any problems if you design your circuit correctly. Comments such as these get started from a small group when they do not design something well, then they blame their lack of design skills on the hardware.
Are your stepper motors rated at 24 VDC Max? If so, this is a MAX voltage and they will most likely run on 12 VDC with no problems. In such a case, you would only need the extra voltage if you are needing more torque. I do not see where you would need a lot of torque unless these are mountain climber robots. ;D
I do not know the specs on your motors, but why not try your 24 VDC steppers on 12 VDC and see what happens. You will not hurt the motors. Perhaps you do not even need the 24 VDC supply.

MP

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