Arduino external power

No ...in MOST cases.

Wherever you purchased the board, should have some form of datasheet.

This should give an idea of the input voltages that it will handle.

Mark

So any current is workable so long as the voltage is within range? Sorry, dumb question, but I don't want to burn my new Mega!

Keith

Current is Drawn, not pushed. So if your circuit only needs 1 amp, it is only going to draw 1 amp even if the supply can provide 50 amps.

Be sure to fuse it at the appropriate level incase of a short, which will draw as many amps is available.

Thanks for the clear explanation of current.

   I bought a 12v, 8 amp power supply for my project to power three servos (moving randomly) and three dc 12v motors (moving in one direction).  The dc motors are powered directly from the 12v power supply, the servos, from dc to dc converter at 6v. The servos run as planned but only two of the motors at a time will move very weakly. When all three are on line, the mosfets (520) become hot.

  The project needs an addional two steppers, some LED's, and a speaker. Does this mean I have grossly underestimated the total current necessary?

Keith

Keith

I explained how to measure the current capabilities of your 'salvaged power supply' in http://www.element14.com/community/message/71204#71204

It might be time to produce the complete wiring diagram and control mechanism to see how you are controlling these motors, etc.

In the 19 posts about this project I can't recall seeing any specs on the DC motors, but you have gone from using a SN754410NESN754410NE to Mosfets to control them.

You haven't indicated the fuse is blowing that was suggested in http://www.element14.com/community/message/71191#71191

so there are two possibilities :-

a.     You aren't driving the Mosfets hard enough (hence the heat).

b.     The salvaged supply is not capable of delivering 8A.

For (a) you can measure the voltage across the mosfet when its turned ON. It should be less than 1v and preferably 0.1v.

You can also measure the voltage across the motor, and the sum of these should equal 12v (or whatever the supply produces when the motors are ON)

For (b) I have already suggested how you can check the supply in http://www.element14.com/community/message/71204#71204 .

• So do the three motors run if you connect them straight across the 12v supply.?
• What voltage is the supply when all three are running.?

Also a (520) mosfet means nothing, there are some other numbers and letters associated with it, although they may not be on it, but you must have a complete part number somewhere.

Does this mean I have grossly underestimated the total current necessary?

Without knowing the total current drawn by the project, how can we answer.?

What figure did you arrive at when you designed it, and decided to use a 12v 8A (? ) power supply.?

Mark

Thanks for a clear explanation of current.  I bought a 12v, 8 amp power

supply for my project to power three servos (moving randomly) and three dc

12v motors (moving in one direction).  The dc motors are powered directly

from the 12v power supply, the servos, from dc to dc converter at 6v. The

servos run as planned but only two of the motors at a time will move very

weakly. When all three are on line, the mosfets (520) become hot.

    The project needs an addional two steppers, some LED's, and a speaker.

Does this mean I have grossly underestimated the total current necessary?

Keith

Mark,

   Tomorrow I will work on a drawing of the setup. The mosfets were to

drive three dc motors, at .17 amps, max efficiency, or, 1.2 amps if

stalled. I will use the SN754410NESN754410NE for the two steppers.

   I may not have been joining all the grounds properly.  Should all three

grounds (Arduino, 12v, and 6v) be connected?  As explained, the 12v motors

are running straight from the power supply while the servos are driven from

the 6v, dc to dc converter. I will draw these details tomorrow after

replacing the mosfets with a tip31.  The specs state that the Arduino five

volts is sufficient while the IRF520 Mosfets need 10v to fully open the

gate.

Keith

Keith

When you do the drawing, I'll be able to comment.

Don't go throwing new issues into the problem by replacing FETs with transistors.

Yes the grounds need to be connected....

Also you can't have

The mosfets were to drive three dc motors,

and

As explained, the 12v motors are running straight from the power supply

It my understanding you have the three DC motors controlled by the mosfet and connected to the 12v supply. (rather than 5 or 6v).

Your current of 0.17A or 1.2 A stalled is well within the mosfet capabilities.

Draw the circuit/connection and I think we will solve your problems....

Mark.

Mark,

   Here is a drawing <http://www.flickr.com/photos/92579016@N08/8554843059/>.

Sorry, can't do a schematic. Hope this helps.

Keith

Understand you can't do a schematic, but there's detail missing.

Perhaps you can just draw it and take a photo that is detailed enought (and not blurry) to be able to see it.

If necessary just include the details of the connections.

It shows a 6v DC-DC converter but you have it fed with 12v, so is it really a 12v to 6v regulator, or is it something truly isolated.?

Can you show how the arduino is powered. (is it 12v into the Vin pin??)

Is the ground from the 12v, 6v converter and Arduino supply connected together.?

You're not showing how you are driving the Mosfet and how the motors connect to them.

ie does the mosfet switch 12v onto the motor, with the other side of the motor connected to earth, or is one side of the motor connected to 12v, and you're switching the ground.

Have you actually tried any of the other suggestions made in http://www.element14.com/community/message/71639#71639

We'll get there, but more detail is required, as in any project.

Mark