High current digital potentiometer?

Hey. Quick question: Does anyone know if it exist high current digital potentiometer you can control with arduino?

Those I find usually use the same current and voltage for input and output. I am currently looking for something that would withstand 10A. And controllable with arduino.

I am going to use it for a coil, i am using PWM and some transistors now. I just burned my IRF520 transistor :P so would like some alternatives.

Thanks Even

Evenaav:
Hey.
Quick question:
Does anyone know if it exist high current digital potentiometer you can control with arduino?

You mean “motorized rheostat”.

The IRF520 isn't a modern device, it has appauling specs and isn't even logic level.

Look for something that's logic level and has Rds(on) < 0.015 ohm.

am currently looking for something that would withstand 10A. And controllable with arduino.

At what voltage, then you will know what power dissipation you will need to cope with.

While modern devices have a low full on resistance if you want to control a high current analogue load it matters little because a lot of the voltage is going to be dropped across your device.

Draw a schematic of the circuit you were using with the IRF520 and take a photo of it with your cell phone and post it. I'll explain why after I see it.

MarkT:
Yeah, i was thinking about controlling a potmeter with a motor, did not now it was called motorized rheostat though :stuck_out_tongue:
Grumpy_Mike:
30V
raschemmel:
The circuit and picture are attached.
Found the circuit her - http://www.societyofrobots.com/robotforum/index.php?topic=14374.0

MagnetControl2.png

Don't use a motorized rheostat. You're going to have a big noisy device that wastes a lot of power.

I'd recommend that you get the PWM method working instead. Use transistors with lower on-resistance and make sure to use a good heat sink.

Hi, I would seriously consider getting the MOSFET off the protoboard, 10A is not what the board was rated at.

I can see that the circuit you are using is designed to give 12V gate voltage to turn the MOSFET on, but I would say you cooked a MOSFET because of a failure in the protoboard.

Tom… :slight_smile:

Several things:

  1. Your Mosfet was under-rated.
  2. Your Mosfet is not Heat Sinked (Radioshack sells an excellent TO-220 finned heatsink.
  3. Your circuit doesn’t have a FLYWHEEL diode to protect the MOSFET from backEMF.
  4. Your breadboard technique is appalling. Try taking a little more time to make it neat.
  5. Try using a better Mosfet like the RFP30N06LE (see attached datasheet).
  6. Try adding a decent heatsink. I don’t think the mosfet was damaged by a failure in the breadboard I think it was all the OTHER
    factors .
  7. Try adding a 1N4007 Silicon diode as a flywheel diode across the solenoid coil with the cathode toward the + end and the andode toward the Mosfet.
  8. What are you using for a power supply ?

RFP30N06LE.pdf (189 KB)

Thanks for the tips. About tip nr3 and 7. i have a 1N4007, but as you can see in the circuit its from the Mosfet to ground, should i change this?

The power supply is 0-10A and 0-30V.

Did the MOS burn because it got to hot? its rated to 10A at 25degrees.

but as you can see in the circuit its from the Mosfet to ground, should i change this?

yes it should be across the inductive load.

Did the MOS burn because it got to hot?

Yes.

its rated to 10A at 25degrees.

But as it gets hotter that current gets smaller, it is called de rating. If you want to keep the 10A then you have to keep the case at 25C, which is not possible without an infinite heat sink.

If you got that schematic off the net the diode you are using is not what is called for. Here is a link to a Schottky diode. You can move your 1n4007 across the load as Mike recommended (the correct location for a flywheel diode is across the load) and add a schottky diode in the location shown on your schematic. The flywheel diode across the load is the most important so move your diode before using the circuit again. Did you measure the coil resistance of that hand-wound solenoid ? Do you have any information on that (number of turns, core material ?coil resistance?)

I have no information on the solenoid. it is an air core coil with 0,3ohm resistance

Evenaav: I have no information on the solenoid. it is an air core coil with 0,3ohm resistance

Well 30V across a 0.3R load is 100A so your current requirement is massive. Much bigger than the 10A you first talked about.

Hi, 100A DC, but if you use PWM, then inductance rears its head due to the fact that you are now using AC current so it will be less.

Tom...... :)

TomGeorge: Hi, 100A DC, but if you use PWM, then inductance rears its head due to the fact that you are now using AC current so it will be less.

Tom...... :)

But not when it is fully on.

Well 30V across a 0.3R load is 100A so your current requirement is massive. Much bigger than the 10A you first talked about.

This INRUSH current (short duration, mS range) can be limited using an INRUSH resistor (low resistance , high wattage, maybe 2 ohm 25W) but frankly, looking at that solenoid , I think you should consider using a Contactor with a Snubber to prevent arcing. You can use a Mosfet to turn on the contactor if you use a 1N4007 across the coil as a flywheel diode. http://www.redlion.net/Products/Groups/NoiseSuppression/SNUB/Docs/12027.pdf

The DC power supply goes up to 10A, so dont need anymore at this moment.

Is it possible to have parallel coupled transistors?

I am going to use it for a coil, i am using PWM and some transistors now. I just burned my IRF520 transistor smiley-razz so would like some alternatives.

You made two mistakes that caused the failure described in your post. 1 The mosfet was under-rated 2 The flywheel diode was in the wrong place.

You have already been given suitable recommenations for a mosfet that can handle your load but unless you have the flywheel diode in place (1N4007) across the load , not like your schematic, you will continue to blow anything you use. Mosfets in parallel is a standard practice in many applications. Parallel transistors is the same concept but mosfets are more efficient and therefore dissipate less heat.

This INRUSH current (short duration, mS range) can be limited using an INRUSH resistor

No that is the wrong way round with an inductor turning on to a DC voltage. Initially the current is small because inductors resist change. As time passes this current rises until it reaches a value determined by the resistance.

High inrush current is obtained with :- 1) A capacitive load. 2) With an inductor powered by AC or with an AC component like a motor winding. Although it is only considered high because it will eventually fall to a value given not by the resistance but the inductive reactance.

The DC power supply goes up to 10A, so dont need anymore at this moment.

Now don't be silly.

Is it possible to have parallel coupled transistors?

It is but they do not work because they will not share current, FETs however will.