SparkFun MOSFET Power control kit, some help needed.

Using Arduino Motors, Mechanics, Power and CNC
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I visited my local Arduino supplier today and picked up 2 of those kits: SparkFun MOSFET Power Control Kit - COM-10256 - SparkFun Electronics They were new for him too so he couldn't fully explain to me how to hook those up. We really didn't understand why there were 2 + terminals and 2 - terminals on the PCB. Can anyone explain how to hook this up? The schematic can be found on the items page. I am planning to power 12V motors with this kit. If possible can you take a print screen of the schematic and show me what voltages go to where?

The way I want to use this kit is to use PWM to control the speed of a 12V motor. Do I need to place this kit before the motor:
e.g. 12V --> MOSFET --> Motor --> GND

Or after the motor:

12V --> Motor --> MOSFET --> GND

Thanks in advance!

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The MOSFET is an N-channel type which I think means:

+12v --> motor --> Drain (MOSFET) Source --> Ground

The signal from the Arduino goes to the Gate on the MOSFET. The Ground of the Arduino goes to the same Ground as the motor.

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Yes - definitely +12V -> motor+, motor- -> drain, source -> GND.

However this is not enough, you need a protection diode across the motor (or a snubber network) to stop inductive spikes - look at some of the relay and motor examples for illustration.

Connect the Arduino pin via a 150ohm resistor to the MOSFET gate and the Arduino ground to the MOSFET source.
The 150ohm resistor will limit the current from the Arduino pin and prevent it being damaged (MOSFET gates look like a hard short circuit at high switching frequencies)

If the motor takes more than 3A on full load you will need a heatsink on the MOSFET too.

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MarkT:
you need a protection diode across the motor (or a snubber network) to stop inductive spikes - look at some of the relay and motor examples for illustration.

The MOSFET that comes with that SparkFun breakout board has internal protection diodes.

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The MOSFET that comes with that SparkFun breakout board has internal protection diodes.

They can only do so much before overloading - check out the unclamped inductive load curve. A backwards diode across the load prevents high voltage spikes rather than absorbing them with avalanche breakdown. MOSFETs are so easy to blow up if you don't protect them, its not worth the risk.

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KE7GKP:
The three-terminal connector is the INPUT. the "-" is the ground, the "+" goes to the power source you are switching, and the "C" goes to the Arduino output pin of you choice. Note also that the "-" terminal also gets connected to Arduino GND.

The two-terminal connector is the OUTPUT. The "+" and "-" terminals go to the load (your motor or whatever).

Note further that there are TWO "footprints" for the 3-terminal input, and TWO "footprints" for the 2-terminal output. That is simply so that you have the option of using wither standard 0.1 inch center header pin connectors, or those nice screw terminals (which have a wider pin spacing)

There you have two different explanations for "why there were 2 + terminals and 2 - terminals on the PCB" because I can't tell which question you are asking? I don't know WHICH "two + terminals" or "two - terminals" you are asking about??

There is a 3 pin wide screw terminal and a 2 pin wide screw terminal. Both the 3 pin and the 2 pin have a + and - terminal on them. obviously the 3 pin terminal has a connection that goes to an ARD PIN. But where do I connect the 12V to? the 3 pin or the 2 pin terminal?

MarkT:
Yes - definitely +12V -> motor+, motor- -> drain, source -> GND.

However this is not enough, you need a protection diode across the motor (or a snubber network) to stop inductive spikes - look at some of the relay and motor examples for illustration.

Connect the Arduino pin via a 150ohm resistor to the MOSFET gate and the Arduino ground to the MOSFET source.
The 150ohm resistor will limit the current from the Arduino pin and prevent it being damaged (MOSFET gates look like a hard short circuit at high switching frequencies)

If the motor takes more than 3A on full load you will need a heatsink on the MOSFET too.

I'm going to the store in a second so I will bring a bunch of diodes and a few 150 Ohm resistors as you suggested, but I'm using a H-bridge to control the motor direction. I don't see how I can add a diode across the motor coil when doing this. Do you mean that I need a diode between the - of the motor and the MOSFET, that would be possible, and probably wouldn't hurt it either.

I won't be installing the MOSFET's until I have all the wire connections ready for my project so this buys me some time, but I plan to start on the code tomorrow. The motors will come nowhere near a 3A load as they only draw 80mA when they spin freely. The power supply only provides a max. of 800mA, and those are made for that type of motor.

If anyone can provide me a screenshot with some text on it to explain what voltage goes to what pin on the terminal, it would be a great help, not just for me, but also my ARD supplier.

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MOSFET Power Control Kit: Description: This MOSFET power control kit is basically a ... We can backorder a further from Sparkfun which we can ship to you in 7 days. ... If you've wanted to use a MOSFET, but need a better way than your ...

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This is what I currently have as a set-up. I did it quite fast so please take the resistor values for granted, they are correct in my project. Same goes for the relay, this one already works.
I know the whole drawing is a bit sketchy, but I guess you can find your way around.

I made a rough outline of what the breakout board looks like. and made the connections I currently have.

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Can anyone confirm this is the correct way to hook these up? I want to power it through PWM, but is this type of MOSFET the right one? (I did exactly what KE7GKP said.)

Here is the MOSFET datasheet. http://www.sparkfun.com/datasheets/Components/General/RFP30N06LE.pdf (I really need to learn how to read those.)

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KE7GKP:

  1. In reality, the (black) wire from the - side of the 12V battery should be connected DIRECTLY to the - input terminal on the Sparkfun board. This is a heavy current path and it should not take the long way around as you have shown.
  2. The diode between the Sparkfun board and the breadboard is not correct. The diode should be across the motor (before the crossover relay). In almost exactly the same position as the diode you have for the relay coil (which is correct). IMHO, the built-in diode in the FET is more than adequate for this circuit and that external diode isn't even needed here.
  3. We don't really know whether the transistor is wired correctly because those pretty Fritzing pictures don't show all the critical details of a circuit (like which transistor pin is which)
  4. We don't know anything about your relay, so it isn't clear whether powering it from the Arduino +5V regulated output is appropriate?

Let me answer by your suggested points:

  1. In reality the black wire goes straight to the power supply -. The wire isn't much longer than 8cm and there is nothing in between. However you did say that it needed to go to the Arduino GND pin too. I wired it directly to the power supply -, would this suffice or is this where I go wrong?

  2. I understand that there needs to be a diode there somewhere, but I don't understand how I am supposed to place that diode in the schematic. Can you draw this out for me? The relay is there so I can control the motor direction. The opinions about the diode are very spread out. I guess as I will never draw more than 800mA from the motor (no where near actually) I can do away with the diode. Can you confirm this?

  3. As far as I know the transistor is wired correctly. I put all the elements on the board the same way as I saw on the Sparkfun website. So the PCB is correct.

  4. This is the same relay as I have used on other projects, they work fine so no worries there. I just drew it in so you could get a basic feel of what I wanted to do.

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I will remove the diodes tomorrow and properly place them over the coil. The transistor for the relay is properly wired, at least in my project. I tested it and it worked so that is not the problem. I'm probably cocking up on the MOSFET board so I will run through my wiring again tomorrow. Thanks for your help and I will keep you updated!

This is what I am working on:

It's a control panel for a model funfair ride. Right now only the relay works and the 7-segment display. The potmeter both uses a map function to determine the digit that needs to be displayed and a map function to convert the 0-1023 to a 0-255 value for PWM.

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