Question on Voltages and Loads using a IRFZ34N Power MOSFET

Projects General Guidance
1

Hello,

I'm a beginner, and I'm creating a project using an Arduino UNO to create a heater for my pet hedgehog. I have a DHT11 (which is fluctuating a great deal lately) reading the temperature near a heating pad I bought from Adafruit that takes 5-12V. I'm using a MOSFET to handle the voltage onto the pad. The code is written so the pad is turned off once it reaches a desired temperature.

I know the power at least is going through all the way to the pad, because when I connect both the USB and a DC wall power supply, I get a 3.5V reading on my multimeter and the pad gets warm. However, once I remove the USB, the voltage drops to around 2.7V. The only question I have wiring wise is where the positive end of the pad would go. The negative goes into the Drain pin on the MOSFET and here I just put the positive pin in my breadboard power rail. Is that okay?

My question is why is this voltage so low? am I using to big of a resistor (10k) or is the MOSFET I'm using the problem? I don't understand since I'm adding both the USB and the DC wall power supply (12V) for power. Would a relay work better in this case? Why?

Any help is much appreciated. Let me know if you want to take a look at the code

2

What is the specification of your DC wall power supply, both volts and amps?

Can you post a schematic of how you have wired it up?

Do not use it with the USB in its present state as you may damage the computer's port. The two supplies should be separate apart from the ground wires and having the load affect the USB voltage suggests you have not wired things up correctly.

3

This is how I have it wired up.

My DC power supply is 12V, 1A

Evernote Snapshot 20170211 132016.png
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4

You are trying to power your load from the Arduino +5V :- that is a great way to destroy things. The +5V end of the load should be connected to the +12V and the -12V should be connected to the Arduino ground.

You have drawn a transistor symbol not a FET symbol.

5

Hi,
OPs circuit

e54fb18b148833332671444a61414d18f8359046.png
e54fb18b148833332671444a61414d18f8359046.png2204×1558 208 KB

Tom... :slight_smile:

6

Thank you, that makes more sense.

Would this be the correct setup?

Evernote Snapshot 20170213 071925.png
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7

Yes that looks right.

8

Would I be able to use a 9V battery to power both the arduino and load by also connecting the battery to Vin? Or would I need a separate source and lower voltage?

9

As the load is a heater then it is likely to draw more current than the Arduino's regulator can supply.