I'm trying to heat two heat pad

Projects General Guidance
1

Hi Folks,

I'm new to arduino so excuse my lack of knowledge. Basically what I am trying to do is to heat two of these heat pads. Heating Pad - 5x15cm - COM-11289 - SparkFun Electronics, using two Tip122's to amplify the current. I have a 1k ohm resistor coming from the base on both transistors. I understand the transistors act as switches as arduino can only output 5v. I have everything hooked up to a 9v power supply but I can't seem to get both heat pads to work. I can get one to work alright. One transistor seems hotter than the other. In the spec of the heat pad it says that the operating current is 600ma. I've attached a schematic.

I was just wondering if someone could help me out and let me know what I'm doing wrong here. Any support would be greatly appreciated.

Thanks

2

Hi,
Welcome to the forum.

Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

OP, fritzy

Tom... :slight_smile:

3

Hi,
What are you using for your power supply?
If it is a 9V battery, like in a smoke detector, forget it, not enough current for what you need.

Your fritzy diagram really doesn't show your circuit well, please draw one by hand, labeling components and pins, such as base, collector etc.

The way you have your heat pads connected, is different for each pad, they should be the same circuit just layed out twice.

Do you have a DMM to measure voltages around your circuit?

How do you aim to control your pads?

Tom.. :slight_smile:

4

Hi Tom,

Thanks for your reply. I'm using a variable voltage source. Tip122 transistors. As there is only one batter I'm unsure how to hook up the second pad if that makes sense. Essentially I have collectors of the transistors linked together. I thought that I had the two of the exact same circuit.

Thanks

5

You should not have the collectors linked . I suggest you google “ using transistors as a switch “‘. You need to produce two seperate identical circuits with each heater connected between the collector and supply positive. Emitters each connected to
0v. The base each to
A digital output via a 220ohm resistor .

Your board connections look wrong

6

Fantastic unreadable Fritzing. Proper circuit diagram is needed to understand what you're trying to do here.

What I do notice is that both the 3.3V and 5V of the Arduino are connected to the same power rail. That can't be right.

It also seems you placed the LEDs in series with the heat pads. Very strange. Image is too messy to see how it's really supposed to be wired.