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Topic: Transistor (Read 2508 times) previous topic - next topic

Liz0905

hello,

I have a question about a transistor connection. I have a heating element of 50W, 12V. I realized that in order to operate it I needed a transistor to provide a sufficiently high current. Can someone please help me how I do it exactly

Thanks!

larryd

#1
Feb 19, 2018, 06:27 pm Last Edit: Feb 19, 2018, 06:31 pm by larryd
A MOSFET would be recommended.

This would be good to review.

http://www.gammon.com.au/motors

And

https://m.youtube.com/watch?t=110s&v=GrvvkYTW_0k    



No technical PMs.
The last thing you did is where you should start looking.

tinman13kup

If you apply ohms law to your heating element, you are going to have a little over 4.1A into that heater. It's not that it is huge by any means, unless you pick the wrong components to deal with it and they simply go up in a little stinky smoke cloud. Watch the heat dissipation.
Tom
It's not a hobby if you're not having fun doing it. Step back and breathe

Liz0905

Okay, I already realized that I needed to use a MOSFET transistor. If I use five heating elements I have to put a transistor in front of each one? How do I know how much current a transistor is going to provide me? And if I do not want to reach temperatures are too high, let's say 50 degrees? Am I using the resistor? And if so, where in the electric circuit do I place it? ... If I understand correctly, i don't need to change my code, I just do a high / low with digitalwrite?

Thanks you very much!

MarkT

Never use resistors for controlling power, that's just waste.  PWM is used for controlling power.  The duty
cycle sets the average power without having any unnecessary waste heat to git rid of.

Firstly to control a MOSFET directly from an Arduino requires a logic-level MOSFET, this is mandatory unless
you want to level-shift to 12V.

MOSFETs are picked by max voltage and on-resistance.   The on-resistance determines the dissipation
for a given current load.

You can switch 5 heating elements in parallel if you want, that's simpler.  Is each one 50W, or the total 50W?

What is the resistance of each heating element? (ie have you calculated that 50W correctly)
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Liz0905

Never use resistors for controlling power, that's just waste.  PWM is used for controlling power.  The duty
cycle sets the average power without having any unnecessary waste heat to git rid of.

Firstly to control a MOSFET directly from an Arduino requires a logic-level MOSFET, this is mandatory unless
you want to level-shift to 12V.

MOSFETs are picked by max voltage and on-resistance.   The on-resistance determines the dissipation
for a given current load.

You can switch 5 heating elements in parallel if you want, that's simpler.  Is each one 50W, or the total 50W?

What is the resistance of each heating element? (ie have you calculated that 50W correctly)
Thank you,

I use those heating elements:

https://he.aliexpress.com/item/AC-DC-12V-50W-Thermostat-PTC-Aluminum-Electric-Heater-Plate-Heating-Plate-Hair-Censer-Insulation-Mayitr/32812392601.html?spm=a2g16.10010108.1000015.15.3d85d6e8UhCjvQ


and i thought use:

https://www.sparkfun.com/products/10213


I have to be able to provide a current for some of the five at the same time or all of them together

Thanks!


Liz0905

If i use a 9V battery for the Arduino, do i need one more battery for my heating elements?!

Thank you.

MarkT

So you want individual control, ie 4A for each MOSFET, those Sparkfun ones are OK, but overkill on
the 60V rating, 30V MOSFETs have lower on-resistance.

0.05ohm x 4^2 = 0.8W per MOSFET, so a small heatsink is indicated.  Get some 10 milliohm 30V
MOSFETs and no heatsinking needed.

To switch all of them together is 20A which is beyond those MOSFETs as I said earlier, <=5 milliohm is
a good figure for that, a bit harder to find as logic-level, but they exist down to about 2 milliohm last
time I checked.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

MarkT

If i use a 9V battery for the Arduino, do i need one more battery for my heating elements?!

Thank you.
5 50W heaters = 250W.  That's serious power.  Standard 9V batteries are good for 0.5W, and are
not 12V!

You should explain what you are trying to do, battery power for heating is usually not a sensible
approach.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Liz0905

5 50W heaters = 250W.  That's serious power.  Standard 9V batteries are good for 0.5W, and are
not 12V!

You should explain what you are trying to do, battery power for heating is usually not a sensible
approach.
I'm trying to do a heating glove

Grumpy_Mike

Quote
I'm trying to do a heating glove
Seriously?
Having 250W in to one hand is going to be an instant barbecue.

Liz0905

Seriously?
Having 250W in to one hand is going to be an instant barbecue.
That's exactly why I said that of course I should not have the maximum power! And not reach temperatures so high!

Grumpy_Mike

You have the wrong heating pad for this design.

Liz0905

You have the wrong heating pad for this design.
And if we assume that I must use this specific element

Grumpy_Mike

And if we assume that I must use this specific element
Then you should not do the project.

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