Transistor

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!

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)

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)

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!

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

Thank you.

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.

Liz0905: 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.

MarkT: 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

I'm trying to do a heating glove

Seriously? Having 250W in to one hand is going to be an instant barbecue.

Grumpy_Mike: 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!

You have the wrong heating pad for this design.

Grumpy_Mike: You have the wrong heating pad for this design.

And if we assume that I must use this specific element

Liz0905: And if we assume that I must use this specific element

Then you should not do the project.

10W is a starting point.

Grumpy_Mike: Then you should not do the project.

Are you serious?! there is no option to use it?!

MarkT: 10W is a starting point.

what do you mean?

Here's the kind of heater you want for gloves: https://www.sparkfun.com/products/11288

ChrisTenone: Here's the kind of heater you want for gloves: https://www.sparkfun.com/products/11288

i have to use a separate heater for each finger

Liz0905: what do you mean?

meaning a 10W heating element is ideally what you should be using.

a 50W - and five of them at that seems to be (to the experts) waay overkill.

i'm a newbie as well, so would also be thinking along your thoughts of "why can't it be used at all" - but i guess there are all sorts of considerations of "under-powering" an element meant to be used for higher outputs.

especially with transistors, where (from what i understand) they are best used in full-on (saturated) or off conditions - the in-between is where a lot of energy is wasted (as heat).

BabyGeezer: meaning a 10W heating element is ideally what you should be using.

a 50W - and five of them at that seems to be (to the experts) waay overkill.

i'm a newbie as well, so would also be thinking along your thoughts of "why can't it be used at all" - but i guess there are all sorts of considerations of "under-powering" an element meant to be used for higher outputs.

especially with transistors, where (from what i understand) they are best used in full-on (saturated) or off conditions - the in-between is where a lot of energy is wasted (as heat).

Ok thank you, but I can use the PMW pin to provide low voltage and thus supply enough current but on the other hand I will limit it to not reach the maximum power as well as the maximum temperatures, Correct me if I'm wrong

i think what all the seniors are saying is that the act of "under-powering" itself is the no-no. (due to inefficient heat dissipation running the device at half-speed)

Liz0905: ...I realized that in order to operate it I needed a transistor to provide a sufficiently high current.

you don't "need" the transistor to provide a sufficiently high current - you need it because the Arduino cannot handle it directly.

you should really look up how transistors work - i'm not quite sure if this applies to MOSFETs but to those "power transistors" (like the TIP120) - they can handle a range of current, as you are thinking - BUT the trade-off is that the power that does NOT get utilised, is wasted through heat - and if you are running the device at, say, even 20% (of it's maximum rating) - that means - you are dissipating 80% as ... ironically - heat !!

-cmiiw-