Arduino Forum

Using Arduino => General Electronics => Topic started by: Liz0905 on Feb 19, 2018, 06:15 pm

Title: Transistor
Post by: Liz0905 on Feb 19, 2018, 06:15 pm
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!
Title: Re: Transistor
Post by: larryd on Feb 19, 2018, 06:27 pm
A MOSFET would be recommended.

This would be good to review.

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

And

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



Title: Re: Transistor
Post by: tinman13kup on Feb 19, 2018, 11:23 pm
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.
Title: Re: Transistor
Post by: Liz0905 on Feb 21, 2018, 11:37 am
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!
Title: Re: Transistor
Post by: MarkT on Feb 21, 2018, 12:12 pm
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)
Title: Re: Transistor
Post by: Liz0905 on Feb 21, 2018, 12:46 pm
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!

Title: Re: Transistor
Post by: Liz0905 on Feb 21, 2018, 02:22 pm
If i use a 9V battery for the Arduino, do i need one more battery for my heating elements?!

Thank you.
Title: Re: Transistor
Post by: MarkT on Feb 21, 2018, 02:25 pm
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.
Title: Re: Transistor
Post by: MarkT on Feb 21, 2018, 02:28 pm
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.
Title: Re: Transistor
Post by: Liz0905 on Feb 21, 2018, 02:35 pm
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
Title: Re: Transistor
Post by: Grumpy_Mike on Feb 21, 2018, 02:41 pm
Quote
I'm trying to do a heating glove
Seriously?
Having 250W in to one hand is going to be an instant barbecue.
Title: Re: Transistor
Post by: Liz0905 on Feb 21, 2018, 02:43 pm
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!
Title: Re: Transistor
Post by: Grumpy_Mike on Feb 21, 2018, 03:30 pm
You have the wrong heating pad for this design.
Title: Re: Transistor
Post by: Liz0905 on Feb 21, 2018, 03:33 pm
You have the wrong heating pad for this design.
And if we assume that I must use this specific element
Title: Re: Transistor
Post by: Grumpy_Mike on Feb 21, 2018, 05:35 pm
And if we assume that I must use this specific element
Then you should not do the project.
Title: Re: Transistor
Post by: MarkT on Feb 21, 2018, 11:47 pm
10W is a starting point.
Title: Re: Transistor
Post by: Liz0905 on Feb 22, 2018, 08:33 am
Then you should not do the project.
Are you serious?! there is no option to use it?!
Title: Re: Transistor
Post by: Liz0905 on Feb 22, 2018, 08:40 am
10W is a starting point.
what do you mean?
Title: Re: Transistor
Post by: ChrisTenone on Feb 22, 2018, 09:24 am
Here's the kind of heater you want for gloves: https://www.sparkfun.com/products/11288
Title: Re: Transistor
Post by: Liz0905 on Feb 22, 2018, 09:30 am
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
Title: Re: Transistor
Post by: BabyGeezer on Feb 22, 2018, 09:39 am
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).
Title: Re: Transistor
Post by: Liz0905 on Feb 22, 2018, 12:32 pm
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
Title: Re: Transistor
Post by: BabyGeezer on Feb 22, 2018, 02:07 pm
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)

...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-
Title: Re: Transistor
Post by: Liz0905 on Feb 22, 2018, 03:45 pm
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)
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-
OK I got it. Sorry for the ignorance. This is the first time I've been dealing with electronics and with Arduino, so I'm trying to understand. If so, if I find the same heating element but with a 10W power supply and use a transistor, should this solve my problem?
Title: Re: Transistor
Post by: JohnRob on Feb 22, 2018, 05:49 pm
The short answer is yes a Mosfet will be able to switch the heater current on and off.

Terminology:
Transistor could be a BJT (bipolar junction type) or it could be a MosFet (Metal oxide field effect).  Both are considered transistors.  However in this forum folks use the term "transistor" for a BJT and the term MosFet as... well a MosFet.


So a Mosfet is a type of transistor.    When used to switch heaters on and off it could be helpful to think of it as a type of relay:


Relay:  when the coil is energized (has voltage on it) the contacts are closed allowing the load to be ON.

Mosfet: When the Gate is energized 5V the drain allows current to flow from the drain to the source.

Hope this helps.



Title: Re: Transistor
Post by: BabyGeezer on Feb 23, 2018, 04:23 am
OK I got it. Sorry for the ignorance. This is the first time I've been dealing with electronics and with Arduino, so I'm trying to understand.
when one is learning, you shouldn't have to apologize for ignorance - the whole point about learning something is because we are ignorant to the facts surrounding the topic !

the folks here are very understanding and patient enough if you can respond to whatever further clarifications they request.


If so, if I find the same heating element but with a 10W power supply and use a transistor, should this solve my problem?
that's probably the other way around - you (ideally) want the 10W heating element.

just to clarify from your earlier post;
this --> https://www.sparkfun.com/products/10213
does not "provide" the current - it *controls* it - the current comes from the power supply unit. (battery, wall-wart, etc.)
Title: Re: Transistor
Post by: MarkT on Feb 23, 2018, 01:36 pm
what do you mean?
250W is crazily high and will burn you.
1W will do nothing.
So 10W is about right as a starting point for designing a warmer like this.  Perhaps it should be 20W,
perhaps not, you need to experiment.  Remember a lot of soldering irons use 40W or less...
Title: Re: Transistor
Post by: Liz0905 on Feb 23, 2018, 02:08 pm
when one is learning, you shouldn't have to apologize for ignorance - the whole point about learning something is because we are ignorant to the facts surrounding the topic !

the folks here are very understanding and patient enough if you can respond to whatever further clarifications they request.

that's probably the other way around - you (ideally) want the 10W heating element.

just to clarify from your earlier post;
this --> https://www.sparkfun.com/products/10213
does not "provide" the current - it *controls* it - the current comes from the power supply unit. (battery, wall-wart, etc.)
Thank you very much!
Title: Re: Transistor
Post by: Liz0905 on Feb 23, 2018, 02:26 pm
250W is crazily high and will burn you.
1W will do nothing.
So 10W is about right as a starting point for designing a warmer like this.  Perhaps it should be 20W,
perhaps not, you need to experiment.  Remember a lot of soldering irons use 40W or less...
Ok, thank you. so for my purpose I can use five heaters with a power of 10W. If I want to power an Arduino with an external battery, Will the next battery be enough for me

https://www.aliexpress.com/item/UNITEK-USB-9V-rechargeable-lithium-ion-battery-1200mAh-6F22-li-ion-cell-for-wireless-microphone-Guitar/32822609362.html


And would I need a transistor for each element? Suppose I use all the heaters simultaneously. Should I connect the heaters in a circuit? So that they are independent of each other
Title: Re: Transistor
Post by: ChrisTenone on Feb 23, 2018, 05:09 pm
What are the gloves to be used for - I suspect that the insulation is as important as the heat source.
Title: Re: Transistor
Post by: Grumpy_Mike on Feb 23, 2018, 06:31 pm
Quote
Will the next battery be enough for me

https://www.aliexpress.com/item/UNITEK-USB-9V-rechargeable-lithium-ion-battery-1200mAh-6F22-li-ion-cell-for-wireless-microphone-Guitar/32822609362.html
No.

Quote
so for my purpose I can use five heaters with a power of 10W.
That is 50W, this requires a current of about 5.5A. That looks way too much for that battery, even if it was not then at 1.2Ah it would last at the most 13 minuets and probably not more than 8 or 9 minuets in practice.

I would have thought 50W in a glove is way too much. What is the purpose of this glove? It makes a big difference. My 50W soldering iron is quite big, you can solder with a 25W iron or even a 15W one.
Title: Re: Transistor
Post by: Liz0905 on Feb 23, 2018, 08:05 pm
What are the gloves to be used for - I suspect that the insulation is as important as the heat source.
I want to measure the temperature of a finger and warm it if the temperature falls below a certain threshold
Title: Re: Transistor
Post by: Liz0905 on Feb 23, 2018, 08:16 pm
No.
That is 50W, this requires a current of about 5.5A. That looks way too much for that battery, even if it was not then at 1.2Ah it would last at the most 13 minuets and probably not more than 8 or 9 minuets in practice.

I would have thought 50W in a glove is way too much. What is the purpose of this glove? It makes a big difference. My 50W soldering iron is quite big, you can solder with a 25W iron or even a 15W one.
ok i got it. what about those:

https://www.ebay.com/itm/PTC-heating-element-60-1-2-5W-12V-consistant-temperature-ceramic-Thermostatic-/152897933551
Title: Re: Transistor
Post by: JohnRob on Feb 23, 2018, 08:55 pm
Hi,

The
Quote
https://www.ebay.com/itm/PTC-heating-element-60-1-2-5W-12V-consistant-temperature-ceramic-Thermostatic-/152897933551
is designed to always be at 60 °C, much too hot for skin.

I did some work with PTC heaters a few years back and they are great for constant temperature, however I've not seen any where the transition (control) temperature is low enough to be useful for contact with humans.


I've not been following closely but have you looked at flat silicone heaters?




Title: Re: Transistor
Post by: Liz0905 on Feb 23, 2018, 09:57 pm
Hi,

The  is designed to always be at 60 °C, much too hot for skin.

I did some work with PTC heaters a few years back and they are great for constant temperature, however I've not seen any where the transition (control) temperature is low enough to be useful for contact with humans.


I've not been following closely but have you looked at flat silicone heaters?





Because I'm really new to the whole thing, I did not even know which way to look
Title: Re: Transistor
Post by: JohnRob on Feb 24, 2018, 12:13 am
HI,

This is not the place you would normally purchase a flat heater but it gives you an idea.

Silocone heaters (https://www.omega.com/pptst/SRFR_SRFG.html)


They could also be flat Kapton heaters.


For a practical understanding of watts and heat look for one of these "GE 4-Watt Nightlight Incandescent Light Bulb".   You can hold it in your hand and get a "feel" of what 4 watts will be like.

Title: Re: Transistor
Post by: allanhurst on Feb 24, 2018, 01:30 am
I guess that these heated gloves might be for a motorcycle.

In which case there is no power supply problem.

Commercial products are freely available - why not investigate these?

Allan
Title: Re: Transistor
Post by: Liz0905 on Feb 24, 2018, 09:03 am
I guess that these heated gloves might be for a motorcycle.

In which case there is no power supply problem.

Commercial products are freely available - why not investigate these?

Allan
The project is part of my studies and one of the goals is to create something that does not exist something that is exactly the same
Title: Re: Transistor
Post by: allanhurst on Feb 24, 2018, 10:33 am
Quote
create something that does not exist something that is exactly the same
??

They do exist, and have been developed over many years.

Do you have a much better approach?

A

Title: Re: Transistor
Post by: Liz0905 on Feb 24, 2018, 12:14 pm
??

They do exist, and have been developed over many years.

Do you have a much better approach?

A


Of course they exist and I studied them, the goal is to use components that are not used in warming gloves available in the market
Title: Re: Transistor
Post by: allanhurst on Feb 24, 2018, 12:49 pm
All such gloves use resistive elements of some sort - normally NiChrome wire, but any power dissipating element would do ..... 

eg a Pentium processor.

NiCr is cheap and effective.

For temperature sensing a thermistor is the obvious device.


Allan
Title: Re: Transistor
Post by: ChrisTenone on Feb 24, 2018, 04:01 pm
Quote from: allanhurst
... eg a Pentium processor.
Cool! You could recycle old, unwanted computers as hand warmers.

Quote from: allanhurst
... For temperature sensing a thermistor is the obvious device.
Wouldn't a device like a TMP36 (such as this one (https://www.adafruit.com/product/165)) be even simpler to use?
Title: Re: Transistor
Post by: allanhurst on Feb 24, 2018, 04:10 pm
TMP36...

Sure,

There's a hundred ways to skin a cat.

I bought 100 10k thermistors for £1.  Though I don't intend to control 50 pairs of gloves.

You don't need an arduino for this job - a simple bit of analog will do.

Ramp generator ( 555? ) , comparator , reference volts source.and power switch device

Allan
Title: Re: Transistor
Post by: ChrisTenone on Feb 25, 2018, 05:03 pm
Of course you are correct - that would certainly be the most cost-efficient to build heated gloves. But that isn't the theme here. It seems our OP wants to make something DIY with parts on hand. And Arduino control has easy appeal. But with 50-250 watts of power inside an insulated glove, I wonder what it's actual use would be.
Title: Re: Transistor
Post by: allanhurst on Feb 25, 2018, 06:03 pm
The ancient LM10, designed by Bob Widlar, would be ideal for this job.....

but I share your puzzlement over the application.


Any help.OP?


Allan
Title: Re: Transistor
Post by: posbuild on Sep 11, 2018, 11:50 pm
250W is crazily high and will burn you.
1W will do nothing.
So 10W is about right as a starting point for designing a warmer like this.  Perhaps it should be 20W,
perhaps not, you need to experiment.  Remember a lot of soldering irons use 40W or less...
I'm intrigued by the project and wanted to see what I could make and get a feel for what wattage a glove heater might need to be. I etched a heater from polyimide film using material that I requested for free from Dupont's website:

http://www.dupont.com/products-and-services/membranes-films/polyimide-films/sample-request-kapton.html (http://www.dupont.com/products-and-services/membranes-films/polyimide-films/sample-request-kapton.html)

The heater I made was this spiral thingie (see picture below) that I then cut up to be one long heater. It has a resistance of 3.5 ohms. It is just long enough to wrap around each of five fingers.

(https://forum.arduino.cc/index.php?action=dlattach;topic=530255.0;attach=273839)

I'm powering it with an old weedeater battery that limits current to 1.5A. The battery is 20V so I'm using a buck converter to take it down to 6V.

To test I wore a thin cotton glove and then wrapped one finger with the heater and turned it on. I could feel it warm up quickly but didn't get too hot. If I put this assembly inside of a winter glove I think it would work even better. At 9 watts it's just right for my tastes.

(https://forum.arduino.cc/index.php?action=dlattach;topic=530255.0;attach=273837)

A thought I had was to adhere the polyimide heater to the glove with thermal glue and then spray it with plasti-dip to give it a rubber coating and make it more water resistant. It would sort of be a hybrid of two different flexible heaters (https://farnam-custom.com/custom/flexible-heaters/).
Title: Re: Transistor
Post by: MarkT on Sep 12, 2018, 12:41 pm
You heated glove prototype is much more efficient at heating the air than your hand.  The outside of
the heater coil should be well insulated thermally, and the power can then be dropped.
Title: Re: Transistor
Post by: posbuild on Sep 12, 2018, 11:15 pm
You heated glove prototype is much more efficient at heating the air than your hand.  The outside of
the heater coil should be well insulated thermally, and the power can then be dropped.
Nice. I wonder how low I could go with power and still have sufficiently useful warming. I'll try putting it inside a good ski glove finger first and then maybe I'll try dipping or spraying with rubber.
Title: Re: Transistor
Post by: MarkT on Sep 13, 2018, 04:28 pm
I think you'll have to do some experimentation with a gloved hand in an icebox!
Title: Re: Transistor
Post by: allanhurst on Sep 14, 2018, 01:03 am
What's wrong with good ole' NiChrome wire?

Allan
Title: Re: Transistor
Post by: MarkT on Sep 14, 2018, 12:31 pm
Well nichrome wire isn't insulated so you'd need to arrange that, and its probably
overkill (you aren't needing fairly constant resistance upto orange heat!)

Steel wire has a reasonable amount of resistance, is available insulated (for garden use
like plant ties), and is cheap and tough.  Stainless steel wire also.