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MarkT

If you drain a PP3 sized 9V alkaline battery at 0.5A most of the heat ends up in the battery due to the
large internal resistance.  Also you won't get anything like the capacity as you would at the 10 hour
discharge rate (which is usually what the datasheet has).  Maybe 1/2 or 1/3rd of the nominal capacity.

The simplest and most efficient way to use a 9V battery as a heater is short it, possible with PWM
control signal!
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

allanhurst

ie your project as stated is impossible.

Allan

TomGeorge

Hi,
Have you got those heater units?
If so what is their resistance?

Tom.... :)
Everything runs on smoke, let the smoke out, it stops running....

allanhurst

The spec is a ptc resistor of 5 -50 W.  Designed to reach 220C

Supply volts 12.

So presumably resistance varies from ( 12^2/ 50) =>2.88 ohms  at say 20C to 28.8 ohms at 220C


You won't drive that with a little 9V block battery with any technology I know.

Allan


Liz0905

The spec is a ptc resistor of 5 -50 W.  Designed to reach 220C

Supply volts 12.

So presumably resistance varies from ( 12^2/ 50) =>2.88 ohms  at say 20C to 28.8 ohms at 220C


You won't drive that with a little 9V block battery with any technology I know.

Allan


Can I connect 3 Li-ion batteries 3.7V 2000mAh serial connection?

thank you!

TomGeorge

#20
Mar 02, 2018, 11:31 pm Last Edit: Mar 02, 2018, 11:42 pm by TomGeorge
Hi,
  • What is the application?
  • What are you heating?
  • What is the temperature you are trying to attain?
  • Do you aim to have temperature feedback to control temperature?
  • Are you aware that this not a "normal" resistive type heater?
  • Are you aware that its resistance changes over a relatively large range with temperature, unlike most heater elements?
  • Do you know what PTC means, (Positive Temperature Co-efficient)?




Thanks ...  Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

TomGeorge

Hi,


Quote
Polymer PTC heating elements

A flexible PTC heater made of conductive rubber
Resistive heaters can be made of conducting PTC rubber materials where the resistivity increases exponentially with increasing temperature.[1] Such a heater will produce high power when it is cold, and rapidly heat up itself to a constant temperature. Due to the exponentially increasing resistivity, the heater can never heat itself to warmer than this temperature. Above this temperature, the rubber acts as an electrical insulator. The temperature can be chosen during the production of the rubber. Typical temperatures are between 0 and 80 °C (32 and 176 °F).

It is a point-wise self-regulating heater and self-limiting heater.[clarification needed] Self-regulating means that every point of the heater independently keeps a constant temperature without the need of regulating electronics. Self-limiting means that the heater can never exceed a certain temperature in any point and requires no overheat protection.
Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

allanhurst

#22
Mar 03, 2018, 12:36 am Last Edit: Mar 03, 2018, 01:00 am by allanhurst
If you are ( as I previously guessed and you half confirmed ) trying to make better electrically heated
gloves for motorcycle use there are some sums to do.

Firstly the power required.
 
This depends on the temperature you wish to maintain the hands at , the external air temperature, the air speed , and the thermal insulation properties of the glove materials

Secondly the difference in power per unit area required in various areas of the glove - obviously the extremities such as the fingertips require a higher rating.

I'm sure the existing manufacturers have made measurements of all the unknowns above to come up with a practical product.

Materials such as the PTC conductive rubber suggested by Tom may be useful.

But if my guesses are correct, why would  you want independent battery power? - a modern motorcycle has a powerful alternator and wouldn't even  blink at this small extra load.

Even if perfectly controlled, your 3 x Li 2AH cells would only power such a pair of gloves at 10 watts  each for about an hour . I've done much longer journeys than that in wintertime on a motorcycle.


Allan

Liz0905

Hi,
  • What is the application?
  • What are you heating?
  • What is the temperature you are trying to attain?
  • Do you aim to have temperature feedback to control temperature?
  • Are you aware that this not a "normal" resistive type heater?
  • Are you aware that its resistance changes over a relatively large range with temperature, unlike most heater elements?
  • Do you know what PTC means, (Positive Temperature Co-efficient)?




Thanks ...  Tom... :)
1.I need to create a heating gloves
3.I try to reach a temperature of 40 degrees
4.for temperature feedback i use the lm35
5.Those are my heating elements when i use the 12V:

https://www.aliexpress.com/item/5pcs-PTC-heater-heating-element-Consistant-Temperature-Ceramic-12V-24V-220V-80-270degree/32804641053.html?spm=a2g0s.9042311.0.0.jwrxbG



So in my plan I thought to use three 3.7V 2000mAh batteries, connecting them a serial connection. Five lm35 sensors connected to analog outputs. 5 MOSFET n channel transistors are connected to PWM outputs and connected to my heating elements.

Thank you so much!

Liz0905

If you are ( as I previously guessed and you half confirmed ) trying to make better electrically heated
gloves for motorcycle use there are some sums to do.

Firstly the power required.
 
This depends on the temperature you wish to maintain the hands at , the external air temperature, the air speed , and the thermal insulation properties of the glove materials

Secondly the difference in power per unit area required in various areas of the glove - obviously the extremities such as the fingertips require a higher rating.

I'm sure the existing manufacturers have made measurements of all the unknowns above to come up with a practical product.

Materials such as the PTC conductive rubber suggested by Tom may be useful.

But if my guesses are correct, why would  you want independent battery power? - a modern motorcycle has a powerful alternator and wouldn't even  blink at this small extra load.

Even if perfectly controlled, your 3 x Li 2AH cells would only power such a pair of gloves at 10 watts  each for about an hour . I've done much longer journeys than that in wintertime on a motorcycle.


Allan
Hey Allan I have no idea where you assumed I was making a glove for motorcycle riders. I make a glove for patients with a particular syndrome that only fingertips need to be warmed, right now without considering heat loss and external spirits

Thank you!

MarkT

If you told us the full details, we wouldn't have to keep second guessing.  Just the fingertips is very very
different from a full heated glove, about 10 times less power is needed for one thing.

I have some questions:

Heat up to 40C from what ambient temperature?

What response time to reach target temperature?  Or is that a steady-state temperature to be
maintained.

Indoors or outdoors or both?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Liz0905

If you told us the full details, we wouldn't have to keep second guessing.  Just the fingertips is very very
different from a full heated glove, about 10 times less power is needed for one thing.

I have some questions:

Heat up to 40C from what ambient temperature?

What response time to reach target temperature?  Or is that a steady-state temperature to be
maintained.

Indoors or outdoors or both?

thank you,

The heating should start immediately and the temperature is relative to the finger temperature
outdoor only

allanhurst

Quote
the temperature is relative to the finger temperature
Oh really?


If you maintain the heated element eg 3C above the finger temp, it will increase temperature indefinitely.


Not the way to go.

Allan

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