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A narrower pulse width will keep the power down, better than a resistor, you want the heat were its needed.
So long as the load (heater wires) can withstand a short duration overload (the on time of the pwm switch), you can to an extent use a higher supply voltage than the load needs, with care double the supply is still practical, its a good idea to put a resistor or trimmer in series with the pwm adjustment pot to limit the max power to the load.
Temperature feedback would be tricky with gloves, I'd just stick to power control.
I am haveing a hard time finding a simple LED for this thing.. it says use a 180 ohm resistors and any LED? https://www.robotroom.com/PWM4.html I wish I had learned electronics long ago.
R(LED) < (Vcc-n*2.1-0.6)/15E-3
and
P of the resistor is P = (I^2)*R
The deal is the following:
Vcc is the power supply used.
n is the # of LEDs in series
Note: you can run out of voltage.
2.1 V is the forward voltage of a typical red LED
Note It can vary, especially by color. Generally you pick the worst drop from the spec sheet.
0.6 is an estimate of the base-emitter drop of a transistor.
Note: MOSFETS: drop nearly 0V. Another concept is used.
15E-3 is a "typical" operating current for a LED.
Note: Again, this is all over the map, 15 to 50 mA is a common spec.
By saying R(LED) is less than, I mean that resistors come in certain values. i.e. 121.3 becomes 120
The resistor used has to be able to disipate the power. 1/8, 1/4, 1/2, 1, 2, 3, 5W are common values.
Thus if you get 0.230 W, you should use a 1/4 W or higher. It's good practice to check with the resistor used.
What? I've got one board that's dissipating 2.76W into a 3W resistor (27 ohm 3W resistor with 320mA passing thru), and I'll bet you can't hold that resistor for more than 3 seconds without burning your fingers. 1W is a lot of power to dissipate, and must be done correctly. The thing about a 7W night light is just that... MOST of the power is used to produce light... only the inefficient part gives off heat.
The thing to do is what was suggested earlier... hook the full voltage across your wire (out of the gloves, preferably), and see how hot it gets, and if there is a need for control first... then work on how to control it (if needed).
Its surprising how little energy you need, if heat is being produced in an insulated environment like inside a pair of gloves with hands that are also producing heat, only a small amount of energy dissapated can make the difference between frozen fingers and comfy.
Dunno, but what I can say is that last time I tried dumping a watt through a 1w resistor it melted the solder on the board and fell out within 20 seconds.
I think its the amount of energy dissipated over the area its dissipated across.
Dunno, but what I can say is that last time I tried dumping a watt through a 1w resistor it melted the solder on the board and fell out within 20 seconds.
I think its the amount of energy dissipated over the area its dissipated across.
Nearly all batteries have a discharge rate, some rc plane ones can withstand 30c, or 30 x the amp hour capacity, a 2.2ah battery can stuff out 66 amps till its flat, the number of recharge cycles however reduces with such a demand.
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An incandescent bulb is only ~5% efficient at converting electrical energy to light, so 95% of the energy is heat.
