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| Sunbeam personal heating pad. With AC thru diode, power is 1/2, right ? H |
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| RJSV:
Hi, I have a heating pad with little controller that has failed, so I'm checking if that can be run using straight battery power, 12 V or 24 V. But I'm wondering, maybe those little controllers only output during one half of the AC input waveform (at 120 VAC input). The power would then be 1/2, correct ? That is because it's essentially only with output for 1/2 the time. Usually, when voltage is halved then so is the current, so that case power is 1/4 of full. Am I correct assuming that ? And, do some consumer type products use a triac, for controlling both AC input polarities ? I measured approx 220 ohms in the pad heater wire, so full output is about 500 mA, and that gives a power of about 60 watts, for the personal heat-pad. If it's a controller that only outputs 1/2 of the AC cycle, having simpler cheaper circuitry, then that means 30 Watts on the high setting. Am I estimating correctly, here ? Thanks. |
| RJSV:
Heating pad and connector. |
| thm_w:
Do you have the controller to open up and look at? What is the specification of the unit, it should tell you if its 30 or 60W on the box. |
| RJSV:
Thanks I'll check that. Opened up it has a controller processor and for the PC board output looks to be a pair of (3 pin) transistors for the 500 mA or whatever. Likely PWM control but I don't know if it switches, like direct off the AC Mains, or switches after some full wave rectification. I'm thinking maybe a cheaper circuit could just deal with switching only one polarity of the incoming AC waveform. I'll do some checking, thanks. |
| RJSV:
Ok, answered my own question, it's with a full-wave rectifier, so my question about AC is n/a. But, still curious, question is if you place a diode on AC Mains coming to the load, then that's going to deliver half of available power (in a simpler circuit without PWM or processor). At any rate the startling thing is, I found an assembly number, 109375N, and DATE: 2008 - 8 - 18. Wow, that was just sold maybe 2021....! |
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