i try to reduce the 12v7ah sla battery to run 8" fan which required 6V, but only 1-15 ohms 2watt registor in series is work but the R is may burn within a minit. what should i do to down 12 v to 6 volt
One motor tends to go faster than the other when connected in series.
In my opinion, a PWM controller should be the best chioce as it produces less loss of power than other voltage stabiliser circuits. I'm pretty sure other people in this forum can advice you an apropriate pwm controller ic.
I agree and who cares if one turns a little faster than the other.
Another option is remove and replace 12 Volt battery with 6 Volt battery.
Yet another option is since a 12 volt battery really has six two volt batteries in it perform surgery on the 12 volt battery. Carefully drill a hole at the junction of the 3rd and 4th cells. You now have two 6 volt batteries.
Disclaimer: This is posted in humor. I really do not suggest opening a "sealed" lead acid battery! But it would work!
Using a linear regulator or resistor to drop the voltage wastes half the power so you might as well use a 6V 7Ah battery which will be half the size or a 6V 14Ah battery which will be the same size but last for twice as long.
Why doesn't the OP stick shis resistor in the air stream in front of the fan. That will keep the resistor from burning up, and it will keep herm warm, too.
Why doesn't the OP stick shis resistor in the air stream in front of the fan. That will keep the resistor from burning up, and it will keep herm warm, too.
Just use a 555 timer IC to drive a power Mosfet or transistor at 50% duty cycle. Its a simple circuit and the fan motor will care less about the being driven that way. Just make the 555 timer run at a frequency above 20KHz so no one can hear it.
use a SMPS circuit or even simpler a PWM control, you can make a decent one from a 555 IC circuit or if you want to make something more of it use a pic to generate the PWM drive
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Where are you getting the V peak and √ duty from?
I assumed that being a 6 volt DC fan its a battery powered. So a 50% PWM duty cycle of 12 volts gives a 6 volt average as far as a DC motor is conserned.