12v Fan Variable Speed in every Minute interval using 555 timer

Hi guys,

I know its to much , Im looking for a schematic design about 12v fan that can automatically reduce its speed in a minute interval . From 100% to 60% to 30% until zero.


regards,

Genrick

You could use a 555 timer in conjunction with a CD4017 Johnson counter to sequentially change the voltage on the fan.
You would need to experimentally determine the voltage needed to give the desired change in speed since the change in speed is generally quite non-linear with respect to voltage.

What is the fan current?

Do you want the speed to stay at zero at the end of the sequence?

How will the sequence be restarted?

1 amp sir , yes sir at the end the fan will be turn off ,can you make a simple schematic circuit about this ?

why not sense hotspot temp and regulate fan speed automatically.

A 3 minute timer is possible with Johnson COunter and Emitter Follower or FET buffer with OP Amp Feedback to reference voltage created by 1 minute clock and 3 stage control but only using extremely low leakage plastic Caps and big >20MOhm resistors. using CMOS Schmitt trigger relaxation oscillator and JOhnson counter or simply using RC decay time constant of 3 minutes, which is normally difficult to achieve in ANALOG even using plastic caps.

I once designed a feedback controller using transistor driver Voltage reference for 50'C and Thermistor epoxied to SMPS hotspot ( transformer) Cost $2 in parts. The fan used 5W at full speed where driver was cool , but at half speed fan was 2.5W and driver was 2.5W so heatsink to frame with insulator was required. But it worked flawlessly using a trimpot for temperature setpoint for fan speed rise with fixed R from 50 to 55'C for 0 to full RPM.

Do you still have the schematic design sir ? Im still new to electronics , we want to use the fan as a blower to cook for rice , which every 5 minutes or less the fan well reduce its speed .

genwockz said:

.................. , we want to use the fan as a blower to cook for rice , which every 5 minutes or less the fan well reduce its speed .

Click to expand...

Initially you said a minute interval, but now you want 5 minutes?
What is the maximum time interval you need?

Hi,

Have you seen the 558 ring counter schematic? It's on page 5 of the datasheet. The not very good version of the 555, the 558.

View attachment Timer 558_3 ne NXP.pdf

What V is avail?

Here is a simple method, to give the load full 12V at power-up, then gradually decline over a few minutes.

The capacitor carries bias current to the darlington transistor. As the capacitor charges, it blocks bias current more and more.



The 1M resistor has the purpose to discharge the capacitor between uses.

You can try various values for the capacitor and potentiometer, until you get the desired taper.

- - - Updated - - -

The above is a resistive drop method. It wastes power. The main transistor will need to dissipate upwards of 3W for a minute. It will need heatsinking.

There is a more efficient way to slow down the fan, by sending pulses of current, at a long duty cycle to start off, then shorten the duty cycle. To do this job, you can use a 555 IC, op amp, and transistor.

I'm too slow... Brad has a nice, simple and effective solution there, looks good, I'd go with that one.

The pdf is a schematic using 3 555 timers and a 4017 to cycle through 100 seconds * 3 (5 minutes total); in theory (never tried that specific circuit) could be on all the time cycling, or just once. Sunny is right - the 555 is not precise enough for exactly five minutes when you need to use large values I suspect, but fine for approx. five mins., that's why I divided it down into three lots of 100 seconds. You'd need to calculate/experiment with the timing components and the transistor resistors yourself.

View attachment timer - Schematic.pdf

crutschow said:

Initially you said a minute interval, but now you want 5 minutes?
What is the maximum time interval you need?

Click to expand...

Sorry sir , 5 minutes interval 4 stages of change in speed.

Although Fans tend to be constant current in midrange as voltage is reduced, max power dissipation in driver is at half voltage, equal to fan power at that speed. Then stall voltage may be around 20% where coil will heat up a bit since there is no moving air, but not for long as current drops.

We assume power is still on while heater is off.

genwockz said:

Sorry sir , 5 minutes interval 4 stages of change in speed.

Click to expand...

But is that 5 minutes for the 4 stages of change or 5 minutes between changes?