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Topic: How do you make the current draw from a device gradual instead of instant? (Read 888 times) previous topic - next topic

David82

I have a load activated by a button. I need it to gradually draw voltage and current as if it is being activated by a slider or knob. What simple, cheap device will do that for me up to 12v 3.5amps?

Grumpy_Mike

Look for a feature called "soft start", you fin it on a lot of power regulators and switches.

retrolefty


I have a load activated by a button. I need it to gradually draw voltage and current as if it is being activated by a slider or knob. What simple, cheap device will do that for me up to 12v 3.5amps?


That's a request I haven't seen before. Perhaps if you wired a digital output pin to a fairly large R/C network that then wires to the gate of a N channel power mosfet, it would turn on (sink to ground) rather gradually causing that slow turn on you require.

Lefty

David82


Look for a feature called "soft start", you fin it on a lot of power regulators and switches.
I'm trying but can't find anything that fits the bill

stoopkid

What exactly is your goal? There may be a more clever way of accomplishing it if there was more information.

dhenry


David82


MarkT

[ I won't respond to messages, use the forum please ]

PeterH

What sort of load is it? Perhaps you could use PWM to power it and gradually ramp the duty cycle up from 0% to 100%.
I only provide help via the forum - please do not contact me for private consultancy.

zoomkat


Can the load be PWM'd ?  What is the load?


Suspected issue:

http://arduino.cc/forum/index.php/topic,140951.0.html
Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   8)

bobthebanana

#10
Jan 12, 2013, 03:43 am Last Edit: Jan 12, 2013, 07:28 am by bobthebanana Reason: 1
I've seen it done like this before. First your load receives power through a 1 ohm resistor (fiddle with the value) and the capacitor slowly charges up to the relay turn on voltage. Once the relay latches, it and your load receive full power since the resistor is bypassed. Make sure you use a high wattage resistor.

zoomkat

Possibly a MOSFET could be controlled with increasing PWM to gradually increased the total current being supplied.
Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   8)

Grumpy_Mike

#12
Jan 12, 2013, 09:49 am Last Edit: Jan 12, 2013, 11:15 am by Grumpy_Mike Reason: 1
OP - you need to put some time measurement into that first graph, the solution depends on how long you want the ramp to take.

You also need to say if the current is AC or DC.

David82


jackrae

According to my son-in-law's father "you move the switch slowly"   :smiley-mr-green:
So much for his knowledge of electrickery

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