Electronic circuits & projects forum - Need help with electronic circuits & projects?

[MikeT]

I have seen a circuit on the 'net that provides power to a 12Vdc motor when activated. It's job is to start the motor slowly and progressively build up to full power over time. I'm not sure but I think it accomplishes this using pulse width modulation.

It would be smart if it could provide power relative to an RPM input.

[MikeT]

Sorry, I forgot to ask the main question!
Can anyone point me to a diagram for such a circuit so I can build my own?

[MikeT]

I found a similar cicruit that ramps the power to an LED up or down, according to a button press but I can't post PDF's here to show it.

How can I post the file please?

[pebe]

I think it will work if you post in the web page like this:

http://www.electronic-circuits-diagrams.com/forum/

[MikeT]

Unfortunately, I didn't bookmark where I downloaded the PDF from so I cannot add the URL but I can zip the PDF.

Having said that, I think I might have found a better circuit, or rather a dedicated IC. Not sure yet, as I didn't study the datasheet fully - hopefully tonight.

[lem787]

Hey Mike. I'm a bit reluctant to download .zip files so i've not looked at the PDF but I did draw out a circuit earlier that I think will do the job. A press of the UP button will cause the motor speed to rise from zero to full speed. The DOWN button will do the opposite!

The values depend on your specific requirements so I haven't drawn them in but here are some basic values..

R1 100K, R2 100K, R3 47K, R4 4K7, R5 4K7, R9 220R, R10 10K, R11 10K
C1 10nF, C2 100nF, IC1 LM324N, IC2 NE555N

These values will give you a PWM frequency of about 400Hz. R8 and C3 set the time it takes to rise/fall from zero to full speed. 22K and 100uF will set a time of about 2 seconds. A 100K pot instead of R8 will let you adjust it between 0 and 10 seconds. R6/R7 set the gain of the triangle wave from which the PWM is produced. This gain can be left at unity but you may notice a delay. Again, you can replace R7 with a 100K pot and fix R6 at 100K. I've drawn the wrong symbol but the FET in series with the load should be an N-Channel HEXFET type with internal diode, like an IRF530. If you're driving an inductive load there should really also be a 100nF cap and diode in parallel with the load (diode reversed of cource).

Hopefully this will be of some help!

[MikeT]

Hi Lem,

Sorry about the zip, I fully understand your reluctance but I can promise you there's nothing but the PDF there.

Either way, perhaps I should have better explained the application first

I have a 12vDC water pump (~7A when running) used for cooling my diesel engine that is currently activated by a preset-able turbo boost pressure switch (hobbs switch?).

Rather than have the pump start at full pressure when activated, I would very much like the pump to gradually increase to full power, either automatically over a configurable time (several seconds) or even better, in repsonse to an analogue signal such as the RPM.

Such kits are known as Progressive Controllers but command a high price, hence my DIY request. What I don't understand is the methods used to achieve progressive control as some use Pulse Width Modulation (such as fuel injectors) but I'm unsure if motors (such as my water pump) require a different method? Perhaps the issue is further complicated by the in-built "pressure regulator" which switches the pump out when a certain pressure is reached? I don't know, just trying to provide as much info as possible.

[lem787]

[MikeT]

Hi Lem, sorry if I've misunderstood you. I don't need the down ramp, just the up one and rather than pushing and/or holding a button to activate the circuit I would like the pump to be progressively controlled from a source such as the engine RPM signal (pulses per second) or turbo boost pressure (which I guess would require additional circuitry?) if possible, otherwise just a normal (automated) on/off signal will suffice.

The "matched" progression is also a poor descriptor, sorry for my inadequacies of expression..... I mean, if using a boost pressure sensor, I would like the pump to start delivering when, say 5psi is sensed and increase proportionately as the pressure rises to full power at 20psi. Or from 2000rpm to 5000rpm. It does not have to be accurate, just progressive.

Thanks for your time.

[pebe]

Hi Mike,

I don't understand the last bit of your statement, 'Or from 2000rpm to 5000rpm'.

Are you saying you want the boost pressure sensor to control the motor speed withing those limits - rather than control the PW ratio?

[MikeT]

Hi pebe,

That's my problem/fault, I have poor expressive skills.

I mean Engine RPM.

Currently, my only option is to have the water pump motor deliver a set amount of water and chose what engine rpm or boost pressure this should start at currently via boost pressure switch. Much better to vary the water flow via water pump motor control so it may be used over a wider range of engine speed or load.

As the engine speeds up, I'd like this circuit to proportionately speed up the water pump. Either that or as the turbo boost increases, proportionately increase the water delivery - whichever is easiest/cheapest?

Accuracy is not important but having the option to pump water roughly according to engine speed or load will make the system so much more efficient.

[pebe]

It sounds like a job for a PIC microcontroller. Have you had any experience with them?

[pebe]

Bump

[MikeT]

Hi pebe,

I have zero practical and almost zero theory of PICs but I do understand their purpose (computer on-a-chip, right?) and a mild tinkering of programming in years gone by. I also have very indepth knoweldge of PC hardware configuration so it's not exactly alien to me, just never dabbled.

In that case, I think you've answered this thread. I may be back for PIC related advice later. Cheers!