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Switching ON a 12Vdc motor for 15 seconds every day at a specific time

by 0505975
Tags: 12vdc, motor, seconds, specific, switching, time
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0505975
#1
Jun20-09, 03:51 AM
P: 1
Hi guys,
My problem is that i have a motor that needs to be turned ON once, every day at a programmable time and for a duration of 10-20 seconds. The power of the motor is bellow 80W.
I have searched throught the net on Merlin Gerin, Schrack and similar catlogues but can't find any programmable time switch that can run in a pulse mode and also on 12VDC (i have a batterie that has to drive the motor and the timer). Usually they have those time switches on 230Vac but i need 12Vdc... Can somebody help me??

To conclude - the facts:
- 12Vdc power supply
- once a day at a specific programmable time to turn ON the motor
- power of the motor is bellow 80W and it is running on 12Vdc also
- duration of the pulse is between 10 and 20 seconds
- it needs to be as simple as possible (in order to be also the cheapest possible)
- it needs to be ready build - not a diy thing (maybe something similar to this: http://www.hugo-mueller.com/weekly-t...,p,en,1,1.html )

thank You very much for any help You can give me
best regards
sunny
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vk6kro
#2
Jun21-09, 08:29 PM
Sci Advisor
P: 4,016
That is so specific that I doubt if you would find such a thing just by using Google.

It is not at all difficult to make one, but not if it is your first DIY project. Do you have someone who would have enough experience to make up a small circuit and connect it to mains wiring?

The easy way would be with a microcontroller. This is not as complicated as it sounds. It would just generate a 24 hour delay, put 5 volts on one of its pins, leave it there for 20 seconds and then turn it off and wait another 24 hours.
You could save a lot of complexity if you could start the process at the time you want the motor to come on one day and then it would come on at that time next day.

If you did want to program the time, you could get an garden irrigation timer and generate the 20 second power pulse from that. Again, no real problem, but you would have to know how to do it safely.
MATLABdude
#3
Jun23-09, 04:24 AM
Sci Advisor
P: 1,724
I agree with vk6kro easiest way is probably with a microcontroller, assuming you know how to program and work with one.

However, a simpler solution may be to go to your local hardware store and buy a timer power unit (the things that turn on appliances, or your block heater, etc.--anything that's plugged into it). The old-style ones have hour(ish) resolution (or possibly 1/2 or 1/4 hour), but there are newer digital ones that may be able to give you down to the minute resolution (i.e. turn on at 8PM, turn off at 8:20PM).

You can use that to turn a relay with a 120 VAC (or whatever mains voltage is where you live) coil. And then splice your 12VDC loop into the relay such that it's interrupted whenever the relay switches off.

The other thing you may be able to do is to just plug in this unit directly to the power timer itself! You mention that it's 12VDC, and something about PWM, but is it being powered from a wall adapter, or through a power supply? If it's a battery, you might be able to find a suitable DC power supply that outputs the appropriate current.

EDIT: Something like this (or a digital version; again your hardware store should carry something like it):
http://www.intermatic.com/products/t...rs/tn311c.aspx

EDIT2: Dammit, I read that as 15-20 minutes a day! Well, you could still use a similar setup, with a time delay relay set for interval timing (i.e. it fires only for a few seconds after a control pulse is applied), and you can turn it off whenever the timer is able to. For instance:
http://documents.tycoelectronics.com...=DS&DocLang=EN

TurtleMeister
#4
Jun23-09, 10:01 AM
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P: 744
Switching ON a 12Vdc motor for 15 seconds every day at a specific time

MATLABdude, I think you need to read the op yet again. He clearly states that he needs to run the timer on the same 12vdc supply that runs the motor. I cannot think of an off-the-shelf solution for this either. As already stated, this would be an easy microcontroller project.
RonL
#5
Jun23-09, 10:27 AM
PF Gold
P: 702
Quote Quote by TurtleMeister View Post
MATLABdude, I think you need to read the op yet again. He clearly states that he needs to run the timer on the same 12vdc supply that runs the motor. I cannot think of an off-the-shelf solution for this either. As already stated, this would be an easy microcontroller project.
I have several inverters, 12 Volt to 120V (smallest is 40 Watts), a simple 2:1 stepup transformer will give 240V. If the OP is not able to connect a few wires, then a EE student, or local electrical service should be able to build the system.

Just a matter of connecting a few wires.
vk6kro
#6
Jun23-09, 11:02 AM
Sci Advisor
P: 4,016
The microcontroller still seems like the best bet to do precisely what was asked.

However, if the motor could run for 1 minute instead of 20 seconds, my sprinkler timer will give 1 minute turn on times. You can set an exact time to turn on. You can set it to turn on every day.

It runs on 24 volts AC but this is quickly converted to 5 volts internally so it would already run on 12 volts DC with slight modification. And it switches the sprinkler solenoids on with the same 24 volts AC via a relay, so it could switch 12 volts as well.

Depends on why the motor was being turned on and if 1 minute would be OK.
pantaz
#7
Jun23-09, 02:31 PM
P: 588
Have you looked into "timing relays"? I've seen them in the McMaster-Carr catalog.
MATLABdude
#8
Jun23-09, 03:57 PM
Sci Advisor
P: 1,724
Quote Quote by TurtleMeister View Post
MATLABdude, I think you need to read the op yet again. He clearly states that he needs to run the timer on the same 12vdc supply that runs the motor. I cannot think of an off-the-shelf solution for this either. As already stated, this would be an easy microcontroller project.
MATLABdude is a MATLABdud, and fails at reading comprehension. That's probably what happens when you're running on 0.5 to 4 hours of sleep a night for a week.


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