Switching 12VDC, 5 minutes ON and 30 minutes OFF?

Question

I need to provide power for 5 minutes and then turn it off for 30 minutes and then again 5 minutes ON, 30 minutes OFF, for 2-3 days. Power is provided from the car battery 12VDC, less than 10 amps.
Thanks,

I need it to automatically switch on and off and I have 555 timer. Does anybody have any plans?

I tried to use LM555 - ASTABLE OSCILLATOR CALCULATOR on this web page
http://home.cogeco.ca/~rpaisley4/LM555.html
with
R1=220k ohm
R2=39k ohm
C1=10000 microF
and 10A relay from Radio Shack
http://www.radioshack.com/product/index.jsp?productId=2062482&cp=&sr=1&origkw=relay&kw=relay&parentPage=search
I connected the output of the circuit to NC on the relay and it worked. There was no electricity flowing when the circuit is on. But it doesn't release after 30 minutes. Actually it never releases. I let it for couple of hours and nothing happened.

Answer 1

There are LOTS of 555 timer circuits on the net.

The OFF for 2-3 days is the tough part... in order to find an RC time constant for 2 days, the current would be lower than the 555 input current required.
Email me, for a few bucks I can program a PIC chip to do this. It will be accurate within a few minutes after 2 days.
[e-mail]

I just read your question again... I think a 555 might work after all. You want ON for 5 minutes, OFF for 30 minutes and repeat for 2-3 days (ie about 48 cycles) right?
Design your 555 circuit RC for 5/30 then send the output to drive your load and a 4040 or 4024 counter... use some diodes and a transistor to logically AND the Q5 & Q6 to get a count of 48... tie the output to the 555 RESET. Now just reset the 4024 chip and the 555 causes the 5/30 for 48 cycles.
Write me, I can draw it and scan it.

Answer 2

Not counting the current draw of what ever is being turned on an circuit cotinously running for 72hrs on a 10 Amp-Hr battery would have to draw less than 138mA..

Using 555 timer IC would require cascading several to get long periods and these long time intervals would be difficult to accurately set.

You can use a 555 as a clock (frequency) source and generate a 220Hz freq which you can feed to either a series of counters or a programmable counter/divider. The idea is to use logic circuits to accurately count a clock frequency to provide a pulse once every 5 minutes. Count this 5min pulse with another counter chip and use a 3to8 or 4 to8 decoder chip. The output of the decoder will shift once every five minutes, The first output on the decoder will be used to trigger the device for five minutes, the next 6 are used to pause and the 8th is used to reset the count back to the first starting the unit again.

220Hz * 60sec * 5 = 66000 pulses
Divide this number of pulses by 16 four times and you will get a single pulse approx once every 5 minutes.

If power consumption is a problem consider a micro controller using a watch dog timer to wake from sleep once a minute. This would be ideal as its standby power draw would be less than 5mA. Each time the uC wake it increments a counter by one and controls an output for your 5on 30 off duty cycle.

A more robust solution and possibly the most expensive is to use a PLC. (About $300 for a 12Vdc Ge Fanuc micro PLC).
The advantage is that it is nearly ready to go and is easily programmed in ladder logic and will absolutely work compared to circuits that you have to develope

Answer 3

The total power of the battery is :

P = V I = 12x10 = 120 watts

Since you want to use the car battery for a max of 3 days, and use the battery for 5 minutes every 35 minutes, then you will switch on and off the battery for:

Number of on/off = 3x24x60/35 = 123 approximately

Total time the battery is being used is t:

t = 5 x 123 = 615 minutes = 10 hours approximately

Therefore, the total consumption of energy (W) in 3 days is:

W = Px t = 120 x 10 = 1200 watt-hour = 1.2 kilowattt-hour

Suppose that the cost of each kilowat-hour is 50 cent

Then cost of this amount of energy is = 60 cents

Which I assume is within the budget. So go ahead and connect your car battery to your electric device the way you want..

Answer 4

How accurate? What's your budget?

Use a C555 timer and a large MOSFET.
All parts can be purchased at your local radio shack.

Cost is about $20

Answer 5

555 and a relay.
http://www.kpsec.freeuk.com/components/relay.htm
555 drives a relay with a transistor + diode.
just get a relay that handles 10 amps....

Answer 6

What's the question?. Buy a toggle switch and some wire.