Ken,

Thank you for the schematic. I finished the build and the timer is working. I do still have two issues to sort out.

The timer does not reset at power on. I had to manually reset by grounding D. I think the AC coupling will fix that but I am not sure?

The other issue is the relay. I got an 80mA relay, measured 160 ohm resistance at the electronics store which is greater than 120ohm as you mentioned. The relay works perfectly with a test light, but when I connect the motor the relay clicks at the right time, but does not always grab the first time. Sometimes it takes two or more timing periods for the motor to start. The circuit measures 15.2 without load, and 11.7 when the motor starts (11.2 with motor and test light). I used a power strip for testing that has an on/off switch to simulate the pool timer on/off for convenience to isolate the monostable Ramsey timer first.

How do I solve this issue? Will a 40mA relay work correctly? Does the relay have too much resistance or not enough?

An interesting observation on timing and power on with relay... The relay has two switch positions on/off (1, 3). If I connect the device to pin 3 the timer powers device for X time and stops. If I connect the device to pin 1 the timer delays powering the device for X Time and then the device is on (monostable). These results were seen manually resetting the timer. Thus there are two ways I could get my correct 20 second output will 1 minute of power from pool timer: timer output3 = power on 20 seconds, stop power and; timer output1 = timer delays power on 40 seconds, power on/power off in 20 seconds by pool timer.

I used a power strip for testing that has an on/off switch to simulate the pool timer on/off for convenience.

So far, I am very happy with the results and see success just ahead...

Jeffrey

 

The timer does not reset at power on. I had to manually reset by grounding D. I think the AC coupling will fix that but I am not sure?

When I tried it with a mock power supply with a large filter cap and no major bleed path, I am getting the same thing. If I just disconnect the DC power it always works. I'll have to look into that...as time permits.

The other issue is the relay. I got an 80mA relay, measured 160 ohm resistance at the electronics store which is greater than 120ohm as you mentioned. The relay works perfectly with a test light, but when I connect the motor the relay clicks at the right time, but does not always grab the first time. Sometimes it takes two or more timing periods for the motor to start. The circuit measures 15.2 without load, and 11.7 when the motor starts (11.2 with motor and test light). I used a power strip for testing that has an on/off switch to simulate the pool timer on/off for convenience to isolate the monostable Ramsey timer first.

How do I solve this issue? Will a 40mA relay work correctly? Does the relay have too much resistance or not enough?

My first guess is that when the relay turns ON, powering the motor, the high motor "starting current" is pulling down the power supply voltage (faster than your meter can measure), tripping out the relay and shutting off the motor, letting the voltage rise, allowing the relay to pull in again...and repeating over and over. You may need a heftier power supply and/or one with a 12V regulator.

An interesting observation on timing and power on with relay... The relay has two switch positions on/off (1, 3). If I connect the device to pin 3 the timer powers device for X time and stops. If I connect the device to pin 1 the timer delays powering the device for X Time and then the device is on (monostable). These results were seen manually resetting the timer. Thus there are two ways I could get my correct 20 second output will 1 minute of power from pool timer: timer output3 = power on 20 seconds, stop power and; timer output1 = timer delays power on 40 seconds, power on/power off in 20 seconds by pool timer.

Good observation!

 

Sounds like you have most of it figured. The CD4060 isn't obsolete, not according to page addendum Page 1. Good luck!

 

The timer does not reset at power on. I had to manually reset by grounding D. I think the AC coupling will fix that but I am not sure?

I think I've got this. It appears that when you turn on the wall wart, the output voltage rises relatively slowly (you need a scope to see it) because of the filter capacitor. Because of this slow rise and the short time constant of R2/C2 the trigger ground is gone before the chip is powered up.

Two changes:

1: Replace C2 (0.01uF) with a 10uF/35V electrolytic capacitor. Note that this one is polarized. See this schematic and drawing for the proper installation.

2. The circuit requires that the power supply be at zero DC volts before it will trigger again, and because there is so little current drain after the power is removed, I recommend adding a bleeder resistor (RL) between +12 and common. This will drop the power supply voltage more rapidly after the one-minute disconnect. Because you were looking at 12 hours between triggers, it may not be absolutely necessary, but it will help a lot in bench testing.

Ken

 

Thank you!

Going to the get parts now. I also picked up two extra trim pots, 250k and 500k. Since the 250k is zero seconds on one end and 60 seconds at the other, I should have more flexibility during the 1 minute of power. I played with the 100k trim pot during bench testing and got exactly 20 seconds.

Jeffrey

 

I picked up a new power supply. The old one was 7W, 300mA. The new one is 40W 3A. The new one has some type of peripheral plug (for a laptop maybe?) and some kind of electronic part in series next to the peripheral plug. Is that some kind of voltage conditioner or regulator? I have to splice the peripheral plug off to use the power supply. Should I keep the cylinder shaped piece in series between the transformer and the timer?

Thanks,

Jeffrey

 

I measured the voltage of the new power supply without load at 12.06V. With load still 12V. I measured with the cylindrical bit and without it at 12.06V. So it doesn't appear to be a critical piece.

The change of C2 to 10uf 25V makes the timer reset. Good news.

Relay trips perfectly with test light. Good news.

Relay still does not want to trip with motor, but the timer did reset like it was supposed to. Mixed news.

I changed the power supply from the new one back to the old one, and mixed up positive and negative. Puff of smoke. Definitely bad news.

The timer is no longer working. That puff of smoke was probably the 555 chip.

I will be at the parts store at 9am tomorrow. Do you think anything else beside the 555 chip fried? I know how to measure the resistors. How do I measure the capacitors? and the transistor Q1?

The relay I bought yesterday was labeled incorrectly by the store. The actual part says 12V 10A, but store said it was 12V 5A. The resistance measure 160. I bought another relay that is actually 12V 5A which tested at 160 ohm resistance. I did not get to test it on the circuit before I fried the kit. Would the 10A be a reason for clicking? The motor and power supply are 3A and the Ramsey 555 kit is specified to drive a 100mA load.

Also, I did not put the bleeder on. Could that be what smoked the circuit? I was on my third or fourth bench test when the incident happened. I quickly disconnected the power, but I am pretty sure that reversing the polarity was the issue, not the lack of bleeder. Lack of bleeder, would just stop it from resetting, correct?

Thank you for watching this episode of "One Circuit to Fry". Stay tuned as "fearless Jeffrey" reloads and goes back to action. <Smiles>

Jeffrey

 

The 5A or 10A is the current rating of the relays' contacts.

The bleeder resistor would not have helped in the case of polarity reversal.

Ken

 

Ken,

Can you please for me a schematic for using two 12v supplies? One for the motor 40w and one for the timer 7w?

 

Here ya' go.

Ken

 

Thank you!

What kind of software do you use to draw schematics? Is there a freeware that I can download?

I am hooked. I bought a protoboard and connecting kit, and double quantities of the chips, R, C, Q, etc. to try more circuits. I got two Lm556 16 pin chip to try that other timing scenario you told me about with 12 hours and x2, x3, etc.

 

Jeffry,

I use ExperssPCB. It's free, easy to use, has a good parts library, and easy to create your own custom parts (like the wall wart transformers).

http://www.expresspcb.com/

It also includes a free PCB layout package, but you can only have the printed circuit boards made through them.

ken

 

Ken,

Would a standard household plug socket conduct 12V? I was thinking that I could connect the 40W 12V supply to a socket and have two receptacles of 12 DC power for the timer and motor instead of two power supplies. The 40W has more than enough power for the timer and motor, I would just need to split it into two isolated paths?

 

That would be doing the same thing as before. Paralleling the wires does not isolate the circuits. Are you thinking of separately fused parallel circuits as in a car? The problem is that if the motor is pulling down the transformer voltage enough to starve the relay, it will do that no matter how you connect the two parts of the circuit to an "inadequate" transformer/power source. You need either two separate power sources...or...one power source that can maintain 12V under the high starting current of that motor. That would be a "regulated" power supply.

Ken

 

Ken,

With a 3amp motor, is the 3amp power supply (40 Watt) inadequate? How do I measure the pulling down factor?

 

Because of the high starting currents, several times the running current, a 3 amp motor on an "unregulated" supply will pull down the voltage a lot as it starts, but recover after that. Your timer and relay won't tolerate that.

Ken

 

Thanks Ken. Setting it up with two power supplies will get me through this project. If I was designing a better model, I probably would want to use a startup capacitor or something like that?

 

Hello Friends,

I completed my circuit. Many thanks to Ken and this site.

Life is good!

Jeffrey