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HELP! 555 timer to control pump

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I am new to electronics, so I apologize for my ignorance.

I working on a project that involves emptying a small tank of water using a solenoid valve. The valve is opened for a certain amount of time by using a 555 timer and a reed relay. When this timer goes low, the valve is closed, and another 555 timer turns on a 12V pump (again via reed relay). I have the 2nd timer set up so that it will run much longer than I actually need it to. When the water reaches a wire at the top of the tank (connected to pin 4 on 2nd 555 timer), I want the pump to cut off.

The problem I'm having is that the pump draws a lot of current, which seems to drop my supply voltage, which triggers the first timer. This results in the valve just opening and closing (pump never comes on).

From what I've read, I think I need some decoupling capacitors. I've tried this, but my circuit still behaves irradically.

Any suggestions?

Thanks in advance.


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Thanks for the advice. I'll try it. The "dip" in voltage seems to be only a transient that lasts while the pump is starting up until it gets to its steady state running condition. I'm not sure what value of capacitor I should use. I suppose I'll just experiment until I get it working correctly.

Thanks again.


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I didn't notice any improvement with 47 uF. I tried a couple of large caps (1000 and 2200 uF) with varying results. Is the decoupling capacitor suppose to handle the sudden voltage requirement of the pump at startup? If so, shouldn't this capacitor be close to the supply leads of the pump?

On another note, I bought a 20 yr old power supply from my local surplus shop for about $14. It has a few transformers and a couple of sets of rectifying diodes. It has 6 different output posts, so it appears that it will give me the decoupled power source that I'm looking for. Not the most elegant solution, but a solution nonetheless.

Thanks again for your help. I'm a mechanical engineer, so I'm quite a novice at electronics. I've already flipped the circuit breaker in my garage a few times and smoked numerous IC's, but I'm learning. Haven't zapped myself yet (knock on wood).

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I'm not sure exactly what you mean by "protective ground". When I built my other power supply, I used and old 3-pronged power cable from one of my old computers. It is my understanding that the middle prong is earth grounded when plugged into an electrical outlet. I wired this middle prong to the metal frame of my power suppply. Is this the right thing to do?

On this 20-yr old power supply, theres a connection labeled "GND", so I'm assuming this is ground. I was planning to wire the middle prong of my power cable to this connector. Bad idea?

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