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HELP needed with relay bounce

Hi All

I've been trying to construct a pressure regulating device, using a 12v

latching solenoid and conventional valve, to protect a filter in a home

irrigation system. I am using a pressure switch which goes contacts open at high pressure/contacts close at falling pressure. These two states in turn trigger 555 timers which in turn drive small 12v SPDT relays.

The relays are configured so that in the relaxed state the circuit connects to the 0v line and when exited by the pulse from the 555, switches to supply 12v for each relay in turn. The purpose of this switching configuration is so that the 12v latching solenoid, which operates the valve, can be switched to close the valve when pressure reaches a high threshold, but then by reversing the supply voltage, is switched to open the valve at a low threshold.

This all works perfectly - until the latching solenoid is connected, whereupon the action of the solenoid causes the relays to bounce erratically.

I have tried various combinations of (non polarised) capacitors and R/C

combinations across the terminals of the solenoid, and/or across the relay. I have also tried using seperate 12v power supplies to power the two sides of the device (timing - relay activation side and power supply for solenoid side)but the action of the solenoid still causes the relays to bounce erretically.

I feel I am running out of options to solve this dilema, but am now considering the use of switching transistors or solid state relays. Only I'm not sure how to switch such devices on and off to give the necessary pulse to switch the solenoid on then off etc.

Any help would be greatly appreciated

Reply to
Chris Knight
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"Chris Knight" schreef in bericht news: snipped-for-privacy@g47g2000cwa.googlegroups.com...

As far as I understand your descryption - we tend to use schematic diagrams you know - switching the solenoid disturbs the 555s which in turn makes the relays bounce which in turn switches the solenoids... Solid state relays will not help to improve this behavior.

One thing you have to do is to decouple the 555s powersupply. A 100nF ceramic capacitor near the power pins is often used. An RC filter on the inputs of the 555s will make them less sensitive for the disturbances. If you use any resistors to set the 555s thresholds, make sure the have low values. Some hundreds of Ohms. You can make a grounded screen around the wires from the pressure switch to the 555s but if that helps either your wiring is bad or the 555 inputs are much too sensitive (or both).

IMHO a 555 is not the best component to achieve your goal. I'd use LM311 or similar voltage comparators.

petrus bitbyter

Reply to
petrus bitbyter

What you might try is a diode to take the inductance spike from the solenoid. Because you are reversing polarity at the solenoid you would have to install the diode before the reversing relay points.

+power-----------------relay points

- side of diode

+side of diode

- power or common---relay points

Another problem may be that your power source voltage is going to low when the solenoid is activated. If this is the case then you could charge a capicator through a resistor then activate the solenoid from the capicator charge

+power resistor resistor +cap-----------------relay points

-cap------------------relay points

-power or common

dave

Reply to
CheapscateDave

Put a meter on you power supply and watch the voltage drop when the solenoid energizes. I am wondering if you have to large of a load on your supply and or it is unregulated. This could make you relay drive voltage fall to a point where the relays de energizer the solenoids to the same and viola.. you have an oscillator........

Find what your you max current is and size your supply accordingly. Use a regulated power supply..

Pat Ziegler Wholesale Electronics Inc.

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Reply to
DBLEXPOSURE

Chris Knight wrote: [in many groups about relay bounce] (Which Jim Meyer thinks is a plumbing problem, not an electrical problem):

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Next time you post to multiple groups

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post just ONCE and put ALL the groups in which you want the question to appear on the Groups line.

This allows EVERYONE who reads the question to easily see ALL the solutions that are proposed.

Reply to
JeffM

Hi, Chris. First off, I'm not sure you've got the right valve for the job. The protection circuit you're using won't prevent filter damage in the event of a power outage. I'd really recommend getting another solenoid valve with a 12VDC coil rated for continuous duty. That would make your control system much easier (view in fixed font or M$ Notepad):

` +12V COM ` | | ` | Normally Closed | ` | Pressure Switch | ` | PS1 | ` | ___ T | ` o--------UUU-----o----------o|o---------o ` | RY1 | -|- | ` | | | ` | | | ` o--------|

Reply to
Chris

Hi Chris

WOW!! I'm completely blow away by the time, thought and trouble you've taken to help with my problem. It seems like you understand my project better than I do, despite my clumsy attempt to describe it and lack of diagram. I take on board the advice regarding the power failure issue. That makes a lot of sense, as failure to switch off will be catastrophic for the filter. I did however only ever intend to drive this system with lead acid batteries so it could be located remote from any AC power source. Nevertheless, a failure of any other kind within the system would bring about the same unacceptable result so I will need to build in some sort of failsafe. I'll consider your suggestions and try and figure out the best way to go. Meanwhile, I am interested in your idea of using relays to disable the circuit, so if you could post with a more detailed description I'd be most grateful.

Just to ease your curiosity about how the 555s are configured to reverse the polarity, I actually use three 555s; or more precisely 1

555 and a 556. The 555 is hooked up to be triggered when the contacts of PS1 open and thence provide the signal for the second side of the 556. I found all my circuit ideas by rummaging through the internet, and in particular Bill Bowden's site. Thanks to Bill Bowden for that.

I'll have a go at implementing your suggestions and let you know how it went.

Thanks again for your help Chris

Reply to
Chris Knight

Hi Chris

WOW!! I'm completely blow away by the time, thought and trouble you've taken to help with my problem. It seems like you understand my project better than I do, despite my clumsy attempt to describe it and lack of diagram. I take on board the advice regarding the power failure issue. That makes a lot of sense, as failure to switch off will be catastrophic for the filter. I did however only ever intend to drive this system with lead acid batteries so it could be located remote from any AC power source. Nevertheless, a failure of any other kind within the system would bring about the same unacceptable result so I will need to build in some sort of failsafe. I'll consider your suggestions and try and figure out the best way to go. Meanwhile, I am interested in your idea of using relays to disable the circuit, so if you could post with a more detailed description I'd be most grateful.

Just to ease your curiosity about how the 555s are configured to reverse the polarity, I actually use three 555s; or more precisely 1

555 and a 556. The 555 is hooked up to be triggered when the contacts of PS1 open and thence provide the signal for the second side of the 556. I found all my circuit ideas by rummaging through the internet, and in particular Bill Bowden's site. Thanks to Bill Bowden for that.

I'll have a go at implementing your suggestions and let you know how it went.

Thanks again for your help Chris

Reply to
Chris Knight

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