DIY ATO with Capacitor across relay coil

[bqq100]

As they say gents, "you can lead a horse to water...".

Using a truly mondo capacitance to run a relay is a bad idea for many reasons. Cost. Reliability. Drive failure. And relay contact damage. Relays are supposed to snap open and closed. Using a cap like this to abuse the relay causes the relay contacts to separate at a snail's pace. This causes lots of arcing that melts the relay contacts. It's probably the best way out there for toasting a relay quickly.

Thanks, that makes sense with the slow turn on/off causing damage. I'm no longer looking at just using a capacitor across the coil. I'm trying to evaluate multiple options and find the one that best fits my needs/wants for the system.

I have not bothered to look at the schematic, but kcress is correct. The relay needs to be switched via a rapid rising and falling edge. There a certainly ways to do this with an RC circuit and transistors or a 555 timer...

In fact, the 555 timer (monostable) would give you the ability to create both the rapid state transistion AND adjustability.


But again, why? Latching (relay) circuits run everything from elevators to water treatment facilities and power plants. They are for the most part bulletproof with no delicate discrete components to be damaged.

Thank you, the 555 timer does look like an interesting option

I believe that the latching relay is very bulletproof, but I don't have 100% faith in the float switches. With the latching relay, if the high water level float switch gets stuck, the entire reservoir could be dumped into the system. A latching relay circuit with a 3rd float switch for backup would work, but I am trying to see what other options exist.

 

[kcress]

You want to set up a second relay in the power chain to the 'outlet'.

You set it up so YOU need to push a button for it to pull in. Once it pulls in it supplies its own coil to keep itself pulled in. Got that?

Now, in the circuit that holds it pulled in, you put a third float switch - the highest one. It needs to be installed so it's normally closed and opens when the water gets higher. Once that float gets floated the circuit is broken that holds the relay closed. The relay opens. Because it opens its other contact set interrupts the power to the outlet.

The cherry-on-the-top is you run the normally closed (when relay unpowered) contact of this relay to a light. So when the normally latched relay is not latched the light is on. This alerts you to an overfill event.

Set this all up and press the button to latch-in the 'safety relay'. Then the systems operates normally using Beans fine scheme above. But, if the water rises for any reason high enough for the top float to open all control is rested from Beans circuit and the pump is disabled while an alarm light comes on.

 

[kcress]

You want to set up a second relay in the power chain to the 'outlet'.

You set it up so YOU need to push a button for it to pull in. Once it pulls in it supplies its own coil to keep itself pulled in. Got that?

Now, in the circuit that holds it pulled in, you put a third float switch - the highest one. It needs to be installed so it's normally closed and opens when the water gets higher. Once that float gets floated the circuit is broken that holds the relay closed. The relay opens. Because it opens its other contact set interrupts the power to the outlet.

The cherry-on-the-top is you run the normally closed (when relay unpowered) contact of this relay to a light. So when the normally latched relay is not latched the light is on. This alerts you to an overfill event.

Set this all up and press the button to latch-in the 'safety relay'. Then the systems operates normally using Beans fine scheme above. But, if the water rises for any reason high enough for the top float to open all control is rested from Beans circuit and the pump is disabled while an alarm light comes on.

 

[kcress]

Site's so slooooooooOOOooow I get a double post a minute apart. :headwalls:

 

[mcgyvr]

Capacitor is close.. You just forgot a few parts. :thumbsup:
here..
see "Power-OFF Time Delay Relay
http://www.bowdenshobbycircuits.info/page2.htm

also numerous other ways.. 555 timer,etc...

You can even buy an off the shelf "delay on break" timer for under $10.

 

[uncleof6]

Capacitor is close.. You just forgot a few parts. :thumbsup:
here..
see "Power-OFF Time Delay Relay
http://www.bowdenshobbycircuits.info/page2.htm

also numerous other ways.. 555 timer,etc...

You can even buy an off the shelf "delay on break" timer for under $10.

So you did the differential equation to determine if the relay would ring? Most hobbyists don't want to get into calculus. Ringing is the capacitor discharging into the inductor, and the inductor discharging into the capacitor, back and forth till the *resistor* dissapates enough energy for the ringing to stop. The only way to know if the relay will ring, is by solving the differential equation. Most do it bucket chemistry, by trial and error.....not good for the relay....

This whole project honestly is off the chart. A simple latching circuit, using some motor control ideas, and it is done. Simple, clean, reliable, time honored. But as Keith said, "you can lead a horse to water......"

 

[mcgyvr]

So you did the differential equation to determine if the relay would ring? Most hobbyists don't want to get into calculus. Ringing is the capacitor discharging into the inductor, and the inductor discharging into the capacitor, back and forth till the *resistor* dissapates enough energy for the ringing to stop. The only way to know if the relay will ring, is by solving the differential equation. Most do it bucket chemistry, by trial and error.....not good for the relay....

This whole project honestly is off the chart. A simple latching circuit, using some motor control ideas, and it is done. Simple, clean, reliable, time honored. But as Keith said, "you can lead a horse to water......"

*** are you talking about.. No need for differential equations or even a worry of oscillations/"ringing". Thats the most basic and proven time delay-off relay circuit you could use... "more than one way to skin a cat".. blah blah blah. The transistor is kept conducting until the time constant set by the capacitor/resistor has expired and then "magically" the relay shuts off.

Not saying that "beans" (well thats been around before he was born) circuit is bad or anything. Its perfectly fine and has been used with limit switches,motor controls, ATOs, etc.. for years (and so has the delay-off relay). But using a time delay-off circuit instead of a second float switch (fs2) is a totally viable solution and not this off-the-wall idea as you make it out to be. Of course a "mechanical" failsafe/size limited ATO container,etc.. should also be employed just as you "recommend" with the bean schematic.

The only issue with using "timed" solutions for any ATO function is that #1 evaporation rates change (mention of a regular wall timer just turning on a pump that I see so many times around here) and #2 pumps output can change with life/clogs,etc... A mechanical float solution can more or less account for that. Any "timed" solution does not necessarily.

 

[BeanAnimal]

"beans" latching circuit...
... really I invented the latching relay circuit. I am just having trouble getting paid for the billions of them in use over the last 175 years.

 

[mcgyvr]

"beans" latching circuit...
... really I invented the latching relay circuit. I am just having trouble getting paid for the billions of them in use over the last 175 years.

Just didn't want people to keep thinking your contributions to the "reef" world included 2 novel ideas.. I'll give you the "bean animal" drain system.. At least till my grandpa says he's been doing that since he was a youngster too. :crazy1:

Now forget this ATO junk..we all need to get together and fix this HORRIBLE RC server.. Its SOOOO slow. Took almost 5 minutes just to be able to post this.. What a joke.. Might be time to move on for a while or actually get some work done.. Its been like this for months now and only seems to be getting worse.

 

[uncleof6]

*** are you talking about..

Thanks, that is all I needed to know.

 

[bqq100]

You want to set up a second relay in the power chain to the 'outlet'.

You set it up so YOU need to push a button for it to pull in. Once it pulls in it supplies its own coil to keep itself pulled in. Got that?

Now, in the circuit that holds it pulled in, you put a third float switch - the highest one. It needs to be installed so it's normally closed and opens when the water gets higher. Once that float gets floated the circuit is broken that holds the relay closed. The relay opens. Because it opens its other contact set interrupts the power to the outlet.

The cherry-on-the-top is you run the normally closed (when relay unpowered) contact of this relay to a light. So when the normally latched relay is not latched the light is on. This alerts you to an overfill event.

Set this all up and press the button to latch-in the 'safety relay'. Then the systems operates normally using Beans fine scheme above. But, if the water rises for any reason high enough for the top float to open all control is rested from Beans circuit and the pump is disabled while an alarm light comes on.

Capacitor is close.. You just forgot a few parts. :thumbsup:
here..
see "Power-OFF Time Delay Relay
http://www.bowdenshobbycircuits.info/page2.htm

also numerous other ways.. 555 timer,etc...

You can even buy an off the shelf "delay on break" timer for under $10.

Thanks, that is all I needed to know.

Thanks guys! I really like the fail-safe circuit kcress described (since it also eliminates the relay as a single failure point) and I do like the idea of using the time delay relay circuit so I can use 2 float switches instead of 3. Only change I'm going to make is to use a FET instead of a BJT. Full redundancy of float switches and relays while minimizing on/off cycles for the pump, exactly what I was looking for! :beer:

Ringing is the capacitor discharging into the inductor, and the inductor discharging into the capacitor, back and forth till the *resistor* dissapates enough energy for the ringing to stop. The only way to know if the relay will ring, is by solving the differential equation.

The capacitor and inductor are isolated from each other by the transistor. There would be no current flow between the 2.

 

[mcgyvr]

Thanks, that is all I needed to know.

Is your name Mark ?
And did you look at the schematic?
The capacitor is NOT across the relay coil.

 

[uncleof6]

No I did not look at the schematic. The topic of this thread is "...capacitor across relay coil." Since this has gone off the deep end, for an aquarium application, I thought I would throw a curve ball, in response to the comment "that capacitor looks fine."

 

[mcgyvr]

No I did not look at the schematic. The topic of this thread is "...capacitor across relay coil." Since this has gone off the deep end, for an aquarium application, I thought I would throw a curve ball, in response to the comment "that capacitor looks fine."

Thanks, that is all I needed to know

hopefully you learned something from Marks site. :smokin: