DIY ATO with Capacitor across relay coil

[bqq100]

Has anyone ever hooked a capacitor up to the coil side of the relay so the pump continues to run for a little bit longer after the target level is reached? This would overshoot the target level a little bit, but would reduce the number of times the pump has to kick on due to a low water level.

Thanks!

 

[uncleof6]

Better would be to use a latching circuit, the design of the circuit itself, reduces the amount of cycling. A flyback diode is used, across the coil, to eliminate flyback: the sudden negative potential seen across the coil, when the power is suddenly reduced or removed. 1N4004, 1N4005, or 1N4007 power diodes would be adequate.

The circuit is very reliable, however, as with most things--a mechanical fail safe should be employed also, as well as a low water level main pump shutoff.

Generally, a debate ensues after this post. The topic would be, mechanical vs electrical ATO systems. In either case, an electrical system would be needed either for the main system, or the fail safe system. Mechanical fail safe for an electrical system; electrical fail safe for a mechanical system.

 

[2hands]

What's wrong with using a timer to only give power to the ATO a couple of times per day?

 

[uncleof6]

What's wrong with using a timer to only give power to the ATO a couple of times per day?

Why use a timer, when the circuit above is simple, reliable, and does not over cycle the ATO system?

 

[kcress]

...

 

[bqq100]

Better would be to use a latching circuit, the design of the circuit itself, reduces the amount of cycling. A flyback diode is used, across the coil, to eliminate flyback: the sudden negative potential seen across the coil, when the power is suddenly reduced or removed. 1N4004, 1N4005, or 1N4007 power diodes would be adequate.

The circuit is very reliable, however, as with most things--a mechanical fail safe should be employed also, as well as a low water level main pump shutoff.

Generally, a debate ensues after this post. The topic would be, mechanical vs electrical ATO systems. In either case, an electrical system would be needed either for the main system, or the fail safe system. Mechanical fail safe for an electrical system; electrical fail safe for a mechanical system.

Thanks for the awesome diagram. I was planning on using the flyback diode in addition to the capacitor. I was also planning on using 3 float switches so there are shutoffs for water too high and reservoir too low, but with a this circuit the high water level float switch is now a point a single failure. Even with the design I have in mind (high water float switch grounding + side of the coil), the relay being stuck on would be an issue, but I'm not sure how often relays fail in the on position.

I don't want to just use a timer because i wanted to setup 2 reservoirs with 2 pumps (1 freshwater and 1 saltwater) and switch to toggle which one is being used. Normally I will have it set to freshwater to top off evaporation, and when I do water changes I will flip it to top off saltwater. I also want to add a push button so I can manually add some water when needed.

This is probably way overboard for a 20 gallon tank w/o sump, but I figure it can always be used again if (and hopefully when) I get a bigger tank! Plus I love to tinker and go overboard with things! :lmao:

 

[emerald crab]

The diagram above works fine, but the two float switches system is very difficult if not impossible to be set for small portions (1-2 oz). Large portions means swings in salinity, not exactly what I want. That was the reason to go for an Arduino based ATO, with delay at start up after power failure, skimmer control, ATO pump works for a minimum 5 seconds at a time, high sump level alarm and ATO cut-off, low water level in the ATO tank alarm and cutoff.

 

[johnwonus]

Off Delay

Off Delay

I love working with Arduinos. One would certanly work for this but in my opinion it may be a little bit overkill. Also, I think you will need a very large capacitor across a relay coil to keep it energized. You could google electronic 'off delay' circuits and I am sure you will find one that you can build with components from radio shack. Just my opinion. good luck

 

[emerald crab]

I love working with Arduinos. One would certanly work for this but in my opinion it may be a little bit overkill.

I don't think it is an overkill. You can get an "Uno" on ebay for $15, I'm pretty shure that you pay more for an approved enclosure and cable connectors. Considering that I had some pins leftover, that I used to make the timers for Ca, Alk and vodka dosing, I think I did pretty good.

 

[BeanAnimal]

The diagram above works fine, but the two float switches system is very difficult if not impossible to be set for small portions (1-2 oz). Large portions means swings in salinity, not exactly what I want. That was the reason to go for an Arduino based ATO, with delay at start up after power failure, skimmer control, ATO pump works for a minimum 5 seconds at a time, high sump level alarm and ATO cut-off, low water level in the ATO tank alarm and cutoff.

1 to 2 ounces? Maybe if your tank were a 1 gallon pico....

Don't overthink the salinity swings

 

[BeanAnimal]

I really shoulda watermarked that schematic....

 

[uncleof6]

I really shoulda watermarked that schematic....

Dang, I knew I forgot something. I usually credit the schematic.

 

[BeanAnimal]

The schematic is mine... but for the life of me I can't remeber who animated... but I am fairly sure (memory is starting to go) it wasn't me, and instead somebody did it for me.

 

[gtafragger]

yes it would be very beneficial. Store bought ato's use a capacitor to leave the pump on for an extra 3-5 seconds.

 

[uncleof6]

The schematic is mine... but for the life of me I can't remeber who animated... but I am fairly sure (memory is starting to go) it wasn't me, and instead somebody did it for me.

My memory already went...... I even watermarked the thing, but it seems RC and photobucket are not playing nicely together. The unwatermarked gif is no longer on the photobucket server..... but it should be gone in the thread.... see:

 

[bqq100]

So I've been drawing out and refining my schematics for this. Initially I was thinking a 1F capacitor across the coil to keep it powered up, but then I realized I needed something to drive the coil (since the logic gates I'm looking at don't have enough juice). Using the capacitor to keep a voltage on the gate of the driving MOSFET requires a much smaller capacitor. Using a 6800uF capacitor should be able to hold the MOSFET on for up to ~70 seconds (assuming my math is right).

If anyone is interested here is the schematic I've been toying with:
Schematic

 

[uncleof6]

So I've been drawing out and refining my schematics for this. Initially I was thinking a 1F capacitor across the coil to keep it powered up, but then I realized I needed something to drive the coil (since the logic gates I'm looking at don't have enough juice). Using the capacitor to keep a voltage on the gate of the driving MOSFET requires a much smaller capacitor. Using a 6800uF capacitor should be able to hold the MOSFET on for up to ~70 seconds (assuming my math is right).

If anyone is interested here is the schematic I've been toying with:
Schematic

The more complicated the plumbing, the easier it is to stop up the drain. Good luck.

Just for grins: The earth is 1 Farad.............

 

[BeanAnimal]

Why complicate matters so much when a simple latching circuit is time tested and bulletproof?

You can substitute optical sensors for float switches and get as much "precision" as you wish..

 

[kcress]

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.

 

[BeanAnimal]

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.