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Coral Vue Hydros

Latching relay for ATO


RK_tek

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Setting up a 20L AIO and want to use two float switches as high/low indicators to turn the pump(aqua lifter) on. With only one float, the ATO will run briefly before the float rises and shuts it off. I'd like to make it where the level has to drop a certain amount then refill to top to keep from cycling the pump on/off as often. I've found diagrams to do this with two 12v relays and momentary switches but don't know enough to make it work with the floats and a 12v float circuit and a 120v circuit to power the pump. I suppose a third 120v relay could be actuated to provide pump power. Any help from the electronically savvy guys/girls will be helpful

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If you are sure you want to use two float switches for this job, you don't need a latching relay at all. You just need a relay to drive the pump. Wire the float switches as inputs to an appropriate logic gate, e.g. XOR, and the logic gate output to the input of a suitably rated opto isolated SSR to switch the power for the pump.

 

However such a setup is very sensitive to the possible failure of the upper float switch, which could overflow your tank. So I'd put the whole thing on a timer so that it will only top up once a day for 5m max, just in case.

 

Osric

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The circuit you have posted will work. I am not sure why he has the diode across the relay input, and the relay shown is not a latching relay (and doesn't need to be). Be sure to put the float switches in the right orientation (up side down) for this circuit.

 

Osric

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The circuit you have posted will work. I am not sure why he has the diode across the relay input, and the relay shown is not a latching relay (and doesn't need to be). Be sure to put the float switches in the right orientation (up side down) for this circuit.

 

Osric

 

I believe the diode has is to handle the voltage spike when the coil collapses. I'm going to try it according to the diagram, but it seems a nicer package could be made with other components. Maybe even incorporate a timer in the circuit

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  • 9 years later...
On 10/28/2012 at 2:10 AM, Osric said:

If you are sure you want to use two float switches for this job, you don't need a latching relay at all. You just need a relay to drive the pump. Wire the float switches as inputs to an appropriate logic gate, e.g. XOR, and the logic gate output to the input of a suitably rated opto isolated SSR to switch the power for the pump.

 

However such a setup is very sensitive to the possible failure of the upper float switch, which could overflow your tank. So I'd put the whole thing on a timer so that it will only top up once a day for 5m max, just in case.


The circuit you have posted will work. I am not sure why he has the diode across the relay input, and the relay shown is not a latching relay (and doesn't need to be). Be sure to put the float switches in the right orientation (up side down) for this circuit.

 

Osric

Haha - 10 years later and I am browsing a forum only to see one of my schematics being wrongly commented on. Sorry to dredge this up, but I hate when poor information is propagated and attributed to me.

Your advice to ditch the simple, proven, robust and effective relay circuit (driven by a 12v wal-wart) for a fragile  XOR logic gate circuit, filtered power supply circuit and opto-isolated relay... is not logical. Any DIYer can follow my basic schematic but few will be able to design using discrete logic gates and supporting components. 

Yes - it is a latching relay CIRCUIT. The relay itself is not a latching-relay, it is a simple DPDT relay wired into a latching circuit. This latch prevents short cycling of the circuit that a single float implementation would cause. FULL STOP.

The diode is called a snubber or suppressor diode and is there to absorb the (significant) voltage spike induced by the coil as the armature is sucked back through it by the spring when the circuit collapses. The unsuppressed spike can easily damage the fragile reed contacts in the float switches. This diode is pretty much STANDARD on all real world relay circuits, but is often omitted in basic diagrams because it is an understood standard. This is not a debatable point, it i simply accepted practice. FULL STOP.  

Float switches - upside down?  No - it depends if they are normally OPEN or normally CLOSED switches. Both would be normally closed types for this design - NC switches would be mounted in a hanging position. NO switches would be mounted "upside down" like a planted tree for this circuit.

The fail-safe for this circuit (I don't want to get into failure modes) could be a timer allowing only top-off during a window short enough to prevent flood, and or a physical float valve set just above the upper float switch. It would mechanically shut off flow in the event that the circuit failed closed. The proper image image is included below, showing the the latch operation.

Enjoy!
Beanspacer.png

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  • 2 years later...
Confeder8

Good evening everyone.

This post is just a life saver for me 

Instead of applying it on my reef, it is implemented on real life usage. Scheme is used in a cement silo feel up with high and low switches.

My heartiest thanks.

Regards

Alok

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