Hi,

I've been playing around with my fish tank and I'm trying to build a circuit to do a simple job - and I'm completely stuck!

I want to put a 3 wire SPDT float switch in the tank and use that to control the water change.

I have 2 pumps (one inlet one outlet) which I need to control.

I will control this circuit using a timer.

What needs to happen is as follows:

Power is applied to the circuit; it starts the outlet pump
Once the float switch gets low enough, it will stop the outlet pump and start the inlet pump
Once the float switch is high enough, it will stop the inlet pump - but crucially NOT start the outlet pump again.

Then the power will be disconnected. Next time the power is recconected - the whole process starts again.


Any ideas?

I'm thinking relays... but I can't work out how to do this - it's maddening me! I don't want to use any PIC's or anything like that... just want to use mains rated components.


Please help me!

 

So you need a toilet flush function, with electrically controlled pumps replacing the drain and supply functions? And you want this process to be initiated by a human, but then to proceed and finish automatically (again, like a toilet)?

What do your pumps require, in terms of power supply?

 

So you need a toilet flush function, with electrically controlled pumps replacing the drain and supply functions? And you want this process to be initiated by a human, but then to proceed and finish automatically (again, like a toilet)?

What do your pumps require, in terms of power supply?

Ummmm.... I think so?! I hadn't thought of it as a toilet... but essentially yes.

I will apply power to the circuit for X time. so each time power is applied, I need it to "flush"! lol

 

You simply wire the flush relay to 'latch' itself when activated by your 'timer', and make sure the latch runs through an un-used set of contacts on fill relay. When the fill relay activates it unlatches the flush relay and the float turns off the pumps. The system won't start again until the timer sends another on signal.

The timer MUST have an 'on' signal that is of a shorter duration than the flush fill cycle time, or the whole thing will start again immediately.

 

What timer? is it resettable via signal wire? Does it have NO & NC contacts?

 

You simply wire the flush relay to 'latch' itself when activated by your 'timer', and make sure the latch runs through an un-used set of contacts on fill relay. When the fill relay activates it unlatches the flush relay and the float turns off the pumps. The system won't start again until the timer sends another on signal.

The timer MUST have an 'on' signal that is of a shorter duration than the flush fill cycle time, or the whole thing will start again immediately.

yep, that's the ticket. You won't use both functions of your float switch, just the low limit.

 

Here's a drawing of what kermit said, if you don't get it.

 

Oh yeah because everyone understands relay/ladder logic diagrams..

 

Oh yeah because everyone understands relay/ladder logic diagrams..

Well they should; it's about the most elementary way to draw it short of filling up a page full of relay symbols and playing connect the dots. I found it fairly self explanatory the first time I saw it, but I guess it's not the same for everybody.


@blindtrevor - if you don't understand the drawing, I can draw it another way

 

Frankly I'd do this with 1 simple on-off-on rocker switch.. Move it to one on position and the outlet pump runs.. Move it to the other on position and the inlet pump turns on. 1 component and done. No fancy float switches..no timers,etc..
Heck for a backup you could just install a float switch on the tank to disconnect the inlet pump in case you forget.. Most important part of having a fish tank is keeping water off the floor..

 

Frankly I'd do this with 1 simple on-off-on rocker switch.. Move it to one on position and the outlet pump runs.. Move it to the other on position and the inlet pump turns on. 1 component and done. No fancy float switches..no timers,etc..
Heck for a backup you could just install a float switch on the tank to disconnect the inlet pump in case you forget.. Most important part of having a fish tank is keeping water off the floor..

Then it wouldn't be automatic. The end goal is to have the outlet going into a drain and the inlet coming from some sort of hidden sump that fills itself with water and aquasafe chemicals... but that's another part of this project!

Also - I didn't mention that there will be a solenoid valve on the outlet that will be connected to the same power source as the outlet pump. That way, once the outlet pump turns on - the valve will open, when power is removed - the valve will shut preventing accidental syphoning.

@strantor - I'm not 100% sure on the ladder logic! (at least I'm honest!)

Can you draw it in a standard schematic circuit diagram at all? Many thanks everyone

 

What timer? is it resettable via signal wire? Does it have NO & NC contacts?

Oh - sorry... I meant that I want to control it with a standard mains timer that you plug in the wall... so it will turn the whole circuit on and off.

The idea is that the circuit empties and fills once - then when the power is removed and reapplied, it does it again.

That way I only need a simple 7 day timer to control when it happens... but for the minute - I just want to plug it in and it will empty and fill once... there must be an easy way without using PIC's??

 

Make sure your timer is set to only stay on for a second, not for the entire duration of the cycle.

 

Make sure your timer is set to only stay on for a second...

A normal lamp timer won't do that, so I think that "pulse" function should become part of the control relay circuit.

 

I've been researching - I may have the answer! Just going through my circuit at the moment to see if it's correct - then I'll post it for scrutiny!

Thanks guys - been a great help so far

 

The comment by wayneh not withstanding, (it's true) I find this funny! It certainly gets your ladder vs conventional schematic point across vividly.

 

It's interesting to look at the tools - the language - people use to communicate complex ideas. Lots of new folks here start with just words, and anybody here very long begs them for a diagram of some kind. Then there are block diagrams, schematics, PCB traces and finally pictures of an actual device. All these tools have their role, and are superior for that narrow role. The more abstract tools are good for communicating strategy and ideas, whereas a "picture" is a lot handier when it's time to actually make all the connections using real devices.

The challenge is to use the right tool at the right time and know when to switch to the next.

 

Right - I think if you look at the circuit you'll understand what I'm trying to achieve - I think my circuit will work (I hope!).

I plan to enclose it all within a UBS enclosure with some over-ride switches and neon indicators on it.

Let me know what you think!

 

Right - I think if you look at the circuit you'll understand what I'm trying to achieve - I think my circuit will work (I hope!).

I plan to enclose it all within a UBS enclosure with some over-ride switches and neon indicators on it.

Let me know what you think!

Could you provide a text explanation for that circuit?

because, As I see it...

1. I don't know how long your pulse is, but if you're expecting RL1 to latch, there's no provision for that.

2. during the brief time of the pulse, your pump & solenoid will be active, but they are in series which will give unpredictable results at best.

3. RL2 will latch, & keep your pump running (maybe) if the level is high (good there), but why not send the pulse straight to RL2? RL1 is pointless.

4. The low level switch will keep an open circuit for RL3 coil if the level is high, but if the level is low, it will connect both sides of RL3 together (electrically common) and RL3 will never switch.

5. Since RL3 never switches, RL4 never latches, and your tank never fills.

6. If RL3 were to switch, I think the rest of the circuit would work.

 

I don't think I'll ever understand the obsession of people to power stuff off their USB port. It has to be the worst idea to ever come down the pike, especially with reactive loads like a relay coil.

BTW, when you get this all working I think it would behoove you to have a failsafe backup to shut the fill pump off in case of float switch failure.