DC pump float switch

[Mrjmegson]

Hey guys, sorry, general question that's nothing to do with renewables.

Ive got a DC pond pump running one of my drum filters, that I need to turn off when the water level drops, to let the level rise again in the filter.

So I want to put a float switch in the line, but I've got 3 positions it can go, and I don't know which is best.

I can go:

Between the mains and the inverter (AC)
Between the inverter and control box (DC)
Between the control box and the pump (DC)

Which is best?

I'm using a switch which is way over powered for the system, so will be fine switching DC.

Cheers,

Jay

 

[Geoff1946]

Confused. An inverter makes AC from DC, so do you mean a rectifier psu ?
Does said item supply anything else except the control box?
What does the control box do?
The DC voltage at which the control box and pump operate may also be relevant to a considered answer.

 

[Mrjmegson]

Lol, rectifier, sorry, got solar on the brain.

No the rectifier just supplies the control box for the pump.

The control box has two functions, it has a 10 step speed variation(so power variation), and can stop the pump for 10mins (a feed function)

So the input of the rectifier is: AC
100-240v
50-60Hz
2.5A

And the output is: DC

24v
5.25A
126W

Hope this is clear.

Cheers for replying.

 

[johnb2713]

I think you need to add a timer or a second float switch or the pump will be on and off very rapidly causing all sorts of issues. As to where to put it, from a safety point of view I would use the low voltage option but I would be switching the load via the timer or a relay.

 

[Mrjmegson]

Hi John,

Thanks for the reply.

The pump will possibly be switching off every 15 minutes or so, until I get my blanket weed issue (actually nitrate issue) sorted, and then it will just keep running unless something untoward happens.

I'm not sure why you would think the pump would be being switched rapidly on and off?

Can you clarify what you mean by the low voltage option from my 3 proposed options?

Cheers.

 

[johnb2713]

The pump will possibly be switching off every 15 minutes or so, until I get my blanket weed issue (actually nitrate issue) sorted, and then it will just keep running unless something untoward happens.

Level drops, switch operated pump stops, level rises a tiny amount pumps starts, level drops, pump stops - stop/start/stop/start in rapid succession. It needs some form of hysteresis built in.
Level drops, pump stops for 3 minutes or until a higher level float switch is triggered.

Can you clarify what you mean by the low voltage option from my 3 proposed options?

On the 24v Side.

 

[Sharpend]

John is quite right, a pump would generally need two switches, a high level and a low level, effectively one to start it and one to stop it. Without this you have little control and the pump would forever be short cycling.
An alternative is as suggested that the pump runs via a timer which could be set for time it needs to run or time it’s off for.

 

[Mrjmegson]

Level drops, switch operated pump stops, level rises a tiny amount pumps starts, level drops, pump stops - stop/start/stop/start in rapid succession. It needs some form of hysteresis built in.
Level drops, pump stops for 3 minutes or until a higher level float switch is triggered.


On the 24v Side.

Cheers for clarifying John, would you go between the rectifier and control, or control and pump?

As for the switch frequency, I've used them before, and they aren't that reactive, the level has to rise almost back to its working level before the switch turns back on, in which case the drum filter will have "hopefully" fully cleaned itself and be allowing water flow, so the level won't drop again for 15 or more mins. That's the idea anyway. Hope I'm right. Lol

 

[Mrjmegson]

John is quite right, a pump would generally need two switches, a high level and a low level, effectively one to start it and one to stop it. Without this you have little control and the pump would forever be short cycling.
An alternative is as suggested that the pump runs via a timer which could be set for time it needs to run or time it’s off for.

Cheers for the reply. I'll obviously follow yours and John's advice if this is an issue, but for now I'll give my plan a go.

Can I clarify the timer idea? Do you mean to use a float switch to turn the pump off, but then have a timer which controls the duration of that down time?

I ask as the duration between the water level being too low is incredibly random, so despite saying 15 mins, that does seem to be the duration once it starts messing up, but it can run for days without messing up.

 

[Richard-the-Ninth]

I have a pump running with a float switch. The switch is designed to be "slow" (As are most sealed add on float switches) The water has to rise a few inches before the pump will start, and likewise fall a few inches before it stops the pump.
Water level sensors on the other hand are instant, so they are better off with a timer, but your average add on float switch there is no need for a timer.

As for where to connect it, I would suggest the 240v ac side (Assuming the switch is rated for 240v ac, which most are)

 

[Mrjmegson]

I have a pump running with a float switch. The switch is designed to be "slow" (As are most sealed add on float switches) The water has to rise a few inches before the pump will start, and likewise fall a few inches before it stops the pump.
Water level sensors on the other hand are instant, so they are better off with a timer, but your average add on float switch there is no need for a timer.

As for where to connect it, I would suggest the 240v ac side (Assuming the switch is rated for 240v ac, which most are)

This one is a very slow acting one, the rise and fall is many inches, it's like the ones on sump pumps.

Can you explain why you would go on the AC side?

Cheers.

 

[Richard-the-Ninth]

I would say it really depends on your setup, my preference is the AC side.

For clarification could you post a "block diagram" (Draw it with pen and paper if you like, then take a picture) of your setup.

 

[Mrjmegson]

Sorry Richard, I'm not a sparky, so that doesn't mean anything to me.

All I can tell you is I have a lead that goes from the mains 3 pin plug, into the power pack, this then has a lead that goes to a controller box that varies the speed of the pump and also pauses it, and this has a lead that goes out to the pump.

The leads to the controller and pump only have two wires, and are much smaller cables, lamp type cable.

 

[johnb2713]

Cheers for clarifying John, would you go between the rectifier and control, or control and pump?

Either would be fine, I only suggest the DC side from a safety point view, 24v is much safer than 240v

As for the switch frequency, I've used them before, and they aren't that reactive, the level has to rise almost back to its working level before the switch turns back on, in which case the drum filter will have "hopefully" fully cleaned itself and be allowing water flow, so the level won't drop again for 15 or more mins. That's the idea anyway. Hope I'm right. Lol

Thats fine, I didnt know what type of float switch or pump size / water circuit etc.

 

[Mrjmegson]

Neither did I John, still don't. Lol.

Absolutely appreciate the reply though, I could easily have missed something, is my recent solar post proves.

 

[Mrjmegson]

I've tried to get the instructions and lead in the pic.

I'm lost with the instructions, they seem to say the same thing for both ways of wiring. I'd assume that if I wire it one way the switch would be on in the up position and off in the down, and vice versa.

I was rather shocked it had 3 wires, I only expected 2.

Anyone shed any light on the instructions, is it a typo?

Cheers.

 

[Richard-the-Ninth]

You are correct, there is an error in the instructions.
Your assumption of how it should work is also correct.

Since there is a mistake in the instructions, I would suggest you test the float switch yourself to establish which is correct. (I will assume Black is common)

It has 3 wires to give you the choice of "up on" or "down on" If it had two wires you would only have one option.

 

[johnb2713]

I've tried to get the instructions and lead in the pic.

I'm lost with the instructions, they seem to say the same thing for both ways of wiring. I'd assume that if I wire it one way the switch would be on in the up position and off in the down, and vice versa.

I was rather shocked it had 3 wires, I only expected 2.

Anyone shed any light on the instructions, is it a typo?

Cheers.

You do get some bad luck with some of your projects!

I would suggest Black and Red will stop the pump when it's low and start when it's high, if it works the opposite way to what you want, then black and blue.

 

[Sharpend]

Brown and black will switch pump on when water level is high therefore emptying,
Brown and blue will be ‘on’ when water is low therefore stopping pump.

 

[johnb2713]

Brown and black will switch pump on when water level is high therefore emptying,
Brown and blue will be ‘on’ when water is low therefore stopping pump.

The colours dont match the cable.