Float switch wiring

[bimini_bread]

Hello,
Just a quick question. I could try it out myself but figured I'd ask first b/c I'm sure someone will have an answer. Is it possible to daisy chain 8 float switches together to one relay. Then if one float switch rises too high it would shut the system down.

Bit of background. I have an 8 tank system plumbed into 1 sump. I'd like to have float switches in each tank to shut the return pump off if any one of the tanks gets too high.

Thanks a lot.

 

[SGT_York]

Very possible,
But why not spend your time improving the overflow drains so the water will never raise?

 

[bimini_bread]

We made some DIY overflows b/c the tanks are not drilled. I trust them but there is a lot of expensive equipment in the room next door so I wanted a redundancy in case there was ever an issue then the pump would just shut down.

 

[smmiller506]

Wire all 8 switches in series. Edit: saw you already had a relay in mind.

 

[CStrickland]

I wouldn't tie them to each other, but if you mean separately on the same line I think it's ok. Only because the wires aren't strong so if it got bumped or yanked you have a chain with some weak links. Where one cord with several splits off would be more sturdy.

 

[RocketEngineer]

The issue with that idea is that it would turn the pump back on as soon as the water drained out of the offending tank. Cycling a pump like that is likely to reduce it's life span.

 

[CStrickland]

The issue with that idea is that it would turn the pump back on as soon as the water drained out of the offending tank. Cycling a pump like that is likely to reduce it's life span.

I thought that's what the relay prevents?

 

[scottwhitson]

You could purchase a timer relay to avoid the cycling of the pumps.

 

[RocketEngineer]

If the overflow is slow, not stopped such as a snail walking across the pipe gets stuck at the opening, then when the water level returns to normal, it will kick the pump back on. Since the snail can't get out of the way, the situation repeats.

What kind of DIY overflow are you using? If it is the PVC design than you would be better off buying a commercial HOB instead.

 

[bimini_bread]

Thanks for all the advice. The relay is connected to a reset switch so when the pump kicks off it has to be manually reset in order for the pump to turn back on.

I currently have it set up with 2 float switches in my sump and it's working well, almost too well. But I want to add an ATO and that will defeat the purpose of having the float switches in the sump. That's why I wanted to put the float switches in each of the tanks instead.

 

[CStrickland]

Just a thought, when you are testing out your relays make sure that you don't lose all your gas exchange when the overflow quits. If it trips and stays down for several hours before you get home, a powerhead moving the surface water could save your tanks.

Iirc Melev has a work around for this ato/overflow float switch problem on his site. Maybe look there?

 

[uncleof6]

***

 

[skeeter_ca]

You might also consider a latching relay. If I understand correctly it will turn the pump off but not back on when the water level goes back down and you could setup a manual switch to turn it back on.

skeeter

 

[Member No. 1]

Wire all 8 switches in series. Edit: saw you already had a relay in mind.

If all the switches are normally closed this would work. But if they are set for normally open, this will not work in series. If one switch closes the others will still be open so the circuit will be open.

 

[uncleof6]

You might also consider a latching relay. If I understand correctly it will turn the pump off but not back on when the water level goes back down and you could setup a manual switch to turn it back on.

skeeter

A latching circuit works in both directions, generally the latch sets to run, and a separate action is needed to "unset" the latch. I would be just the same setting the latch to "off" and the separate action to unset the latch back to "on." The problem with a manual "reset" is if you are not around for an extended time, and considering this system (for the overflows) needs to be "normally" closed, using a latching circuit to turn the pump of, the pump will not run for the extended period of time.

By far the most appropriate system to control flooding from the overflow, would be to use a passive (non-active) fail safe, such as backup drains, that are kept dry, to accommodate failure of the overflow. rather than attempting to build a redundant/fail safe system using electro-mechanical devices that have more than one failure mode, which will become complicated, and less reliable.

A latching circuit is by far the smartest and most reliable design for an ATO system (normally open system) using electro-mechanical relays and switches, with the redundant back up being non electrical, strictly mechanical.

 

[CStrickland]

By far the most appropriate system to control flooding from the overflow, would be to use a passive (non-active) fail safe, such as backup drains, that are kept dry, to accommodate failure of the overflow. rather than attempting to build a redundant/fail safe system using electro-mechanical devices that have more than one failure mode, which will become complicated, and less reliable.

I'm having trouble picturing the backup drains, could you describe that more?
I'm assuming OP hasn't drilled because they have tempered glass like me and are stuck with an HOB that depends on a siphon, so the most likely overflow failure (siphon loss) would not be in the part of the box where the main drains are.

 

[uncleof6]

If all the switches are normally closed this would work. But if they are set for normally open, this will not work in series. If one switch closes the others will still be open so the circuit will be open.

Exactly, plus, with the switches wired in parallel, the redundant back up would become very complicated, because there are two failure modes to both switches and relays, so you end up with both parallel and series redundancy, and there is no back up for the relay; without a fly back diode across the relay coil, there is no protection for the control/logic circuitry.

The bottom line is the OP needs to design the overflows to incorporate a passive fail safe, in the form of a dry emergency back up.

 

[uncleof6]

I'm having trouble picturing the backup drains, could you describe that more?
I'm assuming OP hasn't drilled because they have tempered glass like me and are stuck with an HOB that depends on a siphon, so the most likely overflow failure (siphon loss) would not be in the part of the box where the main drains are.

Correct. However, we are looking at DIY overflows, the reliability of which is questionable from the word go. Whether back up drains would be feasible depends on the design of the overflows. I also know that redundancy and fail safe with "mission critical" objects in the destruction path is not so simple as anything I have seen here. I also do not think that controlling the main pump is the answer anyway, as a single failure can result in the loss of all 8 tanks, rather than just the affected tank.

 

[smmiller506]

If all the switches are normally closed this would work. But if they are set for normally open, this will not work in series. If one switch closes the others will still be open so the circuit will be open.

Most float switches are set to open when they reach the desired level I believe. This shouldn't be an issue.

 

[uncleof6]

Most float switches are set to open when they reach the desired level I believe. This shouldn't be an issue.

Depends on the float switch. Many can be either "normally open" or "normally closed" depending on how you set it up. Some being as simple as turning the magnet housing over.