DIY ATO relay wiring question with illustration
- Thread starter Wetline
- Start date
Yep, it's coming back to me about the spiking voltages in a circuit with a inductor and when you switch the voltage off and kill the emf a surge can be created, which can be many times the operating voltages. I might have explained that a little wrong but the idea is there. I think that was a few years ago when I had the pleasure of learning that in one of my modules. Well I guess if you don't use the knowledge on a consistent basis, you loose (forget, misplace) the knowledge. Ha ha. If I remember right diodes and maybe mov's can be used to shunt the spikes away from sensitive equipment and back to the inductor (coil) or to ground which would be the best solution for the spike. So when the emf collapses the a spike is created and that spike needs to go somewhere. But looking at uncleof6 diagram(which he got from bean animal) I would think the use of diodes would be placed after both float switches to create a direct path for the energy to flow and not let the spike come backwards. I don't know maybe I'm missing something here. I have seen that same schematic somewhere, maybe an over current relay or in a tap changer regulating relay. I know I have seen that same setup somewhere. Maybe uncle or der Wille can explain its purpose or function.
uncleof6
Active member
The diode is placed across the coil of the relay. It is the only place there will be what is called "flyback." The coil of the relay of course stores energy. When the power is removed suddenly, (float switch opens) the coil discharges, the diode gives the "voltage" somewhere to go, rather than burn up the relay. An N4004 diode should be enough. The flyback voltage can be a magnitude higher than the supply voltage. (sometimes 100's of volts.)
The circuit is called a "latching" circuit. It is designed to reduce superfluous opening and closing of the relay contacts. It is the most time tested and reliable method for this type of application. It has literally countless uses, but that is a subject for an electronics forum.
But as others have pointed out, if the pump is a 12v pump, there is not much point in using a relay/latching circuit. However, it can save some wear and tear on the float switches. They are not the hardiest of devices.
The circuit is called a "latching" circuit. It is designed to reduce superfluous opening and closing of the relay contacts. It is the most time tested and reliable method for this type of application. It has literally countless uses, but that is a subject for an electronics forum.
But as others have pointed out, if the pump is a 12v pump, there is not much point in using a relay/latching circuit. However, it can save some wear and tear on the float switches. They are not the hardiest of devices.
der_wille_zur_macht
Team RC
Not specifically but it would be a pretty easy circuit.
Even easier would be to just use a time delay relay, but they're rare enough to make them expensive.
Personally I think it's a preference thing, and you need to be sure to understand the implications from a functional perspective. If all else stays the same, then having really large hysteresis (the time it takes to do an on/off cycle) means you'll have larger fluctuations in salinity and water level within the sump. Also, a latching circuit by nature means that one of the switches will always be submerged, and that's another thing that makes me nervous about these cheapo float switches (they tend to have poor reliability when submerged).
Even easier would be to just use a time delay relay, but they're rare enough to make them expensive.
Personally I think it's a preference thing, and you need to be sure to understand the implications from a functional perspective. If all else stays the same, then having really large hysteresis (the time it takes to do an on/off cycle) means you'll have larger fluctuations in salinity and water level within the sump. Also, a latching circuit by nature means that one of the switches will always be submerged, and that's another thing that makes me nervous about these cheapo float switches (they tend to have poor reliability when submerged).
So either der wille or uncle, can you recommend where to get and provide an example of what a good float switch is. And possibly show us what a bad/ poorly designed float switch is. Just basically trying to get a feel of what is good and what is bad. What to stay away from, and what to purchase. I don't care about price. Maybe if there are good options and the best option we can steer people in a good direction for the diyer. I personally don't like to do something twice. So if it means dropping a couple $20 more on a better option for a float switch. I'm all for it. I would rather save the money up and buy the right components then buy another setup up in a year because I bought cheap stuff. This is not a crack on the op at all, so I hope the op does not take it this way. I just have a different view of things and maybe our situations are different. So any constructive advice on where to get these components and what are good components to get would be greatly appreciated. I see a specific sponsor here at rc that sells a pressure switch for like $70. But how do I know if it's a good designed switch that will last for years to come. How do I know it's not a $10 item at such and such store and being resold under another name. So just looking at some insight for others to buy quality components for a build like this. Tia
Mike
Mike
No offense taken. Cost was an issue in my design and components. I'm not sure how many variations there are in float switch design but maybe their are better ways to seal the wiring than epoxy (like the ones I used). If I had to guess I'd say that the horizontal switches with the wiring out the side of the sump like beananimal's illustration would probably be better than the vertical style switches. Possibly switches meant for chemical applications would be more robust.
der_wille_zur_macht
Team RC
Honestly I don't think it's worth spending a ton on a "better" float switch because you have to spend A LOT to get much better. Most of the hobby-marketed float switches are either Madison M-8000 or knockoffs. They're not the most reliable on the planet but if you treat them right they are not bad, either. To me, there are three important considerations:
1) Don't run any more current than you need to (i.e. use a relay)
2) Don't subject them to lots of voltage flyback, ESPECIALLY if you are driving a larger inductive load on them, like a pump - but even a relay coil causes some flyback (use a flyback diode, like beananimal's design shows)
3) Protect them within the sump - use "snail guards" and protect the wiring.
1) Don't run any more current than you need to (i.e. use a relay)
2) Don't subject them to lots of voltage flyback, ESPECIALLY if you are driving a larger inductive load on them, like a pump - but even a relay coil causes some flyback (use a flyback diode, like beananimal's design shows)
3) Protect them within the sump - use "snail guards" and protect the wiring.
uncleof6
Active member
uncleof6
Active member
hummmm seems it would be a little less complicated if you just turned the "float" over rather than mounting the thing "upside down."
