So I'm building an ATO with a relay. I have both normally on and normally off float switches so i could use either one.
should i use a normally on float switch, so the coil in the relay is always going except when the pump is on, or should I use a normally off float switch, so the coil in the relay turns on to trigger the pump?
I figure less power will be used when the normally off float switch is used. Having the coil on except when the pump is running cant be too good.
Can anyone who knows what im talking about give me some input? thanks.
Full Version: Relay wiring - normally on or normally off?
It's actually normally open or normally closed. Normally closed would be off. I agree that this would be your best choice for the same reasons you already gave.
You only want your pump to come on a few times per day (at low water) right, so most of the time your pump will be off, and your relay will be off, so your want your float switch to be off at high water level, when the float is floating.
I'm assuming that a Normally on or off float switch means that "normal" is when the float is NOT floating (low water level). If that is the definition of "normal" you want a "normally on" float switch (on when the foalt is NOT floating, and off when it IS floating).
If you're going to trust a float switch, just set it up so that if it ever fails by sticking ON, and pumps your entire reservoir into your tank, it won't overflow. If you want a bigger reservoir, I would use two in-line float switches, such that BOTH need to be on for the pump to run. That way you can only have a flood if BOTH stick ON at the same time.
I'm assuming that a Normally on or off float switch means that "normal" is when the float is NOT floating (low water level). If that is the definition of "normal" you want a "normally on" float switch (on when the foalt is NOT floating, and off when it IS floating).
If you're going to trust a float switch, just set it up so that if it ever fails by sticking ON, and pumps your entire reservoir into your tank, it won't overflow. If you want a bigger reservoir, I would use two in-line float switches, such that BOTH need to be on for the pump to run. That way you can only have a flood if BOTH stick ON at the same time.
^ that is the same thing I do, snail gaurds and all still wont stop the occasional oops... wire at all normally open.
QUOTE (kamikaze_fish @ Mar 8 2010, 11:17 AM) 
...Normally closed would be off.
You got it backwards.
The correct terms are normally "open" (for normally OFF) and normally "closed" (for normally ON)
"Closed" means that the contact points in the switch are closed (i.e. touching, i.e. allowing the flow of electricity - ON)
You're right. I do that a lot lol. I get them right when I use them but when explaining I always tell people backwards.
QUOTE (sae647 @ Mar 8 2010, 01:34 PM)
So I'm building an ATO with a relay. I have both normally on and normally off float switches so i could use either one.
should i use a normally on float switch, so the coil in the relay is always going except when the pump is on, or should I use a normally off float switch, so the coil in the relay turns on to trigger the pump?
I figure less power will be used when the normally off float switch is used. Having the coil on except when the pump is running cant be too good.
Can anyone who knows what im talking about give me some input? thanks.
should i use a normally on float switch, so the coil in the relay is always going except when the pump is on, or should I use a normally off float switch, so the coil in the relay turns on to trigger the pump?
I figure less power will be used when the normally off float switch is used. Having the coil on except when the pump is running cant be too good.
Can anyone who knows what im talking about give me some input? thanks.
By your description, you want the "normally off". I don't want to confuse you, but the "normal" position for a floatswitch is what happens when there's no water. What you describe as "normally off" is actually "normally closed" (closed=on), but the water will usually be holding it open (off).
I also put this together a few days ago. It may be of benefit for you.
QUOTE (neanderthalman @ Mar 6 2010, 01:04 AM)
This is a standard relay based ATO, with provision for redundant floatswitches - nothing exotic. I've seen some great DIY jobs of this type, but thought it would also be of value to the community to put together a low-cost and easy-to-use PCB and 'kit' for people to use. I've also added the first feature - the design includes a simple onboard AC adapter - all you have to provide is normal house power.
The 'kit' is basically a digikey parts list for completing the board. It does not include the external floatswitches, pump, or housing, as those are something that are more specific to your setup.
On to the good stuff:
You'll need one of each of the following:
PCB
Transformer
Rectifier
Capacitor
Relay
Diode
Terminal Strip
Total cost - $19.67
The 'kit' is basically a digikey parts list for completing the board. It does not include the external floatswitches, pump, or housing, as those are something that are more specific to your setup.
On to the good stuff:
You'll need one of each of the following:
PCB
Transformer
Rectifier
Capacitor
Relay
Diode
Terminal Strip
Total cost - $19.67
I have an updated version that will be about $30 total parts, but includes onboard fusing and a "one-shot" timer for extra safety. For every time the floatswitch is closed - no matter how long it is closed - the pump will run for a specific amount of time. If you're interested, I can have it ready by tomorrow.
Thanks everyone, I got it built last night and its working perfectly.
And neanderthalman, thanks but like i said I'm all done now.
And neanderthalman, thanks but like i said I'm all done now.
This is a "lo-fi" version of our main content. To view the full version with more information, formatting and images, please click here.