No Voltage switch.

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Crazyn3wf

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Hi,
I need to switch on and off a 120v AC Pump with a float switch, while keeping the switch on a seperate no voltage circuit. Im not sure what I need to accomplish this.

Thanks!
 
no, I do mean no voltage. I know I can do this with a relay if I had voltage on the Switching circuit, but I am wondering if there is a way to do this with no voltage on the Switching side?
 
I guessed he means a set of volt free contacts but the question is very vague.

A 120VAC relay could be connected across the pump motor to switch another circuit.

120VAC is low voltage but many people misuse the term to mean extra low voltage, i.e. <50VAC.
 
Crazyn3wf said:
Hi,
I need to switch on and off a 120v AC Pump with a float switch, while keeping the switch on a seperate no voltage circuit. Im not sure what I need to accomplish this.

Thanks!
Click to expand...

You can't do it with "No Voltage" however it is easily done with Low Voltage and a relay. You have a float switch and it will need to send some sort of voltage to a relay and the relay in turn takes care of the pump.

Ron
 
How about doing it with a "very small voltage"?

Usually, the way a switch works is that you apply a voltage difference between its terminals through a series resistance, and then ask the questions "how much current is flowing through the circuit?" (No current means switch is open; some current means switch is closed),

or you ask "what is the voltage across the switch?" (voltage > threshold means switch is open, voltage < threshold means switch is closed).
 
Reloadron said:
You can't do it with "No Voltage" however it is easily done with Low Voltage and a relay. You have a float switch and it will need to send some sort of voltage to a relay and the relay in turn takes care of the pump.

Ron
Click to expand...

Can this be done with say a 9V DC Battery on the switch side? and if so what type of Relay would need to be used? I would assume the DC Voltage would not be enough to switch something like G2R-1A-T-AC120.

Thanks
 
That relay coil takes a relatively high voltage (but low current) to switch it on. The coil is is designed to operate from 120V AC power, providing the exact opposite of what you want, because there will be 120VAC across the float switch contacts when they are open.
I'm guessing that your requirements are "isolation from the AC power line", and "minimize shock hazard" by using transformer isolation from the AC power line, and using low-voltage DC on the switching side of the relay?

A battery circuit is NOT the way to go, because if this is for a "standby" application, the battery is guaranteed to be dead when needed...
 
Last edited:
The problem is that the float switch will not handel the current of the Pump so I can't connect it direct I need the Relay in between.
I Guess what i need is a relay with a coil that will switch at say 9V or 12V and handel the 120V current on the other end?
 

Sealed Float switches rated at 240Vac and capable of switching directly motors of 2 to 3 HP are in common use.

EDIT:
Added pdf
 

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And yes the Safety is a concern also.
 
Home furnaces and air-conditioning units are full of "low-voltage" transformers, relays, thermostats, etc. For example, the 120V to 24Vac transformer in your furnace sends a current through your wall-mounted thermostat. When the thermostat calls for heat, it closes its contacts, pulling in a relay with a 24Vac coil inside the furnace which powers (amongst other things) the 120V 1/4HP blower motor.

I cite this because this is the method I would use for your application. A 24Vac industrial "control" transformer, a 24Vac relay with contacts suitable for switching your pump are readily available at industrial electric distributors...
 

Thanks, I Think this solution will work well.
 
Crazyn3wf said:
Can this be done with say a 9V DC Battery on the switch side? and if so what type of Relay would need to be used? I would assume the DC Voltage would not be enough to switch something like G2R-1A-T-AC120.

Thanks
Click to expand...

I do it as Mike suggested. I use generally a 12 VDC relay but sometimes use 24 VAC relays. The relays have 10 Amp contacts and they switch the pumps on or off based on the position of the float switch. Relatively simple circuit. I go this way because I don't want 120 Volts AC in our sumps. I should point out that when I say low voltage in AC or DC I refer to a voltage < 50 volts.

Ron
 
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