turn quarter horsepower motor on and off

Thread Starter

whitehaired novice

Joined Jul 15, 2017
289
I need to turn on and off a quarter horsepower sump motor which is nearly always under water. At the moment I plug and unplug it but I want to turn it on and off with a timer circuit. There are a lot of heavy duty relays but I know they will arc. Is there a circuit which will eliminate the arcing? Or could I use a triac?
 

Thread Starter

whitehaired novice

Joined Jul 15, 2017
289
You could use a SSR, What kind of timing periods do you need?
There are many relays that can switch a .25hp motor.
Max.
I have (well, will have as I am building it now) a float switch which will turn on a 20 minute timer (ne555) which will close a small circuit board mounted relay. My hope is to have that operate a 5 or 12 volt relay which will handle the current for the motor. It isn't hard to find a relay with 30 amp contacts but I fear the induction will cause serious arcing. Any help? Thanks.
 

Reloadron

Joined Jan 15, 2015
6,704
I turn a .5 HP sump pump On / Off using a simple common sump pump float switch. Sump gets full the pump turns on and when the sump level is low it turns the pump off. I have yet to have issues with switch contacts. A sump switch like this runs about $20 at any home improvement store and is rated for a 1/2 HP motor so would likely last an eternity with a 1/4 HP motor. The full load current on a 1/3 HP motor is about 7.2 Amps, not much load to switch on and off. A general purpose relay with a snubber would likely work fine or a 10 Amp SSR with a snubber would work fine also.Here is pretty much what I use. There are dozens of similar ones out there designed for motors inductive loads. I also use a float switch to tell me if my sump is getting too full and the pump has failed. Anyway if you want an SSR or Triac circuit then by all means go for it, I would just buy an over the counter 10 Amp SSR.

Ron
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
25,469
As per Ron, I also have a sump pump that has been in operation for 30yrs, switched by a simple float switch.
You do not need a 30amp relay or contactor.
Even cheap automotive relays will switch it, they are 240v insulation rated.
Max.
 

Thread Starter

whitehaired novice

Joined Jul 15, 2017
289
I turn a .5 HP sump pump On / Off using a simple common sump pump float switch. Sump gets full the pump turns on and when the sump level is low it turns the pump off. I have yet to have issues with switch contacts. A sump switch like this runs about $20 at any home improvement store and is rated for a 1/2 HP motor so would likely last an eternity with a 1/4 HP motor. The full load current on a 1/3 HP motor is about 7.2 Amps, not much load to switch on and off. A general purpose relay with a snubber would likely work fine or a 10 Amp SSR with a snubber would work fine also.Here is pretty much what I use. There are dozens of similar ones out there designed for motors inductive loads. I also use a float switch to tell me if my sump is getting too full and the pump has failed. Anyway if you want an SSR or Triac circuit then by all means go for it, I would just buy an over the counter 10 Amp SSR.

Ron
I don't understand, from the picture on Lowe's website, exactly how that switch works. I see that the plug goes in the ac power outlet and the motor gets plugged into the other end of that plug. Does the float get thrown to the bottom of the sump and, when the water gets high enough it floats upright, turning the power on for the motor?
 

Reloadron

Joined Jan 15, 2015
6,704
I don't understand, from the picture on Lowe's website, exactly how that switch works. I see that the plug goes in the ac power outlet and the motor gets plugged into the other end of that plug. Does the float get thrown to the bottom of the sump and, when the water gets high enough it floats upright, turning the power on for the motor?
Yes, that's how they work. A single waterproof cord runs to the float switch which switches the outlet located on the plug. A visit to any good home improvement store will yield plenty of styles and types for a wide range of sumps. Sump Pumps themselves have all sorts of "flavors" these days including ones with battery backup. I just use a simple sump with the style switch I linked to.

Since I am not looking at your sump it is difficult to comment but as an example using a timer you want to make sure you never run the sump dry as pumps hate that. This is why a simple float switch is generally used.

Ron
 

Tonyr1084

Joined Sep 24, 2015
6,890
exactly how (DOES) that switch work(?)
There are two contacts inside near the cord. There's a steel marble (bearing) inside, and when the float rises upright the steel ball will make contact and turn the motor on. They used to do it with mercury switches inside glass bulbs. But mercury is hazardous so it's no longer used. Somewhere in my collection of mostly useless junk I have a mercury wall switch. Silent in operation, no click. Just "Lights ON" or "Lights OFF". No click.
 
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