3 wire float switch to a pump

[SK092170]

I have a float switch hooked up so it controls a 120 v single phase fuel tank pump. It is normally closed when the float bottoms out pumping fuel into the tank and opens when the float rises shutting the pump off I have the line coming in and branching off to a contactor and the other line going through the float switch and to the coil of that contactor. The neutral goes to the pump and also branches off to the coil of the contactor.
The switch is rated for 500 ma. The current should go through the switch to the relay coil which is 28 ma energizing it and then closing the contactor energizing the pump. I seem to have burned out the float switch. Any advice related to this project anyone has would be appreciated.

Thank you

 

[Dsg319]

I have a float switch hooked up so it controls a 120 v single phase fuel tank pump. It is normally closed when the float bottoms out pumping fuel into the tank and opens when the float rises shutting the pump off I have the line coming in and branching off to a contactor and the other line going through the float switch and to the coil of that contactor. The neutral goes to the pump and also branches off to the coil of the contactor.
The switch is rated for 500 ma. The current should go through the switch to the relay coil which is 28 ma energizing it and then closing the contactor energizing the pump. I seem to have burned out the float switch. Any advice related to this project anyone has would be appreciated.

Thank you

Can you draw it out?

 

[ptonsparky]

Do you have delays built into the start/stop sequences?

 

[sparkybob86]

Is it a single float? If it is not what they call a "super single" in other words the float would activate at a position 45 degrees above horizontal and deactivate at 45 degrees below horizontal depending on weather your pumping down or up.if you get a float that was meant to work with a two float system the float contact has very little range to it.that type of float can cause your contactor to chatter and burn up as well as your float.Is this an OEM float? how long had this float been in operation?

 

[GoldDigger]

If the fuel in question is gasoline, I would expect that not just any float switch would be safe, regardless of the voltage needed for the relay coil.

SK092170, you have been a member since 2019. Since then a software change has deleted occupation information from user records. Please fill in your occupation again so we can see your relation to the electrical industry.​

 

[SK092170]

Is it a single float? If it is not what they call a "super single" in other words the float would activate at a position 45 degrees above horizontal and deactivate at 45 degrees below horizontal depending on weather your pumping down or up.if you get a float that was meant to work with a two float system the float contact has very little range to it.that type of float can cause your contactor to chatter and burn up as well as your float.Is this an OEM float? how long had this float been in operation?

It is a vertical float switch, reed type.

 

[SK092170]

If the fuel in question is gasoline, I would expect that not just any float switch would be safe, regardless of the voltage needed for the relay coil.

SK092170, you have been a member since 2019. Since then a software change has deleted occupation information from user records. Please fill in your occupation again so we can see your relation to the electrical industry.​

The fuel is diesel.

 

[SK092170]

Do you have delays built into the start/stop sequences?

No.

 

[SK092170]

Can you draw it out?

Can you draw it out?

Can you draw it out?

Soon as I can figure out how to shrink the pic for the forum.

 

[EC Dan]

If you are using a float switch with little to no dead-band and don't have on/off delays, then you could be continually exceeding the 500 mA switch capacity with the contactor coil inrush current. What is the make/model of the float switch and contactor?

 

[SK092170]

If you are using a float switch with little to no dead-band and don't have on/off delays, then you could be continually exceeding the 500 mA switch capacity with the contactor coil inrush current. What is the make/model of the float switch and contactor?

The float switch I do not have a pn for, the contactor is an ABB DP25C3P-1, 120 vac coil. I could use a RIB in place of a contactor that has a 120vac coil with a 28 ma rating.

 

[SK092170]

Can you draw it out?

 

[EC Dan]

Inrush on that contactor coil looks to be 500 mA, right at your switch capacity. When you say 'I seem to have burned out the float switch', what is the actual state of the switch? Is there heat damage or does it just not switch anymore? Are you sure the switch is rated for 120 VAC?

 

[ptonsparky]

Upfront you need to put a TDR in your control circuit. Have the float energize the TDR. 30 seconds, or whatever, later have the pump come on thru a set of NO contacts of the timer.

 

[SK092170]

Upfront you need to put a TDR in your control circuit. Have the float energize the TDR. 30 seconds, or whatever, later have the pump come on thru a set of NO contacts of the timer.

Thank you for the advice. I appreciate it!

 

[SK092170]

Inrush on that contactor coil looks to be 500 mA, right at your switch capacity. When you say 'I seem to have burned out the float switch', what is the actual state of the switch? Is there heat damage or does it just not switch anymore? Are you sure the switch is rated for 120 VAC?

It does not switch anymore. I see my error with the contactor. Its likely to close to that switch capacity. It is rated 120 volts.

 

[Russs57]

Reed switches don't like inrush current. I suggest adding a small "interposing relay". Have the float switch pull in the coil of a small "ice cube" relay and the contacts of that relay pull in the pump contactor.

Rather or not you need two floats and/or TDR's depends on tank size....float on/off differential...etc. As long as pump isn't short cycling you are fine.

 

[Russs57]

P.S. Might consider adding a snubber across relay coil. Strange as it may sound, when the relay drops out may be what is frying the float switch.

 

[SK092170]

Reed switches don't like inrush current. I suggest adding a small "interposing relay". Have the float switch pull in the coil of a small "ice cube" relay and the contacts of that relay pull in the pump contactor.

Rather or not you need two floats and/or TDR's depends on tank size....float on/off differential...etc. As long as pump isn't short cycling you are fine.

A relay is good advice. I was thinking of using a RIB relay. Coil draw is 28ma. Contacts are rated for 1/2 hp at 120v.

 

[LarryFine]

Reed switches don't like inrush current. I suggest adding a small "interposing relay". Have the float switch pull in the coil of a small "ice cube" relay and the contacts of that relay pull in the pump contactor.

I did that when I put a 4-p contactor in my home-theater breaker panel to switch four of the circuits from the 12v, 15ma trigger output on my preamp/processor. A reed relay was the only one I found with a low enough coil current.

The reed relay controls a 10a cube relay, which in turn activates the contactor. I used this GE panel because the offset breaker location allows enough room for the contactor and little plastic package I put the reed and cube relays in.