Relay Switch to Automatically Turn on/off waterpump

[PujanG]

Sir,

I've made a circuit using Timer IC 555 that automatically starts waterpump (1HP AC motor ) as the water level goes down & switches it off when the level rises. The circuit works fine. It has a 6VDC operated relay switch that can withstand 10Amp 250VAC. But problem is the motor, rated 1HP 5.8 Amps, gets extremely hot when i operate it through the relay switch.

Is it because the motor is trying to draw more current (ie >10 Amps) which the Relay can't pass?
Why does the motor get hot? Is it because of the relay??

Thanks

 

[itsmoked]

One of many reasons the motor could be getting hot.

1) Look at the name plate and see what the RISE is. It could well be enough to freak you out but be harmless to the motor.

2) The relay could be too small. You need to check the relay for what horsepower rating it has at the voltage your motor is running at. It's nowhere near good enough to have a relay's amperage exceed a motor's running current draw. A motor rated relay will list the motor HP it can start and interrupt.

3) You could be abusing the motor in many different ways that would cause it to heat up. Perhaps you have too great a flow thru the pump. Restricted air flow? Loose fan? The motor is spinning too slowly?

Measure the motor's running current with a clamp-on and make sure you're not exceeding the FLA on the nameplate.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MacGyverS2000]

Also, how often does the pump cycle? Frequently turning a motor on/off will heat it up due to the inrush current.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[ScottyUK]

Motors can be well within their capability and still be blistering hot. You could, quite literally, cook on the surface of a Class H motor. How hot is 'extremely hot'?

 

[Erro11]

The motor start-up current can be much larger than the steady-state running current. (Check the motor spec for start-up current if possible.) A rule of thumb is to multiply the steady-state running current of the motor by 5 and use that size relay, switch and breaker. Also note that during turn off that an inductive fly back may produce an arc across the relay or switch thus requiring an MOV to suppress the transient voltage spike. MOVs are cheap. If you have already exceeded the current capability of your relay, it may have failed (welded closed or be not provide adequate closure). Provide adequate ventilation for the motor.
Many times a special protection-relay is used for motor turn-on because a normal circuit breaker with a five times rating will trip if the 5X surge is exceeded but not protect the motor for steady-state over-current. This type of breaker is called an "overload-relay". It allows 5X current at turn-on but after a period of time and will then trip-off at a lower current. Overload-relays are not so cheap.
Google
"overload-relays"
"Digi-key" and search the website for "MOV"
Select one for 253VAC minimum and at least 5X motor current for the transient current value.
Good luck - I assume no responsibility; you are on your own.

 

[PujanG]

Sir,

I couldn't manage to look at the name plate but found the specification from the manufacturer.

http://files.engineering.com/getfil...738-4bcc-a5f4-fc29096df7e2&file=motorspec.JPG

Motor seems to have a Class B insulation. But I guess I have burnt out its insulation in my first attempt to power it up using a very long wire not meant for carrying heavy current load. How do i confirm it? & if so, can i change the insulation?

For now the motor is operational, "hot" though. I've encountered another problem with the relay circuit. The Relay seems to briefly turn itself on when i turn off the circuit; which starts the motor briefly. That's Annoying!

I've attached the Schematic of the Relay Circuit. Please have a look at it.

Thank you

 

[OperaHouse]

When I saw your initial post I thought, If I can't say anything nice about a 555 I shouldn't post. Welcome to the world of the 555 which I won't use for anything. Try putting some caps to ground on each of the inputs like .1uF

 

[PujanG]

Operahouse

I wish you had suggested me not to use IC 555 for anything before hands...
The Rudimentary knowledge of the IC 555 costed me my motor today.

It died due to sheer heat.

F**K the circuit.

 

[MacGyverS2000]

I thought you burnt it up from running it at too low a voltage (due to running a too thin and too long cable)... ?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[waross]

I am still wondering why you need a timer when you have a high level switch and a low level switch.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Other than switching the motor on and off too rapidly, there's not much the control side of the circuit can do to harm the motor. The problem is elsewhere - bad wiring, bad motor, bad attitude, so many possibilities...

 

[davidbeach]

Bill's right though, not much use for a timer in a low on/high off application. Level switches do that job to a tee.

 

[PujanG]

Bill,

I wonder if you are mean i don't need the IC at all..
But the switches are just to simulate the water level. water will act as a conductor to complete the circuit. 3 Exposed wires are placed in the tank, where Vcc is supplied only at the lowest wire.

Hmm... if it can be achieved without the use of IC.. I'd love to see the schematics.

Thanks..

ScottyUK, ya you are right It must be ME, afterall.

 

[ScottyUK]

The motor switching aspect should be trivial. Some greater clarity about the level sensing would be very helpful: what switches / sensors do you actually have available to you? If you can define the problem more clearly then maybe someone can help you solve it.

 

[waross]

There are several level controls available commercially which will control the water level.
An isolation transformer may be used for safety. A relay is chosen which will pull in when water covers all three probes and stay pulled in when the two lowest probes are covered with water.
The relay has at least three poles. The high level probe is connected to the relay coil. The low level probe is connected to the relay coil through a set of normally open contacts.
When the water covers the upper probe the relay is energized and the low limit probe is also connected to the coil through the normally open contacts.
As the water drops the relay stays energized until the low limit probe is above the water level.
To empty the tank connect the second set of normally open contacts to run the pump.
To fill the tank connect the normally closed contacts to run the pump.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[1capybara]

i would use a float switches and eliminate the 555. some float switches combine low and high level indicators into a single signal cable