How to Build a Mains Over Load Protector Circuit for Lathe Machine

The post talks about a basic overload cut off circuit for preserving heavy mains controlled machines for example a lathe machine.

I have previously mentioned one easy overload protector circuit design in one of my earlier articles, the same should be employed for the offered lathe machine overload cut off application.

Talking about the circuit diagram below, we are able to recognize the following main phases in it:

An opto coupler phase related to a bridge rectifier

and a latching relay circuit stage combined with the above opto coupler phase.

The AC mains is supplied at the mentioned left side input, that could be passed on to the load via a load sensing resistor R1 and the connected cut off relay's N/C contacts, N/C stands for typically closed, which means the associates are attached across this point while the relay is in a deactivated condition.

R1 is aptly determined such that a potential difference adequate enough to cause the opto LED grows across it at any time an overload going above the dangerous zone is attained.

The overload cut off procedure is implemented in the following manner:

For provided that the load is within the the regular variety of consumption, the voltage across R1 remains low, maintaining the opto LED disabled.

Nevertheless in case of a short circuit or an overload at the output, which is often in a lathe machine for the offered design, the voltage across R1 shoots and evolves into adequately high in order to turn on the opto LED immediately.

The opto LED on the other hand lights up the connected LDR sealed inside the light proof enclosure leading to its resistance to decrease considerably.

This drop in the the LDR voltage permits a biasing current to the base of R1 which in addition to T2 immediately flips into a latching mode turning on the relay.

The relay associates react to this and provide the essential changeover cutting off the AC line to the load or the lathe machine.

The circuit remains latched and frozen until the power to the circuit is turned OFF and turned on resetting the relay in its initial form. On the other hand the demonstrated push button can also be pressed for the same.

The green LED implies the latched mode of the overload protector circuit as well as makes sure a power off to the output load.

The opto coupler is a homemade device, the manufacturing information can be analyzed below article:

http://homemadecircuitsandschematics.blogspot.in/2011/12/how-to-build-simple-electronic.html

Utilizing an LED/LDR combination for the opto coupler seems to be considerably dependable in its functions, nevertheless a standard LED/transistor opto (for example a 4n35 etc) may also be attempted instead, and may indeed function as reliably, it may be a matter of some experimentation.

R1 can be determined utilizing the following formula:

R1 = LED forward voltage / overload current (in amps)

P1 s for adjusting the sensitivity of the circuit.