Electric shock in water

[garg29]

electric shock on water

Hi friends,
I have build a water tank controlling system, Using normal metallic probes as sensor. As for power supply i'm using normal Stepdown transformer 230v ac to 6-0-6 v and diodes and regulator with capacitors. Now what i'm afraid is, in INDIA due to voltage fluctuations the transformer burners out and there is current leakage between primary and secondary coil of tranformer which results in electric shock in water (due to immersed probes in water). Please tell me how can i build a isolation circuit and/or what more techniques can i use. i cannot change the type of sensor.

i've built the circuit using second part of this circuit

**broken link removed**

Thanks

With best regards,
Amit

 

[IanP]

electric shock water direct current

I would rater concentrate on how to protect transformer than on how to react after it is damaged ..
Undervoltage doesn't cause problems; you have to protect transformer agaist overvoltage ..
Try to install a MOV in parallel with the primary, and a resistor, or thermo-resistor, and a fuse in series with the primary ..
Regards,
IanP

 

[garg29]

electric shock in water

Thanks a lot for replying Ianp. What values of resistors should i take. And still for knowledge is there anyway to do isolation.

 

[IanP]

It can be assumed that the voltage accross the series resistor shouldn't be more than 5% of 230V --> ≈10V ..
I am no sure what is the VA rating of the 230/2x6V transformer, but let's assume it is 10VA ..
That means that the primary current is ≈50mA ..
Bearing in mind that the voltage (5%) is 10V, the resistrs valuecan be ≈200Ω rated for at least 1W ..

As far as the isolation issue is concerned, I wouldn't suggest any other option but 1:1 isolation transformer with one of its poles connected to earth through a parallel RC tank consistng of >1MΩ resistor and ≈10-100nF/250Vac capacitor ..

Regards,
IanP

 

[7rots51]

The trans may break from any phenomenon,so it is better (for safety) use high isolation DC/DC converter at output of transomer (regulated trans output),you can have double layer isolation,DC/DC have 3000VDC isolation and you can buy them easily.


You can use dc/dc for only the probe section of you circuit (probe side isolation) and other parts need not to be isolated ,you can change data by optocoupler for isolation of data!

 

[rajudp]

use a good quality transformer, use the transformer power rating more than what you need in your design. if you encounter the problems you cam make a transformer that can stand upto 270 volt.

 

[darla1]

hi garg

better take isolation volateg range 4kv to 5kv for rural particularly in INDAI

darla

 

[Siniša]

Ground 0 terminal of secondary coil

 

[joebazoka]

Maybe you can use an ultrasonic sensor.

 

[adidav]

The IanP ideas is very good and this will protect the transformer from overvoltage. Also you cand add in parralel with the fusible or resistor a small lamp (AC neon lamp) or a led with the rol of signaling the fault state.

Also an ideea is to use a optocouplers between the sensor and the main unit and a DC/DC convertor for powering the sensor. In this case one optocoupler to send information from sensor. The DC/DC convertor cand be made using a 555 circuit as astabil and small ferrite transformer.

The grounding the whole system is needed also.

A small circuit using a microcontroller like 12F683:
- PWM for genreate the signal for sensor
- ADC for measure the value after sensor
- a sw implemetation of IIC for comunicate with another module