Simple Water Level Controller Circuit with Over Voltage and Under Voltage Cut OFF

I received the following contribution from Mr.Vineesh, who is one of the keen readers and followers of this blog. He is also an active hobbyist who likes to invent and make new electronic circuits. Let's learn more about his new circuit which was sent to me via email.
Dear sir,

Hope you fine. pls find the attached  ckt for a very simple and cheap water level controller. This  ckt is only a basic portion of my own marketed product having unsafe voltage cutoff ,dry run cut off and LED & alarm indications and overall protection .Any way, given ckt includes automatic water level control and high /low voltage cut off. sorry for cannot send the entire ckt  due to limitations.WATER LEVEL CONTROLLER  ckt is  not new concept since we can find 100s of ckts  for water level controller in many sites and books.But This ckt is  simplified with least no: of cheap components. water level sensing and high voltage sensing is doing  with same transistor. I used to put all my ckts in observation for a few months and found this ckt OK. but recently some problems highlighted by some customer,which i will definitely write down  the end of this mail.

CIRCUIT DESCRIPTION

When the water level in over head tank is sufficient , points B & C  are closed through water and keeps T2   in ON condition .So  T3 will be off , resulting the motor in off condition. 

When water level lowers  below  B &C,  T2  gets off  and   T3 on, which  switches  the relay and  pump ON (pump connections not shown in ckt). Pump  get off  only when water  rises and touch the point  A  only , because point C becomes  neutral condition when T3 get ON. The pump  switches on again only when the water level comes down below B & C .

Presets VR2 is to be set to a high voltage cut off, say 250V when the voltage rises above 250V during pump ON  condition, T2  gets ON, and relay  off.

Preset VR1 is to be set to a low voltage cut off say 170V. T1 will be ON until zener z1 loses its breakdown voltage when voltage lowers to 170V,  Z1  will not conduct and T1  stays OFF, which delivers  a base voltage  to  T2 , resulting relay off.

T2 is handling the major role in this ckt. (high voltage cut off boards available in market can be easily integrated to this ckt)

Electronic components in this circuit worked very fine, but recently some  problems were  observed:

1) Minor deposits on sensor wire due to electrolysis in water, needed to be cleaned in 2-3 months( this problem is minimized  now by applying  ac voltage to sensor wire by means of additional ckt, which  will be send to you later)

2) Due to relay contact terminal sparks, generated every time during initial current pull of pump, contacts get worn out gradually.which tend to heat the pump because off in-sufficient  current flow to pump  (observed, new pumps works fine. older pumps heats up more) .

For avoiding this problem, additional motor starter  must be used, so that relay's function is limited to control the motor starter only, and pump never heats up.

PART LIST

R1,R11   - 100K

R2,R4,R7,R9,- 1.2K

R3  -10K

R5  -  4.7K

R6  -  47K

R8,R10  -10E

R12  - 100E

C1   -   4.7uF/16V

C2   -   220uF/25 V

D1,D2,D3,D4- 1N 4007

T1,T2   -     BC 547

T3          -    BC 639( try 187 )

Z1,Z2-    Zener 6.3 V,

VR1,VR2- 10K PRESET

RL - Relay 12V 200E, > 5 AMP CONT ( According  to pump HP)

Thanks& regards

Vineesh Kodambattil.

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