I received the following simple transistorized water level controller circuit 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.
The Circuit Design
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.
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.
R1,R11 - 100K
R3 -10KR5 - 4.7K
R6 - 47K
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)