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Posts Tagged ‘relay’

Solar Battery Charger Cutoff Circuit

August 7th, 2011 4 comments

Using very few components, I have built a solar battery charger cutoff circuitry that would enable automatic cutoff of battery charging when the potential across the battery terminals reached a voltage level chosen by the preset setting in the circuit.  Medium power transistor is operated in Cutoff mode most of the time, so the quotient current of the circuit is fairly low in the order of few mA.  It should be noted that the Vopen-circuit of the solar panel is few volts higher than the voltage when the panel is connected across a load.  So, don’t adjust the preset without connecting the battery. When the circuit is turned on, the battery is directly connected with the solar panel, and hence the voltage perceived by the voltage divider is the load voltage.  When the voltage across the load goes beyond the set point, zener conducts to turn the transistor on, which would pull the relay down and break the charging circuit.  After the battery is disconnected, the voltage perceived by the potential divider circuit is the open-circuit voltage of the panel, which eventually creates a latch effect for the battery charger off condition.  The relay will be ON, till there is sun light and when in the dusk, the input voltage should drop below the threshold voltage to turn off the transistor.

There is a flaw in this circuit. 🙂

When the sun light drops, the relay turns off as the transistor is turned off.  But now, the battery potential will be again available across the potential divider circuit.   There is a potential, oscillation condition here!!

Another Automation Project

May 2nd, 2009 No comments

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Timer Controller for our apartment water pump..

March 29th, 2009 14 comments
We have a 1.5HP compressor pump for pumping water from 350 feet deep to a 100 feet over head tank.  Since, we have water scarcity through out the year, we run the pump following a timing.  Typically in 24 hours, the pump runs for 6 hours in 1 hour slots spaced by 3 hours for water to accumulate in the borewell.

We have assigned the task of switching on and off the water pump to our security guards.  They are doing a good job in keep the pumps up and running, but sometime they either overrun or underrun the pumps.  Being the technical adviser of the apartment, I had decided to replace the security guards to an automatic timer controller.

I did some investigation about timer controllers via Internet and yellow pages but I was not very successful in finding a single stop solution.  There are many vendor who provide water level controllers, but not the timer controller.  So, I decided to go to Parry’s corner in search of an expert who can do the task for me.  I found a vendor in Thambu Chetty street who gave me the contact phone of a person who does erection of pump controllers.  I called the guy and he said he does not handle timer controller, but definitely give me a call back after consulting with his group.

I continued by search in the street and ended at “Switchgears India”, 149/2 Thambu Chetty Street, Chennai 1 and enquired about timer controllers.  He immediately showed me a product which he claimed to be useful for industrial timed switching purposes.  The guy should be Rajesh Bhandari (9840133670).  He showed me the product named “Frontier Timer TM-619H-2”, which had 8 On and Off timers.  There was another engineer who was sitting there helped me in configuring the timer.  When I tried setting the times, I found it very versatile and immediately useful.  They priced this product at Rs 600 without bill or warranty.  The shopkeeper promised that the product is doing well and he had sold over 1000 pieces.  This product also comes with an internal battery for keeping up with the LCD display and clock feature.

The product showed that it can switch on a 2HP motor directly, which I did not believe.  I guess the internal switching is by a TRIAC semiconductor which may burn out if connected directly to an Inductive load like water pump motor.   The shop keeper insisted me to get a Contactor which is typically a Electro Magnetic Relay to do the switching of the pump.  I asked him to offer a product and he gave me a contactor namely “IDEAL ID1-22 1a1b AC220V 50Hz”, which by the spec should be able to switch even a 5 HP motor.

The contactor that he gave is 3 phase relay, which I could use for a single phase motor.  I connected the L1 to supply and T1 to the motor with neutral short directly; L1 and T1 are in N/O connection.  Similarly the contactor had L2 -> T2 and L3 -> T3 for 3 phase switching. I connected the A1 and A2 of the contactor to the Output of the Timer.  The input of the Timer is connected to LIVE supply.  The contactor also provides a N/C connection which I did not use.

I programmed the timer for 6 time slots and connected the supply and load to the contactor.  It works super cool.

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