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Timer circuit with time HOLD when power is OFF

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chargermaintngn

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Hi , i need to make a relay timer hold circuit to drive a battery charger when input supply is present but when the input supply is removed the circuit must hold the time and when the input supply is connected it starts from there, can you help me to make a battery charger with timer.

Thank you,
 
How will the circuit hold the time? will it use current from the battery that is connected to it to hold the time?

You can have a counter, and the clock pulse stops when the supply is removed via a transistor, hence holding the timer value

You will have to have another power source though. just realised charge time will be affected lol.

Perhaps use a clock/alarm clock. Have a 1.5V or 3V output from the input power supply, and when power not connected, the clock will not run. And maybe set the charging time with an alarm clock

With the alarm clock, it can even switch off current to the batteries when charging is complete to prevent over charging

I am talking about an analogue clock btw, not digital as time may be reset due to power loss
 
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If you're using a digital timer, simply inhibit the clock to the timer when the power is not present.

Do you have a timer circuit in mind? If not, then what is the time period the relay needs to stay on for? What kind of display does it require?
 
If you're using a digital timer, simply inhibit the clock to the timer when the power is not present.

Do you have a timer circuit in mind? If not, then what is the time period the relay needs to stay on for? What kind of display does it require?

I said that, but what is going to power the timer when input power supply is not connected? unless he wants to have another set of batteries to run that zzz
 
I said that, but what is going to power the timer when input power supply is not connected? unless he wants to have another set of batteries to run that zzz
It makes the most sense if the battery under charge remains connected when input power is not available, which means there's a power source available. There would be negligible current drain if designed appropriately.

Even if that was not the case, it's simple to make a digital timer that remembers the time when it stopped even without power.
 
Build a CMOS timer based on a 4060 powered from the battery under charge. If the AC goes off, the battery will never even notice the 10s of uA that it will take to keep the flip-flops inside the 4060 in their present state. If the clock is powered from the AC, the clock stops when the power goes off, but the state of the timer logic is preserved. Hell, you even power the 4060 on a coin cell, and it would run for years.
 
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