Two stage Battery Charger Using 555

[thecritic]

I have designed a two stage battery Charger using 555 timer IC in Schimit mode. I would Like you to review it and make some suggestions if necessary.
This Circuit Switches on the Relay Whenever the Supply Voltage is Less than 12.6 Volts (set by VR2) and switches of the Relay whenever the supply voltage is greater than 14.8 Volts (set by VR1). The Relay Swithces between two chargers, one of High Amperes and Other of Low Amperes.

**broken link removed**

 

[ericgibbs]

I have designed a two stage battery Charger using 555 timer IC in Schimit mode. I would Like you to review it and make some suggestions if necessary.
This Circuit Switches on the Relay Whenever the Supply Voltage is Less than 12.6 Volts (set by VR2) and switches of the Relay whenever the supply voltage is greater than 14.8 Volts (set by VR1). The Relay Swithces between two chargers, one of High Amperes and Other of Low Amperes.

hi,
Your circuit will not work.
As you are applying the same battery voltage to the two dividers VR1 and VR2 , the wiper voltages will just track each other, never reach a changeover point

The RESET should be tied to +5V

Also the 22K base resistor is far too high a value, a value about 470R would be a better choice.

There is no clamp diode across the relay coil.

 

[thecritic]

Thanks

The VRs will work fine. (Actually already worked). Its just like the astable multi-vibrator mode of 555 timer in which pin2 and pin 6 of 555 are tied together and same voltage (of capacitor) is applied together.
For the suggestion of 22Kohm, resistor, I replaced with 2k2 and it has been working fine.
thanks.
I also tied 1N4148 diode across the relay.
The only problem I am facing at the moment is that the VRs are very much sensitive. I have a very hard time adjusting them.
(Not shown in the diagrams are 47uF Capacitors placed at various places to suppress spikes)