I have this beautiful old school clock, built in 1952 and still works great.
it's designed to be a slave, driven synchronously from a master clock in the principals office.
It requires a 24 Volt DC pulse once per-minute to operate, I built an AC Line powered driver for it years ago, but needing the line cord sucks.
My goal is to create a battery powered driver for this clock, so it can hang on the wall without wires.
The mechanism has a solenoid coil of about 680 ohms resistance, which would draw about 35 ma @ 24 volts.
The power required is (24 * 0.035) = 0.84 watts, times duty cycle, (0.2 / 60) * 0.84 = .0028 watts (assuming a 200 ms pulse, every minute)
An alkaline "D" cell is supposed to contain about 20 watt-hours of energy, so it might last 1.5 years- (theoretically?)
I am considering the following architecture:
3 VDC power source- 2 "D" cells- I want it to run for at least a year between battery changes.
Micro-controller running 32.768 Khz crystal for time keeping- creating the once per minute pulse.
Simple boost converter to charge a capacitor to around 30 V.
What I am considering is having the boost converter shut down most of the time, then have the converter kick in after every pulse to re-charge the capacitor. This would conserve power, no wasted quiescent current from the boost converter once the capacitor is fully charged.
For simplicity, I was considering having the micro-controller generate the pulses for the boost converter, operating in "fixed-on-time" mode.
A comparator would monitor the capacitor voltage, the micro would stop making pulses once the capacitor is charged.
Anyone have any ideas on how to do this simpler, better, cheaper?
it's designed to be a slave, driven synchronously from a master clock in the principals office.
It requires a 24 Volt DC pulse once per-minute to operate, I built an AC Line powered driver for it years ago, but needing the line cord sucks.
My goal is to create a battery powered driver for this clock, so it can hang on the wall without wires.
The mechanism has a solenoid coil of about 680 ohms resistance, which would draw about 35 ma @ 24 volts.
The power required is (24 * 0.035) = 0.84 watts, times duty cycle, (0.2 / 60) * 0.84 = .0028 watts (assuming a 200 ms pulse, every minute)
An alkaline "D" cell is supposed to contain about 20 watt-hours of energy, so it might last 1.5 years- (theoretically?)
I am considering the following architecture:
3 VDC power source- 2 "D" cells- I want it to run for at least a year between battery changes.
Micro-controller running 32.768 Khz crystal for time keeping- creating the once per minute pulse.
Simple boost converter to charge a capacitor to around 30 V.
What I am considering is having the boost converter shut down most of the time, then have the converter kick in after every pulse to re-charge the capacitor. This would conserve power, no wasted quiescent current from the boost converter once the capacitor is fully charged.
For simplicity, I was considering having the micro-controller generate the pulses for the boost converter, operating in "fixed-on-time" mode.
A comparator would monitor the capacitor voltage, the micro would stop making pulses once the capacitor is charged.
Anyone have any ideas on how to do this simpler, better, cheaper?