Hello. I have been getting great help from members, particularly MikeML, in this thread to make a low-voltage cut-off circuit to protect a battery of 4 AA NiMH cells that will power a small 1.5-2W heater.
The purpose of the heater is to ensure that a hummingbird feeder doesn't freeze when the temperature goes below zero C. Here in the Pacific Northwest (Victoria, BC) the Anna's Hummingbirds don't migrate. So I want to ensure one of their primary winter food sources is available.
The circuit MikeML proposed looks good, and though I am still trying to fully understand it's operation, I have decided to give it a try. However, the battery pack is small and I know we only have freezing temperatures some of the time, so to increase the time span per charge, I would like to make the circuit turn off the load (heater) when the temperature is greater than 1 degree C and turn on again when the temperature is lower than 1 degree C.
If this is a relatively possible thing given my limited experience, I would greatly appreciate the help. I was wondering about using a thermistor, but maybe a temperature sensor module would be best.
In MikeML's circuit, the voltage reference TL431 has a 50kΩ adjustment to set the low-voltage cut-off. If I knew how the voltage reference component worked, I would know if an increase or a decrease in the adjustment resistance raises or lowers the trigger voltage. Then I might know if a thermistor would be able to reduce the trigger when the temperature is high so the load remains off until the temperature decreases. I will have an opportunity to learn more when I receive the parts and can get hands-on.
Would it be better to have a second cut-off circuit in series with the low-voltage circuit? Maybe a similar circuit to MikeML's but with a temperature reference instead of voltage.
Insight would be greatly appreciated. Also, happy American Thanksgiving!
The purpose of the heater is to ensure that a hummingbird feeder doesn't freeze when the temperature goes below zero C. Here in the Pacific Northwest (Victoria, BC) the Anna's Hummingbirds don't migrate. So I want to ensure one of their primary winter food sources is available.
The circuit MikeML proposed looks good, and though I am still trying to fully understand it's operation, I have decided to give it a try. However, the battery pack is small and I know we only have freezing temperatures some of the time, so to increase the time span per charge, I would like to make the circuit turn off the load (heater) when the temperature is greater than 1 degree C and turn on again when the temperature is lower than 1 degree C.
If this is a relatively possible thing given my limited experience, I would greatly appreciate the help. I was wondering about using a thermistor, but maybe a temperature sensor module would be best.
In MikeML's circuit, the voltage reference TL431 has a 50kΩ adjustment to set the low-voltage cut-off. If I knew how the voltage reference component worked, I would know if an increase or a decrease in the adjustment resistance raises or lowers the trigger voltage. Then I might know if a thermistor would be able to reduce the trigger when the temperature is high so the load remains off until the temperature decreases. I will have an opportunity to learn more when I receive the parts and can get hands-on.
Would it be better to have a second cut-off circuit in series with the low-voltage circuit? Maybe a similar circuit to MikeML's but with a temperature reference instead of voltage.
Insight would be greatly appreciated. Also, happy American Thanksgiving!