surely R1 needs to come from the positive supply not negative, like that the transistor will just not pass current
Thanks. Yes i did miss i a wire.
Your existing design has the merits of being robust and inexpensive. The 7824 will give you tighter regulation and current limiting (sort of). It is not true current limiting, but it limits based on thermal, so you will reach some steady state current on an overload. The other caution is that the 7824 have a max Vin of 40 volts, which could be an issue with surges that might occur with lightning. You could add parts to mitigate the surge sensitivity, but the cost will go up.
I would be tempted to stay with what you have and just ass a polyfuse (PTC fuse) to the DC line feeding the transistor. Again thermal protection that will limit current. Simple and robust.
Thanks. It is also my gut feeling that the 7824 is not robust enough.
I have tried the polyfuse solution.
The circuit powers 4 wind sensors.
On installation they did an error (shorted) one sensor. Then they did see that they did it wrong. The polyfuse was so hot that the consumption from the 4 sensors did keep the polyfuse hot
and newer got reset before they changed the PCB.
So the polyfuse is not a fix here.
Current limiting could be easily added to the existing design.
Thanks.
Why did i not think on that ? I am surely getting a little rusty.
I was thinking of adding a current limiter. But thinking in the direction of an extra power transistor+current sensor.
Thanks this must be the answer to my "little" problem. Only 3 cheap/easy components more.