Rubbish-Wake up and admit the truth . Stop trying to hide it behind a veil of reasonablness and fantasy
Gee ,its even easier to burn them out when you put 24 Volts on them. Make that 4 now $10 worth They smoaoke and get hot really nicely.
This is the next stage to run them safely in a 24V 1 Amp environment
I'm thinking the best way might be to separate the boards altogether and zener across the exit point of the 24V board after the 7805.
Wonder why they don't design the 7805 to not put out when the ground is unconnected ?
Maybe there is a device available already?
Seems to me a small fet or mosfet on the output source would fix it only conducting if there is current flowing through to ground.
That would not be too hard to design surely?
Nobody else has offered any solution! Just wind ups
The 7805 is designed to regulate it's output voltge to be 5 volts
With Respect To it's Ground Pin. If if sees more than 5V, it turns down the drive to the pass transistor the output. If less than 5V, it turns the drive up.
If the ground pin is not connected to ground, then the 7805 sees less than 5V across the output, so it cranks up the output as high as it can.
The manufacturers data sheet shows how a part should be used in order for the component to work properly. If it's not hooked up that way, then you can't expect it to work as intended.
Troubleshooting of circuits is quite often a matter of finding what's not hooked up right. Broken or missing connections, shorts, or swapped wires, are always possible causes of a circuit not working. Sometimes it just 'doesn't work.' Other times, the failure is more exciting.
As far as adding a zener, a fuse, or some other form of secondary protection, that is never a bad idea. The decision is one of tradeoffs of the cost of the extra protection vs the potential cost of damaged circutry. But even those protection components need to be properly used, or they won't provide the protection expected.