No, this makes sense. When AC voltages are measured, they calculate the average power generated within a cycle through a resistor and quote whatever DC voltage would generate the same power through the same resistor.
In the end, it means the peak AC voltage is 40% higher than the VAC reading on the voltmeter. The capacitor will charge up to the peak voltage, and if it's not supplying a lot of current, on average it will take this peak value all the time. So, 18*1.4=25, we subtract the voltage drop through the bridge diodes and 24 VDC looks reasonable.
If you have some power resistors you could connect as load, you would find the voltage dropping as the transformer AC voltage drops and the capacitor charging becomes more important.
For the regulators, I'm baffled. Is there a load resistor, i.e. how much current are you trying to supply? The metal tab is connected to ground, could this be an issue?
In the end, it means the peak AC voltage is 40% higher than the VAC reading on the voltmeter. The capacitor will charge up to the peak voltage, and if it's not supplying a lot of current, on average it will take this peak value all the time. So, 18*1.4=25, we subtract the voltage drop through the bridge diodes and 24 VDC looks reasonable.
If you have some power resistors you could connect as load, you would find the voltage dropping as the transformer AC voltage drops and the capacitor charging becomes more important.
For the regulators, I'm baffled. Is there a load resistor, i.e. how much current are you trying to supply? The metal tab is connected to ground, could this be an issue?
Thanks a lot for clearing up the 24VDC for me, that's put my mind at ease!
I've tried putting a resistor and LED on the output to no outcome. The regulators still aren't regulating. I thought they would be putting out 24VDC without a load, not 0V!
This has sort of reconfirmed my suspicions of a short. The metal tab is connected to ground on the 7815, but pins 1 and 2 are swapped on the 7915, making the tab the input. These are currently unconnected to anything, so I can narrow it down to just the legs. I'll pick up some power resistors today to try drawing slightly more current, and check that the diodes are in the correct way. Like I said yesterday, it's frustrating that I cant get such a simple circuit to work, I must be missing so basic!
I've tried putting a resistor and LED on the output to no outcome. The regulators still aren't regulating. I thought they would be putting out 24VDC without a load, not 0V!
This has sort of reconfirmed my suspicions of a short. The metal tab is connected to ground on the 7815, but pins 1 and 2 are swapped on the 7915, making the tab the input. These are currently unconnected to anything, so I can narrow it down to just the legs. I'll pick up some power resistors today to try drawing slightly more current, and check that the diodes are in the correct way. Like I said yesterday, it's frustrating that I cant get such a simple circuit to work, I must be missing so basic!
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