These last three posts have greatly changed my decisions on this project. I have started to question myself for choosing an uoper limit of 5000V. As tsmtech said, if someone uses that much of a voltage level, they probably have their own equipment to measure it. So I decided to lower my voltage limit to 400V.
How about this, do you have any other suggestion?
You still want to be able to 400VDC as well right? Not just 400VAC? If you want to measure 400VDC, then I would not do line powered. It's difficult and expensive to turn 500VDC into 5VDC.
If it's AC measurement only and you want it line-powered (you could still use batteries of course), then I would have two selectable transformers for the regular household range (120VAC-240VAC) and another transformer for 240-400VAC. Within the input range of each transformer, it would need to step the AC voltage down enough so it could be handled by a regular AC-DC converter. So for the minimum input of each transformer, the output voltage would have to always be at least 6-7Vrms (8.4VAC-9.8VAC) so that the AC-DC converter could change it to 5VDC. And the output can't be too high at the maximum input voltage either because the AC-DC converter still needs to be able to handle it. So you have to find a AC-DC converter the minimum and maximum outputs of the transformers.
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