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Transformer tap switching between series and parallel

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nemail2:
Hi all

would this work for transformer tap switching between serial and parallel operation of the (identical) secondary windings?
The transformer (https://www.mouser.com/datasheet/2/410/VPT18_5560-781803.pdf) is designed to be used either in parallel or serial connection, not independently.

Should I do it differently? I plan to use this in one of my lab power supply designs to avoid having to burn all the voltage on the series pass transistor.
Microcontroller and stuff would be on a seperate transformer so I don't run into any issues there.

Thanks!

Cliff Matthews:
Looks OK 2 me..

drvtech:
I'd be tempted to put some protection (a fuse) in line with secondaries to protect against the unlikely situation where the upper contact switches over but the lower contact remains closed. However the mains input fuse should blow so perhaps I'm being a bit 'belt and braces'

nemail2:

--- Quote from: drvtech on April 22, 2021, 09:42:29 pm ---I'd be tempted to put some protection (a fuse) in line with secondaries to protect against the unlikely situation where the upper contact switches over but the lower contact remains closed. However the mains input fuse should blow so perhaps I'm being a bit 'belt and braces'

--- End quote ---

I think I'd like that as well. I want to do secondary side fuses anyway so they could be very well coming before the relay.

Any other protection measures? I figured the relay would have to be a quite robust one, as I'm planning to switch between 9/18VAC @ 4A, right? I saw that the AC ratings for relays are often lower than for DC.

bdunham7:
Definitely fuses on each secondary, but you probably want to make sure and use one DPDT relay so that the switchovers are guaranteed to happen simultaneously absent some strange failure--in which case the fuses will step in.  That really should not require a very large relay, switching 4 amps at under 30 volts is fairly easy, AC or DC.

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