I have a toggle switch that is DPST. Can I put 110 line currentthrough one side and 48vdc through the other side, such that when itturns off the 110ac it also disconnects the DC voltage at the sametime?

That is usually against code and against other safety regs. There needs to be a minimum clearance and creepage distance between the two sides. You'd have to make sure those is maintained, plus whatever else the regulations in your market mandate.-- Regards, Joerg"gmail" domain blocked because of excessive spam.Use another domain or send PM.

Mixing AC with DC - Good Idea?

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zanderson_j 18 years ago

h it

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It's about 12 amps... a linear supply with a large filter cap. I want the output to cut off clean, not wait for the cap to discharge. I think it's more like 36vdc, I just said 48 to be on the conservative side.

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John Fields 18 years ago

View in Courier: +----------------+ | | MAINS>--O--> | | | O---+ S1 | | +--------+ [COIL]- - - -| | O-+--|SUPPLY +|----|----O--> | [LOAD] | & | | K1 | MAINS>---------+--| BFC -|----|-------------+ | +--------+ | +----------------+ S1 is the switch currently wired into the mains side of your supply. K1 is a relay with an AC coil and normally open contacts rated to carry the DC load current. You may have timing issues on power-up, and if you don\'t make some provision to bleed down the BFC after the supply is shut down you may have hot-switching issues with the relay contacts as well on subsequent power-ups. If you don\'t understand I\'ll be happy to go into greater detail. JF

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zanderson_j 18 years ago

itch it

t of

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amps

K1 =A0 =A0|

Thanks

It seems like timing on startup couldn't be any worse than without a relay - it's ready to go when it's ready to go. I *Think*.

To bleed the cap I have a 2k 5w resister that I figure I can wire permanently in place.

Now if the switch was turned back on before the cap was bled, that could be a problem? I don't understand enough about switches and relays to know what that could do to the contacts.

I guess I need to be sure the relay contacts are rated for the 12 amps DC ? I'm guessing that would be a bit heavier than something rated 12 amps AC ?

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Phil Allison 18 years ago

It's about 12 amps... a linear supply with a large filter cap. I want the output to cut off clean, not wait for the cap to discharge. I think it's more like 36vdc, I just said 48 to be on the conservative side.

** It will require a special DC relay ( or contactor) to switch off circa 40 volts at circa 12 amps without serious arcing damage or failure to break. Or a rather large switch with contacts that open very wide and fast.

Magnetic quenching would be of benefit in both cases - ie a permanent magnet to help break the arc.

Also, you must allow for a worst case scenario with the DC current higher than normal.

Good luck.

...... Phil

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Phil Allison 18 years ago

I guess I need to be sure the relay contacts are rated for the 12 amps DC ? I'm guessing that would be a bit heavier than something rated 12 amps AC ?

** Try reading what has been posted already - fool.

.... Phil

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John Fields 18 years ago

it

Assuming the cap is across the supply, (in parallel with the load) and there\'s a load connected directly to the supply, the voltage across the cap (and the load) will rise from zero volts to its final value in some finite time. With the relay in there, there\'ll be a delay from power-up until the relay contacts close which will allow the cap to partially charge up before the load is connected, so there\'ll be a step change at the load instead of the gradual increase from zero. The size of the step will depend on how long it takes the cap to charge up with no load on the supply and the make delay time of the relay.

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Rich Grise 18 years ago

You need to toggle your "caps lock" key.

Good Luck! Rich

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Mixing AC with DC - Good Idea?

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