Electronics > Beginners
Please help with switch selection
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Zero999:

--- Quote from: Ian.M on June 17, 2019, 03:12:48 am ---That's even worse than I thought.   If you used it in any workplace in the USA, OSHA would have your nuts in a vice before you could blink twice,  Also knowingly building and using dangerous device, would void any homeowner's or personal insurance policy you are likely to have.   If you've got any family, for their sake, *PLEASE* don't build it.

--- End quote ---
It's impossible to determine the safety of a project from such a brief description. We don't know the construction details. If it's in a suitable insulated/earthed enclosure, with the appropriate interlocks, then it will be perfectly safe.

To answer the original question: use a low power 1P4T switch, with diodes driving four relays or contactors, which actually drive the load. The switches and relay coils can be powered off an isolated 24VDC power supply, which will isolate the operator from the nasty voltages.
Ian.M:
The O.P. mentions warning signs but doesn't mention enclosure or interlocks. I'd be a lot happier if he had assured us that he was building a fully enclosed battery compartment for it with ex-Microwave door switches or similar for the interlocks. 

Also I don't like the idea for other reasons - a high open circuit voltage Lead Acid charger significantly increases the risk of internal sparking if a battery has cracked internal inter-cell straps, which can cause a hydrogen explosion that is likely to blow the top off the battery and shower the area with high velocity lead and plastic shrapnel and hot acid.  It also increases the risk of external sparking that can be just as dangerous.


StillTrying:

--- Quote from: shanezampire on June 17, 2019, 12:27:47 am ---And I am fully aware that I will have high pulsing current / DC voltage on the ends of bare battery clamps that can and will stop your heart easily.
--- End quote ---

When you connect a cap dropper and bridge rectifier to the mains both of your DC ends are connected to the live mains voltage. Even if charging a 12V battery, both the -ve and +ve ends of the 12V battery are at the full mains voltage.
#TooDangerous  :o
Zero999:

--- Quote from: StillTrying on June 17, 2019, 11:44:06 am ---
--- Quote from: shanezampire on June 17, 2019, 12:27:47 am ---And I am fully aware that I will have high pulsing current / DC voltage on the ends of bare battery clamps that can and will stop your heart easily.
--- End quote ---

When you connect a cap dropper and bridge rectifier to the mains both of your DC ends are connected to the live mains voltage. Even if charging a 12V battery, both the -ve and +ve ends of the 12V battery are at the full mains voltage.
#TooDangerous  :o

--- End quote ---
I don't see anything inherently dangerous about that. It's only dangerous if sensible safety precautions aren't taken. I've seen drill battery chargers with a non-isolated output and they're perfectly safe, because the battery is inside an insulated enclosure and none of the connections are accessible.
StillTrying:

--- Quote from: Zero999 on June 17, 2019, 12:53:34 pm ---It's only dangerous if sensible safety precautions aren't taken. I've seen drill battery chargers with a non-isolated output and they're perfectly safe, because the battery is inside an insulated enclosure and none of the connections are accessible.
--- End quote ---

Of course, but the OP's posts mention "very safe, timer, breakers, and all. Its a battery rejuvenator / desulfator." and "I am fully aware that I will have high pulsing current / DC voltage on the ends", but the live AC mains voltage problem, or isolation, doesn't get a mention anywhere.
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