Electronics > Beginners
Please help with switch selection
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shanezampire:
I have been searching for 2 days straight for a switch. I have learned a lot about switches so it wasn't a total waste but I can NOT find what I am looking for. I just need a simple, small, cheap, panel mount rotary switch. Would like to get it from ebay. I just don't know what the type name or what it would be labeled as so I can search for it proper. I need a 4 or 5 position rotary switch. One where I can connect 110/120v to terminal. When I switch it to (we will call it position 1) it will send the power to terminal (1) .... When I switch it to position 2 - it will send power to terminal (1) and (2) ... When I switch it to position 3 - it will send power to terminal (1) and (2) and (3) ... When I switch it to position 4 - it will send power to terminal (1) and (2) and (3) and (4)

In my mind, I would think I am looking for a switch with 5 terminals. One to hook up the line in, and 4 other terminals to send the power out. Simple! But seems every switch I find, as you turn the switch, it picks only one terminal to make connection to. Its doesn't keep adding to them.

I need it for a capacitive battery charger. I am using 4 different size capacitors of different sizes. I would like to be able to power them in a parallel series depending on the size battery I need to charge.

I know I could just use 4 toggle switches but seems one rotary switch would be much simpler and take us less room.

Thanks in advance for any help!
Zero999:
I hven't seen such a switch before. If it's DC and a small voltage drop is acceptable, you could use a single pole quadruple through rotary switch with ORing diodes. Failing that, you need a 4P4T configuration.
Ian.M:
A capacitive dropper power supply is unsafe for any application where there is even a remote chance of the user (or anyone else) coming into contact with the load circuit.  Don't use one for a battery charger unless it is solely for the internal battery of a sealed double insulated or grounded case appliance with no external connections apart from its mains supply, or unless your battery compartment has a tamperproof lid interlock switch that cuts both poles of the mains supply before it can be opened.

Unlike a toggle switch, most rotary switches don't have a sharp 'snap' action (exception: ones that use cams to operate heavy duty microswitches).  If you use a wafer rotary switch to switch capacitors in parallel with power applied, the contacts will burn as they engage.  Even toggle switches (or rotary cam operated switches)  would be unreliable for this application without a resistor in series with each capacitor to limit the surge current.

TLDR:  You are building a deathtrap. Stop and seek advice before it kills someone.

It reminds me of stories I heard from my mentors when I was a youngster, of the bad old days when people would charge the Lead Acid LT accumulator of their tube radio by placing it in series with an electric heater run off their DC mains supply!
Doctorandus_P:
There are industrial type rotary switches that can switch 230Vac and are stackable, but these are quite big.
Rotary switches also were very common on those old analog scopes, but those were all custom made for those scopes, just like the switches on DMM's.

In my life I've only seen a few rotary switches on the consumer market. Most of those are of not very great quality, and one of superb quality but quite expensive (24 position switch used in switched volume attenuators).

The quickest way to get an impression on what sort of rotary switches are on the market is with a picture search:
https://duckduckgo.com/?q=rotary+switch&iax=images&ia=images

I'm guessing here, but your best option may be to add a little DC power supply, a few relays and diodes to devise a matrix to switch your relay's.

bob91343:
A 4P4T switch is what you need.  There are specialty switches that can do similar jobs but you have to hunt for them.  For instance, the switch on a decade box.

You can get fancy with relays, of course.  Too bulky and expensive.  It's unclear how you want to use it.  First you say you want to hook 120V to it and later say you want to select capacitors.  The latter, of course, is what's done in a capacitance decade box.

If you are switching dc, you can connect diodes to select output in a variety of ways.  For instance, connect a diode from terminal 2 to terminal 3.  In first position, only select terminal 2.  In second position, select terminal 3 and the diode conducts to enable terminal 2 as well.  Continue the logic for as many positions as needed.  This won't work for ac or if you want to conduct current both ways.
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