Help with rotary switch configuration

Factual Questions
1

I need to spec a rotary switch to read voltages from 4 sources. I am measuring a total of (6), 6vdc batteries hooked in series for a total of 36 vdc. I want to sequence a panel mount DC volt meter like this:

Bank 1 (batteries 1 and 2 = 12 vdc)

Bank 2 (batteries 3 and 4 = 12 vdc)

Bank 3 (batteries 5 and 6 = 12 vdc)

Overall (batteries 1 through 6 = 36 vdc).

I know I need a 4 position wafer switch but am not sure how to spec the poles. Everything is non shorting when switched away from the meter. Do I need 4 wafers, or 2 wafers with 2 circuits each, or what?

Dennis

2

You need a double-pole, 4-throw switch. How it is arranged isn’t important.

Something like this:

3

Good find. Just wanted to add…

This switch is probably fine for this application if it is for a non-critical / hobby project. But I wouldn’t use it for a commercial or hi-rel application. Reason being… if the voltage signals are going to a voltmeter, then the signals are considered a “low-level/low-current,” and thus gold contacts should be used in the rotary switch. This switch has silver contacts; silver contacts can cause problems for low level/low current signals. (Note the “Q” at the end of the part number.) I would use the “B” version of this switch if you can find it. Or another DP4T switch with gold contacts.

4

Thanks, guys, I figured DP4T would do it, but wasn’t sure how to specify that in the 14 selectable fields for ordered those switches! I looked for a gold plated contact but didn’t see any of them in stock.

Dennis

5

I wouldn’t be too concerned about silver contacts.
Rotary switches are inherently self-cleaning, due to their wiping motion, and even if they get a bit tarnished, the input impedance of your DMM is essentially infinite (20MΩ or better), so a little contact resistance isn’t going to matter.

6

I don’t disagree. But the OP didn’t state the application. If it’s a commercial, military, or “high reliability” application, then gold-plated contacts must be used for all low-level signal paths, and silver (or silver alloy) contacts must be used for power circuits. If it’s not commercial or military then I wouldn’t worry about it.

7

It’s for a very critical application. My vintage golf cart. I did find a gold plated contact version in stock so what the heck, I bought it. Damn it’s small, only a half inch OD, gonna need my magnifiers to solder to it. I ordered a terminal block to make it easier and a shaft seal because of the possibility of moisture.

Dennis