Unreasonably confused about ohm's law.

[Mike_J]

Bought this plastic one pole 11 position switch that was rated at 250VDC and 150mA. Put it all together after many hours of work and was turning the knob with my thumb and forefinger and it destroyed itself. Not real happy because it was the only 250VDC switch I could find with nearly 12 positions so I went looking for a replacement and found a one pole 12 position switch that was 125VDC and 300mA.


Got the definition out for power and resistance and noted that both had the same power in watts but the 250VDC had about four times as much resistance. Regretfully, I have no idea what the resistance number means in this instance. Just want a switch I can use to test various capacitor values for coupling cap and tone control purposes and another to test for different pF capacitor values across the PI plates, the presence resistor and from grids to ground on V1 of my 5f6a. Have no idea at all whether either is safe to use. Thought the 250VDC would be because I wouldn't be connecting to anything with that high of voltage but I am quite confused and would sure appreciate some clarification.


Thanks
Mike

[thetragichero]

you're thinking too much. paralysis by analysis. you're putting this thing in low current locations
I'd put more thought into the enclosure (ie not a cheap plastic disposable container) and less thought into the switch if it were me

[acheld]

Was the switch rated up to 125VDC, and up to 300mA?

Was there a separate power rating given? or not?

Hopefully the switch itself has minimal resistance.

[Mike_J]

you're thinking too much. paralysis by analysis. you're putting this thing in low current locations
I'd put more thought into the enclosure (ie not a cheap plastic disposable container) and less thought into the switch if it were me

You are going to be so impressed when my tools are presented to the forum. Big upgrade from the sour cream container thanks to many suggestions from forum members.


Thanks
Mike

[Mike_J]

Was the switch rated up to 125VDC, and up to 300mA?

Was there a separate power rating given? or not?

Hopefully the switch itself has minimal resistance.

Here is the part https://www.parts-express.com/Rotary-Switch-1-Pole-12-Position-Non-Shorting-023-660. What I know about switches is minimal but if the current levels in the areas I am going to be using it in are low then it is less of a concern, I think. Will use this switch most likely for choosing between bypass capacitors. Very low voltage there.


Thanks
Mike

[acheld]

Hey there, I don't think you are "unreasonably confused" about Ohm's Law.   I do think the product description is not written with you and me in mind.

If you look at the data sheet for the part, it is "Rated" at 125VAC   0.3A.   I take that to mean that they are "rating" the part for 125VAC (essentially for US mains voltage), and that the user should expect to safely pass 0.3A on a regular basis.   What I think they mean, and what the data sheet author actually intends to convey may be two entirely different things, however.   

There is no power dissipation rating.    When they say: 125VAC   0.3A, they do not mean that it will dissipate 37.5 watts.

But they do say it will take 500VAC for 1 minute.  I don't understand their statement of insulation resistance, but it is the same as the Alpha rotary switches on Mouser.   Honestly, I wondered if this might be a knockoff from the mainland.   It can be hard to tell sometimes.  I've had good luck with Alpha pots over the years.

https://www.parts-express.com/pedocs/tech-diagrams/023-660-rotary-switch-1-pole-12-position-non-shorting-technical-drawing.pdf

Similar spec'd part on Mouser:    https://www.mouser.com/datasheet/2/13/R2511F-1522283.pdf

LOL, don't we wish Alpine control switches were less expensive?

[vampwizzard]

Ratings are typically Max ratings. Insulation test data (hipot) means at what voltage will the insulation material still work before everything shorts.

Dont do conversions on part specs. I’ve been fancy and done the derates from AC to DC and vice versa but there shouldn’t be a need. Treat part specs as max allowable values and get the right one.

[Mike_J]

The only switch with a 250VDC rating is the one I have now purchased a number of. If it looks like I could be close to 250 I will measure to make sure the voltage doesn't exceed that rating. Schematics for all the coupling and tone caps I have seen so far have less than 250 volts on them but regularly, if not almost always have more than 125VDC on them. Thank you for your comments. It is valuable in keeping this safer to use.


Thanks
Mike

[PharmRock]

The only switch with a 250VDC rating is the one I have now purchased a number of.

Just a question/comment about the switch rating.  I think there is a huge difference between a switch rated for 250VAC vs. 250VDC and how many amps the switch is rated for.  The reason I bring this up is because of past experience...I built a Trinity Tramp with an optional switch for the OT primaries to run 6V6/6L6/EL34.  I and others who did this switch observed arcing within the switch (and later reproduced by Stephen at Trinity) .  The solution was to use a huge Carling switch and paint the terminals with that goopy liquid electrical tape stuff you can buy at Lowe's.  From what I read, is that AC current, if arcing occurs, it is "self-extinguishing" due to the alternating current, but DC current has only one way to go and therefore the amp/current rating for DC is substantially less than the same part is rated for AC.

Not sure if this makes much of a difference in your application or not...I'm sure others much more knowledgeable on this than I could chime in with the science/math behind it all.