Micro Switch Amp Rating

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mopowers

mopowers

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I'm trying to determine the amp rating for this particular microswitch at 12 volts DC. Am I reading this correct? It's apparently rated at 0.5A @ 125 VDC and 0.25A @ 250 VDC. Is it then safe to assume then that the amp rating is linear in relation to voltage, thus rendering a 5.0A rating at 12.5V???

Sorry for the poor photo, but this was the best I could get.

upload_2022-1-24_20-27-24.png
 
No that is tricky. DC is actually harder on switches than AC in some ways, and if it is switching an inductive load it gets worse. That is why, EG you see spike/. supressor/ flyback diodes across relay coils. "Somewhere" there should be a DC spec for that buried in the microswitch specs. Otherwise, what I'd do is wander over to one of the electronics websites like Mouser and see if you can find a similar one that lists both the AC/ 125V specs and the DC specs

IT MAY ALSO BE that switch is designed for AC only and simply will not survive well if used for anything very heavy on DC

This all has to do with AC current. When a switch breaks under much of a load, it arcs. With AC as the switch breaks, the AC goes through "zero crossover" at some point and limits the current and power of the ARC. DC is more like a welder. The thing will arc until the gap is wide enough to finally kill the arc, and the higher the current, the worse this can be.
 
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67Dart273 said:
No that is tricky. DC is actually harder on switches than AC in some ways, and if it is switching an inductive load it gets worse. That is why, EG you see spike/. supressor/ flyback diodes across relay coils. "Somewhere" there should be a DC spec for that buried in the microswitch specs. Otherwise, what I'd do is wander over to one of the electronics websites like Mouser and see if you can find a similar one that lists both the AC/ 125V specs and the DC specs

IT MAY ALSO BE that switch is designed for AC only and simply will not survive well if used for anything very heavy on DC

This all has to do with AC current. When a switch breaks under much of a load, it arcs. With AC as the switch breaks, the AC goes through "zero crossover" at some point and limits the current and power of the ARC. DC is more like a welder. The thing will arc until the gap is wide enough to finally kill the arc, and the higher the current, the worse this can be.
Click to expand...

Thanks for the info, but that switch does have DC specs (1/2A 125 VDC, 1/4V 250 VDC). It's a pretty standard nitrous throttle switch (similar to the microswitches supplied with aftermarket automatic shifters). I'm just curious if there's a way to deduce an amperage rating at normal automotive DC voltage. It's weird that it wouldn't have one at a lower DC voltage printed on it since it's used in those applications.

Here's a photo I found online which is a little better than mine.

93f61955-779f-4ba0-a107-afe2f9d7e1d4_1.65a5d2385b2456b14f93411cf40f2033.jpg
 
Somehow I did not see the DC rating LOL I believe amperage is amperage--within DC.
 
I think you are going to have to contact the vendor for the information you want. DC has it's own set of peculiarities. The current rating many times depends on what the load is. If it's a light (resistive) a switch can handle more current. If it's a coil (inductive) the current rating drops. There is just no way I know of to predict what the 12 volt DC rating would be based on the listed ratings. As a note, the switch you have pictured is obsolete and no longer a sale item.
 
Interestingly, the switch that comes with the B&M shifters is only rated at 0.1A at 125VDC, yet they're meant to be used to control the reverse lamps, which draw about 3A.

upload_2022-1-25_7-53-57.png
 
That switch looks like it could survive a 6A at 12.5v but work at 3A easily at 12v. At 250VDC it's .3A, 125V it's .6A so if it's a linear slope, .6x10 would be 6A at 12.5v.. 3A should be easily handled. If it won't, put a 10A Bosch behind it, they only take 150ma to trigger.
 
Well the switch is labeled right on the switch, so I assumed you were pointing out a better choice, ??
 
67Dart273 said:
Well the switch is labeled right on the switch, so I assumed you were pointing out a better choice, ??
Click to expand...

No, the point I was trying to make is that there is no rating for 12 volt DC service. And if you look at the other choices there is no alternative rated for 12 volt DC service. So if the switch is going to be used in a 12 volt DC application the user is on his/her own. As I already mentioned, DC service is a special breed of it's own with its own peculiarities. I don't know of any valid procedure to re-rate a switch for unrated DC service based on given DC service ratings or AC service ratings. As to other vendors using a switch such as this in an unrated application, I can only assume (there's that word again) that they feel comfortable with it based on their experience or they just needed something to work to meet warranty and after that they don't care. I don't know which of these, or other reasoning may be used but if I were doing something like this, I'd use something other than a microswitch.
 
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