Can we use 125VAC 20A switch in place of 12VDC 20A switch?
I have searched my local market and found 125VAC 20A switch. Can i use this AC switch in place of 12V 20A switch as it is not available in market?
Electrical – Can we use 125VAC 20A switch in place of 12VDC 20A switch
electricalpower electronicspower-engineeringswitches
Related Solutions
Replacing a 20 A switch with a 16 A switch without knowing anything else is a REALLY BAD IDEA.
Chances are you won't burn your house down, but how lucky do you feel? Fortunately, 25% overcurrent thru a switch is unlikely to do more than burn out the contacts such that the switch either won't close properly anymore or weld the contacts shut so that it is permanently on. If the switch is in a metal box so that nothing too bad would happen if it reached the melting point of plastic, you probably won't burn your house down.
Even if the space heater doesn't draw more than 16 A, you still have a problem. Suppose stuff happens (which it regularly does to space heaters, they are one of the leading causes of house fires and electrocutions) so that the power wires get shorted. You want the breaker to trip to shut off the circuit. This might not happen if the switch is a weaker link than the breaker. Instead of the breaker popping, the switch might catch fire. In general, it's a good idea to use a switch rated for at least the trip current of whatever power segment it is on.
To paraphrase Dirty Harry: Do you feel lucky? Well do you, punk? Go ahead, use a 16 A switch. Make my day.
SOME FETS around that size are usable.
You will need two in series with opposed polarity for AC.
Join Gates.
Join Sources.
Two Drains are an AC switch terminals.
Drive gate to source with floating voltage (details if needed).
BUT with say 5 milliOhm FETS your dissipation is
I^2 x R = 20 x 20 x 5/1000 = 2 Watts per FET.
With 1 milliOhm FETS that's 0.4 Watts/ FET. 1 mO FET is "special but doable".
Careful design and heatsinking needed.
What are your size constraints and why?
Slightly larger. Just.
5mm x 6mm x 1mm.
30V 100A+.
Under 1 milliOhm so eg say ~ 0.5W at 20A.
In stock Digikey $1.98/1
http://www.digikey.com/product-detail/en/PSMN0R9-30YLDX/568-11554-1-ND/4965575
Heatsink well enough and they will work well.
Need not be "large" but must be adequate.
Added:
I just found this earlier SA Q&A
What transistor or combination of transistors should I use to make a fully controllable AC switch?
Diagram below from Andy's answer matches what I described above.
Isolated gate drive need not actually be truly isolated - ask.
Best Answer
With the exact same 20A current rating? Almost definitely not.
The right answer is always going to depend heavily on the switch in question. In industrial applications I have seen big, heavy switches that actually had the same listed rating for AC and DC applications. From a design standpoint, that is accomplished by designing a switch that can withstand extinguishing a DC arc, and be sufficiently insulated to handle AC voltages. This is a highly unusual case, as it means the switch is significantly more expensive than it needed to be for either case.
Switches frequently have both AC and DC ratings, but in the more common case, the DC current rating will be significantly lower than the AC one. DC arcs take longer to extinguish and cause more wear on the contacts. In a 20 amp application, I expect that an AC switch with the same rating would fail quickly, and badly.