Not sure if this is the right forum, but it is PS related and a pretty general question.
How does one choose a power switch?
I don't mean aesthetically, of course...
What sort of ratings does it need to have?
Does a huge class A pwr amp need something different/better than, oh... perhaps a DAC or headphone amp?
And why?
For example:
There's a pretty crummy one in a case I just got hold of...
Something tells me it won't be adequate.... but I'm not sure how/why...
Made me realize I need a better understanding of this..
Thanks in advance!
Greg
How does one choose a power switch?
I don't mean aesthetically, of course...
What sort of ratings does it need to have?
Does a huge class A pwr amp need something different/better than, oh... perhaps a DAC or headphone amp?
And why?
For example:
There's a pretty crummy one in a case I just got hold of...
Something tells me it won't be adequate.... but I'm not sure how/why...
Made me realize I need a better understanding of this..
Thanks in advance!
Greg
Per..
Yes..
Thank you...
But I was hoping for a bit more information... not just "a bigger amp needs a bigger switch" and the like....
Aren't there specific ratings?
Are those exact? Double X for case Y, or something like that?
What about a generic one... one that looks cheap... Maybe its enough for the preamp/linestage project that the case is intended for?
How can I know?
Let me guess the next answer.... "see if it gets hot" LMAO...
Yes..
Thank you...
But I was hoping for a bit more information... not just "a bigger amp needs a bigger switch" and the like....
Aren't there specific ratings?
Are those exact? Double X for case Y, or something like that?
What about a generic one... one that looks cheap... Maybe its enough for the preamp/linestage project that the case is intended for?
How can I know?
Let me guess the next answer.... "see if it gets hot" LMAO...
Yes, it's not harder than that. The switch should be able to handle the currents involved.
And what do you have against blond, curly-haired virgins?!?!?!?
Nothing. Really. Believe me. Ask Rod Stewart: Blondes have more fun!!
Best regards!
Surprising as it may seem, switches have datasheets. These say what current and voltage the switch can be used for. Choose a switch which is rated for mains use, at the voltage and current you need. Then use a fuse which ensures that this current cannot be exceeded, and a mains cable which can carry this current.
Before you build your first mains powered PSU, build a lamp limiter.
Before you build your first mains powered PSU, build a lamp limiter.
Most real UL rated switches have a current rating cast into the side of the plastic case. X amps at Y volts. Don't exceed it. Don't use AC rated only switches on DC currents.
You're more likely IMHO to see the rating on a used or surplus switch, than a part number which would lead you to a datasheet. Datasheets are for new switches you buy from a vendor that uses part numbers and manufacturer name. Some surplus and informal websites suppress that information entirely even for obviously new parts drawn from a single manufacturer product line.
In my experience, power amps have larger current draw than preamps or radios. So the switch is higher rated and often physically larger. Also in my experience, snap action toggle switches last longer than slide switches for inductive loads like motors & transformers. On a snap action switch you'll hear a pop that indicates the contacts approach and break at high velocity under spring action.
In the exotics category, signal selector switches should have gold or silver plating depending on the voltage and current flow of the signal. These platings are totally inappropriate for AC mains power switches which should be copper or brass plated. I'd suggest reading the Delta relay catalog for an education, but the global moguls have decided to bankrupt them. You'll have to buy a $$$ textbook to learn the information now, or learn to read an oriental language maybe.
You're more likely IMHO to see the rating on a used or surplus switch, than a part number which would lead you to a datasheet. Datasheets are for new switches you buy from a vendor that uses part numbers and manufacturer name. Some surplus and informal websites suppress that information entirely even for obviously new parts drawn from a single manufacturer product line.
In my experience, power amps have larger current draw than preamps or radios. So the switch is higher rated and often physically larger. Also in my experience, snap action toggle switches last longer than slide switches for inductive loads like motors & transformers. On a snap action switch you'll hear a pop that indicates the contacts approach and break at high velocity under spring action.
In the exotics category, signal selector switches should have gold or silver plating depending on the voltage and current flow of the signal. These platings are totally inappropriate for AC mains power switches which should be copper or brass plated. I'd suggest reading the Delta relay catalog for an education, but the global moguls have decided to bankrupt them. You'll have to buy a $$$ textbook to learn the information now, or learn to read an oriental language maybe.
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Arcing behaviour. DC has no zero crossings where an arc between the opening switch contacts will extinguish itself. As the current is maintained, a possible arc might burn for extended times and damage the switch contacts or even weld them closed.
Regards,
Rundmaus
Well, I recall that this very subject (i.e. differences between AC and DC rated switches) was discussed by a knowledgable person (AndrewT?) elsewhere in the forum, though I can't recall where... I'll repost if I can remember.
I'm certainly not knowledgeable, but part of the discussion was that AC current (say 60Hz like it is here) will have no current 60 times per second, and less than peak current most of the time, whereas a DC current has no such cyclical nature. I think that this is one reason why the arcing characteristics are different for AC and DC, and why many switches have a lower rating for DC current.
e.g. http://www.mouser.com/ds/2/418/NG_DS_1-1773878-3_Alcoswitch_AntiVandal_0416-958785.pdf
As suggested by people above, one just has to weed through the datasheets and find one that works (safely) for the circuit.
Best o' luck.
I'm certainly not knowledgeable, but part of the discussion was that AC current (say 60Hz like it is here) will have no current 60 times per second, and less than peak current most of the time, whereas a DC current has no such cyclical nature. I think that this is one reason why the arcing characteristics are different for AC and DC, and why many switches have a lower rating for DC current.
e.g. http://www.mouser.com/ds/2/418/NG_DS_1-1773878-3_Alcoswitch_AntiVandal_0416-958785.pdf
As suggested by people above, one just has to weed through the datasheets and find one that works (safely) for the circuit.
Best o' luck.
> Wondering (NOT questioning) why not gold/silver for AC mains?
Uh, money?
Gold has a place in VERY small circuits (notably audio switching).
Silver is used in power switching. Alloys similar to "coin silver" do well. But there are other materials, notably a hard low-tarnish thin film over a ductile low-cost base metal. There's guys who slave all day to find a contact that saves a part-cent.
If you are building your own switches (NOT suggested), you can buy coin-silver in bulk rolls of vintage quarters and dimes.
> why not AC rated for DC??
AC arc will go out 120 times a second.
DC arcs can be forever.
Sustained arcing will quickly burn the guts out of a switch.
A real-world issue: before transistor inverters, there was a trick to hot-wire a car's generator to make 110V. DC, but many portable saws have "universal" motors which will run on AC or DC. However they used AC-rated switches because they were cheaper/smaller, and 99.9% of the use was on AC. The owner's manual told you "AC only!" I have heard of factory repair depots which routinely replaced arced-out switches without objection, but those days may be gone.
DC rated switches have faster action and wider gaps. As you get over 5 Amps the size gets awkward and there are several odd tricks to make the arc go out quicker.
In practice, an "AC rated" switch *MAY* work OK at much lower voltage. Unless the switch was already over-loaded (Hot!), an arc in air is not very stable below 30V. At 12V it may be almost a non-issue AC or DC. But of course with "improvements" in contact materials, you just can't know. Look-up and understand the specs, or use it only in non-critical flame-resistant settings with constant attention (workbench breadboards).
The "standby" switch used on a million Fender guitar amplifiers has a history of switching 400V _DC_ (100mA) reliably. It is a big old clunker with large contact and gaps, originally aimed at vacuum cleaners which are nasty switch loads.
Uh, money?
Gold has a place in VERY small circuits (notably audio switching).
Silver is used in power switching. Alloys similar to "coin silver" do well. But there are other materials, notably a hard low-tarnish thin film over a ductile low-cost base metal. There's guys who slave all day to find a contact that saves a part-cent.
If you are building your own switches (NOT suggested), you can buy coin-silver in bulk rolls of vintage quarters and dimes.
> why not AC rated for DC??
AC arc will go out 120 times a second.
DC arcs can be forever.
Sustained arcing will quickly burn the guts out of a switch.
A real-world issue: before transistor inverters, there was a trick to hot-wire a car's generator to make 110V. DC, but many portable saws have "universal" motors which will run on AC or DC. However they used AC-rated switches because they were cheaper/smaller, and 99.9% of the use was on AC. The owner's manual told you "AC only!" I have heard of factory repair depots which routinely replaced arced-out switches without objection, but those days may be gone.
DC rated switches have faster action and wider gaps. As you get over 5 Amps the size gets awkward and there are several odd tricks to make the arc go out quicker.
In practice, an "AC rated" switch *MAY* work OK at much lower voltage. Unless the switch was already over-loaded (Hot!), an arc in air is not very stable below 30V. At 12V it may be almost a non-issue AC or DC. But of course with "improvements" in contact materials, you just can't know. Look-up and understand the specs, or use it only in non-critical flame-resistant settings with constant attention (workbench breadboards).
The "standby" switch used on a million Fender guitar amplifiers has a history of switching 400V _DC_ (100mA) reliably. It is a big old clunker with large contact and gaps, originally aimed at vacuum cleaners which are nasty switch loads.
120 times per second - for some reason I was thinking of a half cycle...
Thanks PRR.
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