Anyone know anything about switches and relays?

[slick_9191]

If a switch is rated a 10 amps, and the typical constant flow is 30 amps, will the switchs/relays act as resistor and slow the current to 10 amps after it. or will it act like a fuse and fry/blow??

[gibbonsl]

more then likly the s/w will eather blow or work fine untill it burns up

[Camman]

or will somebody search the internet for answers to homework in an electronics course and find short-media forums

[primesuspect]

it will fry and blow

[profdlp]

it will fry and blow
Literally and figuratively... :(

[shwaip]

or will somebody search the internet for answers to homework in an electronics course and find short-media forums

Sounds more like a do-it-yourselfer question than a homework problem.

If it's an electromechanical relay - it will melt and stop working.

If it's a solid state relay - it will let loose the magic smoke that is packaged in every semiconductor device. After that, it won't work anymore.

Basically - you'll need a relay designed for at least 30A

[slick_9191]

or will somebody search the internet for answers to homework in an electronics course and find short-media forums
hmmm, next time ur working w/ top-end multi-$$$ stuff, 'test' it and lemme know how the high-amperage works out for u.

[Camman]

hmmm, next time ur working w/ top-end multi-$$$ stuff, 'test' it and lemme know how the high-amperage works out for u.

and an internet forum is your top choice for advice working on "top-end multi-$$$ stuff" ????

calm down there, slick, i'm just bustin your balls

[bothered]

If a switch is rated a 10 amps, and the typical constant flow is 30 amps, will the switchs/relays act as resistor and slow the current to 10 amps after it. or will it act like a fuse and fry/blow??
Depends on how well they're made. At the very least they will overheat. They won't limit the current to 10 amps but the hotter they get the more resistance they'll have which will make them hotter which will increase the resistance etc. Eventually they'll burn out. Also the constant current can almost be forgot (as long as it's rated for it) it's the starting current you need to worry about. If you're switching an inductive load, or capacitive, the starting, or inrush, current can be many times the onload current and that's what does the damage. Apart from shortening the life of the gear it can lead to fires and all sorts of problems.

[slick_9191]

Depends on how well they're made....
ya, thats what i was thinking. and camman, this was the closest i could get to forums where electritians hung out. but yall did help thx. ive never delt with amps this high, so its a new factor for me from the usual.

[drasnor]

It could cause a fire. The bigger concern though is the watts (power) you're putting across the switch. If it's rated for 10 A at 120V (standard mains voltage) then the switch is actually rated for a wattage of 1200W (10A * 120V = 1200W) and it would be safe to run 100A at 12V across it (100A * 12V = 1200W). By the same token, if the switch is rated for 10A at 12V, it would only be safe to run 1A at 120V. This holds true for electromechanical switches but there are some caveats for solid state like the switch won't operate unless within some % of it's rated voltage.

Better to be safe than sorry, so leave yourself some headroom and specify 1.5 to 2 times the power you plan to actually use.

-drasnor :fold:

[bothered]

drasnor, sorry but you are making the sort of mistake that kills people. Wattage does not apply to switches. Put 100A through any switch and you'll blow it up, unless it's it is a huge chunky copper thing designed for folk lift trucks. Wattage is the power disapated through a device, not a rating. You try putting 100A through a 5A fuse wire at any voltage you like and watch the sparks fly.

[drasnor]

drasnor, sorry but you are making the sort of mistake that kills people. Wattage does not apply to switches. Put 100A through any switch and you'll blow it up, unless it's it is a huge chunky copper thing designed for folk lift trucks. Wattage is the power disapated through a device, not a rating. You try putting 100A through a 5A fuse wire at any voltage you like and watch the sparks fly. I highly suspect you're right, though now I get to kick my electrical engineering professor :). He mentioned something about resistivity of the material being the reason you could make that happen but in hindsight it doesn't seem to hold up. It's what happens when you get guys working on chips all day I suppose.

-drasnor :fold:

[GHoosdum]

Everything I know about circuit design I learned from Electronics for Dogs (http://www.evconvert.com/eve/electronics-for-dogs)

And my high-school physics teacher. :scratch:

[slick_9191]

The switch measures just 19/32" x 13/16" and is rated 5 amps max....Or just add one of our 40 amp relays to increase the circuit switching amperage.
how is this possible if the switch allows 5 amps max.

[slick_9191]

wait, i think i got it. the switch isnt allowing the power to go directly though huh to the item using the main power. its opening a relay that gives the main power, and the relay is rated higher, but the switch is only grounding, using 5-max amps. Correct?

[profdlp]

Exactly. :)

I've worked on HVAC units (big air conditioners, in this case) which drew hundreds of amps at 480V and were controlled by relays which were triggered by 12V at way less than one amp.

[slick_9191]

hahah, 12v aka battery ran thermostat?

[profdlp]

hahah, 12v aka battery ran thermostat?
That is the right idea.

The one I was thinking of was actually a computer terminal hooked to a relay panel. We controlled all the rooftop AC units and zone dampers, plus 400 Heat Pumps in a 250,000 sq ft eight-story building from a P66 desktop box.