Switch amp rating

 

New member
Username: Zeddy

Hamilton, On Canada

Post Number: 1
Registered: Mar-06
hey im looking for some switches to control various things in my car. the source (fromally known as radio shack) sells some 3amp 120vac toggle swtiches...wondering if they will handle 15amp 12vdc...and how do i figure it out?..is it simply wattage?..eg amps times volts and make sure the wattage supported by the switch is higher then what im pushing through it?...if thats the case then its 360watt switch and 180wats going through it...plenty of room
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11279
Registered: Dec-03
amperes * volts = watts.
However, if you're looking to switch an amp on and off, put the switch on the remote wire, not the main power line. The remote wire is only 12VDC @ ~250mA. It's a low current trigger signal to tell the amp when to turn on and off.
 

New member
Username: Zeddy

Hamilton, On Canada

Post Number: 6
Registered: Mar-06
u didnt answer my question...u just confirmed my watts equation..which i already knew was right..is that how i can figure out if a switch will work?...watts..or is dc volts diff from ac...YES i know ac is alternating current at like 60hz...and dc is direct current...and no its not for a amp power wire...i got that fine..i know there low current..but i need 15 amps to go through a swith...15 amps 12-14vdc...will a 3amp 120vac work?...thats what i wana know...will 3amp 120volt AC swithc handle 15 amps 12-14 volt DC...12-14 cuz the alternator puts out 14...and the battery is usually slightly over 12...
so the answer i want is a simple yes or no...is it the wattage im concerned about?..or is the switch different to take DC instead of AC
 

Silver Member
Username: Fandim

Reno, Nevada United State...

Post Number: 783
Registered: Jun-05
Zeddy - If you're really worried about it, you could use a bosch relay, and just have the switch actually be the ground for the relay, so in effect, when you toggle the switch, it just connects your relays ground, thus doing the same thing as wiring power directly through your switch. (Relays are like $2 at just about any auto part store).
 

New member
Username: Zeddy

Hamilton, On Canada

Post Number: 7
Registered: Mar-06
ya that works..ill go buy 12 switches at 3 bucks a piece AND 12 relays at 3 bucks each..that makes sence...or i could just buy 12 switches that say 15 amps 12vdc for 5 bucks each...crapytire sells them
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11307
Registered: Dec-03
"YES i know ac is alternating current at like 60hz."

Only in north america on 3-phase residential house current. Most industrial can be 220VAC, and in some cases as high as 400Hz.

"g amps times volts and make sure the wattage supported by the switch is higher then what im pushing through it?"

yes, however, you seem to be trying to switch a high current line, which is silly. You use a relay for this. Not a bigger switch.

"but i need 15 amps to go through a swith...15 amps 12-14vdc...will a 3amp 120vac work?"

see above.

simple answer? yes. that would work.
problem is it'll also get very hot.
the way you want to do this is to use a bosch automotive relay rated for the current you plan to draw through it (400 watts/12V) and use a switch on the trigger of the relay. That way you don't get severe heat build up through the switch.

Giving more detail in what you're doing helps us answer you. I'm glad you have a basic grasp of Ohm's Law, but I have a degree in electrical engineering, and am a certified master installer. I know the best way to do this stuff if I know what you're trying to do. I just can't read minds :-)


 

Silver Member
Username: Fandim

Reno, Nevada United State...

Post Number: 788
Registered: Jun-05
Zeddy - Glasswolf is saying the same thing I am. (switching the turnon, or switching ground of the relay will do the same thing.) I just prefer to switch the ground of the relay, to avoid any un-needed breaks/connections in wire that will be conducting a positive charge.

Yes, you could use a bigger switch on a high current line, but like GW said - this is what relays are for.

--------
"ya that works..ill go buy 12 switches at 3 bucks a piece AND 12 relays at 3 bucks each..that makes sence...or i could just buy 12 switches that say 15 amps 12vdc for 5 bucks each"
--------

Then why even post this message? Electronics can get expensive, I'm not going to apologize for that. Really am curious what you're using 12 switches for in an automotive application, though? Just wondering.

Seth
 

New member
Username: Zeddy

Hamilton, On Canada

Post Number: 8
Registered: Mar-06
THANK YOU
finally some one gives me a simple yes or no...jeeze...lol
sorry...but wow..that was like pulling teeth...why does it matter what im trying todo that needs that current...if you notice most of the fuses in a car are either 10 or 15..some can be more..basicaly..i am installing a pushbuton start...and eliminating the key swich...so ill have one switch to turn on the accesories...another to turn on the engine to "run" mode like the key switch does..then press a button to crank the engine. also i want to wire in the power wire for my stereo into a separate switch so i can turn it on without powering half my car by turning on all of the accesories...i want another switch to manually turn of the fuel pump..so i dont have to tear appart my trunk and disconnect it...flick the switch and there goes the fuel pressure...makes it hard to steal the car, specially if that switch is hidden..my budy has one and he can flick the switch so non-shlauntly (spelling?..sorry im not an english major) you dont notice hes doing it...even watching him clim in..i spent 1 hour in his car trying to find that switch...shifter boot...swtich u hit with your foot...under the fabric of the seat ..couldnt find it...so makes it really hard to steal a car with no fuel pump...btw he drives a nissan 300zx Twin Turbo with about 800rwhp...thats no typo...so..MOST of the electronics in a car is 10 or 15 amps...
does that help? now that you people know what im trying to turn on, you realize that i need a switch to take 15 amps?...sorry i didnt break it down for you and explain exactly what i wanted to turn on...hard to comprehend why anyone would want a 15 amp switch for a car, i know..but i do...and you obviosly have never seen the cockpit of a race car either..they have LOTS of switchs...and yes im building a race car out of a nissan 300zx like my budies...not quite as much power..mayb only 500crank power..i know you guys dont care but if i dont explain why i care about having swithcs like a race car youll ask..then ill have to explain even futher. so the ORIGINAL post that i made only needed a yes or no answer, thats glasswolf...
"simple answer? yes. that would work.
problem is it'll also get very hot. "
now was that so hard...?
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11332
Registered: Dec-03
the reason is that if you'd told me what it was exactly that you were trying to do, I could have suggested better ways to do it.. or easier ways at last :-)
It's a cool idea, but you realize this has been done for decades in drag cars so the gear to set up push-button starters can be ordered straight from catalogs without all of the DIY effort.. for what it's worth.
We like to know what people want to do in order to answer their questions namely because if you look through forums, you'll see a lot of times, the people really have no idea what they're doing, and if we just answer yes or no, the result will be a car fire.. then WE get blamed or callas jerks for not telling them it was the wrong thing to do before they went off and did it anyway.

know what I mean?
 

New member
Username: Zeddy

Hamilton, On Canada

Post Number: 9
Registered: Mar-06
i hear ya...and after talking to a budy of my dads whose an electrician he said the same thing..use a relay...the switch may take it but your forcing a lot of current through a switch..which just isnt done...i work at dofasco but im a pipefitter...the guy i talked to was an electrician there (retired) and he said they dont use high amp swithces..its all relays
another thing that gets me is...crapytire wants 45 bucs for a push button for a starter...y?..use a small button and relay...then itl take the 30 amps or whatever your car needs. the source has momentary on push buttons for like 3 bucks..tiny but they will work WITH a relay
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11346
Registered: Dec-03
try www.summitracing.com
they carry everything bfor building cars from street to strip.

your electrician friend is right, by the way. I'm an electrical engineer, so similar background.
relays are designed specifically to interface a low current circuit to a high current circuit, which is pretty much what you're doing going from the starter circuit to the switch.
It's just more efficient (less loss to heat, less danger of melting the switch and causing a fire..)
 

Silver Member
Username: Fandim

Reno, Nevada United State...

Post Number: 797
Registered: Jun-05
Summit racing is great.. One of the three stores they have in the US happens to be less than a 15 minute drive from where I live.. I love that place. ;)
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