Switch Rating

AndyM · Dec 4, 2016

The switch I plan on using for some ROPS lights (2 x 36w LEDs) has a 3 Amp 125 v rating. By my calculations the switch should be good for 30 amps at 12 volts. Any issues I'm missing?

torch · Dec 4, 2016

AndyM said:
The switch I plan on using for some ROPS lights (2 x 36w LEDs) has a 3 Amp 125 v rating. By my calculations the switch should be good for 30 amps at 12 volts. Any issues I'm missing?

Yes. You are missing AC vs DC.

Ideally the switch will also include a DC rating but if it doesn't, a good rule of thumb is to multiply the 120VAC current rating by 1.8 to get the approximate 12VDC current capacity. So limit your current to 5.4 amps.

You might get away with that switch if the LED lights are rated at 14.5V. If they are rated at 12V then I'd look for a heavier switch.

EDIT: I just remembered LED lights are considered an inductive load (like a motor) rather than a resistive load (like an incandescent light). They have a high inrush of current at the moment they are switched on. I'd recommend a heavier (or DC rated) switch for sure.

AndyM · Dec 4, 2016

Torch,

Thanks for the pointing that out. The lights suggest they will accept voltages as low as 9 and up to over 30 so I am not sure what their "actual" rating is.

torch · Dec 4, 2016

AndyM said:
Torch,

Thanks for the pointing that out. The lights suggest they will accept voltages as low as 9 and up to over 30 so I am not sure what their "actual" rating is.

Most multi-meters have a 10 amp DC current setting. Hook up some jumpers and see what the current actually is.

If you are not sure how to do this, the meter will likely have a separate jack for the 10ADC current setting. Set the meter correctly, connect the meter red to battery +, the meter black to the LED +, then a jumper from the LED - to battery -. LED should light and the meter should show the current draw. Like so:

- Battery + ------- 10a meter --------LED strip -------|
|__________________________________________|

dnr2011 · Dec 4, 2016

Switches handle LESS amperage with dc vs ac

Sent from my iPhone using Tapatalk

North Idaho Wolfman · Dec 4, 2016

Use a switch to switch a relay, and use the relay to power the lights!

torch · Dec 4, 2016

dnr2011 said:
Switches handle LESS amperage with dc vs ac

If the voltages are the same. He's going from 120VAC rating to 12VDC so the current capacity goes up, just no where near as much as he thought.

North Idaho Wolfman said:
Use a switch to switch a relay, and use the relay to power the lights!

An excellent alternative.

bxray · Dec 4, 2016

Switch ratings are not calculated like watts.
ie volts x amps.
A 5 amp rating is onlt good for 5 amps no matter what the voltage.
Just like wire size.
#12 is rated for 20amp breaker for 120v or 240v.

So 36 watts/12v = 3 amps so you will want a 5 amp rated switch or better.

Ray

AndyM · Dec 4, 2016

The relay idea seems like a good one; I had planned on setting up an auxillary fuse panel using a relay tied to the ignition. A second relay might start getting crowded (it's a little tractor after all!)

I have room for two switches - if each could handle one LED light; or I might have to break down and get a higher capacity switch. Shame thought, these ones have a nice orange LED that I thought would look great on the tractor!

torch · Dec 4, 2016

AndyM said:
I have room for two switches - if each could handle one LED light

That would be fine. No problem running one of those light bars per switch.

Missouribound · Dec 4, 2016

Rather than re-inventing the wheel....just pick up a switch rated for DC.
It really won't take much with LED's and a relay won't be necessary. If you were switching a winch or some other electrical mechanical attachment you may need a relay....but LED's...not so much.

Tooljunkie · Dec 5, 2016

Riddle me this- if the nice orange illuminated led switch is rated for 125 volts, how will it work on a 12 volt circuit?
Am i missing something?

Daren Todd · Dec 5, 2016

I agree with Missouribound. Just pick up a couple lighted toggles rated for 12 volt at the local auto parts store.

Tj brings up a good point. Lighted switch is 120v AC. How will the light work on a 12volt system?

bxray · Dec 5, 2016

Tooljunkie said:
Riddle me this- if the nice orange illuminated led switch is rated for 125 volts, how will it work on a 12 volt circuit?
Am i missing something?

The 120v would be like psi on a hose.
So a hose rated at 120psi will work with 12 psi.

Some fuses are marked for 240v but work on lower.

85Hokie · Dec 5, 2016

bxray said:
The 120v would be like psi on a hose.
So a hose rated at 120psi will work with 12 psi.

Some fuses are marked for 240v but work on lower.

Bx,

your analogy is a good one - however, PSI of water is more closely related to the voltage of electrons rather than the flow of electrons - aka AMPS. Flow of electrons would be closer to gallons of water per unit of time.

It is true, and amp is an amp - the pure number of electrons if you could count them in ONE amp = 6.25 x 10^18 electrons/second.

However - if you break down a 15 amp single pole switch that cost you 59 cents at lowes, and then look at a 20 amp $$$ commercial single pole, the contacts are worlds apart. In the cheapy - those contacts are the size of BB's - and in the commercial - they are like pencil erasers in diameter.

I DC light switch, typically is built to take a load if made well, and also has a built in light to let you know it is on and looks pretty too! Were as most AC switches do not have that feature, even though you can get them.

Andy,

I would not get the AC switch unless you are fitting it to something special, I would get a good quality DC switch that can be hole mounted with a light built in.

scdeerslayer · Dec 5, 2016

bxray said:
The 120v would be like psi on a hose.
So a hose rated at 120psi will work with 12 psi.

Some fuses are marked for 240v but work on lower.

The switch may work to power the circuit but I believe the question was how the light in the illuminated switch rated for 120v AC could be powered by 12v DC.

To the OP: Go look at marine switches to find a good switch to use on your tractor.

AndyM · Dec 5, 2016

Regards the LED light, I did a workbench test to se if my planned wiring would work out and the system works fine (LED lights, switch works a test light, relay kicks in when it's supposed to). The issue I guess I am stuck with is the capacity of the switch to the ROPS light I had planned to use.

So if I plugged in the switch and it failed, I assume it would just quit - or is it a fire hazard?

BTW The site I bought these switches off seemed like it was targeted to 12v automotive use even if the rating on the switch is listed AC.

85Hokie · Dec 5, 2016

AndyM said:
Regards the LED light, I did a workbench test to se if my planned wiring would work out and the system works fine (LED lights, switch works a test light, relay kicks in when it's supposed to). The issue I guess I am stuck with is the capacity of the switch to the ROPS light I had planned to use.

So if I plugged in the switch and it failed, I assume it would just quit - or is it a fire hazard?

BTW The site I bought these switches off seemed like it was targeted to 12v automotive use even if the rating on the switch is listed AC.

Andy,

shoot us the site - and if it were to quit - YOU would hope the switch just failed, and either it fails do to heat (melts the plastic) or the contacts fail to mate.

torch · Dec 5, 2016

I'm surprised it would quit that fast. Yes, it sounded borderline with two bars from one switch, but OK for one bar. Are you sure the switch is dead? EG: jump the connections and the light comes on?

AndyM · Dec 5, 2016

Torch,

I haven't installed the switch yet - no failure. My question was if I dived ahead and installed the switch would I run the risk of a fire if it failed.

85Hokie
This is the site I bought them from - I found the same switch on a number of "auto" type sites after I bought these (cheaper too as it turns out) but I didn't save the url.

http://alexnld.com/product/12v-16mm...ype-push-button-switch-high-flat-head-switch/

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