Wiring/Amps Tech Question

[ToadSmasher2K1]

I would like to run 2 BD S8 10” lights off the Gen 3 Aux 1 switch (previously the inner fog.)

Aux 1 is 10 amp rated
BD rates each S8 10” at 4.2 amp
*I will not be using the backlight feature*

Obviously 4.2 x 2 = 8.4 amps, which is below the 10 amp rating for Aux 1, but it’s close.

Good idea or bad idea?

@Nex @smurfslayer @The Car Stereo Company @Baja Designs
@4x4TruckLEDs.com

 

[Johnny@Apollo-Optics]

We always recommend relaying every single light connected to any AUX switch. However the general rule of thumb is staying below 80% of the max amp rating which you'd be right above. Will it work? Yes. But any surge of amperage will likely blow the fuse.

 

[smurfslayer]

The answer is:

It depends.

You’re close and you have 2 variables here.
The truck voltage at KOEO / while the truck is running
the voltage B/D calculates the current draw at.
( I know, this is a very simplistic example )
Why?

How Voltage & Phase Affects Amp Draw & HP Consumption

Understanding how voltage and phase affects amperage draw and horsepower output can help you avoid increase power demands and worse, motor failure.

www.marchpump.com

because when voltage drops, current draw can go up.

Ohm's law - Wikipedia

en.wikipedia.org

so using an ohm’s law calculator - extreme examples, if I have 12v 8.5a I have 102w of power. at 14.4v, 8.5a we have 122.4
I’m not even bringing up resistance and voltage drop here.

before it gets out of hand - and I already need to top off my pint, you’re close enough that a relay is inexpensive insurance for the up fitter circuit.

Wire in a relay. I don’t know if I’d go as far as a relay for every up fitter, but if it’s close, it’s worth it to have the added precaution.

 

[The Car Stereo Company]

as stated, use relays. im even more cautious as to use relays at 75% the amperage rating. also, the guage of wire is just as important. minimum of 16ga wire and 12 to 14 for longer runs. you lose power through heat and too small of wire will generate too much heat. feel free to text me and i can give you a complete layout and explain how it works and answer any questions you have (831) 254-7562

 

[ToadSmasher2K1]

Thanks for the responses everyone

 

[wheelman55]

Mr. Toad. This is where I come in and recommend that you purchase Tony Candela’s books, as well as buying all of your automotive wiring from Tony.

Wiring Books - CE Auto Electric Supply - Automotive Electrical Solutions

ceautoelectricsupply.com

He’s an excellent resource.

 

[Nex]

Or just get a switch pro and have them all come on with 1 button.

 

[ToadSmasher2K1]

Or just get a switch pro and have them all come on with 1 button.

I might have to. I’m learning the upfitters aren’t as great as they seem since Ford gave each switch enough amps to run a pencil sharpener

 

[Nex]

I might have to. I’m learning the upfitters aren’t as great as they seem since Ford gave each switch enough amps to run a pencil sharpener

Not the ones from the 80s they didn't!

 

[Nex]

Race Mode turns on all forward facing lights. 4x LP9s, XL80s and S8 light bar.