Wiring led lights - Does this electrically make sense?

[sickwilly]

Trying to wire up some leds and noticed in the user manual it says this
”16 ga max wattage 180w, 14 ga 300w, 12 ga 450w”.
Now I understand that more power can flow thru a bigger wire, but the wire lead coming out of the light itself is 18 or 20 ga. Far as I know THAT would be the limiting factor. It wouldn’t matter how large a wire I ran to the light if the leads coming out of the light itself are 18 ga.
Actually, would running 12 ga wire into 18 ga wire possibly get the smaller section of wire too hot?
Am I right or is it just Monday?

https://www.amazon.com/dp/B07Y1FYYWM?tag=959media-20

 

[franklin2]

Wire has a certain ohms per foot, or resistance per foot. That little lead coming out of the light is less than 6 inches long. How long will your other wiring be? The longer the run, the larger the wire needs to be to control resistance per foot, which will create voltage drop.

That is why they make those headlight relay kits that make ordinary lights brighter. The factory path for most trucks is from the battery, all the way to the fuse box, to the headlight switch, and then all the way back out to the lights. That is a long distance and the factory scrimped on their wiring to save a dollar per truck. It adds up over thousands of trucks.

The relay kit shortens the path from the battery, to the relay mounted near the headlights somewhere, and then to the lights. Much shorter path means less resistance, less voltage drop, brighter lights. That long original path the headlight power took, all it does with the relay kit is power the coil in the relay.

 

[pjtoledo]

correction/amended:

search wire gage current load


checked the item specs, apparently their version of 300 watts of light doesn't quite equal 300 watts of electrical power because the wire harness is only 16 gauge.

electrically speaking, watts divided by voltage equals current, so 300/12.5 = 24 amps. that's a bit too much for 16g wire.

 

[pjtoledo]

Trying to wire up some leds and noticed in the user manual it says this
”16 ga max wattage 180w, 14 ga 300w, 12 ga 450w”.
Now I understand that more power can flow thru a bigger wire, but the wire lead coming out of the light itself is 18 or 20 ga. Far as I know THAT would be the limiting factor. It wouldn’t matter how large a wire I ran to the light if the leads coming out of the light itself are 18 ga.
Actually, would running 12 ga wire into 18 ga wire possibly get the smaller section of wire too hot?
Am I right or is it just Monday?

https://www.amazon.com/dp/B07Y1FYYWM?tag=959media-20

technically, no.
the section of 18 ga wire is only concerned about the current flowing thru it. it has absolutely no concern about what's attached to either end of it.

that being said, the circuit voltage will push as much current thru it as the total load will allow.
that current will be constant thru out the circuit, so when the amount of current increases the smaller wire will be the first to get hot.

 

[sickwilly]

Franklin2
I actually have a couple relays for that purpose. Thats next after I finish the leds if I still feel the need to.

PJ
“that being said, the circuit voltage will push as much current thru it as the total load will allow.
that current will be constant thru out the circuit, so when the amount of current increases the smaller wire will be the first to get hot.”
THAT is my main concern is that small length of wire getting too hot if I use 12 ga for the rest.
My initial thought was to use larger wire than necessary to reduce voltage drop (ya know cause i wanna do it right) but the thought of tying into a considerably smaller wire just made me pause.

 

[Curious Hound]

Franklin2
I actually have a couple relays for that purpose. Thats next after I finish the leds if I still feel the need to.

PJ

that current will be constant thru out the circuit, so when the amount of current increases the smaller wire will be the first to get hot.”

No. It will not. The lights should be connected in parallel. So, each individual light and it's small gauge pigtail wire only carries the current for that individual light.

For example; if you have 2 lights in parallel in the circuit and each light draws 1 amp, the total circuit current is 2 amps. So the wire supplying the circuit must be able to handle 2 amps or more. But, where it spots to the pigtails for those lights, each pigtail will only see 1 amp. So the pigtails can be smaller.

If the lights were connected in series, then all the wiring would see the total current of the circuit. In series, the wires and lights are like links in a chain. They all see the same current. And some other weird things would happen to the voltage that each light gets. But don't get hung up on that. Multiple lights in a circuit in a vehicle should nearly always be wired in parallel.

 

[Curious Hound]

This may be helpful.

What is the Difference Between Series and Parallel Circuits? | Series And Parallel Circuits | Electronics Textbook

Read about What is the Difference Between Series and Parallel Circuits? (Series And Parallel Circuits) in our free Electronics Textbook

www.allaboutcircuits.com

.

 

[pjtoledo]

I was drifting more into general circuit stuff and not paying attention to how these lights are individually wired.
in the included harness do the individual pigtails go all the way back the relay & controller?
or do you have to supply your own wire from short pigtails back to the relay?

and then feed the relay with heavier wire?

 

[sickwilly]

All 3 individual pigtails go back to the relay.
Sorry, I should’ve clarified something. . Im using the included harness for the two 4” lights only. They’re wired up and they work. The 12” light will be wired separately to turn on with the high beams, which i have to make another harness for. This harness is where the original question comes from. Sorry for any confusion.

 

[Curious Hound]

All 3 individual pigtails go back to the relay.
Sorry, I should’ve clarified something. . Im using the included harness for the two 4” lights only. They’re wired up and they work. The 12” light will be wired separately to turn on with the high beams, which i have to make another harness for. This harness is where the original question comes from. Sorry for any confusion.

You can, and probably should use bigger wire to supply the bigger light. It reduces overall circuit resistance because large wire has a lower resistance per foot. Long circuits benefit from larger wire. The overall current in the circuit is dependent on the load. In this case, a 300watt light, 25 amps. That will not change significantly by using larger wire in your harness.

 

[franklin2]

In ex

You can, and probably should use bigger wire to supply the bigger light. It reduces overall circuit resistance because large wire has a lower resistance per foot. Long circuits benefit from larger wire. The overall current in the circuit is dependent on the load. In this case, a 300watt light, 25 amps. That will not change significantly by using larger wire in your harness.

In extreme cases, the size wire can affect the load. The resistance in the wire becomes a load itself, getting warm and emitting heat as a by product. That will affect the load or the total current in the circuit if the wire is small enough. In fact all wire introduces resistance, there is no perfect conductor. You just size it large enough to where the introduced resistance is so low it's not noticed.

You would think we are splitting hairs here, but when you are only dealing with 12 volts, a 1 volt drop is noticeable. If you where dealing with 120v, then 1 volt is not very noticeable. One of the main reasons they got away from 6v systems in cars, and why the military uses 24 volts.

 

[Curious Hound]

In ex

In extreme cases, the size wire can affect the load. The resistance in the wire becomes a load itself, getting warm and emitting heat as a by product. That will affect the load or the total current in the circuit if the wire is small enough. In fact all wire introduces resistance, there is no perfect conductor. You just size it large enough to where the introduced resistance is so low it's not noticed.

You would think we are splitting hairs here, but when you are only dealing with 12 volts, a 1 volt drop is noticeable. If you where dealing with 120v, then 1 volt is not very noticeable. One of the main reasons they got away from 6v systems in cars, and why the military uses 24 volts.

That's why I recommended larger wire fir the harness. However, in the circuit lengths generally encountered in a Ranger, even at 12 volts, you're not going to make a significant difference by going more than one or 2 sizes larger. I generally don't use anything smaller than 16ga on the truck. My big light bar is on a 14ga home run. My comments have been generally aimed at the OP's origi al question and the details necessary for that.

On the other hand, I have worked with circuits thousands of feet long requiring 4AWG wire for a mere 20 amps at 277volts. As background, my career as an electrician began in 1982. Dad taught me ohms law and many basic electronics/electricity principles as early as the mid 70's.

 

[sickwilly]

Ok. I appreciate the responses.I was just trying to wrap my head around how dc current works as opposed to ac. Those small wires coming out of the light were bugging me. The most this light pulls is probably around 40-60 watts in reality. Ive almost got the wiring harness made using 14 ga wire. Im also running the negative wire for the relay coil to the on/off switch inside the cab instead of positive - this seems a bit safer. If it will stop raining on my days off , ill have this done this week. I gotta get a shop built at the new house, not having a sheltered place to work on stuff sucks.