Halogen light overload

how much amps is too much? I have a pair of road shock 100w halogens on a relay and I want too add a couple more on a separate relay so 4 lights total but I’m not sure if it will be too much, thanks

Shane Garcia said:

how much amps is too much? I have a pair of road shock 100w halogens on a relay and I want too add a couple more on a separate relay so 4 lights total but I’m not sure if it will be too much, thanks

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Do you Want to or have to put all 4 on the same circuit? You could run another circuit for just the 2nd pair.
You need to know what the Total current draw is in the existing circuit. Most circuits are fused to open at approximately 75-80% of the fuses rating. As an example, a 15A fuse will blow at +/- 12A.
You will see the biggest draw at the time those lights are switched on. This is what you need to determine wire size and fuse rating. Also, the existing circuit might have other things on it.
Lots of fun math ahead of you. Some guys skip that part and burn down their ****. Don't be that guy.

I don't know where you get your info BUT a fuse shouldn't blow at 75% of rating. It will run at 100% capacity all day long. A 100 watt hallogen will draw 8.33a at 12v but you do want to use a larger fuse in that case because hallogens pull more than that current at turn on then settle down once it warms up. I would suggest a 10 - 12a slow blow to account for the initial surge current and that your trucks alternator charges at around 14v which would cause it to draw more current.

Like I replied in your other thread, it depends on how many amps your alternator puts out. If you draw more power than your alternator puts out, you're running on battery and no part of your electrical system will be happy for very long. You need to know how many amps you alternator is, and how many amps you are already pulling. That will tell you how many spare amps you have and this how many more lights or other accessories you can power. Your 100W lights will each draw a touch over 8 amps each, so 4 is say 35A to be safe... plus ~50 amps just to run the truck. You're already at 85A...

EDIT: Typical OEM alternator is ~105 Amps. YMMV.

add to that anything else you might run: Stereo, amp, air conditioning, etc...

And as said above, if you have enough power for the extra lights, I'd personally put them on a separate fused relay than the first two. You could still use a single switch to trigger both relays.

indept said:

I don't know where you get your info BUT a fuse shouldn't blow at 75% of rating. It will run at 100% capacity all day long. A 100 watt hallogen will draw 8.33a at 12v but you do want to use a larger fuse in that case because hallogens pull more than that current at turn on then settle down once it warms up. I would suggest a 10 - 12a slow blow to account for the initial surge current and that your trucks alternator charges at around 14v which would cause it to draw more current.

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This. I'd recommend two relays fused at 20A each and make sure the wire gauge is heavy enough for the load and the length of the run.

sbarron said:

This. I'd recommend two relays fused at 20A each and make sure the wire gauge is heavy enough for the load and the length of the run.

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A 14awg wire 10' long will drop 0.5v at those currents, an 18 awg same length will drop almost 1.5v so for wire I would go 14 awg or even better 12 awg.

indept said:

I don't know where you get your info BUT a fuse shouldn't blow at 75% of rating. It will run at 100% capacity all day long. A 100 watt hallogen will draw 8.33a at 12v but you do want to use a larger fuse in that case because hallogens pull more than that current at turn on then settle down once it warms up. I would suggest a 10 - 12a slow blow to account for the initial surge current and that your trucks alternator charges at around 14v which would cause it to draw more current.

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Here is one source for the info I provided.

https://www.12voltplanet.co.uk/fuses-guide-uses.html

"Fuse ratings"

Continuous rating
Fuse are marked with the current that they will continuously pass (at a standard temperature) without blowing, known as the continuous rating. It is good practice not to allow the continuous current to exceed 75% of the fuse's rated value to accommodate momentary current surges that might cause the fuse to fatigue over time or blow unnecessarily (nuisance blow).

Another source would be my electronics schooling and 28 yrs working on electronic equipment, including life support equip. Not to be a **** but, you countiued to post and say what I already said. You win I guess.

RoadRamblerNJ said:

Here is one source for the info I provided.

https://www.12voltplanet.co.uk/fuses-guide-uses.html

"Fuse ratings"

Continuous rating
Fuse are marked with the current that they will continuously pass (at a standard temperature) without blowing, known as the continuous rating. It is good practice not to allow the continuous current to exceed 75% of the fuse's rated value to accommodate momentary current surges that might cause the fuse to fatigue over time or blow unnecessarily (nuisance blow).

Another source would be my electronics schooling and 28 yrs working on electronic equipment, including life support equip. Not to be a **** but, you countiued to post and say what I already said. You win I guess.

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True thats why I said 10 - 12a for surges.
You said fuses blow at 75% of their rating which is wring. I base that on 38 years in radar design. Many of those in switching power supply design used in those radar systems.

indept said:

True thats why I said 10 - 12a for surges.
You said fuses blow at 75% of their rating which is wring. I base that on 38 years in radar design. Many of those in switching power supply design used in those radar systems.

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My wording could have been better. Fuses opening at 75% of rating wasn't meant to be all inclusive. We're trying to help a guy that doesn't know a bunch about Ohm's law. I was trying to keep him in the "safe zone". My apologies for being snarky. Ed.

RoadRamblerNJ said:

My wording could have been better. Fuses opening at 75% of rating wasn't meant to be all inclusive. We're trying to help a guy that doesn't know a bunch about Ohm's law. I was trying to keep him in the "safe zone". My apologies for being snarky. Ed.

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Sorry if I came off bad. Same thing trying to help. Happens sometime, we can't help it, we're from New Jersey.

indept said:

Sorry if I came off bad. Same thing trying to help. Happens sometime, we can't help it, we're from New Jersey.

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Faghedaboutit Ohh ayyy.

Truth be told,
my house is SOLD!
One more surgery
and I'm off to Tennessee.

Good luck