Big 3 cable upgrade crashes into ohm's law

[Ehall8702]

inrush currents for starter motors can hit 300-400 Amps. Upsizing conductors never hurts in power system design.

My Amps pull 900a+ , double runs 3/0 ND I still feel it's inadequate.

 

[Ehall8702]

Great post!

No kill like overkill. I have a completely unnecessary big-3 on my truck. I'll likely do the starter wire soon too. TBH though for me its just about replacing 30 year old wiring with new, and I can make my own cables for cheap. 1/0 and 4 awg 100% OFC welding cable is less expensive than buying premade CCA cables.

That being said the wiring for the headlights leaves a lot to be desired. A relay setup is a must IMHO.

NO CCA EVER! It doesn't last two winter's up here.

 

[Erin]

IIRC battery to block, battery to fender/side panel, block to frame, and rear of right side head to firewall. But that's just off the top of my head.

Just went to check an turns out the mechanic who swapped my engine installed the ground from frame to back of the block. So I’ve noticed other grounds from negative post to body & front of the block, and from positive post to starter, then to junction box, and from positive to alternator. The one that’s missing is from firewall to head.

 

[PlayingWithTBI]

The one that’s missing is from firewall to head.

A lot of people forget or don't hook that one back up because it's a PITA to get to.

 

[JeremyNH]

The only thing that matters is voltage loss to the motor. Motors develop torque proportional to the square of the terminal voltage so whatever is lost in the wire effects the running power of the motor. Smaller wire means more voltage loss means lower torque so slower crank. Undersized wire can be damaged due to overheating from overload but it won't happen during the few seconds the starting motor is working. Older cable may have broken strands which effectively reduces the wire size to the motor but if this is your problem then you should just replace it with the same size. Nothing really to be gained with larger wire. And you can't make the comparison to speaker wire. You get the most power delivered to a speaker when the wire impedance matches the speaker impedance. If the wire to speaker run is longer then you need larger wire and if shorter then you need smaller wire. Oversized speaker wire in short runs will produce the same poor performance as undersized wire in long runs. Power circuits don't work this way though so shouldn't be compared.

 

[thegawd]

this is all that I have done one both of my trucks. Iv also replaced the positive battery leads on my sierra with acdelco. these are solderd and double wall shrink wrapped. these are forever. this means I will never get stranded because of a bad ground.

Al

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[thegawd]

while I'm at it heres my thread from GMTC compete with pics of these new grounds installed. I was chasing an intermittent failed ignition switch. I thought I fixed it but nope. what a pain in the ass that was until it completely failed.

https://www.gmtruckclub.com/threads/grounds.1071450/#post-2497802


Negative from the battery to the fender right beside it.

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Passenger side firewall under the heater hoses to the frame.

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Then from the same point on the frame, down and up through a heat shield to the rear passanger side of the engine block.

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theres many more through out the truck but these are the main 3.

Al

 

[Schurkey]

That all depends on what your load is. If you have 55 Watt low beams then take 55W X 2 = 110W/12VDC = 9.16Amps. Of course, it'll be less Amperage with higher voltage but, if you turn on your lights with engine off, you want to be covered. I like to use Amps X 1.5 so, I'd use a 15 Amp fuse. Then you want wire sized for that 15Amp draw.

When upgrading the headlight wire harness using relays, DO NOT use "fuses" to protect the system. Some guys use a single fuse for low and high beam protection, and that's crazy.

When the fuse pops, you're screwed. And fuses--even "slow-blow" fuses pop pretty readily. If there's two circuit protectors, the low beams can fail, but you'd still have high-beams--or vice-versa.

The OEM protects the headlights with SELF-RESETTING CIRCUIT BREAKERS, often built into the headlight switch on older vehicles. I think this is Federal law. 'Course, those circuit breakers don't protect the entire system once you install relays. You'd need another pair in the power supply to each of the relays.

The typical 2X55 watt low beams get a 10-amp circuit breaker, the high beams get a 15 amp breaker. If you have a circuit fault, even if both the high and lows are affected, the headlights flash instead of leaving you 100% in the dark.

 

[Ehall8702]

When upgrading the headlight wire harness using relays, DO NOT use "fuses" to protect the system. Some guys use a single fuse for low and high beam protection, and that's crazy.

When the fuse pops, you're screwed. And fuses--even "slow-blow" fuses pop pretty readily. If there's two circuit protectors, the low beams can fail, but you'd still have high-beams--or vice-versa.

The OEM protects the headlights with SELF-RESETTING CIRCUIT BREAKERS, often built into the headlight switch on older vehicles. I think this is Federal law. 'Course, those circuit breakers don't protect the entire system once you install relays. You'd need another pair in the power supply to each of the relays.

The typical 2X55 watt low beams get a 10-amp circuit breaker, the high beams get a 15 amp breaker. If you have a circuit fault, even if both the high and lows are affected, the headlights flash instead of leaving you 100% in the dark.

To be devil's advocate, why would I ever bother to upgrade wire to run HALOGEN bulbs? Grab leds, adda single relay onto factory wire and be done with it, 4hi mod in 15 minutes . Factory wire is more than enuff for 4 leds, and single relay, if it was to fail leaves headlights to oem operation so no chance being left in the dark! Whole investment is roughly $45 and 30-45 minutes, that's new bulbs,relay,relay socket, a few heat sharing but connectors and the time to install new bulbs and 4hi mod. 6000k 4 sided leds are far superior to any halogen.

 

[sewlow]

LEDs are crap in these housings.