Battery Cable Sizing

[kramttocs]

I see the page for cable lengths but was wondering if there was a chart for the recommended sizes for battery cables.

Have looked around and there is a battery cable site that lists recommendations based on the engine type but was curious what everyone here thought.

Not necessarily looking for stock sizes but more so the best size.

Here are the cables I can think of I am needing (will be custom making them) but please add any I've forgotten.

Positive battery to relay

Positive relay to starter solenoid (Pmgr)

Relay output to starter solenoid (trigger)

Negative to engine block

Aux battery:

Positive battery to isolator

Isolator to main battery

Negative battery to fender

Engine: 460

Going off memory regarding the isolator - there was originally a junction bolt there that I am replacing with the isolator but I can't recall the hot wire size and if it will be big enough. Additionally I don't recall if it has an inline fuse that will be needed.

Also, if any of these requirements change for different engine types, please add those as well.

[Gary Lewis]

Scott - Good questions. Was just wondering that yesterday as I took off the ground cable on Big Blue and thought "That's not very big." And if I have to move the aux battery to the passenger's side I'll have to have new cables.

How are you going to make them? I have a 16 ton hydraulic crimper and it works great if you feed it the good Magnalugs. I made all new battery cables for both batteries on our boat and used 2-0 marine cable. They came out great, and I might consider using that size for my cables.

On the isolator for the aux battery, that circuitry is best shown in the 1985 EVTM on the Charge & Power Distribution - Gas Engine pages. There's even a depiction of the stud you talked about as well as the relay. But there's no true fuse, just a fusible link.

On the grounds, don't forget the one from the engine to the firewall. And while you are at it, you might add grounds from the fenders to the radiator support and from the cab to the fenders. I think Ford did that in later years, but Jim or Bill might tell us different.

[kramttocs]

Scott - Good questions. Was just wondering that yesterday as I took off the ground cable on Big Blue and thought "That's not very big." And if I have to move the aux battery to the passenger's side I'll have to have new cables.

How are you going to make them? I have a 16 ton hydraulic crimper and it works great if you feed it the good Magnalugs. I made all new battery cables for both batteries on our boat and used 2-0 marine cable. They came out great, and I might consider using that size for my cables.

On the isolator for the aux battery, that circuitry is best shown in the 1985 EVTM on the Charge & Power Distribution - Gas Engine pages. There's even a depiction of the stud you talked about as well as the relay. But there's no true fuse, just a fusible link.

On the grounds, don't forget the one from the engine to the firewall. And while you are at it, you might add grounds from the fenders to the radiator support and from the cab to the fenders. I think Ford did that in later years, but Jim or Bill might tell us different.

Haha good. Glad to know I am not alone.

I've actually read your thread on FTE for your boat cables a few times and my 16 ton eBay crimper came today

From that thread I've been tracking down magnalugs and am happy to see 45 and 90 degree options.

I have been leaning towards 1/0 for everything large (positive and negative) but mainly because a lot of those 'multi' battery post connectors seem to max out at that size and I was thinking they would make clean wiring for the aux battery and amp connections.

I was actually going to keep the factory wiring for the engine to ground but good call on the fender to rad support.

Also planning to directly ground the starter back to the engine ground post.

I'll check out that diagram for the aux.

 

[kramttocs]

Haha good. Glad to know I am not alone.

I've actually read your thread on FTE for your boat cables a few times and my 16 ton eBay crimper came today

From that thread I've been tracking down magnalugs and am happy to see 45 and 90 degree options.

I have been leaning towards 1/0 for everything large (positive and negative) but mainly because a lot of those 'multi' battery post connectors seem to max out at that size and I was thinking they would make clean wiring for the aux battery and amp connections.

I was actually going to keep the factory wiring for the engine to ground but good call on the fender to rad support.

Also planning to directly ground the starter back to the engine ground post.

I'll check out that diagram for the aux.

Looks like they used the same factory hot wire for both the lug and aux battery isolator. So I guess that guage is enough? I was thinking I'd need to run a full size battery cable across the firewall.

[ArdWrknTrk]

Scott - Good questions. Was just wondering that yesterday as I took off the ground cable on Big Blue and thought "That's not very big." And if I have to move the aux battery to the passenger's side I'll have to have new cables.

How are you going to make them? I have a 16 ton hydraulic crimper and it works great if you feed it the good Magnalugs. I made all new battery cables for both batteries on our boat and used 2-0 marine cable. They came out great, and I might consider using that size for my cables.

On the isolator for the aux battery, that circuitry is best shown in the 1985 EVTM on the Charge & Power Distribution - Gas Engine pages. There's even a depiction of the stud you talked about as well as the relay. But there's no true fuse, just a fusible link.

On the grounds, don't forget the one from the engine to the firewall. And while you are at it, you might add grounds from the fenders to the radiator support and from the cab to the fenders. I think Ford did that in later years, but Jim or Bill might tell us different.

It's odd that your block-frame-battery ground cable is undersized, Gary.

It's a circuit, and electrons have to flow all the way around the loop.

While the starter is probably the largest draw of most vehicles, it is only used intermittently, so even a heavy draw won't cause the cable to overheat (if it is properly sized for the amperage) something like a winch is much more taxing.

IMO, there's no such thing as to large or too many grounds.

When I did my 3G swap Ryan's kit included 2/0 cable to make up the links between alt -fuse and fuse-battery, so I picked up a 2/0 ground at the truck supply.

Intended for electric/hydraulic plow trucks that are always blasting the heater and have (had!) lots of auxiliary incandescent lighting.

1/0 seems more than ample for most any purpose.

My bricknose had braided straps, both firewall to intake and cab sill pinch weld to cab mount frame 'ear' beneath the drivers feet, circumventing the rubber isolators.

Maybe I can get a pic in daylight.

Still getting this new temporary phone to where I like it....

[85lebaront2]

It's odd that your block-frame-battery ground cable is undersized, Gary.

It's a circuit, and electrons have to flow all the way around the loop.

While the starter is probably the largest draw of most vehicles, it is only used intermittently, so even a heavy draw won't cause the cable to overheat (if it is properly sized for the amperage) something like a winch is much more taxing.

IMO, there's no such thing as to large or too many grounds.

When I did my 3G swap Ryan's kit included 2/0 cable to make up the links between alt -fuse and fuse-battery, so I picked up a 2/0 ground at the truck supply.

Intended for electric/hydraulic plow trucks that are always blasting the heater and have (had!) lots of auxiliary incandescent lighting.

1/0 seems more than ample for most any purpose.

My bricknose had braided straps, both firewall to intake and cab sill pinch weld to cab mount frame 'ear' beneath the drivers feet, circumventing the rubber isolators.

Maybe I can get a pic in daylight.

Still getting this new temporary phone to where I like it....

One of the improvements Ford did on the Aeronose trucks was the battery cables now run to the starter directly (PMGR starter) and the old starter relay is still there, but operates a much smaller wire to the starter solenoid. The body ground is now a pigtail (GM style) from the battery terminal end to the right inner fender. This is a picture of a friend's 1994 F150 battery and relay connections, the positive (inboard) cable has two branches, one to the starter, the other to the relay and remainder of the power, the alternator is connected there. My 160 amp 3G has a 200 amp megafuse in a holder next to the relay.

[Steve83]

...a chart for the recommended sizes for battery cables.

4ga for all gas engines.

...based on the engine type...

Some diesels draw more current due to their higher compression and heavier starters, but most stock-type gas truck engines' starters draw ~140A max, and require about the same-size cables. Only a remote-mounted battery would necessitate an increase of 1 size (2 gauges lower).

Not necessarily looking for stock sizes but more so the best size.

Stock is generally best. Ford engineers know more about designing vehicles than anyone, and they know the company has to warrant their designs, so they design for high reliability.

Relay output to starter solenoid (trigger)

That only has to power the solenoid, so its a MUCH-smaller wire than the battery cables.

https://supermotors.net/getfile/870249/thumbnail/startersolswap.jpg

Isolator to main battery

That depends on what you plan to do with the aux.batt. Ford only intended it to extend the key-off time (reserve minutes).

https://supermotors.net/getfile/905422/thumbnail/battrelayaux.jpg

Negative battery to fender

Bad idea. The fender isn't well-grounded through its (painted) mounting points. Either ground the battery to the frame, block, or firewall; or (better) just run its negative cable directly to the main battery negative (with as few bolted connections as possible).

Additionally I don't recall if it has an inline fuse that will be needed.

Again: depends on your plans. But generally: battery cables are too big to protect. They need to carry all the current available, so fusing it would just cut power when you need it most. This caption explains in more detail:

https://supermotors.net/getfile/849725/thumbnail/fusesblades.jpg

IMO, there's no such thing as to large...grounds.

Although they're popular, big wires don't actually compensate for poor connections or poor circuit design. They can actually hurt, due to being harder to manipulate, bend, and create good connections. Their stiffness may distort the metal they're bolted to, causing a worse connection than with a properly-sized wire. They're also exponentially more-expensive, without any corresponding benefit, over the appropriate size wire with good terminals.

IMO, there's no such thing as...too many grounds.

If they're all large enough to handle the total current that might ever pass through all of them, then you're right. But often, some of the "ground" wires are substantially smaller. So if a big one is removed, or loses connection for any reason, the smaller ones might catch fire due to suddenly being subjected to all the current that the big one WAS carrying. That's why automakers generally DON'T run parallel grounds. If the ground circuit goes bad in one spot, it just shuts down all the circuits it serves - that's safer than setting fire to a smaller parallel wire.

My bricknose had braided straps, both firewall to intake and cab sill pinch weld to cab mount frame 'ear' beneath the drivers feet, circumventing the rubber isolators.

Those are only for RFI - not for power grounding. No measurable current should ever pass through them - only transient "noise".

https://supermotors.net/getfile/907034/thumbnail/radiobondstraps.jpg

[kramttocs]

...a chart for the recommended sizes for battery cables.

4ga for all gas engines.

...based on the engine type...

Some diesels draw more current due to their higher compression and heavier starters, but most stock-type gas truck engines' starters draw ~140A max, and require about the same-size cables. Only a remote-mounted battery would necessitate an increase of 1 size (2 gauges lower).

Not necessarily looking for stock sizes but more so the best size.

Stock is generally best. Ford engineers know more about designing vehicles than anyone, and they know the company has to warrant their designs, so they design for high reliability.

Relay output to starter solenoid (trigger)

That only has to power the solenoid, so its a MUCH-smaller wire than the battery cables.

https://supermotors.net/getfile/870249/thumbnail/startersolswap.jpg

Isolator to main battery

That depends on what you plan to do with the aux.batt. Ford only intended it to extend the key-off time (reserve minutes).

https://supermotors.net/getfile/905422/thumbnail/battrelayaux.jpg

Negative battery to fender

Bad idea. The fender isn't well-grounded through its (painted) mounting points. Either ground the battery to the frame, block, or firewall; or (better) just run its negative cable directly to the main battery negative (with as few bolted connections as possible).

Additionally I don't recall if it has an inline fuse that will be needed.

Again: depends on your plans. But generally: battery cables are too big to protect. They need to carry all the current available, so fusing it would just cut power when you need it most. This caption explains in more detail:

https://supermotors.net/getfile/849725/thumbnail/fusesblades.jpg

IMO, there's no such thing as to large...grounds.

Although they're popular, big wires don't actually compensate for poor connections or poor circuit design. They can actually hurt, due to being harder to manipulate, bend, and create good connections. Their stiffness may distort the metal they're bolted to, causing a worse connection than with a properly-sized wire. They're also exponentially more-expensive, without any corresponding benefit, over the appropriate size wire with good terminals.

IMO, there's no such thing as...too many grounds.

If they're all large enough to handle the total current that might ever pass through all of them, then you're right. But often, some of the "ground" wires are substantially smaller. So if a big one is removed, or loses connection for any reason, the smaller ones might catch fire due to suddenly being subjected to all the current that the big one WAS carrying. That's why automakers generally DON'T run parallel grounds. If the ground circuit goes bad in one spot, it just shuts down all the circuits it serves - that's safer than setting fire to a smaller parallel wire.

My bricknose had braided straps, both firewall to intake and cab sill pinch weld to cab mount frame 'ear' beneath the drivers feet, circumventing the rubber isolators.

Those are only for RFI - not for power grounding. No measurable current should ever pass through them - only transient "noise".

https://supermotors.net/getfile/907034/thumbnail/radiobondstraps.jpg

Thanks Steve.

4ga is good to have as a reference. I am actually starting to lean towards 1ga just because the crimper doesn't appear to have one for 1/0 and if 1ga is plenty...

I don't disagree on the Aux battery being grounded to the fender but that's how stock did it is the only reason I was considering it. I like grounding it to the main battery better.

For the relay to starter (trigger wire): 10ga? Or what is your numerical value of 'much smaller'?

My plan for the aux battery is to run my amp, sub, fog lights and eventually a run to the rear bumper for my trailer winch.

With those goals, the positive between the main and aux would just be for charging from the alt.

I assume the factory yellow wire would be enough for that?

Now lets say if I wanted to use the 'jumper' mode of the isolator. In that case I would need larger?

[ArdWrknTrk]

Thanks Steve.

4ga is good to have as a reference. I am actually starting to lean towards 1ga just because the crimper doesn't appear to have one for 1/0 and if 1ga is plenty...

I don't disagree on the Aux battery being grounded to the fender but that's how stock did it is the only reason I was considering it. I like grounding it to the main battery better.

For the relay to starter (trigger wire): 10ga? Or what is your numerical value of 'much smaller'?

My plan for the aux battery is to run my amp, sub, fog lights and eventually a run to the rear bumper for my trailer winch.

With those goals, the positive between the main and aux would just be for charging from the alt.

I assume the factory yellow wire would be enough for that?

Now lets say if I wanted to use the 'jumper' mode of the isolator. In that case I would need larger?

IIRC my PMGR starter was shown at 40A to pull and 13A to hold.

The instructions said to use 12Ga, and I believe I used 10.

I do think Gary has the chart, as I posted it back on FTE in response to his questions.

It shows all the parameters, such as draw at stall and the torque curve.

[Steve83]

...the crimper...

Solder is MUCH better than crimping in this application, for several reasons.

Or what is your numerical value of 'much smaller'?

I don't remember, but it's in the 1st diagram I posted above. SMN is down for maintenance at the moment...

My plan for the aux battery is to run my amp, sub, fog lights and eventually a run to the rear bumper for my trailer winch.

With those goals, the positive between the main and aux would just be for charging from the alt.

Not if you use ANY of those while the engine is running (alt. working). In that case, the current to those loads could be expected to come from the aux.batt., the main batt., the alt., or any combination at any moment. So the connecting wires between those 3 voltage sources should be sized for the peak load (probably the winch).

I assume the factory yellow wire would be enough for that?

Only if you NEVER use a load larger than that Yellow wire can handle while the engine is running.

Now lets say if I wanted to use the 'jumper' mode of the isolator. In that case I would need larger?

Yes, if you ever expect to pull substantial current INTO the aux.batt. or the circuits connected to it.