Is it a problem to have the positive and negative cables run side by side with no air gap?

[IDIDIDIhoDhoDhoDO]

I need electrical expertise.

I am relocating both batteries to the bed. I needed new batteries but they are expensive. I found two large AGM batteries on the local classifieds that were a few years old in good shape and a good deal. They are large batteries, about the same size footprint as the Group 65 batteries that were original but much taller and about 90 pounds apiece. So I ordered a thick piece of phenolic to make some terminal blocks that will go under the hood where the factory battery trays are so I can connect all the original connections as they should be. Then I will install the two large AGM batteries in the bed. I have 2/0 welding cable that I will then parallel the batteries with then run from the battery bank in the bed to one of the terminal blocks under the hood.

These welding cables from the battery bank to the terminal block will be close to 10 feet long by my guess. It would be a lot more convenient to install if both cables could run side by side right next to each other. Zip tied together basically. I know the starting current in my truck is about 550 amps. My question is, if the positive and negative cables are right next to each other like that for 10 feet while pulling that much current will the magnetic fields counteract each other significantly and cause any problems? And if so, what kind of air gap would I realistically need?

 

[u2slow]

I would jumper with #2/0 and go the distance with #4/0. That's what I did on my van. Can't recall the routing so well, other than I went direct to the starter first. Because of chafing possibilities, I'd put something over the positive run as a sleeve anyway.

 

[MtnHaul]

I have found heater hose to be reasonably cheap and very effective as chafing gear. Never used it as a full sleeve but sliced lengthwise and then held in place with zip ties it has been quite useful. DelCity offers a variety of different types of loom material, https://www.delcity.net/store/Loom-&-Loom-Clamps/

 

[IDIDIDIhoDhoDhoDO]

4/0 is $7 a foot so I think I'll try the 2/0 and see how strong the motor cranks first, I already have 2/0 and some ring terminals sitting around. I might just try some old TIG torch hose cover as a makeshift loom because some of that is also sitting around.

Thanks for your input guys.

 

[u2slow]

12 volts isn't a lot in the first place. Can't afford to lose any along the way.

 

[IDIDIDIhoDhoDhoDO]

That's true. I just checked and 2/0 is 133 kcmil and 4/0 is 211.6 kcmil. That's a pretty big difference. I suppose I can run double 2/0 cables for 266 kcmil for both positive and negative if the voltage drop ends up being significant. Although that's a lot of grommet holes to drill into the bed floor.

 

[divemaster5734]

I need electrical expertise.

I am relocating both batteries to the bed. I needed new batteries but they are expensive. I found two large AGM batteries on the local classifieds that were a few years old in good shape and a good deal. They are large batteries, about the same size footprint as the Group 65 batteries that were original but much taller and about 90 pounds apiece. So I ordered a thick piece of phenolic to make some terminal blocks that will go under the hood where the factory battery trays are so I can connect all the original connections as they should be. Then I will install the two large AGM batteries in the bed. I have 2/0 welding cable that I will then parallel the batteries with then run from the battery bank in the bed to one of the terminal blocks under the hood.

These welding cables from the battery bank to the terminal block will be close to 10 feet long by my guess. It would be a lot more convenient to install if both cables could run side by side right next to each other. Zip tied together basically. I know the starting current in my truck is about 550 amps. My question is, if the positive and negative cables are right next to each other like that for 10 feet while pulling that much current will the magnetic fields counteract each other significantly and cause any problems? And if so, what kind of air gap would I realistically need?

DC voltage doesn't carry EMF's, that's only developed by AC, which is also why all voltage is generated in AC, then rectified and filtered into various levels of DC.
From pulsating DC to pure sine wave.
That said, make sure you have overcurrent protection at the positive battery terminals, BEFORE you make the run to the front.
You need to protect the conductors AT THE SOURCE, long term vibrations can eventually compromise the insulation, and a dead short condition could result in a massive amount of energy discharge, resulting in any number of catastrophic events, from burning down to explosive.
There are inline circuit breakers available for cheap.
You may need to crimp the ends to land them as welding cables are MTW or AWM, compared to AWG.
That means 2/0 will have between 540 to 972 strands depending on the type.
This is done for increased surface area to reduce "skin effect".
If you don't have all the strands bundled and secured it will compromise and reduce the ampacity that the conductor can carry.
There used to be a hot rod truck show on Saturdays and they did an episode on moving the battery to the bed.
I sent them an email and ripped their *** for putting the fuse in the front and leaving the battery wire unprotected between.
They never responded, but two weeks later they added a correction to their battery show and detailed the reason to add overcurrent at the battery.
Be sure you install a barrier between batteries or terminal protectors and obviously secure them from movement.
Zip tied together is fine and makes sense, try to make all the cables the same length, which is critical in parallel runs due to the wire resistance, if one cable is shorter then that battery will work harder due to less resistance, which can cause other issues with performance and longevity.
You can protect the insulation at transitions through body and frame with simple plumbing insulation wrap around the harness bundle and tape intermittently.
4x 2/0 MTW cables will make around 3"-4" diameter bundle.
Good Luck!

 

[franklin2]

You can't use the frame for the negative? Short 2/0 from the batteries to the frame at the rear and then short 2/0 cables from the frame up front to the engine block?

 

[divemaster5734]

You can, but that could cause issues.
It's all about the least resistance, and if there's bolts, nuts, and other parts between the preferred current flow it can cause anything from increased amps to operate, reduced device or charging performance, to unintended alternate paths created.
Definitely need at least one cable directly on the block for first connection, but I'd recommend both as the only massive single draw is in starting. which is when the path to the poles needs to be clear.
There's a voltage drop and additional resistance in every single electrical connection no matter how much care is taken in the prep, and we can calculate the heat loss.
Resistance to current through friction generates heat, the only question remaining is how much.
It's much worse in AC circuits, but still prevalent in DC.

 

[IDIDIDIhoDhoDhoDO]

Thank you for the excellent answer divemaster. I'm glad to be able to bunch up all the cables and not need to worry about EMF. By my calculations a 10 foot length of 2/0 should voltage drop about 0.4 volts at a 550 amp load and a 4/0 should voltage drop about 0.25 at a 550 amp load. Before I get started cutting and crimping cable, do you think I need to run double 2/0 positive and negative cables or is a single of each sufficient?

 

[divemaster5734]

You'll be good with one 2/0 for each.
Being a common ground system it wouldn't hurt to add a negative jumper to the frame by the batteries, with a couple other frame to body jumper spread around.
Mobile electrical switches the negative almost as much as the positive, and the paths are everywhere.
Truthfully, there's no significant loss with this gauge for up to 30' that would have a significant impact.
There's a compound used for heavy duty connections called deox, or noalox, depending on the brand.
It was designed for aluminum to copper connections initially, but I started using it for all battery and exposed terminal connections.
It's a viscous gel that fights oxidation and increases conductivity throughout any splice or tap.
Puck up a small tube at any hardware store and once you prep the wire for crimp, pull off the top and stick the end in before inserting it into the lug.
All your connections will last 4x longer and stay a lot cooler during current flow.
Once upon a time I worked in oil fields and refineries. Have taken apart oil pump motors that only had a single cover to protect from full outside weather and the connections had zero contamination or oxidation which had been connected 10 years prior.
It's well worth the $5 for enough to dozens of taps.

 

[divemaster5734]

That's true. I just checked and 2/0 is 133 kcmil and 4/0 is 211.6 kcmil. That's a pretty big difference. I suppose I can run double 2/0 cables for 266 kcmil for both positive and negative if the voltage drop ends up being significant. Although that's a lot of grommet holes to drill into the bed floor.

I misspoke.
You only need one positive and one negative from the batteries to the front.
I apologize for the confusion. Got a good excuse, but it's just that.

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It's still a work in progress and has changed since this pic, but that's a 2/0 welding cable repurposed dropping down to the starter. So of course I hadn't phased it yet, just jury rigged for first start.
The jumper from the other battery is 2/0 into a hydraulic crimp with epoxy heat shrink to seal.
You don't need two of each running up, just one.
That 2/0 MTW @ 12 V is good for around 600 amps continuous.
I read parallel and my brain just got stuck there.
The only parallel is the battery connection.
Series will increase the voltage and parallel will increase the current.
Don't run two hots, they're not needed.

 

[XOLATEM]

Resistance to current through friction generates heat,

What I am going to say is silly...especially for this serious conversation...

But...I got a vision from this quote that someone could take a truck and put some massive batteries in it and an equally massive starter motor and have an engine with so much turning resistance that...because the ground from the battery went to the frame that the heat was so great that the frame got melted in two....

Told you it was silly...but this would be just the kind of nightmare I would wake up in the middle of the night from....

Speaking of 'skin effect'...wouldn't it be neat if we could actually 'see' the electrical energy emitted from a vehicle while it is running..?

Like some kind of 'aura'...??

 

[u2slow]

As far as using the frame as a common ground, use the same frame rail. Then you're not relying on rivets and other rusty fasteners for high current.

 

[divemaster5734]

But...I got a vision from this quote that someone could take a truck and put some massive batteries in it and an equally massive starter motor and have an engine with so much turning resistance that...because the ground from the battery went to the frame that the heat was so great that the frame got melted in two....

Take a look at some of the EV fires, they do melt the frame.

Told you it was silly...but this would be just the kind of nightmare I would wake up in the middle of the night from....

Speaking of 'skin effect'...wouldn't it be neat if we could actually 'see' the electrical energy emitted from a vehicle while it is running..?

Like some kind of 'aura'...??

Actually, some welders only operate on around 20VDC, it's all about the path.
There's no way to cheat it.
High amps is low volts, and high volts is low amps, which is why welding machines have transformers with huge wire for the windings to handle the load.
Welders don't weld continuously, they have duty cycles of 30%-70%, but you can absolutely use a couple jumper cables, connect a coat hanger to one and the other to metal and run a bead.
You'll smoke the battery if your not careful, but the potential is there.
That's why EV fires are so intense, due to the tremendous amount of energy transfer in a short circuit that can't be opened.

I thought I saw an aura once, then just realized the acid was kicking in...