Using copper flat bar to connect the batteries in a battery bank

[mitiempo]

Originally Posted by rwidman

That is only partially true and misleading. A circuit feeding the starter motor doesn't have to have overcurrent protection.

The reason ABYC does not require dedicated starter circuit fusing is that on large engines it is very hard/expensive to do. On any small engine it is a very good idea. I regularly fuse starter circuits on diesels up to 60 or 70 hp without any problems.

A dedicated starter circuit is one where the switching does not allow the start battery to be used for house loads. If you have a 1/2/both/off switch the starter circuit is not dedicated to only starting and should be fused.

The starter battery can start a fire as easily as a house battery.

[Matt Johnson]

Originally Posted by rwidman

Voltage is part of ohm's law but a fixed resistance is the same regardless of voltage.

Imagine a resistor sitting on a bench. Imagine it is color coded (marked) ten ohms. It has ten ohms of resistance regardless. It doesn't have to be connected to a circuit to have ten ohms of resistance.

Great explanation. Thanks Ron!

Matt

[Barney21]

I dont think a solid link to battery terminals is a very good suggestion. Battery teminals are not built to be bolted solid. Vibration will dislodge them from the plates. Use a copper sheathed web strap, put some anti corrode around the terminal will fix most of the issues.

[Cap Erict3]

Originally Posted by mitiempo

The reason ABYC does not require dedicated starter circuit fusing is that on large engines it is very hard/expensive to do. On any small engine it is a very good idea. I regularly fuse starter circuits on diesels up to 60 or 70 hp without any problems.



A dedicated starter circuit is one where the switching does not allow the start battery to be used for house loads. If you have a 1/2/both/off switch the starter circuit is not dedicated to only starting and should be fused.



The starter battery can start a fire as easily as a house battery.

Your engine start is an emergency circuit. You don't want to blow a fuse when you really need the engine.

It is common to use buss in battery banks. Easy to insulate with heat shrink.

Copper Shield is an excellent conducting paste. Bolt sections together for a flex fit.

[kish]

[QUOTE=Zai;2297936]Does anybody know what size copper bar would I need to get the same effect as 70mm battery cables?

I have always thought that the surface area of the strands were important, so it is not as simple as to calculate the area of a cross section of flat bar. Is this true?

Any other input as to using copper flat bar would be appreciated.



None of the responses to date have addressed the question posed, which is what "size copper bar" is needed to duplicate "70 [sq] mm battery cables"

The answer is that a one inch wide bar that is one eight inch thick which is equivalently approximately 25 mm wide by 3 mm thick will give a cross sectional area of 25 x 3 = 75 sq mm.

This bar would be excessively rigid, potentially battery terminal damaging in a boat scenario and would be an inferior substitute for a stranded cable of 70 sq mm cross section, which would be easier to attach to battery terminals and would be cheaper.

Search eBay for 70 sq mm stranded welding cable and corresponding compression connectors.

[rwidman]

Originally Posted by mitiempo

................ The starter battery can start a fire as easily as a house battery.

Perhaps, but the wiring is where the problem is. Typically, the positive cable goes from the battery to the starter. It's short and well insulated. It can be encased in split loom if that makes you feel better.

The logic behind not requiring overcurrent protection for the starter circuit is that the starter draws so much current that overcurrent protection would have to be rated so high as to not really provide protection.

Ask the ABYC. They are the experts.

[dfelsent]

A few notes on copper conductor dimensions -

For DC current carrying capacity aka ampacity there are many factors.
First is the cross sectional area of the copper.
There is the allowed voltage drop for the load. Load current, conductor length, and cross section factor into this.
The maximum temperature you can tolerate without failure is another.
I have seen circuits that worked fine, except for the fires from the burning insulation and hot wires. I have also seen circuits that just plain blew up throwing bits across the room. Those are the most fun.

For much higher frequency conductors things get different, aka weird. What counts at RF frequencies is the surface area of the conductor. That is why SSB grounds are best copper straps or litz wire (expensive.)

At really high frequencies and currents and voltages things get weirder yet. I have worked with circuits where copper straps with a small kink will spark across the kink. From one part of the copper strap to itself. Going through air was easier then through the kink.

Aboard?

for RF grounds copper strap. Thick enough that corrosion is not an issue. A few inches wide.

For DC (and 50/60 Hz AC cause that's slow as molasses compared to RF) use highly flexible conductors (vibration!), appropriately sized in cross section to comply with ABYC E-11 or other appropriate standard for ampacity. Take into consideration the number of conductors bundled together, the nature of the space the conductors are in, the temperature rating of the insulation, the nature of the supply (fused? battery? breaker? Shore power?) and whatever the standards suggest.
The standard is based on real world experiences as well as theory.

Most every US manufacturer of marine electrical stuff has excerpts or condensed versions of E-11 on their web sites or in their literature.

Look it up in the tables, and presto voila! Your required minimum wire gauge.

Plus sometimes equipment manufacturers provide guidance.

It is all about two things:
1: Fire Safety
2: Making stuff work

[mitiempo]

Originally Posted by Cap Erict3

Your engine start is an emergency circuit. You don't want to blow a fuse when you really need the engine.

There are only 2 reasons a fuse blows.

Incorrect sizing - easy to solve at installation. I have never had a nuisance blow any time I have fused a starter circuit - including on a 6 cylinder Perkins.

A short circuit - this is what you want.

[Sternwake]

I would not use a flat bar for connecting batteries for all the reasons others have mentioned, and one that has not yet been listed.

While copper might not expand or contract very much at temperature, the same cannot be said for the batteries themselves, can it?

Even with an S or a Z shaped into the flatbar, the stresses on battery terminals would be significant, likley allowing some gasses to escape around the studs instead of the caps, and lead to much faster more brutal corrosion.


Seems that a solid copper connection between batteries in the boat, even if not overtorqued, would be be torqued by boat movement in addition to thermal expansion and contraction.. A Wide flat copper bar might hide the fact that it is a green white corroded mess underneath.

[jeepbluetj]

The link to Maine Sail's site I posted perfectly describes why the ABYC unfused starting circuit is not particularly applicable to boats with smallish motors like sailboats and most other pleasure craft. And it's quite easy to fuse even a start circuit correctly. And why if you have a 1/2/all switch it must be fused.

I rewired a 24 foot fishing boat for a friend. The wiring was a disaster. Worst offense was a windlass wired with 12g wire. I replaced it all fresh and new, and I used MRBF terminal fuses at the batteries. Even with extended cranking of the 350 cu inch engine, it has never popped one of those fuses. And it won't unless something goes wrong, because the wire and the fuses were sized correctly.

Another fishing buddy almost burnt down his boat sitting on a trailer in front of my house. Luckily the short was in a reasonably small wire that became it's own fuse. (Yup, I'm gonna rewire his boat too)

If that big red wire chafes through at the engine block, I sure don't want to find out about it by the fire. I just want it to pop the fuse so I can find the problem. Properly sized fuses should never nuisance blow.

[ayates]

Originally Posted by jeepbluetj

... I used MRBF terminal fuses at the batteries. Even with extended cranking of the 350 cu inch engine, it has never popped one of those fuses.

Interesting information, as I am working with a sailing vessel equipped with a Caterpillar 3056 125 BHP 365 cu in auxillary engine, and start battery fusing is one of the items on my list to consider.


Allan.

[mitiempo]

Originally Posted by ayates

Interesting information, as I am working with a sailing vessel equipped with a Caterpillar 3056 125 BHP 365 cu in auxillary engine, and start battery fusing is one of the items on my list to consider.


Allan.

MRBF fuses are only up to 300 amps. ANL are available up to 750 amps.

[Colin A]

Just throw this out there.
https://www.erico.com/category.asp?category=R2028

But normally heavy cable up to a bus bar would be a better idea.

[GordMay]

Greetings and welcome aboard the CF, ayates.