Query.. How do I determine the required tickness of battery cables?

[Canopy Locked]

I'm moving my 2 batteries aft for better weight distribution, but this means I will have to run cables from the batteries to 2 "Bus" bars to which will be connected the existing mess of cables. The cable run is approx 4.6M - The batteries are 2 x 143AH

I was planning on using similar copper cable that I used when fitting the Capstan. The copper core (ie: not incl the external cover) is approx 12mm thick, when measuring the X section of the cut end.

In the opion of those who know about such things, would this be adequate? How does my OD measurement relate to the mm2 measurement I see quoted on websites selling cable?

Many thanks from an electical numpty

Rob

 

[Hoolie]

Of course area = pi x r squared.

In your case this equals 113 sq mm, but allowing for air gap in the cable I guess it's 90 or 100 sq mm.

In the overall scheme of things this is massive cable and more than enough for your installation. I've used 50 sq mm on my new installation with much less voltage drop around the system than before.

 

[chasroberts]

In the opion of those who know about such things, would this be adequate? How does my OD measurement relate to the mm2 measurement I see quoted on websites selling cable?

Rob

From another electrical numpty! The 2mm relates to the cross section area of the cable (I think). If that is the case then the cross section of your 12mm cable would be (Pi x rsquared) ie. 3.214 x 36 somewhere round the 100mm2 area (I think). I'm sure someone will be along soon to dissuade me of this view......

Chas

Rats. Lakesailored. Must learn to type quicker.....

 

[noelex]

12 mm thick OD cable with insulation included will have a cross sectional area of about 35 mm squared. ( the thickness of insulation can vary however, so if you can measure the conductor that would be better).
Is the distance one way or out and return?
What is the maximum current ? ( probably charging)
More detail would help, but I think the size is probably OK looking at your aviator and size of boat.

 

[Mirror Painter]

A useful cross sectional area to diameter conversion here:

http://www.sengpielaudio.com/calculator-cross-section.htm

 

[Canopy Locked]

12 mm thick OD cable with insulation included will have a cross sectional area of about 35 mm squared. ( the thickness of insulation can vary however, so if you can measure the conductor that would be better).
Is the distance one way or out and return?
What is the maximum current ? ( probably charging)
More detail would help, but I think the size is probably OK looking at your aviator and size of boat.

This distance is one way, but sorry not at all sure about the current but from what I have seen here http://www.autoelectricsupplies.co.uk/product/885/category/159 the cable seems good for 240A

Many thanks for your help
rob

 

[VicS]

AWG 0000 (4/0) cable has a conductor diameter of 11.684mm ( I guess that's what you have

The cross-sectional area is approx 107 mm².

You don't say what current these cables will have to carry, whether they are just services batteries or if they will also serve as engine starting batteries. However AWG 0000 has a resistance of 0.16 ohms /1000m.
4.6m will therefore have a resistance of 0.00074 ohms.

Every 100 amps will therefore result in a voltage drop of 0.074 volts.

double that for the total length of positive and negative cables is 0.15 volts

That size cable could safely carry 300 amps. More for a short period or if not enclosed or bundled with other wiring.

It would be far preferable to locate a starter battery closer to the engine.

 

[noelex]

Sorry I assumed 12mm was the overall diameter. I see from reading your post again that is the conducter diameter. That is a big cable.
About 113 mm squared. That will be more than adequate.

 

[Hoolie]

Sorry I assumed 12mm was the overall diameter. I see from reading your post again that is the conducter diameter. That is a big cable.
About 113 mm squared. That will be more than adequate.

I said exactly that in my post #2. Why not read ALL the posts on the thread?

 

[Quandary]

I said exactly that in my post #2. Why not read ALL the posts on the thread?

But if we all did that there might be no point in posting?

 

[Hoolie]

But if we all did that there might be no point in posting?

Absolutely!!!! And I'm guilty (elsewhere) of not even noting the title of the thread

 

[noelex]

I said exactly that in my post #2. Why not read ALL the posts on the thread?

Because I wrote the post before I saw yours. The Internet connection in some of the more remote places, like an anchorage from a boat,can be slow.

But if we all did that there might be no point in posting?

 

[Richard10002]

I'm moving my 2 batteries aft for better weight distribution, but this means I will have to run cables from the batteries to 2 "Bus" bars to which will be connected the existing mess of cables. The cable run is approx 4.6M - The batteries are 2 x 143AH

I was planning on using similar copper cable that I used when fitting the Capstan. The copper core (ie: not incl the external cover) is approx 12mm thick, when measuring the X section of the cut end.

In the opion of those who know about such things, would this be adequate? How does my OD measurement relate to the mm2 measurement I see quoted on websites selling cable?

Many thanks from an electical numpty

Rob

With a 30ft round trip, carrying 150amps, the voltage drop will be about 3.8%

I understand that is an acceptable drop, and would guess you are unlikely to be passing more than 150 Amps very often. What does your battery charger charge at? Are you using an inverter? If so, how powerful?

Don't forget a fuse near the batteries.

Where do you get your cable from? How much?

Cheers,

Richard

 

[deanhomer]

VicS

Is spot on with his calculations, I would imagine that you could get away with a cable of half the size, however if you already have sufficient length of cable to do the job then all will be fine and will save spending out on more cable.

For future reference either 50mm sq or even 35mm sq would probably be sufficient, the most important thing is to fit an inline fuse or circuit breaker as close to the battery as possible, this fuse/circuit breaker should have a current capacity just below that of the cable.