2/0 Battery Cable for 12v 671s?

[Vincentc]

Sorry for the misleading title, should have said 12 volt.

Lilly Marie, 1983 43DC has 2 pairs of 12v batteries between the 671ti's. The current cables appear to be 4/0 welding and the insulation has gotten soft and swollen and the wire strands show corrosion. It does not look like a Hatteras quality job, but perhaps after almost 30 years... I want to replace it with tinned battery cables and new terminals.

I have just set up the batteries for my inverter system using 2/0 cable, have become comfortable working with that and have a stock of 2/0 cable, terminals and lugs as well as a 2/0 wire cutter. Using the same materials for the starter/house batteries would be convenient and reduce inventory, but ...

Is 2/0 cable suitable and a good choice here? I cannot find any specifications in the Detroit manual.

The cable run from the positive posts to their battery switches is about 3 feet, each. The battery pair posts are 2 feet apart and the cable run from the negative post is less than 2 feet.

All 4 negative posts are connected by a single negative cable running from the port engine to the port negative posts then to the positive posts then to the stbd engine.

The cables from the switches to the starters look good.

Thanks,

 

[Genesis]

IMHO 2/0 is not enough for that service. There is a rough 100 amp difference in current-carrying capacity at the same voltage drop and temperature rise between those two cable sizes. Your runs are short which certainly helps but.....

I would source and run 4/0 cable for this application.

 

[SKYCHENEY]

I think 4/0 was OEM.

 

[GJH]

I thought I recalled you having a Magnum MS2812 inverter. If so, how did you end up with 2/0? Did you talk with them about it? The manual specifies minimum 4/0 for that model. I'd make sure you keep the amp loads and charge rate on that thing low if you are using 2/0.

Agree with the others on 4/0 for starting.

 

[Vincentc]

Thanks,
4/0 it will be. Any suggestion a cable cutter for 4/0. I have a 9.5 inch Klein which handles 2/0 well. Don't know about 4/0.

George,
The consensus on the forum was 2/0 and when I spoke to Magnum, the rep said 2/0 was OK considering how close the inverter was to the batteries.

Regards,

 

[GJH]

I guess the manual has to be conservative, and so the specified 4/0 from 0-5 feet. My 24 volt MS4024 specified 2/0 for that distance, and I used 4/0 which I think cost me all of $30 more for the main leads and the inter-battery connections (4 6 volt in series). I see they now want the case ground to be the same size too, gonna have to go back and fix that I guess. Standard has changed from 5 years ago.

Anyway, enjoy your Magnum system, great stuff from a great company.

 

[Nonchalant1]

This is not that hard.

Go here and input voltage, amps required for starter and length of cable. It calculates the safe cable size cross section in sq. millimeters. You do have to know how much power (amps) you will be using.

Then go here and read what AWG cable size those sq. millimeters refer to.

This can be used for MANY applications, like people wondering how big the cables have to be to change from 32V to 24V or 12V, installing inverters, etc.

Doug

 

[Scottbee]

This is not that hard.

Go here and input voltage, amps required for starter and length of cable. It calculates the safe cable size cross section in sq. millimeters. You do have to know how much power (amps) you will be using.

Then go here and read what AWG cable size those sq. millimeters refer to.

This can be used for MANY applications, like people wondering how big the cables have to be to change from 32V to 24V or 12V, installing inverters, etc.

Doug

That's an interesting calculator, but I'd love to know what allowable voltage drop they are using for their calculations. Personally I am less concerned abut the voltage drop on the starting circuit than I am on my inverter feed. .5V drop on my 12V inverter feed can cause premature low-voltage shutdowns. While .5V drop on my 12V starter circuit is really no big deal.

 

[Boatsb]

That's an interesting calculator, but I'd love to know what allowable voltage drop they are using for their calculations. Personally I am less concerned abut the voltage drop on the starting circuit than I am on my inverter feed. .5V drop on my 12V inverter feed can cause premature low-voltage shutdowns. While .5V drop on my 12V starter circuit is really no big deal.

Starter circuits do not conform to the 3% voltage drop of other primary circuits. They also do not carry current for long periods but will get hot.

 

[Boatnut]

It doesn't sound like your cables are that long, the extra cost for the 4/0 cable shouldn't be that much money, for the peace of mind it will give you.

The old cables lasted for a long time, why would you think new ones would last less time?

Measure the cables and have the local battery shop crimp them for you, they have the proper tools and knowledge to do the job right.

I am aware that tinned wire is the best, and understand the technical reasons why, even with that the welding cable lasted 30 years, do you really think tinned will last any longer? After the cables are installed and connected give all the cable ends a good coating of something like Boeshield, the cables will probably out live you.

If you insist on making up your own cables, a fine tooth hack saw will cut them just fine.

 

[J's Dream]

Save yourself a LOT of hassle and aggravation. Go to www.genuinedealz.com

They'll make up your cables, and crimp/heat shrink the ends...and ship everything to you for free. Great company, great prices...been buying wire from them frequently.

Jason

 

[Vincentc]

Purchased 4/0 cable, terminals, shrink tube and solder pellets fron Genuinedealz. The Klein cable cutter for 2/0 ($30 at the electronics supply store) cut thru the 4/0 just fine. A propane torch heated the terminals held in a vise and everything went together fine.

I measured, cut, and connected as I went checking the distances and terminal orientation against the actual boat layout. I found that easier than trying to communicate the distances and terminal orientations to GD. That is why I did not have them crimp the cables. I tested each connection to 100+ lbs tension, none failed.

The old cable ( delco 4/0) was worse than I thought, corroded thru about 20% in some places.

Probably took about 4 hours and getting rid of bad cable is a good feeling.

Thanks for the input.