cable sizing btw paralleled batteries

[Blitz]

I have two house batteries that are:

Group 27, 715 MCA, 175 RC

What is the correct sized wire for paralleling them together for one house bank? Want to see if I have the right sizing (which I beleive are at AWG 4) - no issues but curious???? About an exaggerated length of three foot total; 18" negative & 18" positive...

Would this be the same sizing as the starting cables since max draw??

 

[Maine Sail]

I have two house batteries that are:

Group 27, 715 MCA, 175 RC

What is the correct sized wire for paralleling them together for one house bank? Want to see if I have the right sizing (which I beleive are at AWG 4) - no issues but curious???? About an exaggerated length of three foot total; 18" negative & 18" positive...

Would this be the same sizing as the starting cables since max draw??

The recommended practice is for the cable to be sized to the maximum load your batteries would ever see. This applies for all cables in the system, both neg and pos, and they should all be the same size including the jumpers.

The parallel jumpers should be the same exact length, eg: 18" & 18" not 20" and 18", and sized according to the rest of the cables based on system load.

In your case I am going to guess your starter or an anchor windlass would be your largest draw. Lets say your starter can draw 250 amps (it may very well draw less) and the longest run from the battery to the starter is 6 feet in one direction. That is 12 feet round trip. 12 feet at a 3% or 10% voltage drop, on a 250 amp load, calls for a 1/0 cable run. This means all the cables in the system should be 1/0.

You'll need to know your starter load to more accurately calculate your own system requirements. Usually you can find out the Kw of the starter and then calcualte it from there.

GenuineDealz.com has some of the best prices and rates on custom made battery cables..

 

[Blitz]

You'll need to know your starter load to more accurately calculate your own system requirements. Usually you can find out the Kw of the starter and then calcualte it from there.

GenuineDealz.com has some of the best prices and rates on custom made battery cables..

Original Starter says 1 KW

 

[Bill Roosa]

1 kW starter

Since 1000 watts = 12 volts X ? amps we can deduce
? amps = 1000/12= 83.3 amps
Figure on 100 amps for a cold engine and reduced batter output. you don't want the wires to limit your ability to supply a cold engine with a cold battery.
I don't have the chart in front of me so I can't tell you what size cable to use. WM has one on-line
Other things to consider
Will you be adding an high output alternator in the future or a windlass or electric winch? Size the wire for the max load (one of the above since you would not be running all of them at the same time) you might see after an upgrade

 

[Blitz]

Lot smaller than thought

Since 1000 watts = 12 volts X ? amps we can deduce
? amps = 1000/12= 83.3 amps
Figure on 100 amps for a cold engine and reduced batter output. you don't want the wires to limit your ability to supply a cold engine with a cold battery.
I don't have the chart in front of me so I can't tell you what size cable to use. WM has one on-line
Other things to consider
Will you be adding an high output alternator in the future or a windlass or electric winch? Size the wire for the max load (one of the above since you would not be running all of them at the same time) you might see after an upgrade

My alternator is only 35 amps but may upgrade up to 80 amps so the starter is the deciding factor and if as you say figure 100 Amps (vs over 240 amps suggested previously) then the wire size is AWG 3 using the Blue Sea calculator - this seems like a lot smaller than I thought.
No windlass or electric winches are planned...

 

[Ron20324]

Some people overlook the fact that when you install a new battery and parallel two batteries, you have twice the amps and need to match the cables/fuses accordingly. Also, your size three may be sufficient, but in the interest of moving the volts more efficiently, you really should go a size or two larger. Still, a 3OR 4 sound too small to me. More like a 2 at least?

 

[Maine Sail]

Original Starter says 1 KW

If this is a 1KW Yanmar starter that is a general rating not a peak load. The actual max current draw shown in the Yanmar Service Manual, page 10-9, shows a peak load rating of just under 250 amps for their 1 KW starter. The specs on page 10-9 for the 1KW starter calls for a max of 460 amps or less. I can;t imagine a situation where you'd ever see 460 amps..? It should be sized for the peak load rating and I would use between 225 or 250 unless you have a clamp-on DC meter that will record DC inrush current..

 

[Blitz]

If this is a 1KW Yanmar starter that is a general rating not a peak load. The actual max current draw shown in the Yanmar Service Manual, page 10-9, shows a peak load rating of just under 250 amps for their 1 KW starter. The specs on page 10-9 for the 1KW starter calls for a max of 460 amps or less. I can;t imagine a situation where you'd ever see 460 amps..? It should be sized for the peak load rating and I would use between 225 or 250 unless you have a clamp-on DC meter that will record DC inrush current..

I have a possible source for a DC clamp on meter - I'll use the results from this before ordering any cables. (I don't have any starting problems now, and with your previous help on seperate thread I found that a factory or mechanic heat shrunk terminal at the starter was the issue for sluggish starts.)