starter cable size

[Liambennett]

Hi all,
just about to start the install of there battery starter wiring.
I have a 24V starter on a a Cummins VT555M.
I will have 2 optima blue top batteries in series.
the starter motor will be around 6 feet from the battery bank.
What size cable should I use ?
I can get 2B&S tinned cable or 00B&S plain copper.
Any Ideas ?

 

[Comodave]

I always go with cable as big as possible to get no voltage drop. I would use 4/0. The one time extra cost will benefit the rest of the boats life.

 

[Insequent]

I had Cummins VT555M's initially. My starters were humungous and 12V, non-geared. i had about the same length cable run. My cables were 00, and they were fine. Given you have 24V, I would think 00 is the way to go IMO.

 

[Bacchus]

I'm with Brian on this one.
My cable was 00 for 12V with about 12-15 ft run.
I was able to reduce the run to about half of that and used a salvaged length of 0000. I dont have a lot of data but felt it was an improvement.

I think with 24V and the short run 00 will be fine but would feel better with tinned 00.

 

[O C Diver]

I always go with cable as big as possible to get no voltage drop. I would use 4/0. The one time extra cost will benefit the rest of the boats life.

Nobody ever said, "I wish I had SMALLER gauge battery cables ".

Ted

 

[Bmarler]

It’s a shame you can’t get the 2/0 in tinned copper. I use 4/0 for my 12 volt starter, so I would think 2/0 for your 24v should be ok, but 4/0 is better. Just be sure that you use good heat shrink sleeves over the crimps, preferably the kind with hot melt adhesive inside. Keeping moisture out of the crimps is especially important if not using tinned cable.

 

[psneeld]

Nobody ever said, "I wish I had SMALLER gauge battery cables ".

Ted

Installers do.... bends and bulkhead passthroughs can be difficult.

At some point it becomes complete overkill versus slight overkill.

Knowing what you actually need and going up a size or two is better than not knowing and just buying expensive wire that's difficult sometimes to install. Small, straight, open runs are no big deal and not that much more expensive but I would still want to see the area of install.

 

[O C Diver]

Installers do.... bends and bulkhead passthroughs can be difficult.

At some point it becomes complete overkill versus slight overkill.

Knowing what you actually need and going up a size or two is better than not knowing and just buying expensive wire that's difficult sometimes to install. Small, straight, open runs are no big deal and not that much more expensive but I would still want to see the area of install.

I think we're talking about going between the battery and the engine starter. The breaker panel isn't likely pulling 200 to 400 amps.

The other consideration is to locate the start battery close to the starter. My engine battery cables are about 2' long.

Ted

 

[psneeld]

I think we're talking about going between the battery and the engine starter. The breaker panel isn't likely pulling 200 to 400 amps.

The other consideration is to locate the start battery close to the starter. My engine battery cables are about 2' long.

Ted

Agreed, but I have seen some long runs due to engine room layout....even batteries in different compartments. I understood the OP, but don't know what the run will look like, just it's length.

 

[Bacchus]

Also important is the type & quslity of the terminal lugs. Power lugs (right) are much better than starter lugs (left).
Ensuring they are closed end important to reduce corrosion.
CMS How To has a good complete article on DIY batty cables

 

[C lectric]

I have a V555M, no turbo. My starter is 12V. When I did mine years ago I used 4/0 wire
for absolute minimal Vdrop. The lengths are about 8 ft.
I measured the draw which was about 1,000A+dropping and settling as the engine actually started to roll over to between 700 and 800A.
Yours at 24V will show lower current , likely about 600A at initial rollover start dropping to 350-400A so size it for that.

Otherwise go for 4/0 and never worry about Vdrop

 

[Nick F]

Also important is the type & quslity of the terminal lugs. Power lugs (right) are much better than starter lugs (left).
Ensuring they are closed end important to reduce corrosion.
CMS How To has a good complete article on DIY batty cablesView attachment 142748

Can you help me find this CMS article?

 

[Comodave]

Can you help me find this CMS article?

Go to marinehowto.com. It is there along with many other great articles.

 

[Bacchus]

Nick
Here you go. If you aren't familiar with CMS (Rod is a Commercial Member here) go to his How To main page and be sure to book mark it. Rod really knows his stuff and has written and posted a large number of excellent DIY articles.

https://marinehowto.com/making-your-own-battery-cables/

 

[JDCAVE]

I would defer to the electricians on the forum but IMO, the “voltage drop” has more to do with “voltage sag” at the battery due to the starter load and less to do with the ampacity of the cable. For 24 volts, 2/0 should be lots and an even smaller cable should be fine.

Jim

 

[Circumnavigator]

I'll be heretical and point out that at 500 amps (probably more than you will need), the loss from #2 cables running six feet -- 12 feet round trip -- is 4.1%. If you are stuck on the two possibilities you mentioned, I would go with the tinned #2 -- far less likely to be trouble in the future than the bare 2/0.



I also note that if I needed the ampacity of a 4/0 cable, I would go with two 2/0 cables. That would give 25% more copper than a 4/0, be easier to handle, and be far easier to get a good crimp for the terminals.


Jim

 

[Capt Ray]

+1 for BatterycablesUSA.com

Great online cable building / ordering tool.
Get exactly what you want, professionally terminated.
AND
They get 'em built quickly and out to you in the mail.

As for the original question, lots of good answers already posted.

 

[jgwinks]

Agreed, but I have seen some long runs due to engine room layout....even batteries in different compartments. I understood the OP, but don't know what the run will look like, just it's length.

Ideally the batteries should not be in the engine room, they don't like the heat. That would probably require pretty long cables and is one reason it's rarely done that way. At 24 volts you can use 1/2 the gauge you would at 12v. My batts are in the engine room and the cables probably average 12 feet one way. They are 2/0. 6.354 Perkins engines with massive 12 volt starters, they crank pretty fast.

 

[Circumnavigator]

+1 for BatterycablesUSA.com

Great online cable building / ordering tool.
Get exactly what you want, professionally terminated.
AND
They get 'em built quickly and out to you in the mail.

As for the original question, lots of good answers already posted.

Agreed. Lowest prices I could find, combined with fast service and quality work. A far too rare combination. Recommended.


Jim

 

[janice142]

I have used http://genuinedealz.com several times for wires, including my battery cables. The owner does have all the sizes I needed for terminal ends. I had everything made to my exact specifications (4 gauge for Seaweed's batteries).

He made everything I needed for my solar system too (6AWG) ... I did my own ferrules as I have them -- not sure if he has ferrules in stock or not. He did strip the ends needed to feed into the battery buss bars. The ends for my ferrules were stripped -- saving me one more step.

He put on the terminal ends I needed, added heat shrink and shipped them out ASAP. I believe from order to receipt was three days. He uses Priority Mail. He's near Brunswick GA if memory serves me.

 

[JDCAVE]

I took the approach of making my own cables. At the suggestion of Rod (CMS):

https://marinehowto.com/making-your-own-battery-cables/

I purchased a FTZ crimper and I didn’t regret it one bit. I think I paid $150 USD for it. There’s a lot of crimps on a house bank. This tool works like a charm. I have a fair bit of 2/0 cable leftover when I shortened the lengths of the cable runs on my house bank, so I could practice my crimps a few times before I did the job. The issue of getting mail order cables is there is no room for error. My approach was to crimp one end of the cable, attach that end and then adjust cable length if required before crimping the other end.

Jim

 

[Portage_Bay]

The issue of getting mail order cables is there is no room for error. My approach was to crimp one end of the cable, attach that end and then adjust cable length if required before crimping the other end.

Jim

That's what I did, none of the lenghts are exaclty right. And when you make your own you can align the ends just exactly as they need to be to avoid twisting the cable to get things connected. If I had to do it again I'd make my own cables.

 

[Brooksie]

Always run the ground cable to a starter attachment bolt. don't cause the power to pass through any more C.I. than possible.