New Alternator and Wiring Upgrade

[montenido]

Hi all. I just replaced my 80 amp Balmar alternator with a 120 amp Electromaax. I also am increasing the wiring size to handle the higher current. Well, the old arrangement had long runs of size 6 cable, running from the alternator to a shunt and then to the starter and back to the batteries. I would like to eliminate the run from the alternator to the starter, as it is a long way from my batteries. Can I just run the cable from my new alternator through the shunt and on to the house batteries? I would install a fuse and switch also. Shouldn't the starter still be powered by the existing lead to the batteries even if I eliminate the alternator lead to the starter? I'm thinking that I can simply remove the existing run from the alternator to the starter without hurting anything. Is this correct?

Thanks for any advice.


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[dohenyboy]

Yes this is okay. Typically the alternator is closer to the starter than it is to the battery. Plus, when the engine is manufactured, it ensures the alternator is wired, eventually, to the battery. The starter terminal is just functioning as a post.
I always rewire my alternator directly to the battery.


Why can't things remain where i carelessly left them?

[Stu Jackson]

Sure, and here's why:

OEM 1-2-B Switch Wiring History Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com

[btrayfors]

Direct wiring to the batteries from the alternator is a good way to go. Be sure to use a large cable for that 120A alternator; I'd probably use AWG1 or 1/0.

And, be sure to run a black or yellow negative cable from the alternator to the batteries; using the engine ground isn't great because it involves too much resistance.

And, yes, you need a fuse in the alternator positive located very near the batteries, either an ANL or a MRBF (terminal) fuse....150A would be appropriate sizing.

A safety cutoff switch is also a good idea, provided that it can be installed in such manner that nobody trips it unintentionally....that could blow the alternator diodes if the engine is running at the time.

Bill

[roland stockham]

I may be misunderstanding but this does sound odd to me however there are several pieces missing.
You do not mention the size of the engine which should determine the cableing to the starter. Manual should give required CCA. Start batteries are small and light by nature so why not just move it so it is next to the engine.
You also say nothing about the size and type of batteries you have or the alternator controller. It is the, charge voltage and absorption capacity of the batteries not the size of the alternator that governs charge rate. Just changing the alternator probably does not need any wiring upgrade unless the system was very out of balance before hand.

[hellosailor]

Depending on the length of the run from the starter to the battery, you might want to replace that cable as well. If the distance is significant, going to a larger cable will also boost your starter voltage and make your starter last longer and start the engine faster.

[montenido]

Thanks for the great comments and information. My boat has a Perkins 4-154 which generates about 60hp. I have a 525ah battery bank which I use for house and starting. I already have a duo-charge that charges the B batteries. The whole mess runs through a Zantrex monitor.

When I looked at the wiring for the starter, it was pretty small, much smaller than I would expect, which is what generated my question to begin with. If I remove the wiring from the alternator + to the starter, then It looks like I should run a new larger wire from the battery switch to the starter. This will be 10-12'. Any suggestions as to what size it should be? Not sure what a starter draws.

Thanks for all the great info, when I return to my boat I will bring everything I need to get this wrapped up. In the meantime, I just de-powered the new alternator using the Balmar controllers belt setting. That should limit the amps flowing through the old wires.

Thanks again everyone.

Cheers, Bill

[hellosailor]

Bill-
If you look for replacement starts online, or in a service manual, you may see them referenced the EU way as "two kilowatt" or similar. I'd making a WAG that it is a two or tow and a half kW starter, which at 12v nominal, typically pulled down closer to 10V while engaged, could be 200A draw. That could easily put you in 00-AWG territory so...find & run the numbers, then compromise with the wallet. "The best" technical solution may be a bit richer than you want or really need.(G)

[Stu Jackson]

Originally Posted by montenido

When I looked at the wiring for the starter, it was pretty small, much smaller than I would expect, which is what generated my question to begin with. If I remove the wiring from the alternator + to the starter, then It looks like I should run a new larger wire from the battery switch to the starter. This will be 10-12'. Any suggestions as to what size it should be? Not sure what a starter draws.

Bill,

Try this:

Engine Starting Loads - Amp Draw Data (by Maine Sail)

Engine Starting Video / Real World Amp Load Data - SailboatOwners.com

"Bumped up" to your 60hp engine, size 00 wire would be waaaay overkill. The starter is most likely engine grounded, right? So size the wire for the distance from your batteries to the switch C post and to the starter.

On our M25 21 hp engine, I've been using the #4 AWG that was installed from the batteries to the switch to the starter for the 17 years I've had this 29year old boat. Everyone tells me it's too small, but, heck, it still works!

Because I've run the AO to the house bank, I deleted the wire between the AO and the starter. Simple.

Good luck.