Alternator wiring question

[THECUSCUS]

From what I've read on this site, it seems most prefer to run the alternator output to the house battery. This makes sense. On another thread, someone stated you could connect the wires from an ACR to the 1 & 2 posts (battery side of course ) on your battery switch to save "lug pile up" on your battery and maybe even have a cleaner wiring run. My question is, if the battery switch is closer to my alternator than the battery, can I run the alternator output to the battery switch where the wire from the house battery attaches? And should the alternate wire be fused at some point? Seems like this should work and I would have the advantage of the heavy gauge wire that already goes to the battery. Am I missing something?

 

[centerline]

you have it figured correctly...
it would make no difference what lug in the system its attached to, providing it has a direct and straight thru shot to the battery without running THRU a switch or component.
the bigger wire from the switch to the battery would be better than a smaller wire.

do not fuse the alternator wire. if the fuse blows, the alternator can also...(not actually blow up, but burn out the regulator or diodes)
unlike an old generator system, an alternator should never be electrically disconnected from the battery while its working....

 

[THECUSCUS]

Thanks for the reply CL. I have been reading way to much on wiring, an am getting paranoid. Oh, the joy of reworking a 35 year old boat! Just wait until you actually start diving into your "new" one!

 

[Chris Patterson]

I'll go out on a limb and open the floodgates of reprisals, but my alternator is wired with #6 wire running to the 'common' side of my battery switch. I can flip to house, or start, and charge from the switch easily. I understand that this is 'not recommended', but unless I bonk my head, I'm not gonna run it through off anyway. And the idea of anyone ELSE on my boat playing with the battery switch, is the same thinking process going on if someone picked your gun up out of the drawer and started loading it. I think it's fair to say I don't have people that stupid on my boat..

By the way, I crank off of an HP31E, using 4/0 cable. That setup would easily crank a small dozer, so a three-hole Mitsi engine is nothing. And it does not run thru the switch, only an on/off dedicated switch. The on/off/both is just for charging, which incidentally uses #4 from the switch to the batteries.

 

[seadaddler]

House

I have a heavy wire going from alternator to my house bank 4-6volt and been like that since I changed it a year after new in 2007.
No thinking about what position the battery switch is at house or start.
nick

 

[Maine Sail]

do not fuse the alternator wire. if the fuse blows, the alternator can also...(not actually blow up, but burn out the regulator or diodes)
unlike an old generator system, an alternator should never be electrically disconnected from the battery while its working....

If the alternator runs direct to the battery or batt side of the switch the alt really needs to be fused at the battery or switch end. If following current safety standards this is a requirement.

Any over current protection (OCP) / fusing should be a bare minimum of 125% of the alternators max output but preferably 150% or more. If this fuse blows, you wanted it to, because it likely prevented a fire..... In normal use it will be next to impossible to blow this fuse with the alternator.

These fuses are NOT to protect the alternator/device they are there to protect the wiring as are battery bank fuses and most OCP on a boat.....

Alternators, like solar or wind, are "self limiting" devices and thus do not require a fuse at the alternator end of the wire.

If the alt output wire gauge matches that of the battery switch wiring, eg: 1GA alt wire and 1GA battery cable wiring, then the fuse on the house bank can safely act as over current protection for both wires.

If the alt wire is 6GA and the battery wire is 1GA then the alt wire will need its own fuse at the battery switch or at the battery bank.

Keep in mind that many battery switches were not designed with a post height intended to accommodate much large lug stacking.

In addition to the over current protection my installations include a "service switch" in the alt B+ so that the engine can be shut down for instances when a tech or yourself are working on it. I generally use the Blue Sea mini battery switches and locate them in the engine bay close to the alt so it can easily be seen by a tech. It is also labeled "Alternator Service Disconnect"..

This is an example of a house bank positive bus, alternator OCP and an alternator service disconnect switch.

 

[weinie]

I prefer the alternator wire on the switch so that I can easily disconnect the battery if I have to troubleshoot the starter.

 

[Maine Sail]

I prefer the alternator wire on the switch so that I can easily disconnect the battery if I have to troubleshoot the starter.

Only the alt would be live but see last paragraph in above post....... Starter remains on the "C" post of the battery switch and is still turned off with the battery switch......

 

[THECUSCUS]

Thank you MS. Your posts are a wealth of information. Your posts have set me straight quite afew times. I find myself thinking while doing boat projects, "how would MaineSail do this?"

 

[weinie]

Only the alt would be live but see last paragraph in above post....... Starter remains on the "C" post of the battery switch and is still turned off with the battery switch......

yeah, but that hot alternator post is right where my two starter wires and starter fuse is. I rewired the starter last year after the contacts became corroded and the fuse holder started to crack. The access is horrible in my engine compartment. I have to reach over the alternator with needle nose pliers to to disconnect the wire terminals on the starter if I want to test the wires.

 

[Maine Sail]

yeah, but that hot alternator post is right where my two starter wires and starter fuse is. I rewired it new last year after the contacts became shoddy and the fuse holder also broke. The access is horrible in my engine compartment. I have to reach over the alternator with needle nose pliers to to disconnect the wire terminals on the starter if I want to test the wires.

This is why if wiring to the battery bank you should have an alternator service disconnect. If you are comfortable with leaving it on the "C" post, there is no issue, but many a boater has wound up with a fried alt when a crew member or the owner has passed through OFF with the alt loaded so many prefer to route to the house bank. There are also circumstances which ideally require the alt fed to house bank such as external regulation with proper voltage sensing or the use of Echo or Duo chargers & ACR's / combiners etc... Also the alt B+ would ideally have a "boot"....