Stupid battery switch/inverter question

[mitiempo]

The alternator output should always be fused within 7" of the battery, as every other wire connected directly to a battery should be. The fuse should be rated at 150% of the alternator output. It will never blow from output as alternators are self limiting. But if a short occurs due to wire chafing or some other reason the diodes are the least of your problems.

This happened to someone I know and the alt output wasn't fused. Took a long time and a lot of money to re-wire the engine room and replace everything damaged by one red hot wire.

[Bill Seal]

How about connecting the ALT out to the common terminal on the 1-2-both switch. If the switch is off, there's no starter. AND if you're dumb enough to turn off the switch while the engine is running and fry the alternator, you'll only do it once.

[Stu Jackson]

Originally Posted by Bill Seal

How about connecting the ALT out to the common terminal on the 1-2-both switch. If the switch is off, there's no starter. AND if you're dumb enough to turn off the switch while the engine is running and fry the alternator, you'll only do it once.

Bill, that's sooooo 1980s thinking. The goal is to REMOVE the AO from the 1-2-B switch and send it directly the house bank, so there is always a battery at the end. Most newbies have no idea how a 1-2-B switch works and that's why we have been suggesting doing exactly the opposite of what you suggested.

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 Forums

The Short Version of the 1-2-B Switch Stuff: Electrical Systems 101 This is a link to the Electrical Systems 101 Topic, reply #2

What are ACRs, Combiners & Echo Chargers? (by Maine Sail)
Battery Switch Question ? | SailboatOwners.com Forums

[starcruiser]

Perhaps. But if the alternator needs working on, why not just disconnect it from the system?

[mitiempo]

Originally Posted by starcruiser

Perhaps. But if the alternator needs working on, why not just disconnect it from the system?

That is what happens when the fuse is removed.

Remember that if wired directly to a battery (house bank ideally) that the wire is hot when removed from the alt.

[sully75]

For the record we are still talking about the 5a alternator on my outboard?

I am confused: currently it's not hooked up to anything. How could hooking it up to something and then breaking that circuit destroy it?

[mitiempo]

Originally Posted by sully75

For the record we are still talking about the 5a alternator on my outboard?

I am confused: currently it's not hooked up to anything. How could hooking it up to something and then breaking that circuit destroy it?

If an alternator is running and has an output to batteries the diodes are at risk if the circuit is opened. If it is not connected there should not be any damage.

[Stu Jackson]

Originally Posted by sully75

For the record we are still talking about the 5a alternator on my outboard?

I am confused: currently it's not hooked up to anything. How could hooking it up to something and then breaking that circuit destroy it?

Just a reminder to re-read reply #16 on page 2, it answered your question.

[Boatguy30]

The charging/ lighting coil AC goes thru a rectifier on an outboard to become unregulated dc current. It's very common to not have them hooked up and it will not cause any issues.

I actually have a 100 amp breaker on my outboard battery leads in case the starter or solenoid shorted.

Just so happens I just put an inverter on also with the inverter running off the same 100 amp breaker. The chassis ground is a bit confusing. Only thing I can work out is it provides come safety if a hot 12V lead were to touch the case. But I'd imagine the main house fuse (ABYC requirement) would blow in this instance.

[Boatguy30]

Just ran my outboard for a few minutes and tried the breaker. The idea was to protect the boat from an electrical fire and secondary was to cut out unregulated charging on very sunny light wind days.


So at about 1800 rpm fast idle I was putting out 5.3 amps. Flipped the switch no amps. Flip it back 5.3. No issues.


If you have an outboard in a well or anyway enclosed or inboard of the transom I would highly recommend you fit a breaker so you can turn off the power to the engine when no needed. All the wires under the cowl are very tight and plenty of potential chafe and therefore short spots.


Also potentially a theft protection as if the motor is electric only like many Yamahas it would be difficult for any thieves to get the boat moving.