Sense Wire for OEM Alternator

[V&J]

We have a 1991 Catalina 30 with a Universal M25XP engine. The OEM 51 amp alternator output now goes to the starter B+. We’ve read that a better idea is to wire it directly to the house bank. (Our house and reserve batteries are connected to an ACR.) The alternator now has a sense wire also connected to the starter B+ post.

When discussing connecting an alternator having an external regulator directly to the battery, Maine Sail shows the sense wires of the regulator connected to both positive and negative battery posts. I assume our OEM alternator has an internal regulator. If we connect it directly to the house bank, should we also move its sense wire directly to the house bank + post? In that case, how would the sensing circuit be grounded? For that matter, how is our alternator itself grounded? Just by the bolt connecting it to the engine block?

We’d appreciate any advice you might have for us.

 

[jviss]

I will defer to @Maine Sail on this topic, but, yes, the alternator is grounded via the engine block; you should have one main ground for these systems, to avoid ground loops. And yes, it's common now to wire the alternator output to the house bank, and also the sense wire. I am surprised that the alternator with internal regulation has a sense wire, but there you are. And then the ACR will take care of your "reserve battery."

 

[Hayden Watson]

As far as I know an alternator with an internal registration will not have a sense wire. The small gage +12v wire is the excision wire mutual does not control the current output.

 

[jviss]

excision wire mutual

What?

 

[Hayden Watson]

What?

Stupid cell phones!
Should have been
"The small gage +12v wire is the excitation wire and it does not control the current output."

 

[jviss]

Stupid cell phones!
Should have been
"The small gage +12v wire is the excitation wire and it does not control the current output."

Got it!

 

[ggrizzard]

"The small gage +12v wire is the excitation wire"
Excites what?

 

[Hayden Watson]

"The small gage +12v wire is the excitation wire"
Excites what?

It excites the magnets in the stator. Some alternator have permanent magnets which means they are self exciting but most are not.

 

[V&J]

I will defer to @Maine Sail on this topic, but, yes, the alternator is grounded via the engine block; you should have one main ground for these systems, to avoid ground loops. And yes, it's common now to wire the alternator output to the house bank, and also the sense wire. I am surprised that the alternator with internal regulation has a sense wire, but there you are. And then the ACR will take care of your "reserve battery."

Thanks JVISS et al. About this alternator having a sense wire, I know next to nothing about this. I made an assumption that this has "internal regulation" as I don't see any separate device that might be an external regulator. In any case, I have seen some diagrams of what looks like this same Prestolite alternator. In addition to the +output, they show a purple wire which is the excite wire, an orange which is the AC tap for the tach, and a small orange with red stripe wire labelled sense. I have all those same wires so I assumed that orange/red is a sense wire. It's attached to the starter + post. We'll probably leave everything as is for now because our priority is replacing the old harness with the gummy bears and adding some fuses. Thanks much.

 

[jviss]

I have all those same wires so I assumed that orange/red is a sense wire.

I think that's a good assumption.

 

[jviss]

As far as I know an alternator with an internal registration will not have a sense wire.

Well, now you know that there are (plenty of) alternators with internal regulation and remote sense wires!