Help needed wiring my new alternator sense wire.

[Privilege]

I’m currently installing a new Hitatchi 80amp internally regulated alternator to my Yanmar 4JH. The charging current goes straight from the battery terminal to my house bank via a heavy dedicated wire. I have a harness going from the Yanmar panel to the engine which has a T terminal to connect at the back of the alternator. The trouble is, the harness is also connected to the starter and therefore to the start battery. I assume therefore that the sense wire is sensing the starting battery voltage which will cause a problem for the charging regime. I can’t really run a separate wire from the sense terminal to the ignition switch as the Yanmar panels are all sealed. Any suggestions would be welcomed. Please talk to me in simple terms!

[stormalong]

Add a relay, activated by your ignition switch that energizes the alternator from the house bank.

Is your tachometer driven by the alternator? A different alternator may require adjusting the tach.

[Privilege]

I’m a bit of a beginner when it comes to alternators but if I understand things correctly, the exciter wire is only on for a short while so there’s no problem having that come from the start battery. The sense wire though controls whether the alternator provides a charge current so that needs to be reading the voltage on my house bank.

[stormalong]

Originally Posted by Privilege

I’m a bit of a beginner when it comes to alternators but if I understand things correctly, the exciter wire is only on for a short while so there’s no problem having that come from the start battery. The sense wire though controls whether the alternator provides a charge current so that needs to be reading the voltage on my house bank.

Does the internal regulator have a separate voltage sense wire? Most use the same wire as the exciter wire. Most internal regulators use the exciter current as long as the alternator is running. An easy test would be to start the engine with the wire designated to go to the ignition disconnected, connect it to any +12V source and the engine should slow a bit due to increased load. Then disconnect it and the engine will speed back up.

The biggest issue with internal regulators is that they are not designed for bulk charging. In cars the battery stays pretty full since little power is used without the engine running. The regulator is designed to put that little bit of engine start power back into the battery and then cover the loads of the car while it is running. On a boat you have a different story. You are using power without the engine running, the batteries are depleted and you want to put all that power back into the battery. That is where an external regulator shines. It is designed to bulk charge and when the battery is near full it cuts back the charging rate to "float" the battery. Unfortunately most alternators are not built to do a bulk charge for a long time either and they will overheat and have a shorter life. That is why good external voltage regulators have temperature sensors.

If you are cruising your electrical system needs to be more robust than if you are returning to the marina and plugging into the power grid every night.

[EngNate]

The pic is cut off but it looks like the lead wire coming out is labeled sense, just put a ring terminal on it and connect to the battery stud. It does not need to be switched, the current draw of this circuit is extremely low, maybe as much as a car stereo's memory backup. The turn-on wire generally is energized all the time with key-on, although it is only required to start operation. If you want you can use a relay to only connect the sense wire when in operation - ask for a 'Bosch' type standard relay with mounting tab at any auto parts store. Connect the relay terminals as follows: '85' to the harness wire going to the horizontal terminal in the pic, '86' to one of the two B(-) studs, '31' to the B+ stud, and '87' to the sense connection. Plug the harness connector(s) in.

[Wotname]

Originally Posted by EngNate

The pic is cut off but it looks like the lead wire coming out is labeled sense, just put a ring terminal on it and connect to the battery stud. ................

No, don't do this

The lead wire is a stator output for tach sensing. It should have around 7VAC on it and possibly coloured yellow.

[smac999]

I don't see a sense wire in the diagram. lots of alts don't have one. unless it's the left side that is removed. it probably senses internally off the B+ post.

the top one is stator output which is tach. the lower one for lamp is not going be to a voltage sense as it's going through a lamp resistor. this will have 12v when the key is turned on and this likly excites it. I'm not sure what the upper plug is. but it seems to be outputing voltage. not sensing. you might want to figure out where this on goes.

just don't hook up the old factory charging wire from B+ to the starter post as well as your new house cable. otherwise you perminatly connect the start and house battery together.

ideally you'd add an exernal regulator for best results like a balmar mc 614h

[Wotname]

This diagram should help. It is typical of '3' terminal Hitachi alternators fitted to Yanmars but it may not be exactly the same as your unit.

The 'R' (or sometimes the 'IGN') terminal is at the top of the 'T' shaped twin spade connector. The lower one is the 'L' terminal.

Initial excitation is via the 'L' terminal and once the alternator rpm exceeds the 'rise' speed, it self excites via the internal excitation diodes.

Sensing is via the 'R' terminal (ie though the ignition switch).

The keen eyed reader might notice a typo in the Hitachi diagram.

[smac999]

based on that diagram you are pretty screwed. you can't just feed house voltage to r because l and r combine inside the alt. and you'd be paralleling the engine and house battery through that internal resistor.

best you could do would be to feed l and r with house power on a relay switched by the ign. but you'll lose the dash lamp. and you'll have to put a resistor on the L line because the alt can ground it.

since it's only 80a I would consider running the big cable to the engine battery. if you have an ACR between banks you won't notice any diff with a small alt.

if it was 200a alt different story. but for that you'd defiantly be external reg.

though it also shows battery + joins with R so that can't be right... it shorts out the ignition switch, your engine key would always be turned on. even with no key in.

[Wotname]

Originally Posted by smac999

........

though it also shows battery + joins with R so that can't be right... it shorts out the ignition switch, your engine key would always be turned on. even with no key in.

Yep, that's a typo (I believe). The joint dot shouldn't be there (AFAIK). The internal line from the BAT+ to the capacitor should 'jump over' the R line just like it 'jumps over' the L line.

[Scubaseas]

See below. DO NOT wire sense to B+.

https://www.google.com/url?sa=i&url=...AAAAAdAAAAABAX

[Wotname]

Originally Posted by Scubaseas

See below. DO NOT wire sense to B+.

https://www.google.com/url?sa=i&url=...AAAAAdAAAAABAX

This link took me to a externally regulated 80 amp Hitachi alternator.
The OP states he has an internally regulated 80 amp Hitachi alternator.

[Scubaseas]

Originally Posted by Wotname

This link took me to a externally regulated 80 amp Hitachi alternator.
The OP states he has an internally regulated 80 amp Hitachi alternator.

The wires still go to the same terminals. B+ to B+, DF to DF, etc. The configuration of the wires are the same regardless if internally or externally regulated. The "R" terminal is for an Ammeter

[Wotname]

Originally Posted by Scubaseas

The wires still go to the same terminals. B+ to B+, DF to DF, etc. The configuration of the wires are the same regardless if internally or externally regulated. The "R" terminal is for an Ammeter

Hmm... the link takes me to a page like this https://www.pbase.com/mainecruising/image/164620540

There are no DF or R terminals on the page I see.

I am confused!!!!!!

What would normally be the 'R' terminal (top of the T), it states it is 'unused'.

[Scubaseas]

Originally Posted by Wotname

Hmm... the link takes me to a page like this https://www.pbase.com/mainecruising/image/164620540

There are no DF or R terminals on the page I see.

I am confused!!!!!!

What would normally be the 'R' terminal (top of the T), it states it is 'unused'.

Not as confused as I am. Been up 38 hours. Sorry. Df and such is DIN speake not JISC speake. I assume this is a second alternator being installed? If you are simply replacing the factory with a high output one just plug it in. If this is a second install you can run a wire to the existing R terminal. "R" is the one on top as Wotnot says. And of course B+ and grounds.

There is no tach connection (sense wire) on the 4JH alternator, it's a peizo pick up off the flywheel/bell housing