Hitachi 35 sense wire - Dual Battery Banks

[Simplicity30]

I am in the process of re-wiring our 1978 O'Day 30. I have taken much useful advice from this forum and have decided to go with 2 x 12V 120 Amp/hr wet cells paralleled as a 240 A/hr house bank and a totally separate starting battery.

I plan to run all charging sources to the house bank, and wire an echo charger to charge starting battery. I will be using a 1-2-Both switch as a 'use switch' for the house bank, and an 'on/off' switch on the starting battery (with terminal '2' of the 1-2-Both switch wired to the common post of the 'on/off for emergency-only starting from house bank.)

My question relates to how to wire my LR135-05 Hitachi alternator to both charge and sense the house bank. It has a 'B' (battery), an 'E' (ground), and an 'L' (lamp) terminal. The 'B' and 'E' I will obviously wire to the house bank + (pos) and to the engine - (neg). So far, so good.

It is my understanding though (quite possibly incorrect) that the internal voltage regulator on the Hitachi gets it's voltage sensing (and hence - output regulating) information from the 'lamp' wire. The 'lamp' wire must go to the ignition switch so it is live when the key is on (and dead when the key is off) , to 'excite' the alternator.

If this is true, wouldn't the regulator be getting it's sense information from the starting battery - which is connected to the key switch - and regulating it's output based on the state of charge of that battery, even though whatever output current there is will be going to the house bank?

When starting battery gets full-up, the alternator will cut back charge even though the House bank may still be quite depleted (from the big party the night before - but that's another story...)

If I were to put that 'L' wire direct to the house battery bank it would be live all the time, which I suspect would not be a good thing.

Someone else here posted a similar question to this but the answer involved leaving the 'L' wire to the ignition switch and wiring a relay to switch it to the house bank when the key was on, and, to be honest - I was lost right there.

I am trying to achieve a complete separation between the house and starting batteries - with the exception of the Echo charger - and I am also trying to achieve simplicity in terms of the fewest connections, components, short wire-runs, and cognitive capacity (mine.)

So, is there a simple way to wire the entire alternator circuit to the house bank and have it perform as intended? Or am I way off the mark to have posed the question on the first place?

The fact that I have searched for two nights straight and I can't seem to find any more than one other person asking this question makes me want to believe that I am over-thinking the issue.....

Please tell me I am over-thinking the issue!!!

[Reefmagnet]

"B" is the voltage feedback sense for the regulator. The ignition lamp "L" provides initial excitation for the field coils. Once the alternator is, well, alternating it self excites and hence the warning lamp extinguishes. In fact the regulator controls the field coil voltage and that is how the actual regulation works.

I've had the same setup as you, battery wise. I opted to dump alternator charge into the starter battery and use a VSR (voltage sensitive relay) to parallel to the house bank. This allows the alternator to automatically charge both banks with the engine running and also allows the starter battery to contribute to the house bank amp hours. My solar charger was connected to the house bank only (I relied on the starter being an AGM to reduce self discharge, but a wet cell would have been fine with the half regular use anyway). No 0-1-2-both switch needed, just simple on-off for each bank and a small toggle switch to manually switch the house banks to engine start if required using the VSR. Simple and it works.

[GordMay]

Greetings and welcome aboard the CF, Simplicity.

[Simplicity30]

Thanks Reefmagnet for the reassurance. From your reply, it sounds as though I can leave the 'L' wire in the starter circuit and the regulator will still put out current based on the SOC of the house batteries.

The 'B' wire currently runs to a fuse block mounted on the Yanmar 2qm15, then appears to run back to the starter + post. I have yet to peel back the harness insulation to confirm this, and that there are no other branches etc.

Assuming this to be the case though, I should be OK to take the 'B' wire off the starter post and run direct to the house battery bank? Is this what is normally done? I assume I would have to go a size bigger for the wire, to account for the extra 3' of wire run? In any event, a larger wire wouldn't hurt...

I think I would like to run the alternator charge to the house bank - it seems to be the common wisdom, not to mention, I've already paid about $150 for the Echo charger.

Any other opinions on this 'L' wire - or any other advice regarding wiring this alternator would be most welcome.

Thanks

[Simplicity30]

After writing my last post, I came across this older post on a very similar topic:

http://www.cruisersforum.com/forums/...re-112501.html[PHP][HTML]

The alternator described seems to be different than my 3-wire Hitachi, but there seems to be some disagreement among the respondants about just how the sense wire works........ Then the thread dies off........

Have I uncovered a contentious of issue?

I only ask because I just put 3 new batteries, a new 40amp charger, Echo charger 2 ANL fuse blocks, a Mega fuse block, 2 bus bars, all new battery cables and a bunch of new wire, so.... It should be obvious that if this dosent work, my boating is over because my wife will not let me spend another penny!

A better alternator set-up will likely be on the list for next year, but for the time being, I dont want to over-charge / under-charge my new batteries on those long windless motor days.....

[Simplicity30]

Mystery deepens...

I have traced the 'B' wire from the Alternator, it goes to the starter, but also to a fuse and then heads aft in a large wiring harness to points as yet unknown. One would assume it also heads to the ignition???? I have yet to confirm.

The Yanmar manual is woefully inadequate on this point, though it does show 2 wires heading to the key switch.

Now I am really lost with how to modify this system....


I also noticed that the alternator is an LR135-31 not an LR135-05.

[Reefmagnet]

Think of the "B" as performing two functions. The first is to supply charge to the batteries and the second is to sense the battery voltage for regulation. Additionally, the wire connecting to the "B" terminal is often supplying current to other loads on the circuit. Some alternators have a separate sense terminal "S"?? The reason for this additional sense terminal is that it allows the voltage to be sensed directly off the battery with no other load or charge current on the wire. This means that it provides a more accurate reading of the actual battery voltage. This is not absolutely essential, though is good if the batteries are located far from the alternator. For example, my engine has an alternator with a sense terminal, but it is not connected to anything as standard and instead uses the "B" terminal to sense voltage for regulation.

With all that said, you may be over thinking the situation. The "B" is connecting to your starter simply because the starter has a heavy lead connecting it to the battery. The fused side as you say is most probably the supply for the control panel or maybe the glow plugs; I can't answer this one but the wiring schematic should reveal it. In any case, as long as this stuff stays on the input side of your charger, it shouldn't be an issue. If you don't have a copy of the schematic, you should get one.

P.s. if you read CF for long enough you'll see many, many threads are filled with variously levels of disagreement ranging from mild to wild lol.

[cal40john]

Originally Posted by Simplicity30

Mystery deepens...

I have traced the 'B' wire from the Alternator, it goes to the starter, but also to a fuse and then heads aft in a large wiring harness to points as yet unknown. One would assume it also heads to the ignition???? I have yet to confirm.

The Yanmar manual is woefully inadequate on this point, though it does show 2 wires heading to the key switch.

Now I am really lost with how to modify this system....


I also noticed that the alternator is an LR135-31 not an LR135-05.

Standard wiring harness on Yanmar assumes your one connection to the battery is at the starter, so the output of the alternator goes there.
The wire with the fuse in it is the power wire to everything Yanmar.

[Maine Sail]

B+ is sense...

[Simplicity30]

OK, I think I understand that the 'B' wire goes aft to the ignition switch as the 'supply' so that when you turn the key, the 'L' wire gets it's exciting power to excite the alternator.

I am not trying to be deliberately obtuse, but....

If the 'B' wire only went to the starter because it is the best and biggest route to the battery, then I would just re-route it to the house bank. If I do that though, it will be taking that ignition supply function with it, and I assume that then the house bank would be connected - when the key is on - to the starter, which in turn is connected to the starting battery - which is the opposite of what I am trying to accomplish.

It would seem to me that I have to get that 'B' wire out of the ignition circuit and have the ignition switch supplied from the starting battery only.

Honestly, I have looked for a better wiring diagram than what is in the Yanmar manual, but none seem forthcoming. I will try to post that diagram, but it is very simplified and of not much use

I am scared that if I just reroute that'B' wire without fully understanding what all it does, I will be asking for trouble.

Then I would have to route a wire from the starter - which is connected to the starting battery - to the fuse block on the engine, and hence to wherever else that power goes....

So, the ignition switch 'supply' would come from starting battery. When the key is 'on', the 'L' wire would be powered and go to the alternator - which is connected to the house batteries!!

Please, don't be scared to talk to me like a six-year old on this topic, because I think that is what I need to get my head around this.

Deep inside I know that I am missing something (or perhaps inserting something that needn't be there) because I know that many people have their alternator charging the house bank only, so it must work. I just don't want to damage anything.

[Reefmagnet]

Originally Posted by Simplicity30

OK, I think I understand that the 'B' wire goes aft to the ignition switch as the 'supply' so that when you turn the key, the 'L' wire gets it's exciting power to excite the alternator.

I am not trying to be deliberately obtuse, but....

If the 'B' wire only went to the starter because it is the best and biggest route to the battery, then I would just re-route it to the house bank. If I do that though, it will be taking that ignition supply function with it, and I assume that then the house bank would be connected - when the key is on - to the starter, which in turn is connected to the starting battery - which is the opposite of what I am trying to accomplish.

If you disconnect the existing wire from "B", then add a new wire to "B" terminal and connect that wire to your house bank. You have now split the circuit. The engine electrics will still run off the starter battery, but the alternator output will go to the house bank.


It would seem to me that I have to get that 'B' wire out of the ignition circuit and have the ignition switch supplied from the starting battery only.

The above will achieve that

Honestly, I have looked for a better wiring diagram than what is in the Yanmar manual, but none seem forthcoming. I will try to post that diagram, but it is very simplified and of not much use

I am scared that if I just reroute that'B' wire without fully understanding what all it does, I will be asking for trouble.

Then I would have to route a wire from the starter - which is connected to the starting battery - to the fuse block on the engine, and hence to wherever else that power goes....

It sounds like the wire to the engine electrics is connected to the back of the alternator? Move it to the live side of the starter solenoid.

So, the ignition switch 'supply' would come from starting battery. When the key is 'on', the 'L' wire would be powered and go to the alternator - which is connected to the house batteries!!

Field coils inside an alternator (where the "L" connects) are a separate circuit to the alternator itself. The field windings control the alternator output via magnetism only (if you aren't aware electricity is generated by passing a conductor through a magnetic field. The stronger or faster changing the field, the more electricity is produced). There is some combination of circuits via the regulator, but it can be ignored for all practical purposes

Please, don't be scared to talk to me like a six-year old on this topic, because I think that is what I need to get my head around this.

Deep inside I know that I am missing something (or perhaps inserting something that needn't be there) because I know that many people have their alternator charging the house bank only, so it must work. I just don't want to damage anything.

I've spliced my replies into your questions to add context. Don't forget that you must connect your circuit so that the alternator "B" is always connected to the battery regardless of battery switch position otherwise it can cause your rectifier diodes to blow. TBH, if it were me, I'd just add a VSR instead on a configuration such as yours.

[Simplicity30]

OK, got it!

I am going to take the 'B' wire from the alternator directly to the 'house' battery bank - and nowhere else.

I am going to run a new wire from the big main + post on the starter (where the big red cable comes directly from the starting battery - where the above-mentioned 'B' wire used to go) to supply the 30 amp fuse / ignition harness.

The 'L' wire will run back to the alternator as it now does.

The 'E' wire will run to ground as it now does.


This will work?

[Simplicity30]

Oh, and... - Thank You!

[Reefmagnet]

Sounds like a plan!