Alternator Output Wiring

[idearat]

Hi folks.

I'm adding a starting battery to my old boat, paralleling the two identical batts it had to double the house capacity. I understand most of the bits required, but I want to confirm one point. I want the alternator output wired directly to the house bank, and the starter to the start batt (via switch). The way it's currently wired, the (small, automotive) alternator out runs via a 6-inch wire to the starter solenoid, on the same stud as the starter cable. That cable goes to the Common stud on the old 1/2/Both switch, so it seems to carry both starter and alternator current.

Can I simply disconnect the alt out from the starter, and run it to the house batts? Is there any reason the alt and starter need a direct connection?

Thanks for any help!
Perry.

[SailFastTri]

I would suggest you consider leaving the wiring the way you have it, and adding a battery combiner (which is a voltage sensing relay). The battery combiner will connect the two banks when either battery bank gets to 13.2v or higher (only under charge) and will keep them separate when not under charge.

The reason to keep the wiring the way you have it is so you always have a charged starter battery, and therefore will be able to start the engine to charge both. The combiner has the advantage of being able to "read" the charge situation so it is more reliable than trying to remember to open and close the manual battery switches.

(Battery combiners are under $100, and I have no financial interest in them.)

[daddle]

Yes you can do that. If the alternator or separate regulator has a voltage sense wire you will need that to go to the same battery bank as the positive lead. Sometimes the voltage sense is via the 'ignition' wire that enables the alternator ... and I suppose there are other ways someone may have wired it up.

There is some danger in accidently having the sense wire and the output wire lead to different batteries.

[delmarrey]

Originally Posted by SailFastTri

I would suggest you consider leaving the wiring the way you have it, and adding a battery combiner (which is a voltage sensing relay). The battery combiner will connect the two banks when either battery bank gets to 13.2v or higher (only under charge) and will keep them separate when not under charge.

The reason to keep the wiring the way you have it is so you always have a charged starter battery, and therefore will be able to start the engine to charge both. The combiner has the advantage of being able to "read" the charge situation so it is more reliable than trying to remember to open and close the manual battery switches.

(Battery combiners are under $100, and I have no financial interest in them.)

Ditto! This the smartest way IMHO.
If you have to switch batteries you may forget. Another thing to remember is if you have batteries of different ages or sizes hook together the weakest battery will demand more power, causing over charging of the bigger/better batteries.

[idearat]

Thanks for your comments.

delmarrey and SailFastTri, I'm definitely with you. Among the other 'bits' I mentioned, I am planning to use a series regulator (Magnum ME-SBC) instead of a simple combiner, to draw off just the current needed to charge the start battery, and run all charging sources to the house bank. I'll also replace the 1/2/both switch with a Blue Sea Dual Circuit switch that isolates start from house circuits.

daddle, thanks... that's just the kind of caution I was looking for. The alt is a Prestolite with an onboard regulator and just 3 wires; I guess I'd better figure out if one of the other two is a sensing wire.

If I can't easily separate the alt out from the start, I can run the existing wire to the Start side and use an actual combiner (since most of the charge current will be running through it), but I prefer the series reg to paralleling different sizes and types of banks, so I'm hoping it's possible.

Cheers...
Perry.

[cal40john]

Originally Posted by delmarrey

Ditto! This the smartest way IMHO.
If you have to switch batteries you may forget. Another thing to remember is if you have batteries of different ages or sizes hook together the weakest battery will demand more power, causing over charging of the bigger/better batteries.

How's he gonna put a combiner on there with the alternator output wired to the starter? Yes he has to take that wire off.

John

[delmarrey]

Originally Posted by cal40john

How's he gonna put a combiner on there with the alternator output wired to the starter? Yes he has to take that wire off.

John

He can just add one more wire to the starter, the combiner lead.

I have three batteries. The two starter/house batt's are charged separately using a diode block and the third is up forward with the combiner for the windlass and washdown pump. The alternator wire is connected to the common of the diode block and so is the lead for the combiner. And there is a fine igniter wire between the starter and alternator to start the system.

[cal40john]

Originally Posted by delmarrey

He can just add one more wire to the starter, the combiner lead.

I have three batteries. The two starter/house batt's are charged separately using a diode block and the third is up forward with the combiner for the windlass and washdown pump. The alternator wire is connected to the common of the diode block and so is the lead for the combiner. And there is a fine igniter wire between the starter and alternator to start the system.

You're still missing the point of the original question. His alternator output wire right now goes to the starter, only the starter nowhere else. The single and only one start/charge wire comes off of the starter and goes to the start battery. He's asking if the wire between the alternator output and the starter can be removed when he runs a wire from the alternator output to the house bank.

Yes it can be removed.

[DeepFrz]

Yes, it should be removed. You are right to run your alternator output to the house bank with a "combiner" of some kind to your start batteries.

[btrayfors]

Originally Posted by cal40john

The single and only one start/charge wire comes off of the starter and goes to the start battery. .

Aaah, not quite.

The OP stated that the alternator output wire goes to the solenoid, and that the starter wire goes from the same solenoid terminal to the common terminal of a 1-2-Both-OFF switch.

Presumably, he now has the house bank on one position, and the start battery on the other position of the 1-2-BOTH-Off switch.

Bill

[btrayfors]

Perry,

Starting all over again, the preferred method would be:

1. All onboard charging sources (alternator, battery charger, generator, solar, wind, etc.) leading directly to the house batteries, with an appropriate CPD (current protection device) located close to the batteries. This should be a fuse with a high ampere interrupt capacity (AIC) like the new terminal type fuses by Blue Sea Systems or an ANL fuse or a Class T fuse. Other types of fuses and most breakers should NOT be used.

2. An external regulator for your alternator is preferable. One like the Balmar MC-612 is ideal.

3. A battery combiner or, better, a voltage follower device (like the Xantrex EchoCharge or Balmar's Duo-Charge) should be used to tap current from the house batteries when they're under charge to keep the start battery topped off. Completely automatic operation...no turning of switches needed. The Magnum ME-SBC would work OK, but it's basically a combiner device with adjustable settings which has cutoffs for high inrush current (like when you connect a fully charged start battery with a depleted house bank). IMHO, the voltage follower devices are better.

Bill

[cal40john]

Originally Posted by btrayfors

Aaah, not quite.

The OP stated that the alternator output wire goes to the solenoid, and that the starter wire goes from the same solenoid terminal to the common terminal of a 1-2-Both-OFF switch.

Presumably, he now has the house bank on one position, and the start battery on the other position of the 1-2-BOTH-Off switch.

Bill

Read post #5

[btrayfors]

cal40john,

Yeah, I saw that. It says what he's going to do, not what he now has.

Bill

[SailFastTri]

Originally Posted by btrayfors

snip
3. A battery combiner or, better, a voltage follower device (like the Xantrex EchoCharge or Balmar's Duo-Charge) should be used to tap current from the house batteries when they're under charge to keep the start battery topped off. Completely automatic operation...no turning of switches needed. The Magnum ME-SBC would work OK, but it's basically a combiner device with adjustable settings which has cutoffs for high inrush current (like when you connect a fully charged start battery with a depleted house bank). IMHO, the voltage follower devices are better.

Bill

Why do you think an echocharge or duocharge is better than a voltage-sensing relay (combiner)? The latter is more efficient (no voltage drop and no power converted to heat) and simpler, and usually less costly. All are completely automatic.

[cal40john]

Originally Posted by SailFastTri

Why do you think an echocharge or duocharge is better than a voltage-sensing relay (combiner)? The latter is more efficient (no voltage drop and no power converted to heat) and simpler, and usually less costly. All are completely automatic.

If you go to a 3 stage charger that allows the battery to go to a high voltage during bulk phase you're overcharging the start battery that was topped off early on. If you stay with the automotive style regulator it doesn't matter.

John