Batteries

[captaingary]

I just replaced my Gel cell batteries with     (4) T125 Trojan golf cart batteries in a series parallel combination. I also replaced my starting battery. I plan to mount the starting battery to the port side of the engine. I was told by the dealer that I should run the alternator wire direct to the house bank to minimise the voltage drop then connect the house bank to the starting battery with a battery combiner. Has anyone else wired this way?

[Stu Jackson]

Gary

This makes sense, as long as YOU understand it.

Usually, the alternator wiring is run to the 1-2-BOTH switch, which allows you to choose which battery bank you want to charge from the alternator output. Running it directly to the house bank makes sense with a combiner.

The combiner combines (clever, huh?) the batteries together whenever there is a charging source present, and disconnects the start & house banks when the charging source is removed.  It's simply a relay.  It just replaces the switch to choose where to send the charging sources and automatically sends it to both banks.

This way, you can have ANY single output charging source (alternator or charger or solar, etc.)connected to the house bank and at the same time be charging the starting battery without flipping any switches.

The purpose of connecting the combiner to the house bank and then downstream to the starting battery, instead of the other way around, is that you need most of your charge in the house bank, and do not need to run all that current through the combiner if it went start to house.  The starting battery is almost always fully charged, since it only uses a few amps, and thus minimal amp hours, to start the motor.  Remember that the batteries will only aborb (or accept) what they need.

If you use the combiner, then also connect your charger to the house bank.  If you have a two output charger, I suggest that you check West Marine's Advisor columns on the combiner, since I don't think it'll work with charging sources at both banks.  West Marine also used to send out, by fax, copies of their combiner installation manual so you could understand it in more detail.

Some people do not like combiners because they feel that it tends to overcharge the start battery.  Since the start battery uses so little, this is probably true, but it will only accept, through the combiner, what it needs anyway.  The single greatest advantage of the combiner is that you don't have to worry about the switch when charging.  That means it's safer when you're motoring, so no one is ever tempted to move the 1-2-BOTH with the engine running, which could fry your alternator.

Our start battery is #1.  The alternator still runs through our switch, since I haven't gotten around to rewiring that part yet for reasons I won't bore you with here.  I set the switch to #1 for starting and leave it in that position when motoring.  The combiner  charges both batteries.  Our alternator is still the stock old 55 amp.  After we shut the engine down, we switch the switch to #2, the house bank.  When just running the engine for charging at anchor, I start the engine with #2, since the house bank is more depleted and the current will run through the combiner first to the house then to the start battery.

There are also a number of other ways to arrange switches in lieu of the 1-2-BOTH arrangement, also covered pretty well in West Marine Advisors and Calder's manual.

I did install a Zap Stop on the alternator.

Al Watson posted a simplified wiring diagram with a combiner on the C34 website, think it's in Projects.

Finally, don't forget to change your charger settings from gel to wet cell, or whatever setting your new battery manufacturer suggests.

Stu