Isolating my starter battery

Maine Sail · Mar 30, 2009

robfmcc said:
Boat: 1998 Beneteau 352

Goal- I want to isolate my starter battery from the house bank.

Problem - I keep forgetting to flip that damn switch and the starter battery drains.

Info - I can isolate the starter battery from the house battery by removing the jumper on the battery switch panel - or at least I think I can. The next question is how do I recharge the starter battery after starting? To clearify - the starter and house batteries will need to be charged by the alternator while running the engine. How do I control both battery banks, not overcharging the starter battery ( now that it has been isolated) and recharging the house batteries?

Am I missing something?

You can run your alternator output directly to the house bank then add an Echo Charger (made by Xantrex) between the house and start banks.. You'll be under 250.00 for this entire project and you'll never have to worry about frying alternator diodes by disconnecting a load vie the battery selector switch.

You can also use an automatic charging relay but the Echo Charger really is the cats meow. it never actually combines anything but rather bleeds off up to 15 amps of charge current from the house bank to charge the start bank with..

Franklin · Mar 30, 2009

Hunter does it pretty simple and cheap. Buy a starter solenoidfrom an auto-parts store. Mount in protected area to keep salt off. Run both battery banks to it for the big wires. The wire that flips the switch is tied into the key for the engine. So when ever the engine is on, the banks are connected for charging, but as soon as you turn the engine off, the banks are seperated again. Great thing about that approach is you can get that part anywhere.

Bob V · Mar 30, 2009

K.I.S.S.

My last boat had a seperate starter battery wired in with echo charger.

This time around I just put it in a locker with the cable needed to hook it into position B on the switch unconnected. I keep the switch in the both position which results in 3 4-d batteries hooked up parallel for all purposes (house and start). I charge the starter periodically when I am on shore power with a seperate charger that I use for my electric dinghy batteries. If I ever need it, the plan is to disconnect battery B and connect the little Optima Starter battery. Then change switch to B only so I don't drain my starter into the big dead 4-d's. I also have a pair of Optima deep cycle batteries for the dinghy. If I ever woke up to dead batteries while cruising I could disconnect the dead ones (leave them in place) and connect in two little deep cycles for house load on A and the starter battery on B.

I suspect I will never need them but it's nice to know they are there. I would not gamble on not having them but I don't need them ready to go at a moments notice so this system works for me.

Stu Jackson · Mar 30, 2009

You're not the frist one with this requirement

First, please note that your B is wired somewhat differently than most other boats, and you mentioned: "I keep forgetting to flip that damn switch and the starter battery drains..." You didn't mention a 1-2-B switch. My friends with B's have a series of switches in their aft cabins that control the banks.

Before you begin this process, obtain or locate the wiring diagram for your boat, and then carefully plan, plan, plan you new installation.

Maine Sail is right about the benefits of the echo charger for your planned enhancement. If you do a search on "echo charger" (use exact phrase) on thsi board, you will find tons of information explain how it works, right here. It is superior to a combiner (or simple relay) as Maine Sail has explained.

On our C34 Message Board, we also discuss these issues. A representative sample, which includes a wiring diagram of my boat, is here: http://c34.org/bbs/index.php/topic,4623.0.html. Please also note that Reply #23 includes a referenced link right back to this board and another of Maine Sail's excellent posts.

Neil McDonald, on this board, has contributed to the discussions. Here's one on echo chargers for ya! http://forums.catalina.sailboatowners.com/showthread.php?t=105813 Check out some of Neil's previous posts, where we've discussed other items of interest to you.

We recommend that you call it your reserve bank. One of your options is to never use it unless you have to and use the house bank to run everything, including starting your engine. Keep the reserve bank just for that, a reserve, emergency, backup. Keep it charged. Just don't use it to start the engine all the time. Then you could consider not having to rewire anything!

Your boat, your choice.

sailaway78 · Mar 30, 2009

Several good suggestions

Most of the suggestions posted are pretty good. Since the Benny is wired quite a bit differently than anything I am familiar with, will not comment on you specific question. However, I do disagree strongly with those who suggest running on both all the time, start and house. If you do this, two things can happen, neither one good. First, if you run on both, there is absolutely no need for a start battery, as all will be charged or discharged together. Both is just the same as one, and the idea of having a start or emergency battery is moot. Second, if you get a bad battery in one bank, it will keep the entire system from fully charging. So if you have a bad cell in a start battery, it will keep the entire system from fully charging. I like the KISS principal, and simply run with a 1 - 2 - Both switch. Rarely use 1, and never have a problem remembering, when I have it on.

Stu Jackson · Mar 30, 2009

Nice N Easy said:
However, I do disagree strongly with those who suggest running on both all the time, start and house.

Not sure if anyone ever said this. I keep saying "It all depends on how it's wired."

Many people have finally understood the need to remove the al;alternator output from the 1-2-B switch, move it to the house bank and determine how they charge their reserve bank. Thus the banks are never combined.

I discussed this in detail with my disdain for the Dual Circuit Switch.

I find the 1-2-B switch superior to the alternative methods of multiple switches, and find being able to use either bank for either putpose (engine start or house loads) a vast improvement over the old OEM wiring with the alternator output going through the 1-2-B switch.

There are tons of links, this is but one: http://forums.catalina.sailboatowners.com/showthread.php?p=520854

If you do a search on the phrase "It all depends on how it's wired" by exact phrase and message and author, you'll find a lot of the posts that include discussions of this very subject.

One could do the same for "wiring diagrams" and finding Maine Sail's posts here on this message board.

larryw · Mar 31, 2009

robfmcc-
Benes are wired in the European style, with three, sometimes four, switches in the aft cabin. My Bene 400 has three because there's no aircon (no need in SoCal) or genset. I have a 430 AH house bank and a dedicated start battery. I installed a West Marine battery combiner that senses the voltage and closes a switch whenever it senses a charge voltage, then opens the switch when the voltage falls below a certain level and it works with shore power or alternator output. I never have to remember to fllip any switches. It's not perfect, but it's worked for me for over ten years. I use a Honda EU2000 whenever I'm anchored or on a mooring cause I don't like to run the main engine for battery charging.

Deadhead · Apr 1, 2009

Beneteau Wiring IS Weird

My Beneteau 343 has 3 battery isolation switches mounted in the aft cabin. (1 black & 2 red) It is probably similar to your 352 in that 1 switch controls the ground (negative) side of the batteries and the other 2 switches are for the positive sides of the house battery and the starting battery, respectively. These switches open/close the cabling circuits on each battery.

When I recently added a battery monitor I installed the required shunt in the negative cabling. I found that the ground cables of each battery are tied together on the same side of the black battery switch. When the black switch is closed the negative side of the engine starter circuit, amongst other things, is engaged. When either of the red switches is closed a complete circuit is established and the engine may be cranked.

Basically, either battery can start the engine. The down side is that unless the red switch for the starting battery is opened to interrupt the circuit this battery will be drawn down with the house battery when running accessories. Also, if both red switches and/or the black are opened when the engine is running the alternator diodes burn up. Beneteau makes this very clear in their literature.

The bottom line is that, at least on my 343, there really isn't a jumper to remove that will isolate the starting battery. The 2 negative battery cables are crimped together into the single terminal connector that attaches to the battery side black isolation switch. I think it would be necessary to replace the (essentially) single cable with 2 separate cables and put a combiner (1-2-both) switch somewhere between these cables and the existing switch.

When I finished the battery monitor installation I thought briefly about how to actually isolate each bank but I had not reached any conclusion. It now seems about as clear as mud.

larryw · Apr 2, 2009

Deadhead is right; I had to move some battery cables on the switches and remove the jumper between the two red ones in order to achieve isolation.

Ron20324 · Apr 3, 2009

Rob, when I start my B323 it is with the "engine"(it is a 24, the other 2 are 31s) battery switched on. I have THREE red battery switches now. By the time I'm out to the sailing grounds, it has recharged enough, so when I shut down the engine I switch the engine battery off, and the house batteries "on". They get a boost charge when starting the engine for anchoring or whatever the end-of-day requirements are. Some things, you just gotta remember to do on a boat.

My guess is Larry has- on his engine battery switch- a battery cable, the starter cable, and shore-powered charger cable on one lug so that they are always ready to run. The lug on the other side of the engine switch still has the "positive buss" jumper to the house battery switch. Normally in the "off" position, the battery is isolated, but if it's dead, putting the switch in the "on" position connects it to the house battery for starting.