Starting Battery Setup.

[1970Columbia34]

We are repowering from a gas to a diesel motor. I was thinking about adding a dedicted 3 battery just for the motor. I don't want of need it tied to the current house batteries. He is my idea add the 3 battery soley for starting, hooks all batteries up to the alternator for charging, and also to the charger, we have a Xantrex Truecharge 20 that will charge 3 batteries. would this setup be fine? Thanks.

Scott

[josrulz]

Hi Scott, in the interest of full disclosure, I'm not an electrical expert. I just happen to be studying some of the same issue for our boat. I have have two house batteries, one in each bank. I'd like a 2 battery house bank and a separate battery in the other bank for starting. Here's what I've learned thus far, though someone might be able to add to this or offer alternatives. There are a few ways to accomplish what you're mentioning, but there's one principal common to all of them.

You shouldn't hook up the alternator to the house bank and the starting battery all together, at least not as simple as that. First of all, they might be different type batteries, but even if they are the same, they will be at different level of discharge every time. Charging them all in parallel will shorten their lifespan.

Ideally, you would have alternators (one for each bank), but this is a tall order. Assuming like me you will only have one alternator, it would be good to have one with a smart regulator for changing. You could set up the alternator to charge the house bank only, then wire a Xantrex Echo Charger (or similar) between the house batteries and the starting battery. When the Echo Charger senses a charge to the house bank, it automatically sends some of the charge to the starting battery to top it off. This is what I plan to do, and I've heard here on the board and read elsewhere that it's a reliable set up.

From what I understand, you could then just wire your AC charger to the house bank as well, and the echo charger will do the same thing there. So you'd only need one "channel" of your AC charger in this case.

There are other ways to do this, I believe, and others may offer some additional suggestions, alternatives, or corrections. I hope this helps as a start.
-J

[Deadeye]

Scott, that's a good idea and is common practice. A start battery is built for short-term high-current loading and house (deep cycle) batteries are made for a long gradual (and deeper) discharge. When you talk to someone who sells batteries, that's the first question they'll ask.

If your charger has 3 outputs, they're already isolated within the charger. Otherwise, they would need to be charged through an external isolator like josrulz mentioned.

Another option you might want to consider is to wire a parallel switch: a momentary pushbutton on the dash energizing a battery solenoid that connects the house and start batteries into one common bank as long as the button is pressed. That way, if the start battery should run down, you can get the engine started of the house bank to get the engine running and start putting amps back into the batteries. It's like a set of jumper cables for your boat.

[1970Columbia34]

Dead eye yes our battery charger does have 3 outlets on it and were only using 2 right now, but that only does the charging of the batteries when at the dock, what about when we are out on the water "with no wind" and motoring the alternator charges the house batteries, what about hooking the new dedicated starting batterying to the alternator do I need the other equipment talked about above? This is our current charger Xantrex Technology Inc. - Boats - Truecharge 20+ & 40+ (90-135 VAC) - Product Information

Scott

[hellosailor]

Scott, I'd vote for the simpler (KISS) way that the trend has gone in recent years. One starter battery, reserved for starting, and one large house bank. Not two house banks.

The reason is that this is "enough" and keeps everything else simpler. Your house battery bank is larger--so you will not need to discharge it as deeply, and that will give it much better life. And if you do run it flat--you've got the isolated starter battery anyway.

The alternative is just to use two large house banks, each capable of starting the engine. You can size that properly by finding out the power draw for your starter motor (expressed in kilowatts) and simply checking to see if your battery bank is large enough to supply that many kilowatts for a very short time (an "impulse" load). The battery maker will have that information for you.

But three battery banks? Odd as it seems, you're just adding more potential failure points. That's why commercial jetliners have gone from 4 engines to 2 engines. Oddly enough, twice as many engines means 4x as many ways to have one fail.

[1970Columbia34]

Hello sailor I agree want to keep it simple. I want to setup what you are taking about leave our house bank alone (2 batteries) and just add a starting battery right there next to the motor. I can charge all 3 from my shore power charger has 3 outlets and we only using 2 right now. 3rd can charge the starting battery. But what is the simplest way to charge the house bank and the starting battery from 1 engine alternator? Thanks.

Scott

[1970Columbia34]

Anyone?

[btrayfors]

Scott,

Use a Xantrex EchoCharge to keep the starting battery charged. This sits between the house bank and the starting battery and, whenever it senses a charge on the house batteries, it bleeds off enough to keep the starting battery topped up. No maintenance, no intervention needed. Fully automatic.

And, I'd rewire the battery charger to charge the house bank only (one wire). The EchoCharge will take care of the starting battery.

Simple, no fuss, easy to implement and to troubleshoot if needed.

Bill

[1970Columbia34]

can someone draw or show me a wiring diagram for this setup? thanks.

Scott

[sailingdog]

As BTrayfors pointed out... the alternator being wired directly to the house bank will also reduce any chance of killing the diodes in the alternator.

As for house banks... really should only have ONE house bank. The electrical system will be simpler and more efficient if you only have one large bank. A single large bank provides more working capacity than two smaller banks of the same total amp-hours due to the Peukert effect.