Battery Bank. two banks or one

[rsn48]

I'm the electrical illiterate type and so I have used one chap to help installing my electrical goodies. He has left and I found another friend who is an electronic freak and is willing to continue the job. Of course, the master plan in friend "A's" mind is different from friend "B." Here is one difference I think (realize these guys tell me what and why they are doing it, but often they might as well be talking Hebrew to me).

I have four golf cart batteries, one starter battery for the engine, and one portable rechargeable jumper battery. I think my friend's A plan called for all four, two wired in series, to be monitored by one Zantac Battery monitor, so two sets of batteries equals one battery bank. My friend's plan B plan calls for two battery banks of two batteries each.

He asked me if I wanted to tie the engine battery into the electrical system to use if the engine battery went dead. After thinking about it and realizing I carried a spare rechargeable emergency battery, I decided to leave the engine battery on its own (except for recharging purposes with my 40 amp charger).

In one way I like the idea of two separate battery banks using the gold cart batteries; in another way not. If separate banks, I would seem to have more control over them, however I think it would be easy to drift over the 50 % discharge rate before switching over to the second bank.

Also friend B told me I'd need another Zantrac Battery monitor to keep track of the second bank. Is there any advantages of two banks or should they be kept as one bank for charging, discharging and monitoring purposes?

[By Invitation]

In my opinion, you are much better off with one large battery bank rather than 2. I just did an entire refit and designed one large bank. I really see no advantage on a cruising boat to have 2 house banks. You want as much ah as possible from the main bank so you never discharge below 50%. Use a simple crossover switch from the main bank to your starting battery to use when the starting battery is low.

Just my 2 cents.

[senormechanico]

I agree. Go for one big bank. As long as you have a separate starting battery, you're golden.

Steve B.
PS if you really want to go deep into it, google for the Peukert effect. That's why I recommend one bank.

[Terra Nova]

Originally Posted by By Invitation

In my opinion, you are much better off with one large battery bank rather than 2. I just did an entire refit and designed one large bank. I really see no advantage on a cruising boat to have 2 house banks. You want as much ah as possible from the main bank so you never discharge below 50%. Use a simple crossover switch from the main bank to your starting battery to use when the starting battery is low.

Just my 2 cents.

Yo By,

yours is the best choice. In this case (the four identical batteries combined into) one house bank is greater than the sum of its' parts (two weaker 2-battery banks). What I mean to say is that time between charges can be more than doubled. And you will be able to charge them more simply. The whole installation is simpler.

Leave the odd battery out of this system.

best, andy

[btrayfors]

Yes, it is the preferred way these days to have a single large house battery bank, rather than two or more separate ones. In addition to the benefits mentioned above, you can make better use of whatever onboard charging capabilities you have, since you can charge at twice the rate -- in your case -- that you could with two separate banks.

In addition to figuring out how you're gonna configure the batteries, the really important thing is to figure out how you're going to charge them adequately. Undercharging is the primary cause of failure/deterioration in house batteries.

My recommendation: connect all charging sources directly to the house batteries. Keep the engine starting battery separate, and keep it charged with a device like an EchoCharge (now from Xantrex) which senses a charge on the house batteries and delivers up to 15A to charge the starting battery. These work very well, are automatic, and won't overcharge your starting battery.

Remember that on most boats much of the alternator power is wasted if it's connected just to the starting battery, since the amount of power required to start an engine is very small (a lot of amperage but for a very short time...seconds). That starting power is typically replaced in a few minutes after starting the engine, after which the alternator just idles along. A much better plan is to use the alternator to charge the house batteries -- together with a smart regulator -- and to use a "spillover" device like an EchoCharge to maintain the starting battery.

Bill

[Maddog]

I use an ACR from BlueSea. Does the same thing as the Echo Charger. It is so much better than the isolator I use to use. it's almost like I have a new battery bank. I'm sure that I have added a year or two of life to them. Check out the e-series battery switch too. These two products have provided me with a worry free 12v dc system.

[btrayfors]

Yes, the Blue Sea 7600 CL-Series BatteryLink ACR is a good choice. It can handle about 4 times the current of the EchoCharge, is about the same price or even less, and has very good specs.

This is definitely the way to go. I've used the EchoCharge now for 2 years, and love it. WAY, WAY better than isolators and other classic solutions.

Bill

[hellosailor]

rsn, take a look at blue seas, balmar, and some of the other marine electronic systems makers webs sites, you'll see a lot of options diagrammed out.

Then, pick a diagram, print it out or copy it, and use it as the basis for your system. MAKE A PAPER DRAWING of what you plan to do. Feel free to post an image of it up here for comment, show it to your friend, debate it.

But having a diagram of the system is a priceless installation and troubleshooting aid, among other reasons because you will need to have terminals swaged on every power cable, and the + and - cable lugs are different sizes, so you want to mark cable lengths and fittings before you order them to get them right.

By all means, the modern thought is to put all four of the golf cart batteries in one house bank, in parallel. The quality of the connections and the evenness of them is important, and each battery should have a marine grade primary fuse installed ON the battery itself to protect them (and your wiring) from crowbar failures. Fuse, not breaker.

Using just the starter battery for starting--and leaving it hard wired to the starter and alternator and nothing else--is also perfectly valid. You can add a manual switch for emergency starting from the house bank--or you can just keep a set of jumper cables on board, they may find other uses.<G> Whether you use a 1-2-both-off switch, or two separate on/off switches (one marked "for emergency starting only") is up to you. Either way works. If you use one switch only--it is possible for a guest, etc, to set it wrong, so convenient isn't always best.

Of course that's all just the start. The alternator size (output) regulator, cabling choices, etc. all make the difference between a robust system, and one that eats batteries. Ideally you size them all to work optimally together.

[rsn48]

Thanks for the responses; I have forwarded them on to my friend as he continues to mount his battle plan. I did go to blue Seas but didn't see any diagrams, but I may have missed it; if they are there, they aren't labelled very well.

[hellosailor]

For example: Add a Battery - PN 7650 - Blue Sea Systems

The diagrams tend to be illustrations on each product page, or drill down from the "Resources" tab on the top line of their home page,

Resources - Blue Sea Systems and you'll see technical resources and product briefs listed like:

Battery Isolators and Automatic Charging Relays - Resources - Blue Sea Systems which is a product explanation and diagram.

They also do presales support on the phone. And there are some vendors (like Jack Rabbit Marine) who sell a lot of top end stuff and have good reps for advice as well.

But I like the pencil and "stick it on the wall" test best. Once you're done, stick it on the wall for 48 hours and once in a while, you'll walk past and say "No, that's not quite right, is it?".

[GordMay]

Originally Posted by hellosailor

... But I like the pencil and "stick it on the wall" test best. Once you're done, stick it on the wall for 48 hours and once in a while, you'll walk past and say "No, that's not quite right, is it?".

ABSOLUTELY!

[camaraderie]

Here's some good system options:
Marine Battery System Hookups

[rsn48]

Thanks all, I'm still monitoring this thread and forwarding info.

[Sandero]

I rewired Shiva about 2 years ago. My upgrade included and Optima start batt added to 3 yr old 8D AGMs. I have 2 - 55 watt solar panels using a PV14 charge regulator, and an echo charge and a sulfator. All charging is to the main house bank. I redid all the cables and connectors and a BlueSea 8080 switch with a Link20 monitor. The altenator is a high output 125 amp, run with a MaxCharge 612 smart regulator.

This system is working fine and the batts are usually quite full up and I take no special measures to limit electric usuage. The boat sits on a mooring in the summer and the solar panels top off any deficits left at the end of the weekend of living aboard. Our refer is an engine drive so to run it we are charging the batts and making hot water as opposed to a 12v refer which is draining them!

Use the right gauge cable, proper connectors on clean terminals.

So far so good.

Jef
sv shiva

[Starbuck]

Bill Trayfors,

Your post #5 is very clear and instructive. A pleasure to read for another electrical illiterate.