House Bank - 2 separate or 1 parallel

Stu Jackson · May 11, 2014

#4, disconnect the failed basttery, don't need a switch.

Put all four together as one bank (obviously series/parallel with 6Vs) and use the 1-2-B switch for a reserve battery.

You're overthinking this.

Don S/V ILLusion · May 11, 2014

Given two options, choose the one Calder recommends.

Maine Sail · May 11, 2014

scherzoja said:
When designing a house bank with four 6v golf cart batteries @ 12v (assume 200AH for each of the 2 batteries), is it better to keep the series pairs separate (two banks @200amps each) or combine the two banks in parallel, creating one bank @ 400ah?

I have read Calder's book and he recommends paralleling them and I understand why.
I have also read that paralleling batteries is not a good idea (http://continuouswave.com/whaler/reference/dualBattery.html, see section entitled "Single Engine/Dual Battery").

It seem like paralleling them is better, but how does one mitigate the risks of paralleling?
1. charge rate difference because of age: start with same age batteirs
2. unequal SOC: design a charging system that charges all four simultaneously
3. internal resistance differences among the four causing unequal charging and load supply rates: ??? how significant is this issue
4. One of the four batteries fails, causing the entire bank to fail: install a 1-both-2-off swtich to break the parallel and remove the failed pair.
5. ?? any other drawbacks to paralleling two banks batteries?

Thanks

#1 Ignore that entire Whaler thread. It was written by someone who does not understand Ohm's law, charging or batteries. It was written based on a "what I think happens" point of view basis, not on what actually does happen... Unfortunately there is lots of misinformation on the net....

#2 One large bank hands down.... I have written at length on this subject, on this site before, from an actual scientific and solid electrical perspective that actually follows Ohm's law...

Nigel is correct but there is also more to consider which he did not touch on. One large bank for reasons beyond even what Calder touches on.

It is more efficient to charge one bank than two, unless using 100% free energy, and even then "finishing" two banks is less efficient due to the longevity of the time acceptance limiting and "finishing" takes.. The larger bank will also not be as dramatically affected by the Peukert effect or Peukerts Law and you'll actually get some more amp hours out of a larger bank with the same load than you do with two smaller banks with the same load.

For example a bank with a Peukert of 1.27 and a average load of 8A looks like this if you were to draw the bank to 10.5V and use all the capacity.

100Ah bank, Peukert 1.27, load 8A = 89 Ah's
200Ah bank, Peukert 1.27, load 8A = 212 Ah's
400Ah bank, Peukert 1.27, load 8A = 512 Ah's
600Ah bank, Peukert 1.27, load 8A = 857Ah's
800Ah bank, Peukert 1.27, load 8A = 1235 Ah's

This means that a single larger bank will have shallower discharges, not just because it is one large bank, but if the load stays the same and you increase bank size you will actually get more out of the larger bank due to Peukert than you will by using two smaller banks at the same average loads.

You mitigate risk in any bank by buying all batteries from the same lot and date code, equalizing them for approx two hours before installation, if they are going to be in series, balancing them in parallel prior to use, charging them properly, wiring them properly and monitoring specific gravity, if flooded. Yearly capacity tests also confirm condition and allow proper programming of a battery monitor.

In an ideal world every bank would be series only, but we don't live in an ideal world and series only banks also have huge issues such as batteries in the string getting out of balance. Parallel batteries can't get out of balance, they are all at the same SOC, only the series cells can... All batteries can lose capacity.

Stu Jackson · May 11, 2014

1. You're right, the parallel break switch is wrong, you'd combine one bank into two separate banks. No need to do so at all. Keep the four 6V as one bank.

2. Read this: http://www.sailnet.com/forums/electrical-systems/72295-xantrex-echo-charger-rant.html The echo charger won't work that way. The alternator output has to go to the house bank.

Otherwise, I haven't reviewed it in detail.

Compare yours to these:

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: http://c34.org/bbs/index.php/topic,6604.0.html

mitiempo · May 12, 2014

I agree with Stu - the alternator and any other charging sources have to go to the house bank for more than one reason.

1. The Echo Charge is a battery follower and only passes current one way. It has an input and an output.

2. The Echo Charge only passes up to 15 amps from the charging battery to the other (auxiliary) battery. Your method would limit the house bank to 15 amps. With charging sources wired to the house bank it will see the full output of any charge sources - alternator, shore power charger, solar or wind gen. The start battery is not down more than a fraction of an AH from a start.

3. Even if the Echo Charge was bi-directional device, which it is not, it makes no sense to pass the current the house bank will accept - a lot usually - to a fully charged battery first.

eherlihy · May 12, 2014

Your diagram is very clear. I like the tool that you created the diagram in. What is it?

Regarding your diagram; I would move the connection from the alternator to the house positive bus. Also, if the occasion arrives to throw the emergency jumper (SW 3), the reason better not include a short anywhere on your starter circuit. Otherwise, you'll be throwing a whole lot more amps at that short. I would wire the ON lead from SW 3 directly to the starter, or have a 1, B, 2, Off switch connecting the starter to the two banks.

sea_casper · May 12, 2014

One small point, voltmeter needs ground connection.

Probably "starting" battery not needed/justified.
Then you don't need echo and emergency switch.

Carry small auto "jump pack" for emergency starts, works on your car too, especially when you com back from extended cruise, and you find "someone" has left lights on.

Add solar panel(s), largest you can fit.

Maine Sail · May 12, 2014

If you are going to use the three switch method be sure it is wired PROPERLY. This is one of the most miswired switch scenarios I see.

Alt goes to house...

The parallel switch is wired to the LOAD SIDE of switch 1 & 2......

tailwind · May 12, 2014

With one bank, is there a potential problem with not ever fully charging the house bank since you are always drawing on it?

bobbyfingers2001 · May 12, 2014

Charging

Disregard

Benny17441 · May 12, 2014

There are unquestionable benefits to having a single larger bank rather than two smaller banks. One such benefit is that you can draw a larger capacity in Ah's from the larger unit but the bigger question is whether you need and will use that extra capacity? Everything is a trade-off and you do get a benefit but at a cost. If you hook up the 4 batteries together you would need to purchase and replace them at the same time and provide timely maintenance. There is always the risk that a single bad cell in one of the batteries may kill the whole group. There is value in another thing which is redundancy or backup. Two separate banks can back-up each other and continue providing power in the case one failed or was accidentally discharged. If you can go between opportunities to recharge with the use of just one bank you I would think the benefits of having two separate banks would outweigh the benefits of a larger single. Analyze your use of the boat and your power requirements and configure your banks according to what makes the best sense for you. On paper a single large battery makes sense but does it for you?

GeorgeC1 · May 12, 2014

You have a positive feed going to the shunt. A positive feed would go the the battery monitor to power it, but both sense leads of the shunt get connected to the battery monitor. The battery monitor measures the voltage drop across the shunt and uses this voltage to calculate the current passing through the shunt.

Maine Sail · May 13, 2014

GeorgeC1 said:
You have a positive feed going to the shunt. A positive feed would go the the battery monitor to power it, but both sense leads of the shunt get connected to the battery monitor. The battery monitor measures the voltage drop across the shunt and uses this voltage to calculate the current passing through the shunt.

The Victron BMV uses a + lead to the shunt due to its wiring & the PCB mounted on the shunt...

I would urge anyone looking for a battery monitor at this point in time to strongly consider the Balmar Smart Gauge. It is significantly easier to use, to install, and stays accurate without complicated programming & re-programming..

It was recently featured on Panbo too... Balmar Smart Gauge - Panbo

weinie · May 13, 2014

Why not do what Stu mentioned above?
You can start your engine using the house bank just fine.
Just connect the starter to the C post of your 1/Both/2/ switch and the second battery which is now your starter battery becomes your reserve bank.
You will save yourself one large wire and you won't need that on/off switch.

Maine Sail · May 13, 2014

scherzoja said:
Weinie,
The start system (battery, cables, switch) is existing. I'm just replacing the house batteries and fixing deficient battery wiring problems.

You can save yourself some wire length by creating a jumper to the 2 position of the 1/2/B from the On/Off..