Paralleling Battery Banks

[FlyingCloud1937]

I have read a number of topics at this sight in re paralleling battery banks located in different areas of the boat, all being charged from a single charge source.

So I thought rather then posting to topics that are giving some bad advice. It would be better to focus it in one thread.

By charging parallel banks located far away from each other from a single charge source, will lead to one bank being under charged, and possible the other bank being over charged. This is a poor practice, and will lead to shortened battery life.

Lloyd

[David M]

Not really, as long as your connectors are clean and have minimal resistance. Any resistance (tiny voltage drop) over distance will be so minimal that you will never notice any difference in your batteries charge levels.

If you have really small gauge wire with dirty terminals, then yes, there can be a noticeable difference in your batteries charge state because of a voltage drop over the length of the wire run.

Your battery charger will not overcharge a distant battery unless there is a problem with the charger itself. If anything, it will under-charge a distant battery by the scenario I just described.

I have four 8-D's in three different locations. This is my experience with doing the same thing.

[oldjags]

So, where's the best place to connect the charger if your battery banks are located all over the boat?

Seems like it would make more sense to connect the charger to the terminals on the master AB switch rather than run a separate wire from the charger all the way to the individual banks. That way you can use the existing heavy gauge battery wire to take the charge back to the battery.

Is this a legit way to do it, or is it already done this way?

[Dockhead]

Indeed, and I am probably one of the recent culprits. If you create distributed battery banks, you should pay attention to possible voltage drops to one bank, causing the problem described by Flying Cloud. In our case, two banks of 220AH * 24v each, we are double protected from this problem by (1) two banks equidistant from the charger; and (2) for belt and braces, two banks connected with 50mm2 welding wire to equalize voltages.

I recently advocated to someone integrating a bow thrusters bank with a house bank. I should have mentioned this problem - my bad. The wiring should be designed to avoid a difference in voltage during charging.

[David M]

Wiring size can be gauged so that there is a difference in recharge rates. Just take into consideration that the smaller the gauge the longer the time it will take the battery to recharge. It is analogous to running a smaller water pipe. The tank will eventually fill up with either sized pipe. The down side to larger wire is weight and cost.

[Andina Marie]

Originally Posted by FlyingCloud1937

I have read a number of topics at this sight in re paralleling battery banks located in different areas of the boat, all being charged from a single charge source.

So I thought rather then posting to topics that are giving some bad advice. It would be better to focus it in one thread.

By charging parallel banks located far away from each other from a single charge source, will lead to one bank being under charged, and possible the other bank being over charged. This is a poor practice, and will lead to shortened battery life.

Lloyd

That is not correct. They are in parallel so they are at the same voltage. You can't overcharge one and undercharge another if they are at the same voltage. To overcharge the voltage would be high enough that the charging current has dropped below one amp. Ohm's law says the voltage drop is ohms X amps. So as the Amps drop to zero so does the voltage drop and when fully charged they must be at the same voltage.

If they are far apart with a light gauge parallel cable, then when you apply a load to one, it may be supporting a higher percentage of the load due to the resistance to the other battery but the moment your load is removed, battery to battery current will equalize the charge.

[FlyingCloud1937]

Sorry all, For starting this topic, and not staying to participate, had to run to a job.

First lets talk about batteries. Most bats don't die of old age. Most bats are murdered long before their design useful life.

Anyone that maintains a battery bank, is a "BANK MANAGER"

But to be a Professional Bank Manger, you have to manage the bank right.

Number one cause of premature death is Sulfation, caused by chronic undercharging. Next cause is chronic overcharging, aka positive grid plate corrosion.

A battery can suffer from sulfation in one cell of a multi-cell battery, as well as suffer from one cell being overcharged, while all other cells appear to be normal.

Battery banks built as series, parallel and or series/parallel can also suffer single cell, as well as individual battery sulfation/corrosion. It's called cell balance, that's why we use a hydrometer to measure the health of a battery.

To proper charge a battery/bank you have to charge proper, which means the charge has to sense the battery it's charging, then apply the proper charge regime to the bank.

That means a proper controlled bulk charge, then a controlled absorption charge with proper votage, current and time, ending in float stage...if the battery remains out of service.

Lets take one example to which I'm talking about, we have battery bank 1 servicing the house loads, and battery bank 2 serving the starter loads. Typically these are two different types of batteries, as well as 2 different sizes, the house bank being heavily used 50% SOC, while the start bank is lightly used 95% SOC.

Both banks are isolated from each other, as they should be. You only have one charge source, and somebody convinces you to install one of the fancy new combiner relay/solenoids. It's job is to combine the banks when the bank with the charger reaches above a certain voltage say 13.2.

What do you think is going to happen....yes, the charger when turned on sensing the house bank is going to go into bulk charge mode as it should. Once the house bank reaches 13.3 volts, it's going to parallel the much smaller bank that already is at 95% SOC, and overcharge it, until at some point the charger thinks that the house bank is charged.

But really happens in time, is it confuses the charger into thinking that the house bank is already at absorption when its not, cut back on the bulk, and time out on the absorption phase and leave the house bank under charged, while it overcharged the start bank.

This is one issue I find on a regular basis.

Lloyd

[FlyingCloud1937]

Next scenario, we have on large house bank made up of 4 bats paralleled. Problem is we only have room to install 2 bats in the engine room and the other 2 bats have to located some where else.

The bank of to closest to the charge/load source is going to do the lions share of the work, and receive the more charge, while the other 2 lough along. Eventually your going to run into cell imbalnce, and it's going to be sooner then later.

Even if you managed to make the cables the same length to each pair of bats to the load/charge source, you're going to be constantly fighting against cell balance issues. The bats in the engine room are most likely going to operate at much higher temps, then the other 2 remote mounted bats.

I know ohms laws says....but what it doesn't say is that if you take 2 identical cables say 5 feet in length, one runs in a straight line to the bats 2 in a cool space, the other has to go through the engine room and it's temps, to bats 1, but also has to make a couple or three 90 degree turns. Will in fact effect the charge and load in and out of each bank, and cause cell balance issues.

Now lets say we are doing this scenario with the forward windlass/thruster bats which have loads separate of the house loads at the other bats...

Well you get my point.

Lloyd

[Noname]

Are you talking about a shore power charger source or your alternator?

[jannpage]

Seem to me that the best solution is to add another master switch. I have done that on one of my boats. That way I can keep all banks isolated from each other and use or charge any bank I chose.

[FlyingCloud1937]

Originally Posted by Seaduction

Are you talking about a shore power charger source or your alternator?

It doesn't matter the charge source, to properly charge, the charger needs to sense the bank its charging. It should be a smart charger, with bulk, absorption, and float to maintain the bat at optimum health, so as to achieve the designed life.

Lloyd

[FlyingCloud1937]

Originally Posted by jannpage

Seem to me that the best solution is to add another master switch. I have done that on one of my boats. That way I can keep all banks isolated from each other and use or charge any bank I chose.

That works as long as the charger is sensing the bank its charging at the time, and is allowed to bring the bats through the full charge regime.

One thing to remember each battery bank determines it 's time in absorption, so that can be an issue.

I have seen many installs where the absorption period is left in the factory default, no matter the needs of the bank. Some banks need a longer absorption period and some shorter, it all depends on the specific bank.

To short of time in absorption leads to chronic undercharging, and to long leads to chronic overcharging.

Lloyd

[FlyingCloud1937]

Least I for got...they should all be temp compensated.

Lloyd

[cal40john]

Didn't think this is where your original post was going. To me you're making the case that if you're stuck in this scenario that you shouldn't use a smart charger and put up with the extra time charging your batteries in a constant voltage system. I disagree with your statement that if you don't have a smart charger you're killing your batteries. Sure you're getting the batteries charged faster, but unless you were close to getting the batteries charged under your old charging system it's unlikely you're going to completely charge the batteries with a smart charger.

Or you could go the echo charge route.

John

Originally Posted by FlyingCloud1937

Sorry all, For starting this topic, and not staying to participate, had to run to a job.

First lets talk about batteries. Most bats don't die of old age. Most bats are murdered long before their design useful life.

Anyone that maintains a battery bank, is a "BANK MANAGER"

But to be a Professional Bank Manger, you have to manage the bank right.

Number one cause of premature death is Sulfation, caused by chronic undercharging. Next cause is chronic overcharging, aka positive grid plate corrosion.

A battery can suffer from sulfation in one cell of a multi-cell battery, as well as suffer from one cell being overcharged, while all other cells appear to be normal.

Battery banks built as series, parallel and or series/parallel can also suffer single cell, as well as individual battery sulfation/corrosion. It's called cell balance, that's why we use a hydrometer to measure the health of a battery.

To proper charge a battery/bank you have to charge proper, which means the charge has to sense the battery it's charging, then apply the proper charge regime to the bank.

That means a proper controlled bulk charge, then a controlled absorption charge with proper votage, current and time, ending in float stage...if the battery remains out of service.

Lets take one example to which I'm talking about, we have battery bank 1 servicing the house loads, and battery bank 2 serving the starter loads. Typically these are two different types of batteries, as well as 2 different sizes, the house bank being heavily used 50% SOC, while the start bank is lightly used 95% SOC.

Both banks are isolated from each other, as they should be. You only have one charge source, and somebody convinces you to install one of the fancy new combiner relay/solenoids. It's job is to combine the banks when the bank with the charger reaches above a certain voltage say 13.2.

What do you think is going to happen....yes, the charger when turned on sensing the house bank is going to go into bulk charge mode as it should. Once the house bank reaches 13.3 volts, it's going to parallel the much smaller bank that already is at 95% SOC, and overcharge it, until at some point the charger thinks that the house bank is charged.

But really happens in time, is it confuses the charger into thinking that the house bank is already at absorption when its not, cut back on the bulk, and time out on the absorption phase and leave the house bank under charged, while it overcharged the start bank.

This is one issue I find on a regular basis.

Lloyd

[Noname]

I'm not sure I understand your question. There are shorepower chargers that will do 3 banks while monitoring each ones state of charge and applying appropriate voltage. I just installed a promariner 1240i to maintain the start battery and house bank independently. The 2 banks are not parallel but they can be paralled via a second bat switch that I installed. If I am on alternator power, the start bat needs very little charging, so I can divert the alternators output into the house bank. One bad cell in a bank of 3 batteries can cause havoc unless the bats are monitored separately. Good Luck. Its a condition we all deal with at some point. Fortunately, today there are forums like this nowadays that help us all.