Dual Bank Charger

[VONCE]

I understand multiple bank chargers, but if your batteries are connected in parallel, wouldn't the charger only "see" them as one battery? If not, how does it differentiate the banks if the batteries are physically connected to each other? I have (two) batteries wired in parallel and I have a dual bank charger - I disconnect them from each other when I charge, though. Is this necessary?

 

[scokill]

 

[Coheeba]

If you are running a 12v system with two 12v batteries i.e.one for sys and one for house; the charger should have separate connections to each battery, separate from the boats internal connections. That way the charger sees each battery separately and gives each battery what it needs as far as amperage. All boat switches would be in the off position when charging.

With a dual bank charger, in effect you have two separate chargers. You could use a single battery charger and have the batteries in parallel and still charge both batteries it would just take longer.

 

[David Analog]

I understand multiple bank chargers, but if your batteries are connected in parallel, wouldn't the charger only "see" them as one battery? If not, how does it differentiate the banks if the batteries are physically connected to each other? I have (two) batteries wired in parallel and I have a dual bank charger - I disconnect them from each other when I charge, though. Is this necessary?

On most any contemporary chargers (but always check with your manufacturer to be safe) you would not need to disconnect one bank at a time. Yes, if the two batteries are fixed in parallel as one, the dual bank charger isolation is circumvented, the batteries are viewed as a single battery, and the charger essentially becomes a single bank in function.
However, there may still be an advantage to having a dual bank charger in this scenario. Even though the overall charger capacity may be adequate for the job, the drivers of each individual bank are often limited to the demand of a single battery. So this would distribute the workload of charging two batteries across all available parts = goodness.

 

[Jgorm]

I charge batteries in parallel all the time. I'm to cheap to justify a dual bank charger. I have them wired so I can flip a switch and have them connected. I charge multiple vehicles at the same time with the same charger.

 

[Coheeba]

The only issue is when you parallel two batteries of different charge the higher voltage battery is in effect charging the lower voltage at high current until they reach the same potential/voltage. If they are reasonably close, tenths of a volt it is not an issue. If the voltages are of a greater difference 1-2 volts the equalization is not good for the battery. Once or twice not a big problem but if you are continually doing this it is damaging to the battery. That's why dual bank chargers or good because they treat each battery separately and provide what the battery needs at the correct amperage. This is the issue with the DVSR. One other note batteries of (different chemistry should never be mixed) /design/age should not be mixed.

This is a great site if you want to learn more (a lot) about batteries. http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

 

[VONCE]

So my main concern here is over charging. Let me explain/ask/confuse...

@David Analog - You said "the two batteries are fixed in parallel as one, the dual bank charger isolation is circumvented, the batteries are viewed as a single battery, and the charger essentially becomes a single bank in function." I understand this, and I agree. Therefore, when the dual bank charger is hooked up - one set of cables to each battery - the charger kicks on both banks for both batteries. But since they are connected in parallel, everything is getting distributed equally. Here's where I have the questions: So if one was 3/4 charged, and the other was fully charged, the charger (at least one bank) will still be putting out charging juice. But again, due to the parallel connection, it's getting distributed to both, and the one that is fully charged is now getting overcharged, right?

@Coheeba thanks for the link and the additional info.

 

[Coheeba]

So my main concern here is over charging. Let me explain/ask/confuse...

@David Analog - You said "the two batteries are fixed in parallel as one, the dual bank charger isolation is circumvented, the batteries are viewed as a single battery, and the charger essentially becomes a single bank in function." I understand this, and I agree. Therefore, when the dual bank charger is hooked up - one set of cables to each battery - the charger kicks on both banks for both batteries. But since they are connected in parallel, everything is getting distributed equally. Here's where I have the questions: So if one was 3/4 charged, and the other was fully charged, the charger (at least one bank) will still be putting out charging juice. But again, due to the parallel connection, it's getting distributed to both, and the one that is fully charged is now getting overcharged, right?

@Coheeba thanks for the link and the additional info.

Your welcome.
If the two batteries are in parallel the voltage will never be different (they are in effect one battery) and will charge/discharge at the same rate, unless you have an isolation switch (Emergency parallel).
If you have two separate batteries with different voltages and you wanted to parallel them, I would charge them individually prior to hooking them in parallel.

 

[VONCE]

Hm yeah I guess I never thought of it that way. But that makes complete sense - when they are paralleled, they eventually equalize and have the same charge/voltage. I get it now. Guess I was over-thinking things. Story of my life.

 

[David Analog]

So my main concern here is over charging. Let me explain/ask/confuse...

@David Analog - You said "the two batteries are fixed in parallel as one, the dual bank charger isolation is circumvented, the batteries are viewed as a single battery, and the charger essentially becomes a single bank in function." I understand this, and I agree. Therefore, when the dual bank charger is hooked up - one set of cables to each battery - the charger kicks on both banks for both batteries. But since they are connected in parallel, everything is getting distributed equally. Here's where I have the questions: So if one was 3/4 charged, and the other was fully charged, the charger (at least one bank) will still be putting out charging juice. But again, due to the parallel connection, it's getting distributed to both, and the one that is fully charged is now getting overcharged, right?

So using two identical batteries on the same bank is very common when additional amp/hour capacity is required....whether a towboat or tournament fishing boat....whether series or in parallel. When they are discharged and recharged the same this is completely permissible. As mentioned above, the two identical batteries essentially behave as one just as independent cells behave as one battery.
There is a very small chance of one battery with one bad cell taking out the other battery due to charging inequities. But normally batteries are replaced before this becomes a serious concern. It then becomes a good idea to separate and isolate paralleled batteries once after the season and once before the season to measure a) their full state of charge, and b) their state of charge after a day of rest in isolation. If you had six batteries in parallel you might do this once every several months, in other words, the frequency of isolated testing would be commensurate with the size of the bank, cost of the bank replacement, and the calculated risk. But with just two batteries in parallel an early problem and inequity is very unlikely.
Charging independent banks is another matter, and paralleled shore charging should be avoided. Is it the end of the world? Not exactly, but it's not good. Consider that your boat charges two banks in parallel when running. Unfortunately you lost perfection the moment one charging system is connected to two battery banks.