Charging batteries in Parallel question

[BillyK]

Can someone explain to me how joining two batteries to produce a larger 12 volt bank in parallel can be charged as two separate batteries as shown in the included picture?

doesn't the fact that they are connected turn this into one single battery that is now charged by two outputs?

I'm thinking that in this configuration, you would want to 'equalize' the batteries by disconnecting them from each other to charge independently.

Anyone have an opinion or scientific fact to share about this? i have this setup now on board our sailer, two deep cycles linked for more tank, and a single for emergency starts as needed..

Thanks.

 

[RichH]

I wouldnt do it this way I'd run combiners to each batt. to precisely charge each battery based on its individual 'acceptance'.

In the offered schematic, if each batt isnt at the same acceptance level, one is going to get overcharged and the other is going to be undercharged.

 

[BillyK]

I wouldnt do it this way I'd run combiners to each batt. to precisely charge each battery based on its individual 'acceptance'.

In the offered schematic, if each batt isnt at the same acceptance level, one is going to get overcharged and the other is going to be undercharged.

Thats what i was thinking. i'll need to look into what a combiner is..

 

[RichH]

Combiners: http://www.yandina.com/combInfo.htm

 

[Kettlewell]

If the two batteries are connected as shown in parallel they act and look just like one bigger battery to the charger. It would seem silly to connect both batteries to the charger, but I don't imagine it would make any difference in how well the batteries are charged. If you want to keep the batteries separate for some reason then the two separate charging circuits could be used to charge the two separate batteries. But, per the diagram you have essentially one big battery.

 

[BillyK]

i don't think a combiner is what i need.. that enables you to charge two batteries off of one charging source. What i need is something that separates the two batteries when on a charge.. either that or i just go with the setup i have here.. i don't know that once battery will be overcharged since i'd think the battery that has a lower SOC would accept higher amperage as the internal resistance would be lower than the higher SOC battery.

 

[Kettlewell]

If the batteries are connected in parallel, as shown, they act just like one bigger battery. One battery can't be overcharged and one undercharged--they are essentially one battery.

 

[Winkfish]

Billy, why do you need to separate your batteries when charging? Why do you need to hook up both AC outputs?

 

[BillyK]

Billy, why do you need to separate your batteries when charging? Why do you need to hook up both AC outputs?

i was curious as to the point of the diagram. If its essentially one big battery, then why do they suggest connecting both batteries? i could have gotten a 2 battery charger rather than the 3 battery charger. it's not a big deal since i already have it wired and set. It's more of a curiosity and learning experience now.

 

[Maine Sail]

i was curious as to the point of the diagram. If its essentially one big battery, then why do they suggest connecting both batteries? i could have gotten a 2 battery charger rather than the 3 battery charger. it's not a big deal since i already have it wired and set. It's more of a curiosity and learning experience now.

Perhaps because if you don't connect both charger leads you lose half the chargers output? Some chargers do this.

The ProMariners do it differently and need all outputs "connected", both pos and neg as they sense voltage to determine what type of bank they are connected to voltage wise. these chargers can charge 12V & 24V banks so need the voltage sense at each terminal. By not connecting one output to a battery it can mess up a ProMariner ProSport charger and cause it to not work. Batteries wired in parallel are still being charged as one battery but you have two, or three feeds to keep the internals of the charger happy. You can simply stack both positives & negative leads "across" the bank and get the same result.

Electrically speaking it does not matter one iota if you connect both outputs to one battery in the bank or each output to each battery. If the batteries are in parallel you are charging one battery but BOTH outputs on the ProSport chargers, or all three if a three bank unit, need to be connected.. If you do stack the leads it is best to put the two + leads on the + of one battery and the two - leads on the - of the other battery..

 

[Kettlewell]

Perhaps because if you don't connect both charger leads you lose half the chargers output? Some chargers do this.

OK, that makes sense. I suspect he wants to have two separate banks for some reason and therefore needs to get rid of the battery cables paralleling the two banks, and then have a battery switch like a 1, 2, Both switch that can be used to select one bank or the other. Then the charger leads can just go to each bank and keep each bank topped up based on its needs.

 

[BillyK]

OK, that makes sense. I suspect he wants to have two separate banks for some reason and therefore needs to get rid of the battery cables paralleling the two banks, and then have a battery switch like a 1, 2, Both switch that can be used to select one bank or the other. Then the charger leads can just go to each bank and keep each bank topped up based on its needs.

i have three batteries on board.. two are true deep cycle 105ah batteries in parallel and a third an auxiliary starting battery. The charger i bought was a 3 battery charger. At the time i was ordering it made sense to order a three battery charger. Now it doesn't to me. The charger can send all of its amperage to any of its three leads depending on the SOC of each of the bats and what they'll accept.

so i guess in the end, i could have saved some money and bought a smaller charger that only has two leads and treat my parallel bats as one battery.. but i do like the ability to disconnect the two in the house bank and charge them separately from time to time to make sure they are equalized if that even makes sense. it does in my foggy universe at least..

what got me to open up the thread was to see if there was a reason to do this that some electrical engineer could give.

 

[Kettlewell]

If the two deep-cycle 105 ah batteries are the same vintage and same type it doesn't matter whether or not they are in parallel or separate when you charge them or equalize them. It also doesn't matter that you have two charging leads to the two of them instead of one charging lead. They will only take as much charge as they can accept either way if the charger is the type that delivers as much charge as possible to any one of the leads, up to its max. It is simpler to just leave the two batteries always in parallel and use them as your main bank. I don't see why your wiring diagram you showed in the first post won't work fine for charging both together--it just won't be possible to charge them separately, which I don't see any need to do.

 

[BillyK]

If the two deep-cycle 105 ah batteries are the same vintage and same type it doesn't matter whether or not they are in parallel or separate when you charge them or equalize them. It also doesn't matter that you have two charging leads to the two of them instead of one charging lead. They will only take as much charge as they can accept either way if the charger is the type that delivers as much charge as possible to any one of the leads, up to its max. It is simpler to just leave the two batteries always in parallel and use them as your main bank. I don't see why your wiring diagram you showed in the first post won't work fine for charging both together--it just won't be possible to charge them separately, which I don't see any need to do.

Sounds good.. Thanks for the input.

 

[Joe]

Or....... set up two separate battery banks... with two 1-2-off switches, and let the charger act as an isolator.

 

[Bill Roosa]

Perhaps the two outputs are isolated inside the battery charger. I know that is how mine is. If you take an ohm meter and read across any of the three + red wires to the charger (disconnected of course) you do not get a circuit. That way if you have three banks you do not over ride the design of having three banks (for isolation start, house 1, house 2) and can actually have three separate batteries.
And only 1/3 of the output is available on each output wire.

 

[Andy1237]

I think Bill is correct. Its amps! I think my charger sends like 10 amps to each of the 3 batteries, two of which are wired parallel in Bank A. So rather than 10 amps trickling to one battery, each battery is getting 10 amps. Quicker charge, and if one battery does fail, at least the other one is still getting charged.

 

[Steve Dion]

It depends on your charger. Our newer XC Xantrex charger does NOT split the amps based on the banks. It puts out xx amps to each battery and then cycles off to another bank.

The XC charger also can charge up different battery chemistries from a single charger (up to 3 banks).

 

[Maine Sail]

The ProSport chargers need the outputs connected to work correctly because they are "auto sensing". They can be used to charge both 12V and 24V banks or 36V if it is a three output unit. Without the leads connected the charger can't see a load and its voltage and won't operate. Many 12/24V solar charge controllers also do this "auto sense" and won't turn on if they don't see a voltage or load..

You can use them as a single output charger by stacking the leads ...

 

[BillyK]

The ProSport chargers need the outputs connected to work correctly because they are "auto sensing". They can be used to charge both 12V and 24V banks or 36V if it is a three output unit. Without the leads connected the charger can't see a load and its voltage and won't operate. Many 12/24V solar charge controllers also do this "auto sense" and won't turn on if they don't see a voltage or load..

You can use them as a single output charger by stacking the leads ...

That's what i have, the ProSport 20 with the three battery leads.. at this point, i''m just going to run the leads to each individual battery and be done with it..