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Old 19-08-2019, 09:46   #1
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How To Charge A Two Battery Bank

Hey all,


Need a little help. I have two AGM batteries currently wired incorrectly (previous owner). I don't have a charger currently and my solar panels aren't sufficient.


I intend to rewire per Method 2 cited here: SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank


As a stop gap, I got a portable charger. Which battery terminals should I attach the charger to? The posts that connect to the breaker panel/neg bus? Or do I need to charge each battery individually?


Thanks!
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Old 19-08-2019, 09:59   #2
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Re: How To Charge A Two Battery Bank

After you hook the batteries in parallel per method two, all you have to do is hook your charging source to one negative and one positive post.

Probably at either end would be best like method two mentions

I can charge my two 12 volt batteries which are in parallel with just my 65 watt panel while at the marina with nothing running
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Old 19-08-2019, 10:16   #3
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Re: How To Charge A Two Battery Bank

The quick response is much appreciated!
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Old 19-08-2019, 13:38   #4
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Re: How To Charge A Two Battery Bank

The charge sources and load leads should all be attached to the same two posts, using buss bars or distribution posts, boxes etc to minimize stacking at the actual posts, say 2-3 ring terminals max.

A fuse and maybe isolation switch should be closest, except for non-power monitor wires e.g. voltage sensing wires, SoC meter leads, etc

If any charge sources don't use separate voltage sensing wires, then their output leads should be as direct as possible.
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Old 20-08-2019, 07:23   #5
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Re: How To Charge A Two Battery Bank

Thx john! Not sure I'm completely following you. I only use solar for charging at this point. I'm assuming a charging bus would receive the positive wire from multiple charging sources before sending the voltage to the batteries via a single wire? In my case is that necessary given only one charging source?
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Old 20-08-2019, 08:25   #6
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Re: How To Charge A Two Battery Bank

The SC must get as accurate a reading of voltage **at the battery posts** as possible.

Indirect connections prevent that.

Better charge sources use a pair of V sensing wires separate from the power output, 4-wire charging

the sensors go direct to posts, power can then route through buss, fuse etc, but if 2-wire only best to put on the posts, every device adds V drop.
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Old 20-08-2019, 13:14   #7
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Re: How To Charge A Two Battery Bank

"Which battery terminals should I attach the charger to?".
The reason for the different connections shown is first to minimize the total voltage drop due to the wire and bus bar resistances and second to minimize the voltage differences as seen by each battery. The short answer is if the wire and bus bar are reasonably properly sized and the charger is not very high Amperage, for a temporary application it will make no practical difference. If the temporary charger is near the permanent charger capacity then I would suggest connecting it to as close as reasonably possible to the center battery.
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Old 20-08-2019, 20:07   #8
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Re: How To Charge A Two Battery Bank

Quote:
Originally Posted by lvictorlucas View Post
"Which battery terminals should I attach the charger to?".
The reason for the different connections shown is first to minimize the total voltage drop due to the wire and bus bar resistances and second to minimize the voltage differences as seen by each battery. The short answer is if the wire and bus bar are reasonably properly sized and the charger is not very high Amperage, for a temporary application it will make no practical difference. If the temporary charger is near the permanent charger capacity then I would suggest connecting it to as close as reasonably possible to the center battery.
Guys, appreciate the answers but what questions are you answering?? Center battery? I only have two. Let me know which one is the center one. Lol


John, I was asking about the charging bus you brought up. I'm assuming "SC" = solar charger? I only have a suitcase panel. The mppt controller is at the panel.
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Old 20-08-2019, 20:12   #9
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Re: How To Charge A Two Battery Bank

The SC should be located as close as possible to the battery.

I gave as complete an answer as I could, perhaps re-frame your question?

If you don't have a charge buss then never mind, my point is direct is better.
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Old 20-08-2019, 22:05   #10
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Re: How To Charge A Two Battery Bank

with 2 batteries and a small portable charger it's not going to make any diff.

you're over thinking it.
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