Is there a difference between wiring methods for AGM deep cycle solar batteries?

  • Thread starter Thread starter eddie90
  • Start date Start date
  • Tags Tags
    Solar Wiring
AI Thread Summary
When wiring AGM deep cycle solar batteries, two methods exist: connecting leads from the same end or from opposite sides of the battery bank. While some believe that connecting from opposite sides promotes more even charging and discharging, others argue that both methods are electrically identical if cable sizes are adequate. The key factor is the gauge of the cables used; if they are too small, voltage differences may arise, leading to uneven performance. Calculating the voltage drop based on cable resistance is crucial, with recommendations to upgrade cable size if the drop exceeds 0.1 volts. Ultimately, ensuring proper cable gauge and connections is essential for optimal battery performance.
eddie90
Messages
48
Reaction score
1
Good day,

When dealing with AGM deep cycle solar batteries, is there a difference between the following two wiring methods?

By the way, I found these pictures online but they describe the two scenarios

Basically the two are almost identical but on one you are grabbing your positive and negative leads from the same end of the battery bank. And the second method, you grab them from opposite sides.

I've seen these two different methods but I was told that it is better to grab the leads from opposite sides as it charges and discharges the batteries more evenly.

Thank you
 

Attachments

  • batterywiring2.jpg
    batterywiring2.jpg
    16.7 KB · Views: 445
  • batterywiring.jpg
    batterywiring.jpg
    11.1 KB · Views: 453
Engineering news on Phys.org
eddie90 said:
Good day,

When dealing with AGM deep cycle solar batteries, is there a difference between the following two wiring methods?

By the way, I found these pictures online but they describe the two scenarios

Basically the two are almost identical but on one you are grabbing your positive and negative leads from the same end of the battery bank. And the second method, you grab them from opposite sides.

I've seen these two different methods but I was told that it is better to grab the leads from opposite sides as it charges and discharges the batteries more evenly.

Thank you
The connectivity looks the same to me. Am I missing something?
 
berkeman said:
The connectivity looks the same to me. Am I missing something?
That's the thing lol to me it seems like its the same thing.

In case you don't exactly get what I am asking, look at this pic and compare it to the first one I uploaded. Would these 2 setups behave the same way?
 

Attachments

  • batterywiring2.jpg
    batterywiring2.jpg
    19.9 KB · Views: 455
eddie90 said:
I've seen these two different methods but I was told that it is better to grab the leads from opposite sides as it charges and discharges the batteries more evenly.

If the cables are big enough, there will be negligable voltage differences between batteries in parallel, and thus negligable unevenness. But if the cables are too small it could make a difference. If there is a problem, use thicker cable, rather than fooling with the connections.

The cable gauge that you use has an ohms/foot (ohms/meter) rating. Calculate the voltage drop over the distance of cable between batteries. If it is more than 0.1 volts, then use a bigger gauge.

Example, 8 gauge copper cable 0.00063 ohms/foot. Say 2 feet between batteries, so 0.0012 ohms total. Say 100 amps current. The voltage drop is 0.12 volts. In that case, I would upgrade to 6 gauge cable.
 
  • Like
Likes CWatters and billy_joule
eddie90 said:
I've seen these two different methods but I was told that it is better to grab the leads from opposite sides as it charges and discharges the batteries more evenly.

That's rubbish.

Your two pictures are electrically identical.
 
  • Like
Likes eddie90 and berkeman
anorlunda said:
If the cables are big enough, there will be negligable voltage differences between batteries in parallel, and thus negligable unevenness. But if the cables are too small it could make a difference. If there is a problem, use thicker cable, rather than fooling with the connections.

The cable gauge that you use has an ohms/foot (ohms/meter) rating. Calculate the voltage drop over the distance of cable between batteries. If it is more than 0.1 volts, then use a bigger gauge.

Example, 8 gauge copper cable 0.00063 ohms/foot. Say 2 feet between batteries, so 0.0012 ohms total. Say 100 amps current. The voltage drop is 0.12 volts. In that case, I would upgrade to 6 gauge cable.

The cable I am using is 2 gauge, see image. I can't figure out the ohms per foot. I found a table online that says its .1593 not sure if that's right
Also all the batteries are right next to each other, all the connections are about 20" long. EDIT**:10"
 

Attachments

  • 20151124_143112.jpg
    20151124_143112.jpg
    50.6 KB · Views: 394
  • 20151124_143422.jpg
    20151124_143422.jpg
    64.4 KB · Views: 407
Last edited:
billy_joule said:
That's rubbish.

Your two pictures are electrically identical.
That is kind of what I thought lol but I need to make sure
 
eddie90 said:
The cable I am using is 2 gauge, see image. I can't figure out the ohms per foot. I found a table online that says its .1593 not sure if that's right
2AWG copper wire is 6289 feet per Ohm, so 1/6289 = .000159 Ohms per foot.

c289_pocket_ref_3rd_ed_inhand.jpg
 
BTW, are you using an inverter to make AC Mains voltage from the 12V battery bank, or is your whole system 12V? :smile:
 
  • #10
My bad, I meant to say 10" long. Its short cables
 
  • #11
berkeman said:
BTW, are you using an inverter to make AC Mains voltage from the 12V battery bank, or is your whole system 12V? :smile:
Yes sir, the whole system stays at 12V. Its powering a mobile surveillance unit. A few IP Cameras, IR sensors, sirens etc
 
  • Like
Likes berkeman
  • #12
billy_joule said:
That's rubbish.

Your two pictures are electrically identical.

That is not a 'schematic' diagram. The connecting leads and contacts have a finite (possibly measurable) resistance. Re-draw the diagram with little Rs instead of ideal connecting wires and the two layouts are different. The point is, how significant are the Rs? If the Rs are significant then the problem can be solved - for free - by changing the connections. With a decent Hall Effect Tong Ammeter, you could, perhaps, measure the difference between the currents from the three banks before making any changes. The characteristics of the PV cells may well compensate, in any case.
 
  • #13
sophiecentaur said:
That is not a 'schematic' diagram. The connecting leads and contacts have a finite (possibly measurable) resistance. Re-draw the diagram with little Rs instead of ideal connecting wires and the two layouts are different. The point is, how significant are the Rs? If the Rs are significant then the problem can be solved - for free - by changing the connections. With a decent Hall Effect Tong Ammeter, you could, perhaps, measure the difference between the currents from the three banks before making any changes. The characteristics of the PV cells may well compensate, in any case.

Absolutely correct and because batteries are dynamic a small imbalance in the charge/discharge rates of each battery on the parallel string will cause the imbalance to increase over time as one or more battery discharges and charges before the others. The very small interconnect wire resistances serve as equalization resistors at high current levels and using the opposite string ends as the string connection point makes the resistance to each battery closer to being equal if all the batteries are at the same SOC.
 
Back
Top