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Wiring batteries


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Glenn as you already know sure it will still work even if its not ideal.  Its just that way you wont get as equal load and charge balance among all three batteries as if done right......

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

Its YOUR choice Im not here to tell people how to do things lol

 John T

 

 

 

 

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1 hour ago, GlennWest said:

Would it be acceptable to pull from center battery.

Anywhere along a common connection is electrically the same. The difference comes from any resistance from whatever you are using to connect the positive posts together and the negative posts together. The larger the material used for that, the less effect that your connection's location will matter. If you use a heavy busbar rather than battery cables or wire, that difference will be negligible. 

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Glenn, FYI here’s what the Smart Gauge tests results indicated and what THEY had to say about the differences as to how multiple batteries are connected. These are NOT my calculations so if anyone has a disagreement take it up with them not me. THEIR (not mine) results show it indeed makes a significant difference as to load and charge balance versus the method of connection.

 AGAIN sure it still works EITHER way its just that if you want all batteries to share the load and charging the same you may want to at least consider how you wire them…  ITS YOUR CHOICE NONE OF OURS

 SMART GAUGE TEST RESULTS AND THEIR CONCLUSIONS.      

 

 Now in all fairness, many people say "but the difference is negligible, the resistances are so small, so the effect will also be small".

The problem is that in very low resistance circuits (as we have here) huge differences in current can be produced by tiny variations in battery voltage. I'm not going to produce the calculations here because they really are quite horrific. I actually used a PC based simulator to produce these results because it is simply too time consuming to do them by hand.

 METHOD 1

Battery internal resistance = 0.02 Ohms
Interconnecting lead resistance = 0.0015 Ohms per link
Total load on batteries = 100 amps

The bottom battery provides 35.9 amps of this.
The next battery up provides 26.2 amps.
The next battery up provides 20.4 amps.
The top battery provides 17.8 amps.

METHOD 2

After this simple modification, with the same 100 amp load....

The bottom battery provides 26.7 amps of this.
The next battery up provides 23.2 amps.
The next battery up provides 23.2 amps.
The top battery provides 26.7 amps.

METHODS 3 AND 4 (to achieve even better balance with multiple batteries) NOT SHOWN HERE, GO TO THEIR WEBSITE for all test results

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

Best wishes Glenn, you asked the question and I gave an answer, now its up to you….and  either still "works" even if not the best balance........ 

NOTE I support your or anyone's decision to wire however they please. I cant say I have always done things the absolute best  perfect way and you should connect them however its best for YOUR situation be it prefect or almost prefect or questionable lol. Go for it its YOUR money YOUR batteries none of ours......Im only here to help the best i can...  

John T Retired n rusty electrical engineer so no warranty  

Edited by oldjohnt
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Posted (edited)

John I still had a #4 on the battery that difficult to get to. So what I did was hook up negative side with #4 from each battery to shunt. My bms max out at 100 amps each. So total of 300 amps of 48v. Actual voltage is 58v. My positive side is currently daisy chained with 2/0. Hooked up shunt with dual #2/0.  My change back with 3 individual hots to buss bar. I was hooking up my victron smart shunt. Little disappointed in it. Sitting in living room my phone don't connect to it. Have to go to bedroom directly over it to get signal. Move to living room and loose it.

Edited by GlennWest
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Glenn my observations agree with John T.  Small differences multiply over time especially in lithium batteries where there are small differences in  voltage for various SOC.  In your case it seems you have ample battery so maybe a loss of capacity isn't a problem and different wiring may suffice.

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18 minutes ago, Randyretired said:

Glenn my observations agree with John T.  Small differences multiply over time especially in lithium batteries where there are small differences in  voltage for various SOC.  In your case it seems you have ample battery so maybe a loss of capacity isn't a problem and different wiring may suffice.

I just think if I invested such a HUGE amount in multiple Lithium batteries I would want them ALL BALANCED the best possible, even if sure what Glenn proposed will work fine and Im sure a bunch out there (maybe most systems) are wired how he intends or even worse lol

 Best wishes Glenn, Im sure you will have one fine system regardless

 John T  Hey I don't claim to have my system all wired perfect either grrrrrrrr just giving what I consider a good answer

 

Glenn PS to your post above  "John I still had a #4 on the battery that difficult to get to. So what I did was hook up negative side with #4 from each battery to shunt"

MY RESPONSE

 Iffffffffff you have 3 separate cables, preferably all the same length, from EACH battery Negative to your shunt THATS NOT THE SAME AS ALL NEGATIVES DAISY CHAINIED AND YOU TAP IN THE MIDDLE WITH A SINGLE CABLE TO THE SHUNT   That's sounding more like Smart Gauges Methods 3 or 4 which "may" be fine, but Im unsure exactly how you're wired so just take a look at the Smart Gauge website and Im sure you will figure it out............. 

Edited by oldjohnt
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My negative side is no longer daisy chained. removed cables and ran separate #4 to shunt, 3 cables. Positive side is still daisy chained. May change. Came off daisy chained with 2 2/0 cables to buss bar. Positive post easy to get to. at top of batteries.

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8 hours ago, Will B. said:

You should check this attached white paper.  Provided by Avanti Lalwani at Briter Products.  I WILL be re-doing my 4x Battle Borns this way.

Okay, couldn't attach (too big), linked instead.

https://dwo.net/BatteryWiringDoc.pdf

Interesting it doesn't show a 3 battery setup. It is all in pairs. Mine not. 

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10 hours ago, Will B. said:

You should check this attached white paper.  Provided by Avanti Lalwani at Briter Products.  I WILL be re-doing my 4x Battle Borns this way.

Will B Thanks for sharing that information. You posted   BatteryWiringDoc.pdf (dwo.net)

Agrees with the information I posted:                               http://www.smartgauge.co.uk/batt_con.html  

which states in part: 

"Now in all fairness, many people say "but the difference is negligible, the resistances are so small, so the effect will also be small".

The problem is that in very low resistance circuits (as we have here) huge differences in current can be produced by tiny variations in battery voltage. I'm not going to produce the calculations here because they really are quite horrific. I actually used a PC based simulator to produce these results because it is simply too time consuming to do them by hand."

 

A good thing is how such a simple re connection as used in METHOD 2 so greatly improves battery balance

 

13 hours ago, GlennWest said:

My negative side is no longer daisy chained. removed cables and ran separate #4 to shunt, 3 cables. Positive side is still daisy chained. May change. Came off daisy chained with 2 2/0 cables to buss bar. Positive post easy to get to. at top of batteries.

Hey Glenn, since 1) Your Positive side is easy to get to   2) You ALREADY have the negative side corrected and  3) Its so relative cheap n easy to rewire the Positive side   4) Considering such a huge investment in batteries and being best if ALL expensive batteries are balanced,,,,,,,,,,,,,,, I "recommend" you do as BOTH  articles above agree BUT ITS YOUR CHOICE NONE OF OURS 

Fun thread best wishes let us know how it turns out

John T

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