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Discussion Starter · #1 ·
I've built a few Li-ion 14.8v battery packs now and I am very happy with them. My question is why do I have two seperate leads coming from my packs "one for charging and the other for balancing" and the same packs for sale on battery websites only have the single lead. I built my packs to their specs with the NON-Equilibrium PCB and poly switch. Do I even need the seperate leads or should I build it like they do??? Maybe I'm just confused about what the PCB does. Thanks.
 

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The packs on Batteryspace and all battery simply rely on the PCB for over/under voltage protection. That's a measurement of the first cell to go over or under voltage, not the pack voltage, so if there is a weak cell in the pack it will always be the first to be cut off via the PCB and will get weaker and weaker over time and the pack will become out of balance, with each charge/discharge cycle it will get worse.

I build my own with balance leads and a poly switch and so far so good after over a years use.

I would stick with what you are doing as you are happy with your packs and have a balance charger.

The new balancing PCBs look interesting but are so expensive for one in each battery pack, makes a balance charger look like great value.
 

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bncrshr77 said:
I've built a few Li-ion 14.8v battery packs now and I am very happy with them. My question is why do I have two seperate leads coming from my packs "one for charging and the other for balancing" and the same packs for sale on battery websites only have the single lead. I built my packs to their specs with the NON-Equilibrium PCB and poly switch. Do I even need the seperate leads or should I build it like they do??? Maybe I'm just confused about what the PCB does. Thanks.
Do you really mean one set of leads for charging and one set for discharge? Some of the battery space protection PCBs are setup that way. They have separate discharge and charge connections. I reverse engineered one of those PCBs and decided I could eliminate one set of leads as long as I wasn't discharging at a really high rate. The protection PCBs have back to back FETs for controlling charge and discharge. One set of leads was for the connection through both FETs and the other bypassed one of the FETs. That let them use less powerful FETs and still support high currents. Problem is it's been a while I can't remember which order the FETs where in and which lead could be eliminated. What part number is your protection PCB? And is there any chance you can scan and post a picture of the little instruction sheet.

They tend to use PCB-S4A5-GS in most of their pre-built packs. That PCB has a single set of leads for charge and discharge.
 

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Discussion Starter · #5 · (Edited)
Ok, the PCB I used is PCB-S4A8S-GS from batteryspace. I just looked at the PCB-S4A5-GS and it does not have the balancing function either. This is where I'm looking. I would like to get away from the balancing lead if possible so I have less "junk" hanging on my battery. I use a hyperion charger so maybe I have to use the balance lead?? The site I'm looking at is here. http://www.batteryspace.com/pcmforli-coli-mn-nibatterypacks.aspx
 

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The PCB that you have
:http://www.batteryspace.com/pcbfor148vli-ionbatterypack5alimitwithfuelguagesocket.aspx
is only designed to use a single lead for both charging and discharge and as you say it will not balance. It relys on all the cells in the pack being identical in age, capacity etc and as the pack ages will end up "monitering" the weekest cell as the pack gets out of balance.
If you have good cells that mach each other then they may stay in good shape for a long time and lots of packs are made this way.

If you want to ensure that they are always in balance then either fit a balancing PCB or balance leads and use a balance charger.

I think I have found your charger via google and as it has all the bells and whistles then you may as well use them.

A 4 cell balance lead is only tiny anyway and can be done quite neat, this is my 5cell....
 

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Discussion Starter · #7 ·
Ok, now my next question for ya is do I even need to waste the money on a PCB and polyswitch if I'm using the balancing function on my charger? Thanks again for the answers.
 

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Yes, it monitors the discharge and that is important from a safety perspective. It also monitors the charge if you are applying the charge to the main leads. I'm pretty sure the Hyperion charger applies the main charge current through the main lead and only applies small balance current through the balance connector. I think the Hyperion can charge without the balance connector, but I won't swear to that since I don't have one. What happens if you only plug in the main connector?

I have some packs with balance connectors and some without. Over the last couple of years the packs have faired about the same. But all my packs were built with well balanced cells initially. I've opened the ones without balance connectors back up and have checked the balance. They are all as well balanced as the ones with balance connectors. Balancing is a lot more important in applications like RC, where the really high discharge currents put lots of stress on the pack.
 

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Discussion Starter · #9 ·
Makes sense to me. I've hooke my packs up a few times without the balance lead connected and it promptly tells me so and waits for me to hook it up. I guess that since I have the charger with the balance function then I might as well go ahead and use it. Thanks for the input!!
 
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