# pack sections getting out of balance



## bigmotherwhale (Apr 15, 2011)

Are you using a bms, could it be malfunctioning?
does one side of the pack get hotter than the other for any reason?
have you looked at the voltages of each cell under charging 

check each cell condition with a load test or cycle test and also let it sit and see if any cells discharge themselves, write out a chart or something to see if you have bad cell 
if it is a bad cell you have the option of replacing it or getting an active bms that can nurse weaker cells(£$) 

checking the connections on the cells cant hurt, it could cause an imbalance easily check the parallel cell connections


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## bwjunkie (Jul 31, 2013)

thank you, I will be looking at individual cells some more, I have swapped some cells from front to back and got no change, meaning they still reacted based on location, meaning the newly swapped cells did the exact same thing that their neighbors did. 

The parrellel bars is something I do need to closely check, this stuff is all pretty new, but some of the bars were hand-crafted from raw copper sheets and some were not.

The tempreture point is a big one, but more confusing because the rear pack should be getting much colder during driving AND charging, so I would think it would be less full after charging? but instead it is more.


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## kennybobby (Aug 10, 2012)

How did you read these voltages--did you measure each cell, or are you just measuring the packs and dividing?

You didn't answer about the BMS question.

It sounds like you might be OVER-CHARGING your packs. The resting open-circuit voltage at 100% SOC is not 3.7 or 3.42.


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## Sunking (Aug 10, 2009)

bwjunkie said:


> My front pack segment of 12 cells (most neg side of total pack) is at 3.42v per cell while the rear are at 3.7 after charging is finished. Then I drive 50 miles and re-charge. and I'm back to 3.42 in front and 3.7 in rear.


This is not possible. I assume you made a typo or brain fart.

The 2/0 AWG is NOT the problem, so quit chasing that ghost. The voltages you are stating are Open Circuit Voltages, or put another way not being Charged or Discharge. No current is flowing, thus no power. Without current, there are no voltage drops on wires to account for. So quit chasing that ghost. 

I have no experience with Winston Cells, just Calb and GBS. But the voltages you are stating cannot be right. A fully 100% charged LFP battery that has been rested will have an OCV = roughly 3.397 to 3.4 volts. So I am good with 3.4 volts per cell after being fully charge. Check.

This is where we part ways. WTF 3.7 volts on a rested LFP cell? So 3.4 vpc is the only correct answer. Lastly you drive 50 miles and are telling us you are still 100% charged up. 

OK giving you the "benefit of a doubt" we can already conclude you:

DO NOT HAVE a BMS equipped with Balance Boards, or something seriously wrong with it if you do have BMS.

If you had Balance Boards, and charged the batteries until all the Balance Boards turn on, and and after current tapers to terminate. All the dang cells had better be the same voltage and come to rest at 3.4 volts.

Most Balance Boards turn on around 3.5 volts, and never higher than 3.6 volts. So where did 3.7 come from? You do have a balance problem that should not exist if you use Balance Boards. No cell should measure 3.7 volts rested OCV. Either that or something is really different about Winston batteries I am not aware of.


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## Overlander23 (Jun 15, 2009)

OP doesn't mention measuring cell voltages after rest. Open circuit voltage fresh off a charge can certainly hit a measured 3.7v, but anything that high will be dropping to rest over time. How long after charge termination are these readings taken?

OP says he drives 50 miles and then *recharges* before measuring an imbalance.

What is the total pack termination charge voltage?


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## bwjunkie (Jul 31, 2013)

I have a mini BMS with 3.8v bleeder modules. as listed http://minibms.mybigcommerce.com/minibms-cell-module/ 
And a Manzanita PFC20 with a manual voltage cutoff setting, which has no numerical figure just a potentiometer adjustment. The pack voltage is 128 nominal (3.2v). I don't know the "charged" pack voltage. somewhere around 142?

I was not talking *resting *voltages, I'm sorry I didn't clarify that in the original post, I forgot that is a common usage. I've been measuring cells after a charge is finished and any bleeders have completed. So those are the numbers I have which are not well rested.

I am measuring individual cells with a meter. 

From what I can tell the mini BMS bleeder circuits will cease to bleed once the cell is down to 3.7. I say this because I've seen cells bleed down to 3.7. Then yes the next day the cell will be *resting *between 3.5 and 3.6. 

I have measured some cells while charging is taking place and near full (meaning the manzanita is in the last cooldown phase or whatever you call it with the purple light), so I have measured that the front pack cells never reach above 3.42, even when the back cells are 3.7. 

I do realize we are talking about the very top end of the voltage curve, so maybe this is too difficult to figure, but I have 12 batteries in front that are all consistently exactly around 3.4 (3.37 resting) with 28 back batteries are all consistently exactly around 3.7 (3.55 resting). 

thanks for the replies

josh


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## kennybobby (Aug 10, 2012)

If it were my car, i would want to know my charger output voltage and current to ensure that overcharging could not occur.

i suspect that the BMS is causing your issue.

Just from reading the minibms manual it indicates that a bypass circuit which can shunt up to 0.75 Amps will activate at the purchased voltage (3.8). Good luck with that.


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## bwjunkie (Jul 31, 2013)

One thing I haven't considered is that I have 3 of these little volt meters always monitoring the front pack in 12v segments: http://www.amazon.com/Voltmeter-2-5..._sim_60_3?ie=UTF8&refRID=0A6H3AW8B0ZRGRA47X0G

It is the left over of what I was doing when I had no BMS, and I still enjoying having them on there. But nothing on the rear pack except the mini BMS. At 5-15ma I didn't think the volt meters could cause this issue in a matter of days (and maybe it is not) but I thought I would mention it. I will run my full cycle test again without the meters connected.

josh


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## Sunking (Aug 10, 2009)

bwjunkie said:


> I was not talking *resting *voltages, I'm sorry I didn't clarify that in the original post, I forgot that is a common usage. I've been measuring cells after a charge is finished and any bleeders have completed. So those are the numbers I have which are not well rested.


Josh rested voltages are the only ones worth mentioning. The voltage under charge or load is meaningless as it tells you nothing.

Bottom line is cells Do Not Get Out of Balance under normal use. If you are charging and see some cells at 3.7 and others at 3.4 tells me the cells at 3.7 volts are lower capacity cells than those at 3.4 volts.


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## Sunking (Aug 10, 2009)

kennybobby said:


> Just from reading the minibms manual it indicates that a bypass circuit which can shunt up to 0.75 Amps will activate at the purchased voltage (3.8). Good luck with that.


Translated means get ready to replace your batteries.


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## bwjunkie (Jul 31, 2013)

Sunking said:


> The voltage under charge or load is meaningless as it tells you nothing.


Isn't that how the charger chooses when to stop? And how the BMS decides when to shunt? I don't see how that classifies at meaningless.

As for this issue, the resting voltages are still higher in the back pack. I have measured in the morning and seen the rear pack at 3.5 and the front at 3.4.


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## racunniff (Jan 14, 2009)

bwjunkie said:


> One thing I haven't considered is that I have 3 of these little volt meters always monitoring the front pack in 12v segments: http://www.amazon.com/Voltmeter-2-5..._sim_60_3?ie=UTF8&refRID=0A6H3AW8B0ZRGRA47X0G
> 
> It is the left over of what I was doing when I had no BMS, and I still enjoying having them on there. But nothing on the rear pack except the mini BMS. At 5-15ma I didn't think the volt meters could cause this issue in a matter of days (and maybe it is not) but I thought I would mention it. I will run my full cycle test again without the meters connected.
> 
> josh


15ma drain over three days is one full Amp-hour: 15mA x 24(h/d) x 3d = 1080mAh = 1.08 Ah - if you left it resting for a long time, you may have drained the front pack much more than the rear, leaving you significantly out-of-balance. And this is progressive if you never put more Ah into the front pack than the rear.

Running the full test cycle without the meters (and after re-balancing the cells) is a good idea.


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## Sunking (Aug 10, 2009)

bwjunkie said:


> Isn't that how the charger chooses when to stop?


No Sir. A charger for LFP batteries is a CC/CV mode. Charge terminates when Charge Current tapers to 1 to 3% of C at a specified voltage. Sounds like you have a 40S pack. With a 40S pack your charger should be set to 140 to 144 volts. Do not know the AH capacity of the pack, but if it were say 100 AH you terminate when the current tapers down to 1 to 3 amps. That only works good if you have a 1S battery. 

If you have passive dumb Balance Boards, you are pretty much screwed IMHO. A passive Vampire board turns on at some voltage of 3.4 to 3.55 volts, and Shunts a fixed amount of current. The Shunt Current depends on the model and can be as low as 150 ma up to 1 or 2 amps. With me so far?

So there you are charging away at say 20 amps and your first Vampire Board Turns on when a cell reaches 3.55 volts and then Shunts 1 amp of current around the battery leaving 19 amps still flowing through the battery over-charging it. This continues until you finally get to the last cell, and its Vampire Board turns off and charging stops. Well now you have 39 cells over charged and one properly fully charged. 

Do you have a problem with that? I would. The proper way to Top Balance is to use Active Balance which means your Vampire Boards need a way to communicate with the Charger to limit current . It also means your Charger, Batteries, and Vampire Boards need to be matched to work together as a unit or team.. Let's say you have a 40S 100 AH battery pack. You want to charge somewhere between C/10 (10 amps) up to C/2 (50 amps). You want your Vampire Boards to Shunt 1 to 3% of C and in this example lets say 1 to 3 amps. What we find is 2 Amp Vampire Boards with a signal link to the Charger. 

So initially when you start charging. the charger is in CC mode and pumping say 20 amps or C/5. Than some time later your first Vampire Board turns on and sends a signal to the Charger. When the Charger receives the signal from the first Vampire Board reduces charge Current to 2 amps. Your Vampire Boards are rated for 2 amps. So when the Vampire Board turns on it Shunts that 2 amps around the battery and it stops charging while the others continue to charge at 2 amps. When the Charger sees all 40 Vampire Boards have turned on, the Charger Shuts Off. The Vampire Boards will Turn Off when the cell voltage drops to 3.4 volts.


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## Sunking (Aug 10, 2009)

bwjunkie said:


> One thing I haven't considered is that I have 3 of these little volt meters always monitoring the front pack in 12v segments: http://www.amazon.com/Voltmeter-2-5..._sim_60_3?ie=UTF8&refRID=0A6H3AW8B0ZRGRA47X0G
> 
> It is the left over of what I was doing when I had no BMS, and I still enjoying having them on there. But nothing on the rear pack except the mini BMS. At 5-15ma I didn't think the volt meters could cause this issue in a matter of days (and maybe it is not) but I thought I would mention it. I will run my full cycle test again without the meters connected.
> 
> josh


Josh get rid of the monitor boards. Those are Parasite Loads. As stated those monitors all use battery power, and unevenly throwing the capacity out of balance. Lithium batteries do not go out of balance like others unless you have a Parasite sucking power.


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## bwjunkie (Jul 31, 2013)

Sunking said:


> When the Charger sees all 40 Vampire Boards have turned on, the Charger Shuts Off. The Vampire Boards will Turn Off when the cell voltage drops to 3.4 volts.


Are you talking about a different BMS?

On page 2 of the MiniBMS manual it says:
"When first cell reaches HVC it will cause BMS to shut down the charger, effectively protecting your battery pack. "

*So it does not wait for all 40 boards.
RIGHT?
*
jfc


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## bwjunkie (Jul 31, 2013)

Sunking said:


> Josh get rid of the monitor boards. Those are Parasite Loads...


Yes the Monitor boards draw <4ma, which I agree is a parasitic load. I ran without a BMS for months, but I do a fair amount of prototyping battery boxes and different configurations with more or less cells, so I prefer a protection mechanism so I don't make a human error and bloat my batteries.

Thanks for the input
josh


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## Sunking (Aug 10, 2009)

bwjunkie said:


> Are you talking about a different BMS?


I am talking about what I think a BMS is, which is radically different from what you have. 



bwjunkie said:


> On page 2 of the MiniBMS manual it says:
> "When first cell reaches HVC it will cause BMS to shut down the charger, effectively protecting your battery pack. "
> 
> *So it does not wait for all 40 boards.
> RIGHT?*


*No Jeff is does not work that way. You have a Dumb Vampire Boards with a NC signal loop. NC = Normally Closed relay contact. What means each board has a very small relay with a single set of contacts. Being NC means under normal operating conditions (Vampire Board Turned Off) the contacts are Close or Short Circuit. So if you use the Loop Detector circuit, you have all the Contacts wired in series and have continuity on your control loop. 

So what you get as soon as the very first Vampire Board turns on, it's NC contact Opens up. If the Vampire Boards are wired in Series, as soon as that First Vampire Board Turns off and you have to wired to control your charger, the Charger Turns OFF, leaving the other 39 cells less than fully charged. charged. Which is great if you are running a BOTTOM BALANCED pack, but worthless if you are Top Balancing because all charging stops as soon as the first cell triggers a Vampire Board. 

Now if you ran an individual pair of wires to each Vampire Board to a 40 channel Logic Controller Very Simple AND Logic, you can run a simple program to give you 2 signals to control the Charger. 

1. When first Vampire Boards turn on, the Controller tells the Charger to reduce current to the value the Vampire Boards can Shunt.. The shunt will bypass charge current around the full cell, and passes it on to lower charged cells. 

2. When last Vampire Board triggers, charge shuts off and all cells are Top Balanced. 

So with 20/20 hind site from reading your replies, and additional information you have supplied I think I can conclude what is going on, and how to fix it. Or at least make it workable for you.

1. It looks to me like with your Parasite Loads ( Monitor) on some cells, and not on others has caused your initial Imbalance Issue that gets worse over time with each charge cycle. 

2. Your passive Vampire Boards are compounding the problem, when it should be fixing the problem with every charge cycle. However, in the manner in which they are being used. defeats the purpose. If you have a series loop controlling the charger. Your charger is turning off when the first cell is fully charged, leaving the other 39 cells short of the mark. 

3. 1 and 2 are compounding problems feeding each other causing the batteries to become more out of Balance with each cycle. 

Corrective Action.

1. Get rid of the cell monitor, or add them to the rest of the cells. If it were me in your shoes. I am getting rid of the sell monitors, or completely change charge and protection strategy with different equipment. Assuming you do not want to spend any more coins, opt to get rid of the monitors. 

2A. You gotta get your pack Balanced, either at the Top or Bottom. You can do Bottom Balance real easy with what you have and basically operate the same way I do. Wire all your batteries in parallel, and them completely discharge them to 2.5 vpc. Rest over night, check, repeat if necessary, Anything with a over night resting voltage of 2.4 to 2.6 is good. For me al it took was one pass. I set the disconnect at 2.4 volts, and rested over night. By morning every cell dead nuts on 2.53 volts at 0 AH capacity. 

Once Bottom Balanced connect the batteries in series and use your Vampire Boards with a single series NC Loop to turn off your charger. As soon as the First cells reaches 100% capacity, the charger shuts off just like you do know. You will have only 1 cell fully charged, and all the others will be something less. Again you will have one lonely cell that gets fully charged and as a result a slightly higher voltage than all the others when charged up. Do not be fooled the cells will be perfectly Balanced. No cell voltages will be Balanced, that only happens at the Bottom. What you will have is 40 cells with the exact same capacity in Amp Hours. Only your lowest capacity cell will ever be 100% charged. Example let's say you have 100 AH rated cells. Due to manufacturing variance the actual capacity of each cell varies a bit. Say you lowest is 95 AH, and highest is 105 AH. So when you get the first cell fully charged up, it is the weakest of 95 AH. Well that cell is at 100% SOC capacity, all the other are something slightly less. But every cell is perfectly Balanced with 95 AH capacity. 

2B. Your other option is a Top Balanced system and I assume that is what you want. You might be able to do it with what you have, or you might not. Depends on what your Charger is capable of. If your Charger can limit or lower Charge Current to a value equal to or less than what your Vampire Board Shunt Current rating are, you can use what you got. Wire the Signal loop up, and when the first Vampire Board turns off signals the Charger to reduce Current to say 1 amp if your boards can pass 1 amp or more. Terminate charge when last Vampire Board turns on. Charge voltage would be set to 3.65 vpc or on a 40S 146 volts. When done every cell had better be 3.4 volts rested OCV.*


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## Overlander23 (Jun 15, 2009)

I think a lot of this really depends on what your charger is doing. Certainly the cell monitors will be an imbalance in the system. Over time if there's no compensation, the cells that are drawing additional energy will have a greater and greater deficit. I agree with Sunking that you're probably caught in a vicious cycle, but I think it may have a lot to do with your charger settings.

If a basic charge profile involves doing the bulk of charging at Constant Current (CC) and then switching to Constant Voltage (CV) to finish, a charger set to too high a voltage may never see the CV mode if the BMS is tripping early.

To recap, CC mode dumps max amps into the pack and is used for the bulk of charging. Usually when a set pack voltage is reached, the charger switches to CV mode where it holds the pack at a specific voltage while the current drops. The charge finishes when another milestone is hit, usually the charge current dropping to a percentage of the pack capacity and/or a time limit.

Some chargers have program capabilities with multiple profiles that allow for different behaviors to occur at various voltage/current/time points. But the basic CC/CV program is as described above.

I'll whittle it down to the 3.8v option with the MiniBMS, as that is what MiniBMS recommends for Winston chemistry and is probably what you have. If everything is top balanced, you're looking at a charge voltage cutoff at 152v.

Scenario 1 (Ideal) - If everything is perfectly balanced, the charger starts in CC mode, dumps energy into the pack until the pack voltage hits 152v, and then the charger switches to CV mode, maintaining the pack voltage at 152v while the amps drop to a cutoff point. Everything is perfectly balanced and the shunts on the MiniBMS never activate which means they never max out, and therefore never trigger a charger shutdown. The charger ends the program without any BMS intervention. All cells are balanced at full.

Scenario 2 (Slight imbalance) - Charger starts in CC mode, hits 152v, and switches to CV mode. Cells that were attached to an imbalanced load lag behind others. An imbalanced load could be any number of things; a battery monitor load on only some cells; a weak cell due to manufacturing; a weak cell due to a previous event; a cell located in a more hostile location. The cells that don't lag start to want to edge up beyond 3.8v. The MiniBMS shunts kick in and bleed off excess energy to keep those cells at 3.8v, allowing the lagging cells to catch up. The CV charge current with a slightly imbalanced pack stays low enough for the MiniBMS shunts to shunt excess power. Eventually, the lagging cells come up to 3.8v and the charger shuts down without direct BMS intervention. All cells are balanced at full.

Scenario 3 (Larger imbalance) - Same as scenario 2, except the imbalance is large enough that the MiniBMS shunts can't bleed off the excess power. This would mean the CV charge current is greater than the MiniBMS' shunting capabilities because the undercharged cells require more current to keep charging. To "save the cell" the MiniBMS triggers the charger to shut down. Lagging cells stay under voltaged. The only cells that hit termination voltage are the fullest ones, the ones that triggered the charger shutdown. Pack ends the charge imbalanced.

Scenario 4 - (Imbalance grows) - Once Scenario 3 occurs, it just compounds if the load imbalance is never addressed, only now the charger is never hitting CV mode, cells are never getting their finishing charge. Pack imbalance grows.

Scenario 5 - (Charger end voltage set too high) - This would magnify the effects of an imbalanced pack since the cells would never ever see the CV part of the charge. Scenario 1 stays the same, but the slightest imbalance now triggers a charger shutdown. Scenario 2 is never allowed to occur.

In conclusion, you never want to be in a situation where the MiniBMS is shutting down the charger. It means the charge current is too high, either because the endpoint charge voltage is too high or the pack is imbalanced to a such an extent that the shunts on the MiniBMS can't handle it.

The MiniBMS is really meant to start with a perfectly balanced pack and then compensate for some drift, but only if the charging parameters are properly configured. The MiniBMS might be able to compensate for the parasitic losses from the battery monitors, but only if allowed to do their job. Setting a charge voltage too high results in too much current for the MiniBMS to bleed off, which essentially bypasses the balance part of MiniBMS.


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## Sunking (Aug 10, 2009)

Just looked your maximum shunt current is .75 amps, and fuses/open at 1 amp. I also agree with the last reply if the charger is working properly using a very simple 1-Stage charger of CC/CV and terminate charge when tapers to .03C, NONE of the Balance Boards should ever trigger assuming the batteries properly Top Balanced to begin with. If the pack capacity was 100 AH, then the charger should turn OFF as soon as charge current tapers to 3 to 4 amps. If one should trigger, it WILL BE overcharged to some extent. 

With a limited BMS functions of Mini or Passive Bleeder Boards is it works under the pretext the cells are properly balanced to begin with, and can only make small drift corrections that occur with normal use. They do not have the capability to make any significant correction in a timely manner. If you go more than 2 days between charge cycles, those parasitic loads adds up and beyond what your Mini-BMS can do in a cycle. 

Just my two-cents. End result is you need to manually Re-Balance your pack, and make some modifications like remove parasitic loads.


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## EVfun (Mar 14, 2010)

What if the parasitic load that is causing the slight but growing imbalance *is* the cell boards? Even 1/10th of a milliamp is almost 1 amp hour per year. That would end a functional bottom balance. It will cause notable issues charging with a top balanced pack. I think you would want 2 high voltage set points. A lower one, say 3.45 volts, that turns on the shunt. A higher one, say 3.8 volts, that terminates the charge. Then you would want all the cells to shunt every charge so that they any difference in load caused by the cell boards (or any other reason) does not compound. 

I was using the cell boards from Australia without the signal loop connected. I set the charger so it would barely reach 142 volts (39 cells.) Then, at low current I got all the boards flashing the shunt LED and none would run away. I didn't like taking the cells that high every cycle. Now I am top balanced without the boards and charge to 133.5 volts and hold for 40 minutes. The pack is remaining balanced, with about 0.01 volt more spread after 2 years.


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## Overlander23 (Jun 15, 2009)

In an optimally operating shunting BMS system, the parasitic losses from the BMS boards would be equal and therefore irrelevant. But if the individual board draws are unequal, the amount they draw between charges is small enough for the shunting system to equalize. Of course, the system has to be working correctly for this to happen. There would not be a growing imbalance over longer and longer periods of time.

The point of a shunting BMS is to maintain top balance. The shunt is supposed to maintain a specified cell voltage point (shunting charge away into heat) while lesser filled cells catch up to the shunt voltage.

If you start shunting at 3.45v you'll never reach the upper 3.8v voltage. The reason why a higher (generally higher than 3.55v) shunting voltage is chosen is because those higher voltages are where the CV current is lowest. That's less energy to dissipate through the shunt.

There's an argument to be made for terminating charge at any particular voltage (3.45v, 3.55v, 3.6v, 3.8v, pick your poison) for cell longevity, but the initial shunting current will be greater the lower the voltage chosen.


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## kennybobby (Aug 10, 2012)

Can current be measured in the shunt path while charging?

It seems if you were to activate a shunt circuit with 5 Ohms of resistance (3.8V/.75A) in parallel with the cell terminals (with xxx milli-Ohms internal resistance) that most of the current would take the path of lowest resistance--what limits the current to keep it from charging the cell?

CC/CV charge profile typically has the current taper during CV stage down to cutoff at C/20, so for his 2x60 Ah cells that would be 6 amps at end of taper.

i could understand turning on a shunt with a bleed resistor after charging is completed to bring cells down to a target voltage, but not sure about stopping a high cell from continuing to charge. 

If you hold 3.8V on a cell until the taper is down to 0.75 A will it get over-charged or could it get damaged?


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## bwjunkie (Jul 31, 2013)

kennybobby said:


> i could understand turning on a shunt with a bleed resistor after charging is completed to bring cells down to a target voltage, but not sure about stopping a high cell from continuing to charge.


Its true the shunt itself cannot stop overcharging. After shuting starts the minor .75a equalization process, if charging continues to push the already shunting cell past 3.8v it sends a message to the brain to abruptly shut down charging. The abrupt shut down is not normal. in a healthy system this "never happens" because all cells climb the final stage together and the charger tapers before any cell reaches 3.8.

I'm starting to see how top balance is not as "perfect" as I once thought, because the top curve is a little inconsistent, but I still like the safety shut off to take place at the top because I am not there, and happening in the middle of the night. The over-Discharge scenario would exist while driving, so at least I am there to view whatever information I've made available for myself.

josh


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## Sunking (Aug 10, 2009)

kennybobby said:


> It seems if you were to activate a shunt circuit with 5 Ohms of resistance (3.8V/.75A) in parallel with the cell terminals (with xxx milli-Ohms internal resistance) that most of the current would take the path of lowest resistance--what limits the current to keep it from charging the cell?


You are assuming a battery is a passive resistor and it is not. 

A bypass shunt is nothing more than a resistor in parallel with a battery using a current regulator to limit shunt current to some specific value, it will not stop any excess charge current through the cell. It will only shunt up to its maximum rating. Anything above that is still flowing through the cell. The only possible way to make it work like you think is as soon as the first Vampire Board Turns On, you have to signal the Charger to limit current to the value of the Shunt. 

If your charge is pumping 20 amps and the first Balance Board turns on and shunts .75 amps around a cell, you still have 19.25 amps flowing through the cell and over charging the battery. 

I see a lot of people here referring to CC/CV as some magic power supply, when in fact is nothing more than a fixed Float Voltage power supply with Current Limit. You can build one with about 5 electrical components and for of them are nothing more than resistors, and a simple 3-pin regulator. 

Balance Boards are not capable of balancing an out of balance pack in a timely manner. They can only keep already Balanced Pack in Balance. That is the flaw in the strategy.


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## bwjunkie (Jul 31, 2013)

In the case of Ewert Orion (which I also own but am not currently using) the balance boards are inside the brain, and it *can *balance an "out of balance" pack by turning down the current of the charger via Canbus messages, then turning the current back up (to 1 amp or 5 amps etc) after the 5watt shunts do some work. Could take all night or several days but it is designed to top balance your pack without user intervention. 

I stopped using it because of wiring routing issues so I don't have much first hand experience on how well it performs this balance job.

josh


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## Sunking (Aug 10, 2009)

bwjunkie said:


> In the case of Ewert Orion (which I also own but am not currently using) the balance boards are inside the brain, and it *can *balance an "out of balance" pack by turning down the current of the charger via Canbus messages, then turning the current back up (to 1 amp or 5 amps etc) after the 5watt shunts do some work. Could take all night or several days but it is designed to top balance your pack without user intervention.


I have an Orion Jr, and and use it as a cell monitor and gas gauge. Makes no difference if it is the Jr or the Standard model they both Shunt 150 ma and that is it. Orion specifically states it cannot be used to Balance an Out of Balance pack. It can only keep a Top Balanced Pack in Balance. 

Yes it can send a signal to a charger to tell the Charger to limit current to 150 ma. Big fricking deal as just even an imbalance of 1 AH takes 10 hours to correct at 150 ma. Imagine if you had a significant imbalance of say 10 to 15 AH. You are now talking weeks to Balance at 150 ma. So yeah it can balance if you are young enough to see it happen. Us ole farts are not getting any younger and do not have time to watch grass grow. We gotta a Bucket List to work on. 

IMHO the only way to make Vampire Boards capable of really doing any serious Balance act is if they are Smart so they can signal a Charger to adjust current to the Shunt Value and the Shunt would need to be at least 2 to 5 amps to be practical and capable of Balancing a pack in a reasonable amount of time. 

This is one reason I quit Top Balancing and switched to Bottom Balance. Sill have the Orion, and it does control my charger. It turns off the charger when the first cell reaches 90 to 95% SOC. In the event my pack ever gets out of Balance, I will do what anyone should do, connect the cells in parallel and Discharge them to 2.5 volts again. If I were to Top Balance connect in parallel, set the charger to 3.4 volts and let it charge until current stops.


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## bwjunkie (Jul 31, 2013)

Sunking said:


> . Orion specifically states it cannot be used to Balance an Out of Balance pack. It can only keep a Top Balanced Pack in Balance.


This is what they actually say on page 30:

"The Orion BMS is not designed to do an initial balance on a battery pack that is *more than* about 10-15 amp hours out of balance."

http://www.orionbms.com/manuals/pdf/operational_manual.pdf


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## Sunking (Aug 10, 2009)

bwjunkie said:


> This is what they actually say on page 30:
> 
> "The Orion BMS is not designed to do an initial balance on a battery pack that is *more than* about 10-15 amp hours out of balance."
> 
> http://www.orionbms.com/manuals/pdf/operational_manual.pdf


OK do the math with a .15 amps of charge current. How long to does it take to put 15 amp hours in at .15 amps? Does 100 hours or 4 days sound reasonable to you?  

Now if the Boards can bypass say 3 amps, then 5 hours is doable. But .15 is only for small corrections. Not an initial balance or re-balance. As was stated earlier in a properly operating system Balance Boards do not ever do anything or ever turn on. Having said that if you have an Orion: Why do you have Vampire Boards?


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## bwjunkie (Jul 31, 2013)

"reasonable" is an opinion, and we all know what opinions are like... everybody's got one.

There are times I'd rather wait 4 days than re-wire all my batteries to parallel and then back to series. Just depends on my circumstances.

Back to the solution.

I will remove the three front pack volt meter "monitor boards", and turn my charger on to .5amp, let the front pack catch up, and do another cycle test and report back.

josh


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## Sunking (Aug 10, 2009)

bwjunkie said:


> "reasonable" is an opinion, and we all know what opinions are like... everybody's got one.


 Josh sorry if I offended you, was not my intent. So please accept my apology. I was trying to make sure you are aware of all the options so you can make an informed decision that is right for you.


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## bwjunkie (Jul 31, 2013)

accepted, no worries, I appreciate your thread activity which is certainly better than no activity. 

Josh


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