# Calb cells in series max charge voltage



## onegreenev (May 18, 2012)

No. 3.5 volts should be for everyone including those using BMS systems. Its not 100% full but during the charge that voltage is in the upper curve of the charge cycle. From there to 3.65 volts there is very very little in the way of usable AH's that is is considered pretty much moot and does not need to be used. You can use if you like 3.65 volts and still be fine. With my fast charging setup I limit my charge to 3.5 volts because at high currents that charge voltage jumps pretty high.


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## Ziggythewiz (May 16, 2010)

Where'd you get those numbers?

3.38 is the max resting voltage. 3.65 is the specified charging voltage for finishing a CC-CV charge from C/20 or higher.

3.5 would be a safer voltage than 3.6 for a string of cells simply because they won't all be at exactly 3.5, some are higher some are lower and you don't want them going too far past the specified 3.65.


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## dbeluscak (Mar 2, 2013)

Hey guys, 
I was going to post a new thread but noticed the topic of Calib cells tonight. I tried contacting them via email for a price quote and got no response. It's been almost a week. Do they not sell to the DIY crowd? It seems like the best batteries are limited sale to the OEMs...

Thanks


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## Ziggythewiz (May 16, 2010)

Sure they do. Who are you contacting? Keegan at calibpower is usually pretty responsive. I get my cells from him, but through Don Blazer for better rates.


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## onegreenev (May 18, 2012)

Ziggythewiz said:


> Where'd you get those numbers?



3.65 was at one point a safe charge point and it still holds true. But yes, 3.5 anymore is the better choice as I stated. I still use 3.65 for my cells and all my cells always rest at 3.35 volts. Some folks actually see 3.4 volts. 

Where do you get 3.38 as the MAX resting voltage? 




> 3.5 would be a safer voltage than 3.6 for a string of cells simply because they won't all be at exactly 3.5, some are higher some are lower and you don't want them going too far past the specified 3.65.


Hopefully you won't have any that go above 3.7. If you charge to 3.5 you should not have any over 3.7. If you do you might consider replacing or adding into the pack another cell to take up the slack. 

I do recommend 3.55 as a good end voltage.


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## Ziggythewiz (May 16, 2010)

onegreenev said:


> Where do you get 3.38 as the MAX resting voltage?


CALB, Jark R went into the chemistry behind it, many others. Most people just round to 3.4 though. Different flavors may tweak that up or down.


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## onegreenev (May 18, 2012)

I see. Well then 3.55 volts for the final it will be or less. Mine still settle at 3.35 so mine are good.


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## vmrod (Jul 2, 2010)

onegreenev said:


> Hopefully you won't have any that go above 3.7. If you charge to 3.5 you should not have any over 3.7. If you do you might consider replacing or adding into the pack another cell to take up the slack.
> 
> I do recommend 3.55 as a good end voltage.


I have a Manz.Micro PFC-30. It is voltage programmable, so I will not need to add cells for safer charging purposes.

My Lithiumate Lite should start balancing over 3.4V (I think that is what is recommended, but I could change it to whatever). It will also limit the voltage on the cells to 3.6V (again, I think but it is programmable).

The charger will cutoff when a normal charge is complete, or the BMS will turn it off during a fault of any kind.

So, considering the protection and the proper total charging voltage, I guess 3.6V is safe for me, and that 3.5V is for cells in series when there is no protection.

FYI. Although I cannot flip to the specs page, I believe I saw the voltage data on the Calb cell cutsheet.


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## Elithion (Oct 6, 2009)

vmrod said:


> Individual cells charge to 3.6v
> Cells in series 3.5v
> Why?


Don't confuse the terminal voltage with the OCV (Open Circuit Voltage).
Specifically, don't confuse the terminal voltage when you stop charging voltage, with the OCV when the cells are at rest after a full charge.

For single LFP cells, or with LFP cells in series with cell level control (i.e.: a properly connected BMS), the end-of-charge terminal voltage is 3.5 V or above. The higher the final current, the higher that voltage. The higher the 100 % SOC cell resistance, the higher that voltage. For BMS that do IR compensation, that voltage varies from cell to cell.

For cells in series with no cell level control (i.e.: no BMS, or the BMS does not control the charger), then no-BMS-proponents suggest you use a maximum charger voltage that calculates to some lower voltage per cell, so that, on the average, the cells are at that lower voltage at the end of charge. But, in reality, some cells are at an even lower voltage, and others are overcharged. So, when you hear two different numbers for end-of-charge terminal voltage it is because you are following the no-BMS-proponents.

You will not hear different numbers for end-of-charge terminal voltage from your BMS manufacturer because the maximum cell voltage is the same regardless of whether the cell is on its own or part of a series string: in either case, the cell is protected from over-voltage.

Finally, the OCV at rest of a full LFP cell is 3.4 V. That is because, once the charge has stopped for some time, the terminal voltage (which was high due to the charging current)) finally relaxes down to the internal OCV for a LFP cell at 100 % SOC: 3.4 V.



vmrod said:


> Is the lower voltage number (for cells in series) for the guys that don't use a balancing BMS and use pack voltage to indicate a completed charge?


The point is not if the BMS is balancing or not. The point is whether there is a BMS that controls the charger based on cell level voltage, or not.


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## vmrod (Jul 2, 2010)

I know the difference between OCV and battery terminal voltage. 
I also think it doesnt make a difference, if rhe cells are in series or not. 

I need to dig up that document and post it, so you guys can see where my question comes from.


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## Ziggythewiz (May 16, 2010)

If the cells are identical, it doesn't matter that they're in series. But they're not, so it's good to have a bit of a buffer. How big that buffer should be depends on how close the cells are.


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## Elithion (Oct 6, 2009)

Ziggythewiz said:


> it's good to have a bit of a buffer


Again, that's not applicable with a BMS that controls the charger based on cell-level voltages.


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## vmrod (Jul 2, 2010)

I found that link to the Calb specs that differentiates charging voltage.

http://blog.evtv.me/store/proddetail.php?prod=ca100fi

...just to prove I wasn't dreaming. (at least this time)


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## Elithion (Oct 6, 2009)

vmrod said:


> I found that link to the Calb specs that differentiates charging voltage.
> 
> http://blog.evtv.me/store/proddetail.php?prod=ca100fi
> 
> ...just to prove I wasn't dreaming. (at least this time)



Once again, that's not applicable with a BMS that controls the charger based on cell-level voltages.


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## onegreenev (May 18, 2012)

vmrod said:


> I found that link to the Calb specs that differentiates charging voltage.
> 
> http://blog.evtv.me/store/proddetail.php?prod=ca100fi
> 
> ...just to prove I wasn't dreaming. (at least this time)


3.6 volts is from CALB. 3.5 is from Jack Rickard's recommendation. The voltage stated is charge voltage and not static at rest after charge voltage. 

You don't want your resting voltage at 3.6 or 3.5 volts.


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## EVfun (Mar 14, 2010)

If you wait 12 hours after the charge finishes you don't want any cells over 3.4 volts.


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## ElectriCar (Jun 15, 2008)

I've found I don't need a BMS therefore I don't use one and because of that if I tried to charge to 3.6, even 3.5 I'd begin to boil cells. Even when very well balanced over time due to their minute variances in internal resistance I suppose, they get out of balance a bit. If you'll read my upgrade thread you'll see what I've learned. That may help you. 

So what I do is charge to around 3.43 vpc or so. That is a safe point I've found where all the cells are for all intents and purposes, full. That of course reflects the use on a Zivan NG5 charger and their lithium program which tapers the current to nearly nothing and eventually stops, holding the voltage for a time before shutting down. 

So long as you have a charger capable of doing that, they will be charged. You'll see in my article that trying to raise the voltage to 3.5 or so will only add maybe 100 watts or so to a 32kw pack, which to me isn't worth the risk of boiling electrolyte and shortening cell life.

In time when I've got many many miles on my pack, I may find the need for a BMS but at this time, no thus no cell-level circuit boards to short and ruin a $200 battery.


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