# Sinopoly Technical Data



## Elithion (Oct 6, 2009)

OCV != terminal voltage

When cell manufacturers tell you that the voltage cannot drop below a certain voltage, they are really talking about Open Circuit Voltage. That is, if a cell is loaded and its voltage drops to 1.5 V, and then the load is released and the cell jumps back to 3.3 V, the OCV never went below 2.8 V.

If you know what you're doing, then you can take advantage of that fact.
However, most installation do not have a BMS that is capable of doing IR compensation, and therefore, those installation should use the 2.8 V as a terminal voltage limit, and suffer with low performance in the winter.



Analog BMS: no IR compensation.
Digital BMS: only 4 of 48 BMSs perform it
Also, the minimum voltage that the cell manufacturers tell us is high, because they know we're going to cheat.


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## TEV (Nov 25, 2011)

Elithion said:


> OCV != terminal voltage
> 
> When cell manufacturers tell you that the voltage cannot drop below a certain voltage, they are really talking about Open Circuit Voltage. That is, if a cell is loaded and its voltage drops to 1.5 V, and then the load is released and the cell jumps back to 3.3 V, the OCV never went below 2.8 V.
> 
> ...


Can you please telling me what settings should I use in the Lithiumate Lite for Calb SE100AH to get good performance without damaging the cells ?

Thank You

P.S. EV2012 I apologize for using your thread.


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## Elithion (Oct 6, 2009)

TEV said:


> Can you please telling me what settings should I use in the Lithiumate Lite for Calb SE100AH to get good performance without damaging the cells ?


Click the LiFePO4 button in the GUI. That's it!









If you want to turn-on IR compensation, check the "IR compensation" box in the advanced settings:









For the CALB 100 Ah, enter 1.5 mOhm for the "Cell resistance".

Let us know how it goes.


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## EV2012 (Oct 13, 2012)

Elithion said:


> OCV != terminal voltage
> 
> When cell manufacturers tell you that the voltage cannot drop below a certain voltage, they are really talking about Open Circuit Voltage. That is, if a cell is loaded and its voltage drops to 1.5 V, and then the load is released and the cell jumps back to 3.3 V, the OCV never went below 2.8 V.


Okay, I understand. But the question is, could the cell be damaged, if the voltage drops below 2.8V under load?


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## Elithion (Oct 6, 2009)

EV2012 said:


> could the cell be damaged, if the voltage drops below 2.8V under load?


Could? Yes. 
Would? It depends. 
To answer that question, you would have to do an analysis that takes into consideration a few factors. Or you could use a sophisticated BMS that does that analysis for you, on the fly, and updates it as conditions change.

Cell manufacturers assume (correctly) that most users are not equipped to do that analysis, so the specs specify a relatively high value for the end of charge cell voltage.


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## EV2012 (Oct 13, 2012)

Elithion said:


> Cell manufacturers assume (correctly) that most users are not equipped to do that analysis, so the specs specify a relatively high value for the end of charge cell voltage.


I developed a BMS which reduces the current tremendous if voltage drops below a defined voltage for longer time, e.g. 2.8V for max. 5s. So I can drive the car to the next charging station.

I don´t know what to do now, because Winston says 2.0V to 2.5V is okay.
Sinopoly says minimum voltage must be >= 2.8V.
Is the Sinopoly cell so much worse? Especially in winter?


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## sourcefinder (Dec 17, 2010)

> When cell manufacturers tell you that the voltage cannot drop below a certain voltage, they are really talking about Open Circuit Voltage. That is, if a cell is loaded and its voltage drops to 1.5 V, and then the load is released and the cell jumps back to 3.3 V, the OCV never went below 2.8 V.


I agree. Have seen this at my Winston very often.

I think Sinopoly cells and Winston cells are very similar (as they are fighting at court), but Winston offers on the datasheets curves for up to 5C, Sinopoly only 1C. In the datasheet they also say 3C is ok. 

I think best thing is to set up the capacity at only 80% in the bms, then you have left some power when it is zero. And as long as the cells are aboce 2,8 in idle, it is ok.


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## Elithion (Oct 6, 2009)

EV2012 said:


> Is the Sinopoly cell so much worse?


No. They are effectively the same.



EV2012 said:


> Especially in winter?


Temperature performance of typical prismatic cells:


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## EV2012 (Oct 13, 2012)

I searched for more technical data of the Sinopoly cells. Now I found this specification of the 200Ah cell SP-LFP200AHA. 

This cell is also a LiFeYPo4. I always thought this cell is a pure LiFePo4 cell, because I read this often in the internet.

So I am still wondering, why are the cut off voltages so different to the Winston cell, which is also a LiFeYPo4 cell?

The Winston cell allows a range from min. 2.5V to max. 4.0V
The Sinopoly cell allows a range from min. 2.8V to max. 3.8V (3.7V operating)

If I take the recommended voltage levels from Sinopoly, I have a smaller range available than with the Winston cell. I think the capacity will be more restricted than with Winston cells.

I thought the min./max. voltage levels are related to the chemical and physical condition of the cells ...

I am really confused, because I have to define the LVC and the HVC of my BMS.
If I consider the life time of the cells, I have to reduce the max. voltage range to LVC = 2.85V (stop driving if one cell hits LVC) to HVC = 3.75V (stop charging if one cell hits HVC).

Has anybody the Sinopoly cells in use? What are your recommondations?


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## Elithion (Oct 6, 2009)

2008: Thundersky says 4.25 V
2010: Thundersky says 4.0 V
2010: Sinopoly says 4.0 V
2012: Sinopoly says 3.8 V

All along: A123: 3.6 V

See a trend?

My unconfirmed understanding is that the higher voltage helps certain processes the electrolyte, but it also crosses into an area in which calendar life is reduced.
My sense is therefore that the manufacturers have been slowly decreasing the max voltage specification, as they realize that on the balance you're better off with a lower voltage.

As you already know, there is little charge to be gained above 3.4 V OCV.

The range 3.4 to 3.6 V is perfect to do voltage-based balancing; afterward the charger goes off and the voltage drops to about 3.4 V as balancing completes.


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## EV2012 (Oct 13, 2012)

You are right, they reduced the upper voltage over the years ... obviously they are still in a learning process ... 

I planned to start balancing at 3.65V and to stop charging if one cell reached 3.75V. I think I have to start balacing at 3.6V.

But why are there so big differences between the suppliers at the lower voltage levels? Winston from min. 2.0V and Sinopoly strictly at 2.8V.


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## Elithion (Oct 6, 2009)

EV2012 said:


> why are there so big differences between the suppliers at the lower voltage levels?



Because there is no well defined point along the voltage vs SOC curve where charging should stop
Because they specify only one value for both the voltage where _they_ stop discharging during their cycle testing, and for the voltage where they want _you _to stop discharging
Because there are conflicting effects from picking a low or high value
A high value means that they measure a lower capacity
A low value means that the capacity vs cycles line is steeper (fewer cycles)
 
Because the user in not likely to know the difference between OCV and terminal voltage, and, in any case, is not likely to have the equipment capable of distinguishing the two while in operation
Without such a BMS, discharging must stop when the _terminal _voltage under load drops to the specified voltage
With a BMS that can do IR compensation, discharging must stop when the calculated _OCV _drops to the specified voltage: you can get a bit more charge out of a battery, but you're in an area where the cell is more sensitive to damage
 
Because, regardless of which voltage is specified, you're still a bit away from the drop dead voltage where nasty chemical reactions permanently damage the cell (~ 1.9V)
Because they have to deal with applications that do not use a BMS, and they are trying to reduce the number of times they get unfairly blamed for cells damaged by over-discharge, so they like to raise that minimum voltage



EV2012 said:


> Winston from min. 2.0V and Sinopoly strictly at 2.8V.


You'll note that 2.0 V is under load and at low temperature (when the cell resistance is highest). If you were to turn off the load at that point, you would see the terminal voltage jump back up to 3.3 V OCV.











2.0 V OCV would be crazy: you would be right at the edge of where the bad chemical reactions start occurring.


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## Ziggythewiz (May 16, 2010)

There's no reason to fuss so much over it. There's so little power down that low anyway. Don't take em below 3 vpc resting and 2.5 under load (for normal people).


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## skooler (Mar 26, 2011)

The Winston cells are not as good a quality of the Sinopoly cells from what I have heard.

The voltage difference is probably so Winston can rate the capacities of their cells higher as they are using the knee on either side of the charge curve. 

As an example, that extra capacity by charging the cell to a higher voltage and discharging lower could be the difference between the cell being rated at 180Ah and 200AH.

Its all about tryig to squeeze more cash out of the end user.


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## Siwastaja (Aug 1, 2012)

skooler said:


> The Winston cells are not as good a quality of the Sinopoly cells from what I have heard.


Heard from where?


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## skooler (Mar 26, 2011)

Siwastaja said:


> Heard from where?


Email correspondence with Sinopoly (potentially biased) and also some independent tests, I'll see if that information is releasable.

Basically the spec on Winston has marked time for the last few years whereas the Sinopoly Spec has improved quite significantly.


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## TEV (Nov 25, 2011)

Elithion said:


> If you want to turn-on IR compensation, check the "IR compensation" box in the advanced settings
> 
> For the CALB 100 Ah, enter 1.5 mOhm for the "Cell resistance".
> 
> Let us know how it goes.


I am very please with those settings. The BMS "Warning" buzzer is not complaining any more.

Thank You.


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## electric85 (Apr 10, 2008)

EV2012 said:


> Hello,
> 
> I ordered about 36 Sinopoly 200Ah cells for my ev convertion.
> 
> Thank you for your help!


Where did you order from? I Havent been on this site in a while but am now ordering batteries in the next week or so. I've decided on Sinopoly but wanted to see if there is a competative north american dealer, or if direct through Sinopoly is the way to go.


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## Elithion (Oct 6, 2009)

electric85 said:


> Where did you order [Sinopoly] from?


EVolve Electrics has various sizes of Sinopoly cells in stock. They will sell you also a BMS.


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## Ziggythewiz (May 16, 2010)

Sinopoly used to claim 5000+ cycles at 70% DOD. When did that drop back to 3000?


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## electric85 (Apr 10, 2008)

Elithion said:


> EVolve Electrics has various sizes of Sinopoly cells in stock. They will sell you also a BMS.


yes, where did you order sinopoly from...direct?


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## EV2012 (Oct 13, 2012)

I ordered the cells at ev-power.eu. For me it is important that I don`t have to fight with the customs, because I live in Germany.


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## skooler (Mar 26, 2011)

EV2012 said:


> I ordered the cells at ev-power.eu. For me it is important that I don`t have to fight with the customs, because I live in Germany.


Don't forget that you will need to pay VAT (19% for Germany?)


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## EV2012 (Oct 13, 2012)

skooler said:


> Don't forget that you will need to pay VAT (19% for Germany?)


Yes, you are right, I payed 19% VAT. I have the cells already since a few weeks. But I had no trouble with other fees for the customs and absolutely no problems with transportation issues.


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## EV2012 (Oct 13, 2012)

So, good news for Sinopoly cell owners.
Last week I talked with a real lithium ion cell expert about LiFePo4 cells.
He knows the chemical composition of this cells.
He told me, that this type of cell works down to 2.5V without damage.
With load 2.0V is no Problem. OCV should not fall below 2.5V.
At lower temperature you get a voltage drop on the electrolyt because of a higher restistance of the electrolyt.

This are the values which are already recommended by Winston and also valid for the Sinopoly cells. 
So now I know the voltage levels I have to adjust. The minimum voltage will be 2.5V at 0°C and 2.8V at 50°C. Below this levels for 2 seconds the current consumption will be reduced and the battery has to be charged.
With this adjustment I have no fear to damage the cells.


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