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Good Chinese BMS review
#21
(03-07-2019, 06:30 PM)Ebarnett Wrote: Thanks Sean, I've see some other posts recommending 4.0 as the max charge voltage to help with battery life.

SOC vs voltage is not a linear function.
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#22
(03-07-2019, 05:21 PM)Ebarnett Wrote: I hate to ask a stupid question but I'm going to.  Ajw22, you mention charging to only 90% of cells max voltage.  On a battery with a Standard charge of .5C of 1500ma and 4.2v wouldn't the max charge voltage need to be .9 x 4.2 = 3.78v per cell.  How did you come up with 4.05v.  That comes to about 98% not 90%.  Please show me where my math is incorrect.

Thanks.


It's not really based on maths.  What one can do is to look at a charge or discharge graph for that chemistry like this one:
https://learn.adafruit.com/assets/979
and look up the Voltage vs DischargeCapacity at your desired C rating.
Temperature, battery model, internal resistance (esp with older cells) all throw this off, so you should expect an accuracy of at best +/- 5%.  

Just to correct your _math_: you need to consider that the usable voltage range is 4.2V ~ 3.0V .  
So the calculation should be 3.0V + (4.2V-3.0V)x90% = 4.08V
But as Cherry67 state above, this would be a very poor approximation because "SOC vs voltage is not a linear function."
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#23
Excellent thanks.
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#24
This china bms together with victron multigrid does it all. Multigrid does cc/cv and can also control Eltek flatpack2 chargers via can bus in order to increase charging current. Therefore bms does not need to control charging process...
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#25
Yes it does. The Victron does not know about individual cell voltages. It only knows about total voltage.
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#26
(03-16-2019, 07:53 AM)Charly144 Wrote: Multigrid does cc/cv and can also control Eltek flatpack2 chargers via can bus in order to increase charging current.

How ?

Can it request a lower charge rate when cells are in bypass ?
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#27
Yes, multigrid lowers amperage when defined voltage is reached. As well for itself and the flatpack2...
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#28
(03-16-2019, 01:30 PM)Charly144 Wrote: Yes, multigrid lowers amperage when defined voltage is reached. As well for itself and the flatpack2...

Charge current will naturally taper towards terminal voltage - could you explain how the Multi talks to the Eltek via CAN please ?
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#29
I have no details on that but victron confirms integration with flatpack2...
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#30
(03-16-2019, 02:47 PM)Charly144 Wrote: I have no details on that but victron confirms integration with flatpack2...

Could you provide a link please - specifically the CAN control.
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