new diy lith-ion charger current not decreasing!?!?!? any ideas?

Thread Starter

bigjoncoop

Joined Feb 1, 2019
154
hey my fellow diy'ers..

i've just bought a handful of CC/CV adjustable boost converters in order to charge a bunch of 40v batts for resale. I'm in the middle of testing one out before "deploying" them all and i'm watching the volt/amp meter and the current is basically staying steady even as the voltage is raising!?!?

on all my other cc/cv power supply's the current decreases as the voltage rises.... so far on this one, the battery has increased by 6v but the current is still holding at 2.85a. it actually has increased. i had it set at 2.79-2.80

should I be worried? or just keep and eye on it and see if it starts to fall as the battery is getting almost full?

i dont believe there is any other way of setting the parameters for CC/CV.... and i assume they are all "supposed" to work the same correct?
received_612238079544582.jpeg
thx

PS. I just turned the voltage setting down and the voltage does drop quickly as it approaches full voltage so i think its ok.... just my other cc/cv supply's seem to start dropping current much sooner

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*** IF YOU ARE NEW TO LITHIUM ION BATTERIES AND CHARGING THEM, IF THEY HAVE MULTIPLE CELLS IN SERIES (IE. THE BATTERY IS OVER 4 VOLTS) YOU SHOULD USE A CHARGER OR BMS WITH A BALANCING FEATURE!!! ALSO YOU SHOULD CHARGE AT A "1C" CHARGE RATE TO BE SAFE OR NO HIGHER THEN FACTORY CHARGE SPECIFICATION !!!
AND
*** IF WHILE CHARGING, YOU FEEL THE BATTERY GETTING WARM AT ALL THEN STOP!!! EITHER YOU ARE CHARGING WITH TOO MUCH CURRENT/AMPS OR THE BATTERY IS DEFECTIVE!!! BE SAFE
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Last edited:

KeithWalker

Joined Jul 10, 2017
1,599
I would expect the current to stay the same until the cut-off voltage is reached. If the current decreases with voltage, the current regulator is not doing a very good job.
Regards,
Keith
 

BobTPH

Joined Jun 5, 2013
3,008
You cannot safely charge a multi-cell Li ion battery that way. You need balancing circuitry to ensure that single cells do not overcharge. You are literally playing with fire.

Bob
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
154
I would expect the current to stay the same until the cut-off voltage is reached. If the current decreases with voltage, the current regulator is not doing a very good job.
Regards,
Keith

hey keith,
i fly racing quad copters and on every other lithium ion charger ive used the current drops in proportion to the voltage, consistently the entire charge cycle... not saying that is the correct way, just sayin...



You cannot safely charge a multi-cell Li ion battery that way. You need balancing circuitry to ensure that single cells do not overcharge. You are literally playing with fire.
Bob
Yeah you should normally balance when charging batteries with multiple cells in series... but if you start with a pack with cells that are already balanced its normally fine to charge a few times without balancing as long as your check individual cell voltages from time to time (maybe every 5 charge cycles...) But i do have 3 10s bms's /w balance i am going to implement... in that picture i had just hooked up those cc/cv boost converters to test them before going all in...

---------------------------------------------------------------------------------------------------------------------------------------------------
*** IF YOU ARE NEW TO LITHIUM ION BATTERIES AND CHARGING THEM, IF THEY HAVE MULTIPLE CELLS IN SERIES (IE. THE BATTERY IS OVER 4 VOLTS) YOU SHOULD USE A CHARGER OR BMS WITH A BALANCING FEATURE!!! ALSO YOU SHOULD CHARGE AT A "1C" CHARGE RATE TO BE SAFE OR NO HIGHER THEN FACTORY CHARGE SPECIFICATION !!!
AND
*** IF WHILE CHARGING, YOU FEEL THE BATTERY GETTING WARM AT ALL THEN STOP!!! EITHER YOU ARE CHARGING WITH TOO MUCH CURRENT/AMPS OR THE BATTERY IS DEFECTIVE!!! BE SAFE
-----------------------------------------
 

crutschow

Joined Mar 14, 2008
26,790
every other lithium ion charger ive used the current drops in proportion to the voltage, consistently the entire charge cycle...
They may be designed to do that.
But a normal CC/CV power supply will keep the current essentially constant until the set voltage is reached, at which point it sharply drops.
That's why they are called CC/CV.
 

KeithWalker

Joined Jul 10, 2017
1,599
If the charging current drops during the charge cycle, it will take longer to charge the battery than if the current remains the same. You get what you pay for!
Keith
 

oz93666

Joined Sep 7, 2010
737
"40V" does not give a definite number of cells ....

Makitek "18V" are 2p5s ... 5 in series 4.2x 5 =21V max ...

So first you need to know how many cells are in series ...

The usual way to charge cells is to keep constant current up to 4.1V , then the current trails off as it reaches 4.2 V

So if your "40V" battery is 10 in series , the voltage should only start to reduce at around 41V ... but this is not at all critical , Neither is the max voltage per cell(within reason ) you can safely charge to 4.35 per cell , it will hold more power but greatly reduce the life ...

Charging to a lower voltage will massively extend life ... 3.93 is optimum giving 3000 cycles , compared with 4,2 giving only 400 cycles
 
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