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Adjusting charger's voltage


EUCMania
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11 minutes ago, EUCMania said:

Some people here use Charge Doctor to charge only up to 80% of the capacity to prolong the battery life. The problem is that by doing so, the cell balancing is not triggered, which may damage battery pack. Thus, periodically, one still have to charge to 100% to let cell balancing to work. 

 

 

 

 

Is this true?  I know it's printed in my King Song user guide, but I wasn't sure if it's a legitimate issue or not.  I rarely charge my KS18 to full. 

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14 hours ago, Cranium said:

3) Cutoff current.

wouldn't a current cutoff impede the balancing process? I was in the believe that the charger light turning green only means that the current is below some threshold because the battery voltage has come close to the charger voltage, but that the charger is still operating as before.

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15 minutes ago, Mono said:

wouldn't a current cutoff impede the balancing process? I was in the believe that the charger light turning green only means that the current is below some threshold because the battery voltage has come close to the charger voltage, but that the charger is still operating as before.

I thought he meant that the current doesn't completely cutoff, but goes way down to a trickle charge mode?  So, the battery would charge to a certain point, but no cell would discharge, the charger could be left on all the time, and the battery would stay full, but never discharge.

So I am wondering if anyone has forgotten to unplug the charger for weeks at a time, and if that caused any problems.

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16 minutes ago, Mono said:

wouldn't a current cutoff impede the balancing process? I was in the believe that the charger light turning green only means that the current is below some threshold because the battery voltage has come close to the charger voltage, but that the charger is still operating as before.

The cuttoff current is solely for the purpose of ending the charging cycle.  A LiPo charging cycle starts with Constant Current at the rated current for the power supply.  Once the target voltage is close to being achieved, the charger goes into a constant voltage mode and keeps the voltage steady by decreasing current to top off the battery.  Once the charging current is down to around 100mA at the target voltage, the battery is fully charged and the charger shuts off.  If you change the target voltage then this process will occur at that voltage (whether lower or higher).  

rcheli-diagram-charge_graph.png?attachauth=ANoY7cq9D2koGP0is7iEAkj4YbBMv_IdF4sWywH-0GGByoYO9GL7g5EfIYBooS8eQ3qsu9ByYzFZ39pN2GRE3fSWaR2AgDipOL1WSzgen6ezOPtcT0JaXRVEYaLFl2xHcCa8jY4n6q0PI7Cp-m6VMTYcswHYJEiL8i4MFy4gL0lMfSYASCzJbSkwXbgiUxG3k3jsNE5lal3VIuPKltPL3nFcqANJ4Vt-EZ7yKSH4mShwfeKsXL1z5m1MHKWvsROvqrf_cpZ9omN0ZkEQqMpwlSYtOR0EmZwEEumIAri9PGnU31wOTKUkRIU%3D&attredirects=0

But the balancing process is in the BMS and not the charger so it won't directly impede the balancing process.  It can indirectly affect it if you lower the charging voltage below where the balancing starts though.

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To my understanding the voltage of the charger doesn't change unless it is opened and adjusted through the pot. That is, to my understanding, the charger delivers always the same voltage, but it limits the current which is otherwise a direct consequence of the voltage difference between charger and battery and the resistance of the circuit. The changing voltage we measure while charging is, so I thought, due to the changing state of the battery and the current flowing.

I am positive that my chargers never shut off when they switch to green light (they switch at 0.4A), even if I leave them connected for +24h, because the current I measure never drops to zero but flattens out to a constant value, 0.03A, IIRC. (I had attributed this to the BMS and the continued balancing process, though the current remains constant even when I would think balancing must be essentially finished).

I also didn't think that balancing is in operation when the charger is unplugged or off, but I have no specific information to confirm or refute this idea.

I have a charger which delivers a too low voltage and I will check in the next few days whether the limit current is the same.

Edited by Mono
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4 hours ago, Mono said:

To my understanding the voltage of the charger doesn't change unless it is opened and adjusted through the pot. That is, to my understanding, the charger delivers always the same voltage, but it limits the current which is otherwise a direct consequence of the voltage difference between charger and battery and the resistance of the circuit. The changing voltage we measure while charging is, so I thought, due to the changing state of the battery and the current flowing.

I am positive that my chargers never shut off when they switch to green light (they switch at 0.4A), even if I leave them connected for +24h, because the current I measure never drops to zero but flattens out to a constant value, 0.03A, IIRC. (I had attributed this to the BMS and the continued balancing process, though the current remains constant even when I would think balancing must be essentially finished).

I also didn't think that balancing is in operation when the charger is unplugged or off, but I have no specific information to confirm or refute this idea.

I have a charger which delivers a too low voltage and I will check in the next few days whether the limit current is the same.

I would recommend looking at this web page to help you better understand how Lithium type batteries charge:   

The page goes over (in more detail) what I was talking about.  Then you can try to determine where the current draw is coming from you are seeing.  If you are measuring using something like a watt meter at the outlet then it could be due to the electronics in the charger and not any type of actual charging.  

UiMaONt.jpg

Edited by Cranium
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I assume that in our case a bulk of the charging logistic takes place in the battery packs BMS and not in the charger. Of course I am not measuring charge current at the grid outlet :D

Edited by Mono
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2 hours ago, Mono said:

I assume that in our case a bulk of the charging logistic takes place in the battery packs BMS and not in the charger. Of course I am not measuring charge current at the grid outlet :D

Yes, much more!  The charger is a very dumb device in comparison!  Look at all the things a BMS circuit can do:

 

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The constant current sources with a "?a?long side" transistor is the old, tratitional technology. With switching power supplies a constant current supply is realised via a shunt resistor to measure the flowing current and keep it constant by changing the pwm duty cycle accordingly (feedback loop). So no power dissipation by dropping the voltage is needed.

By this, if the desired current is not flowing the voltage is regulated upwards and has to be limited by the design.

For the serial li ion packs with bms the charger should provide some low current indefenitely (which the bms can bypass completely once the cells are fully charged) to enable balancing. Also some higher currents could be possible, since the bms can cut off the charge side once the first cell reaches a certsin maximal voltage.

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2 hours ago, esaj said:

I could be wrong, but I've assumed that the "cutoff"-setting in the wheel chargers only triggers the (usually) red/green-LED for showing charging/ready. At least my Charge Doctors (sitting between the charger and the charging port, so measuring the output from the charger to the battery) have always showed that there's still current going into the battery after the led turns green, and I've run it down to showing 0.00A (they only show down to tens of milliamps), which takes quite a long time, but would seem to indicate that the charger keeps putting out current until disconnected (either from the wall plug or the charge port) or until the battery stops drawing current entirely. Of course different chargers could work differently.

Must be that different chargers may behave differently but what you are describing is trickle charging which from my understanding is bad for Lithium based batteries.  Below about 100mA, you really aren't adding anything noticeable to these large batteries.  The charger that I used to build the high power charger was demonstrated to cut off the current when it dropped to the set point I set after it reached the target voltage.  Unfortunately, I'm unable to test other EUC chargers since their voltage is above what my load tester can handle.  Unless I get something more substantial like a BK Precision 8500 or better.  :) 

 

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17 hours ago, Cranium said:

Must be that different chargers may behave differently but what you are describing is trickle charging which from my understanding is bad for Lithium based batteries. 

I have no real reason to believe that the BMS wouldn't take care of this problem. It would be anyway much better handled there, because the BMS is closer to the specific characteristics of the battery.

I have about half a dozen chargers of different types and brands and none of them I have seen change its charging behavior or stop charging when the light turns green.

EDIT: the other part of the equation is that it is not so outrageous to ask the user to disconnect the charger some time after the battery is fully charged. I guess that should be done anyways not only to pamper the battery.

Edited by Mono
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32 minutes ago, Mono said:

I have no real reason to believe that the BMS wouldn't take care of this problem. It would be anyway much better handled there, because the BMS is closer to the specific characteristics of the battery.

I have about half a dozen chargers of different types and brands and none of them I have seen change its charging behavior or stop charging when the light turns green.

To be honest, I've only tested this on the charger I purchased and set it this way to general Lithium charging guidelines which don't take into account anything between the charger and the battery. 

It could be that the manufacturer specific chargers are that way because, as you stated, the BMS takes over at this point.  It could be providing some output to allow the BMS to continue to balance rather than continuing to charge.  I've never really tested for this but it would certainly be possible to do with setting a cell out of balance on purpose and seeing what happens after the green light comes on.  I could only currently do this with a Ninebot charger/battery though.  Doing this with other charger/battery combinations would require de-sleeving the battery pack to discharge and perform measurements on the battery cells.

 

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  • 1 year later...

I have a gotway tesla, with original charger.

Meassuring with no load at the output contact between pin 1-2 i get around 82.5V and led is kept green as the multimeter does not have enough of internal resistance to trigger "charging" (red led).

Edit:

After removing glue i can turn pot +/- 1/4 of a turn. But now regardless of i how i turn the pot i get 84.1V (fully clockwise 1/4 turn to 84.2 fully counter clockwise 1/4 turn) how on earth could voltage change like that? Even if i reset it to middle pos where it meassured 82.5V before opening charger (after opening charger 83V though which is strange) but now i CAN'T get it below 84.1V which is to high for the 2x 84v packs? Right?

End edit

I have meassured the battery packs before all this and they show slightly higher voltage than output (82.5) from the charger (both batt packs show 82.7V when charged full, about 3h of green led) but the multimeter precision is +/-0.7V at worst case so that could just be a meassure diff from batt pack internal resistance vs charger internal resistance.

 

Regardless, as i see it i need to tune up voltage every 10th or so cycle to make sure BMS equalize the batteries in the packs fully? 

Charging at 82.5V in beteeen (90%) is actually good for longevity for the packs, but never charging full to 84V is not.

Hence i opened my charger And look, the pot vr1 is there glued shut on my charger as well. So should be output voltage trim pot?

Now would it be safe to increase voltage to 83.3V (on meter that had a +/-0.7V max error, keeping voltage at 84V max not to impede with cell max voltage) to make sure balance kicks in?

You can see the blue glued vr1 pot in the image on my original Gotway tesla charger, only pot in there

15654810775545296260464204012800.thumb.jpg.646f7caa347be5b683343d998b3a3a9e.jpg

Edited by Boogieman
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