New to all this . Could someone please explain why the resistance of a protected 18650 reads higher on my Miboxer charger when it is charged for the first time upon receiving it from Liion Wholesale . The automatic charge rate is also very low , .20 amp . After it is charged , taking all day , the resistance reads much lower . What is the science here?
One other question, shouldn’t the charge current increase to something in the 1 amp range as the cell comes out of discharge state? The current does increase but only to .3 or .4 A . I got tired of waiting for it to complete charge last night so I took it off before bed . When I returned it to the charger in the morning, the rate was higher and the resistance was lower .
After 8 hours and still not close to being done charging (same thing with 3 new cells) , I manually stepped up the charge rate to 500ma.Why the C2-6000 stays at such low rate is puzzling .
Miboxer sets charge rate based on internal resistance.
What cells are you charging?
What was the voltage when they arrived to you?
Mi Boxers are the first lithium ion chargers I know of to use automatic charge current selection,and they are being very cautious.
C is a constant used for battery charging.It is the amp-hour rating of the cell.For a 3Ah (3000mAh) cell,C is 3…A safe charging rate is 0.3C so around 1 amp.The C constant means that all Li Ion cells charged at 0.3 C should take about 3.5 hours to charge,regardless of cell size or capacity. 0.7C is fast charge,takes about one and a half hours.
My Mi Boxer C2 6000 does the same as yours at the start.I simply go manual ,0.3C,and in less than 5 minutes,if I go back to auto,it is about what current I put in,and the internal resistance measurement is realistic,but I normally leave it on 0.7C manual })still within manufacturers spec.
Protected cells have higher IR so the charger thinks they are older,override to 0.3C,but stay in proximity(golden rule)
If your cells brand name ends in “fire”,you NEED to check out HKJ’reviews.
link Battery Reviews and Tests
2 of the cells I am using are Sanyo 18650GA 3500 mah . 1 is a Panasonic 18650B 3400 mah. All from Liion Wholesale . All protected . They were shipped at 3.5v , 26% I think the charger said . The resistance started at 350 mohm and ended at 135 mohm. I thought that odd . So with a new cell, I can just manually set 1 A , even at very low voltages? I would of thought the charger would have increased the charge rate on it’s own, just as it decreases the rate at the end . The other Panasonic 18650 Bs I have start at about 1 A when the voltages are about 3.8 or so .
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As li-ions heat up their current capability’s increase, I’d assume that the IR is declining as they heat up also.
Charging a 3500mah battery at 500ma should take around 6 1/2 hours.
Divide the capacity by the charge rate should give you a close estimate in time if the battery is depleted.
I may be wrong here, but wouldn’t the NiteCore SC4 charge rate also be considered sort of automatic (up to max pre-selected current), although its time-share feature sort of negates it (if charging other than only slots 1 & 2).
I think I remember reading a review of this charger and the IR function was accurate, but it looks like you are getting high readings. The GA cell IR is around 50 mOhms. High readings could be caused if the contact resistance is high. Try putting the cell in again to see if the IR changes.
Maybe like someone said, the IR is higher due to the protection circuit?
Clean the contacts of the battery and charger. Try a different slot. And finally, yes you can set it manually to 1A charge rate safely. It will go back down as the battery gets closer to being fully charged and be fine.
I wonder how accurate the IR readings are on some of these chargers. I recently charged a cell then out of curiosity tested the IR in the other bays. At start of charge it read 18 milli ohm. On the second round of testing I got 94, 46, and 6.
as you see they are not very accurate and repeatability is poor.
Not sure about the c2-6000, but on my c4-12 the IR readings are not very consistent. See my review here:
Also, it is normal for IR to be lower on a fully charged cell. Some charger manufacturers specifically state in their user manual to only test IR on a fully charged cell for consistency.
Why can’t the IR be measured with a DMM?
It can be, but typically not just with DMM alone…
Thanks for that but I am afraid it is above my head. Why can’t the IR be measured just like measuring a resistor? Also, all my protected cells read in the 100-200 m ohm range (new cells)and seems high to me .This is from charger.
d-t-a wrote
I may be wrong here, but wouldn’t the NiteCore SC4 charge rate also be considered sort of automatic (up to max pre-selected current), although its time-share feature sort of negates it (if charging other than only slots 1 & 2).
I checked the SC4,and it measures capacity and sets 500 mA up to 1200 mAh and 1000mA over that.The MiBoxers measure IR and set initial current from that(conservatively),until it has worked out capacity,when it boosts current.
Yesterday I had 8 30Q Samsungs in the charger to test IR before and after soldering button tops(BLF GT coming in er April-ish)The currents were different for each cell,and to 2 decimal places.
Yeah,IR was all over the place with 8 new 30Q’s with delivery voltage,30 something to 150 ish milliohms , but the average was always lower after the button tops were added.Longer cells let the spring put more pressure on the contacts,and maybe new,clean contacts.
Because the IR values are too low to measure by a DMM. It’ll likely just show 0 on your DMM. Plus, the internal resistance of DMM leads themselves woud greatly skew the results.
For protected cells, this is actually quite possible/normal. The protection circuitry impacts internal resistance quite a bit.
Thanks, makes sense now.