Xtar Dragon VP4 Plus show same value... - Page 1
Forum section: electronics / beginners

author: ElectricPower
author_rank: Frequent Contributor
timestamp: January 27, 2021, 03:02:43 am
content: I have an Xtar Dragon VP4 Plus charger i use to test battery capacity with. But i wonder why the charge/discharge results at the end wery often is exactly the same?You can see it on the video under.

author: ETITsynthesizer
author_rank: Contributor
timestamp: January 27, 2021, 03:42:49 am
content: can you provide more information please so that someone can make some kind of useful conclusion from your data? for example, the sample that you tested is the same but what is it being compared to? provide information on the two things being compared. what size battery, where it was purchased, was it purchased at the same time presumably from the same batch and manufacturer? will you provide other data about overall capacity so that we can see if the max discharge rate and max charge rate are invariant regardless of battery total stored mAh or watt hours? have you ever tested two different batteries with this machine that had different max discharge rates? this would be one way to test if the machine used to perform the test is working correctly. you can also verify the device discharge tests by sticking a load resistor a known value in the current path that is then connected to a precise volt meter with data logging. using ohms law you can compare the results of the volt meter with the results of the battery testing device in question. this also requires the load resistor to be small enough to not significantly interfere with battery testing while at the same time being large enough to leverage the precision of the ADC that is built into the digital volt meter. There is a trade off there and likely if the cheap battery tester is lacking precision this is a result of the same problem that the manufacturer is facing.

author: ElectricPower
author_rank: Frequent Contributor
timestamp: January 27, 2021, 08:04:00 am
content: QuoteAfter a full cycle test (full charge, discharge and full charge) for testing capacity i get the total capacity for charge and discharge that blinking in the display after finish test. This is "rescued" batteries from old laptop batteries. 18650 cells.Charge current is set to 1 amp.After test cyclus is finish i can read booth charge capacity and discharge capacity. These numbers is almost always different. But wery often i get exactly the same value. A little strange...?

author: uli12us
author_rank: Contributor
timestamp: January 27, 2021, 09:02:19 am
content: I bought one of these chargers some 3 months ago and send it back. The 4th station showed always 100-150mAh less than the left 2.the 3rd always in the range of 80mAh. The inner resistance measuring was a pain, not a feature, because you can only measure the cellresistance not the R from a Nickelstrip, vs Copper, brass or nickelplated-Iron.

author: GLouie
author_rank: Regular Contributor
timestamp: January 27, 2021, 08:24:55 pm
content: I have this charger and it works fine for me, but as you note will show slightly different discharge/charge capacities.I have always assumed that there will be small changes in the cell chemical's behavior, and detecting the low voltage cutoff and full charge is not perfect. I have not worried, as long as the difference between indicated discharge and charge capacity is small.When exactly the same, I assume is mere chance.

author: uli12us
author_rank: Contributor
timestamp: January 28, 2021, 11:22:08 am
content: No, thats not a different reading from different cells. If I have 1520mAh in the 4.th Holder than I have always with the same cell 1570 in the 3rd place and 1650 in the first two. Thats not really the problem. but which value is the right one for the cells. Better I have a false but consistent value in all cases than a probably right value in which of the holders. I needed the charger to measure the capacity of the cells to combine it for a 7s 4 or 5p Akkupack. So I need 28, 35 cells with nearly the same capacity. The resistancemeasurement is only a nice looking but useless gadget. Its much better it works for each holder in the charger. Why can't the manufacturer adjust all 4 holders to the same value?