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Any voltage or impedance differences when charging 8s?

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Any voltage or impedance differences when charging 8s?

Old 05-28-2023, 03:24 AM
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jak_kkaall's Avatar
Join Date: May 2006
Location: , ROMANIA
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Default Any voltage or impedance differences when charging 8s?

Hi, I have the ISDT T8 charger for years now, all good until now when I use it to 8s. The question is, do 8s chargers in general or this one in particular have errors when used to their limits that is to charge 8s?
I've builded three 8s8p lithium ion packs from 21700 Samsung INR 40t 4000mA 35A new cells fron the well known Nkon european company. All cells had 3,44v. They are to be connected in series to form an 2,8kw 24s8p electric paramotot battery.(project on openppg forum/community/builds/eppg project-2,8kw battery.) problem described on page 13.
From first charging (the three 8s 32v packs in parallel) I've saw that one cell nr one on the charger (last cell in the pack) the voltage tends to remain behind like 3,62v discharged or 4,07v charged and other cell groups 3,66-68 and 4,08-09 (verified with a volt meter)
Also the impedance is around 6mohms on this first cell of all three packs and all others have like 0,7 mohms! (This is when all three packs are charging in parallel so a cell group with this impedance is basicaly 24 4Ah cells in parallel that is 96 Amps). When I connect only one 8s8p pack to the charger the impedance is 18mohms on this particular cell group and others have 2 - 2.5mohms this also on each of the three packs which kind of excludes the probability of a bad or disconnected cell or wire.
A well known electric patamotor builder and RC user told me that 8s charger tend to have errors on last/first cell when used with 8s packs and after years he didn't find the cause yet.
So I've made myself wires so I can hook up only two group cells through the balancing wire and the results where all over the place, I mean one time a cell group shows 18 mohms and the second group 43 mohms, next time the one with 18 has 52mohms etc..but this way I realised that the last/first cell group didn't show the same huge difference from other groups like it did when all 8s are charged together so all groups are probably fine.
I've worked a lot att his battery, it cost me a fortune, above 1.000 euros and I whant to fly with it so I realy need to know if I can trust it or the charger, and If I need another charger that realy handles 8s so bee it. Really need your oppinion on this. Appreciate it. Thank you!

8s8p pack 30v 32A

Bending 1,5mm alu sheet

Making batt case

Almost there..

Aluminium case with three compartments, 20kw Mad M50 34kw motor, 140cm carbon prop from E-props.

All three packs in the carbon wrap covered case

The 17kg battery on the paramotor frame.

A lot of wires..

Last edited by jak_kkaall; 05-28-2023 at 07:32 PM.

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