stunthanger.com
General control line discussion => Open Forum => Topic started by: Paul Taylor on June 24, 2025, 01:01:14 PM
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This charger shows cell resistance when charging. The other batteries are showing eight ohms. This is a brand, new thunder, power battery and the settings Look a little off. What do ya think?
(https://uploads.tapatalk-cdn.com/20250624/3cdbc49d169de80f44a79562e4d9afc0.jpg)
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This charger shows cell resistance when charging. The other batteries are showing eight ohms.
8 ohms? That seems very wrong, 4-5 mOhms is pretty believable.
Brett
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The others look like this.
(https://uploads.tapatalk-cdn.com/20250624/db30d2a6402f589daa33284fc16c9f26.jpg)
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8 ohms? That seems very wrong, 4-5 mOhms is pretty believable.
Brett
Thanks Brett.
I’m concerned about the 1 ohm cell. ???
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Paul
those readings are in MILLI ohms, not Whole ohms if you will.
Carl C
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Paul
those readings are in MILLI ohms, not Whole ohms if you will.
Carl C
Thanks I was not aware. So it's not a problem?
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Thanks I was not aware. So it's not a problem?
Thats what the little m is for.
Not a problem. If it was really 8 ohms, you could only get 2.5 amps out of it, even with a dead short.
Brett
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Thats what the little m is for.
Not a problem. If it was really 8 ohms, you could only get 2.5 amps out of it, even with a dead short.
Brett
I'm so glad we have people on this forum that are way smarter then this old country boy. :)
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I'm so glad we have people on this forum that are way smarter then this old country boy. :)
Ohms law is pretty simple - V= I x R voltage, current resistance If your battery is about 20V open-circuit (when there is no current flowing out of it) and it has 8 ohms of internal resistance, even if you shorted it out at the terminals (0 ohms), you still have 20 = I X 8, or I=20/8 = 2.5 amps.
The reason that these batteries are capable of discharging effectively and efficiently at these very high currents is due to their low internal resistance. It's also the reason you can't use something like 2 9V transistor batteries to even turn the motor over, as soon as you turn it on, the relatively high internal resistance causes the voltage at the motor to be almost nothing, all the energy is getting sucked up internal to the battery.
Brett
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Well, I just received four new Thunder Power 6S 2200 mAh batteries, and after the initial cycling, cells are reading 20-30 mOhm. No bueno...
If after initial flights they get hot and continue reading high R, I will contact their quality org.
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8 milli-ohm is very good. Internal Resistance is a good way to monitor battery health
Here’s what I use
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8 milli-ohm is very good. Internal Resistance is a good way to monitor battery health
Here’s what I use
Thanks for posting this.
I saved it off.
Might pin it in electric
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its not that easy first is this DCR or ACR?
I would suprised if it is measureing DCR. ACR is a lot easier to measure. But eaither way the improtant item is not some much the value but how it changes over time. If tis is DCR that is a very good charger.
in the context of LiPo batteries (Lithium Polymer batteries), DCR and ACR refer to different measurements of internal resistance, which is a critical indicator of a battery's performance and health.
DCR (Direct Current Internal Resistance)
What it is: DCR measures the battery's internal resistance when a direct current (DC) load is applied. It's often calculated by applying a short pulse of high current (discharge or charge) and then measuring the voltage drop across the battery terminals. Ohm's Law (R = V/I) is then used to determine the resistance.
What it includes: DCR encompasses all the resistive components within the battery, including:
Ohmic resistance (R0): This is the instantaneous resistance from the electronic components, electrode materials, electrolyte, diaphragm, and contact resistance.
Polarization resistance (Rp): This accounts for the slower voltage drops due to electrochemical polarization and concentration polarization, which involve the movement of ions.
How it's measured: Standardized methods like IEC 61960 often involve applying a discharge pulse (e.g., 0.2C for 10 seconds, then 1C for 1 second) and calculating the DCR from the voltage and current differences.
Significance:
DCR is a crucial indicator for evaluating a battery's power capability and cycle life. A lower DCR generally means a battery can deliver more current with less voltage drop.
It varies with the battery's State of Charge (SoC), State of Health (SoH) (aging), and temperature. As a battery ages, its DCR typically increases.
It's particularly relevant for applications where constant, high DC current is drawn, like in electric vehicles or power tools.
ACR (Alternating Current Internal Resistance)
What it is: ACR measures the battery's internal resistance using an alternating current (AC) signal, typically at a specific frequency (e.g., 1 kHz or 100 Hz). Instead of a DC load, a small AC current is injected, and the resulting AC voltage response is measured to determine the impedance. Only the "real" part of the impedance (resistance) is considered for ACR.
What it includes: ACR primarily reflects the ohmic resistance (electronic and ionic resistance) of the battery, as the high frequency of the AC signal doesn't give the slower chemical and diffusion processes time to significantly contribute to the impedance.
How it's measured: ACIR measurement equipment applies a small AC current and measures the AC voltage, then calculates the impedance (Z = Vac / Iac).
ACR is often the "internal resistance" value quoted in battery datasheets because it's a quick and relatively easy measurement.
It's useful for cell sorting in battery pack manufacturing, as it provides a consistent and comparable value for initial cell quality.
While it's a good indicator of instantaneous electronic and bulk electrolyte resistance, it doesn't fully capture the complex electrochemical processes that contribute to voltage drop under real-world DC loads.
A rule of thumb is that ACR is approximately 70% of the DCR value for the same cell.
Yes I am a battery nerd.
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Nothing short of awesome, Dave!
Dave Mo…
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You may also want to list the battery capacity as well, smaller batteries generally have higher IR values so knowing the capacity gives the value some context. I generally cycle my batteries a few times before actually flying them and I normaly see the IR drop a little by the 3rd or 4th cylce.
Good luck
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Thanks, Dave.