Thundersky winston lifepo4

[pavlik1]

Hello. I recently purchaced 16pcs of thundersky yellow battery 100ah.
One of them had very high self discharge and was replaced by the seller.
As a replacement i got a newer one.
The new one has a negative terminal made of copper.
The other 15 has both terminals made of aluminium. Why is the difference? The seller did not answer this question so far.

The new one is changing the voltage during charge and discharge much more compared to ths rest of the pack.
Any advice for measuring internal reststance.
What is the value or Ri at 50A?

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[pavlik1]

The rest

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[fechter]

I haven't ever seen one with a copper terminal. It must be a design improvement. Copper has less resistance than aluminum.

Thundersky batteries have quite a bit of sag at high load. This is normal. They can also puff, but I see you have yours nicely compressed with plates. This is highly recommended.

To measure Ri, there are lots of ways. You need to place a heavy load on the cell with something while measuring the voltage. Load could be a big resistor, heating element, light bulb bank, etc. To measure on a single cell, you could possibly use a long piece of copper wire as a resistor.

I'm sure there is some standard test method, but I just apply the load for about 3 seconds and measure voltage. Remove load and measure voltage again after 3 seconds. Since the voltage constantly changes, you need to pick a time frame to measure at.

 

[pavlik1]

hello

The internal resistance measured with two resisitors, app 30 ohm and app 2 ohm



much higher than the datasheet value of 0.45 mohm altho i do not know how the datasheet value is obtained.
any idea for representative Ri measurement that can be compared with factory values

 

[fechter]

Your test is good. Those are believable numbers. Guys used to call those cells "Thundersag" for a reason.

It's possible the datasheet numbers are AC measurements, which will be much less than the DC measurement (and much less useful).

 

[pavlik1]

Thank you, will measure again aftrr few cycles

The same sag with headway cels I have.

Will wait for graphene battery from Murcia Spain [emoji1]

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[fechter]

The A123 cells have much less sag but are more expensive.

 

[EbikeAus]

I have CALB cells, they have one copper, one aluminum terminal like in the pic

 

[pavlik1]

Just a side note. The above Ri is including the copper connections between cells and the 2x junctions aluminium to copper.
The best is to use cupral shums. Unfortunately I Do not have any.

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[igor0428]

The difference between your internal resistance measurement and the datasheet value is because of the measuring method.
Your using the DC load method and almost every manufacturer gives the numbers using AC impedance method. Here you can read more about it:
https://batteryuniversity.com/learn/article/how_to_measure_internal_resistance

 

[Honk]

AC impedance as test method is useless.
It doesn't reflect how a battery performs at continuous load by an electric motor.
I prefer the resistive load test as this reveals what to expect from the battery.

 

[pavlik1]

So far so good, after more than 1000km

at 100A load less than 100mV between cells, including not perfect connections between few packs :wink: