The battery builders club

Seems like a good place to ask… anyone?

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Continuing my last post, we we’re able to take the flexway er battery apart. I was really impressed by the mechanical engineering and thought put in to it😁 The groups however were not okey, first and last group were 0.2v down from the others and the fourth group was 0.6v lower, replace the cell/s? Also, cells were Lishen lr2170la, I know it’s not good to practise but can I use something similar to it’s values?

LTO (lithium-titanium-oxide) battery chemistry is very interesting. These batteries are said to have profound cycle-life, at 10,000 to 30,000 cycles to 80% DOD. The following company claims to have 21700 LTO cells with an 8C discharge rating, and 4500 mAH capacity, though I think they are full of shit, as some of the specs just don’t make any sense. Regardless, LTO is the safest lithium chemistry with far-and-away the longest cycle life.

lithium-titanium-oxide

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@massy two lipo’s in parallel is definitely better, im getting the right power now.



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Good to hear! I ultimately went with a Bonka Power 75C 150C burst 5200 mAh as it was available locally. Seems to work fine with a single battery so far!

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Do we have any cycle count * cell capacity vs current draw tables? Like a total mAh before the cell is toast

How much current draw affects capacity loss as the cell is cycled? No.
It’s very cell dependent and would take thousands of total cycles to derive the data…for each cell.

IMO, there’s not much of a difference between reasonable current levels as long at the cell stays below about 60°C. For huge short-term pulses it depends on how much damage is done…how much lithium is plated out, how much electrolyte decomposition there is, etc.

I haven’t seen any specific data for that as the manufacturers always say to test for your particular application. And IMO no company is going to share that product development data they spent so much time and money on.

Hmm…I’m wondering if there’s a short version of this I could do to verrry roughly estimate where real capacity loss starts happening. I’m guess it’s where the cells start getting pretty hot and there are very few uses that allow the cells to continue to do that. Just a guess though.

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This is more hypothetical than anything really, but it would be nice to know how much of a battery has been used and how much longer it could be expected to go for

In say for the sake of argument a P42A is 3500 mAh at 10A and decays to 70% capacity after 600 cycles at which point the cell is to damaged to be safe, so at 10A the cell has a 1.785 KAh life span, and there’s some sort of curve for every current draw

If I have a 4P battery I’d expect something on the order of 7 KAh for the pack and if I integrate the current draw based on the current to total KAh rating of the pack I’d have an accurate % lifespan remaining on the pack…probs only useful on something like a car but still would be interesting

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Characterizing a cell like that could work but I’m thinking there could be an easier way.

By measuring DC IR increase along with the 0.2C capacity as the cell is cycled I think you can get the data needed. I say that because the research papers I’ve seen use the degree and rate of change of capacity and IR to estimate the end-of-life point for any cell without all that testing.

This automatically takes the current draw and usage profiles (continuous, pulsed, etc.) into account since how the cells were used doesn’t matter. You use the cell until the capacity has dropped and/or the IR has increased (indicating the increase in voltage sag, reducing run time) by a certain level that matches the minimum level of performance you’re willing to accept for that application.

By tracking the degree and rate of change for capacity and IR you can estimate remaining life.

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Hey folks. I had to strip the waterproofing on my battery apart for my Tyneeboard mini 2 as water had gotten in. It’s now all dry and looks like it’s working perfectly. However I’m wondering two things:

  • can I wrap the battery in masking tape for the time being whilst I ride it in the summer unwaterproofed, or does it need to be in lithium paper, which I don’t have at hand?

  • does anybody have any good links for materials like lithium paper, some foam sheet, and heatshrink that will do the trick in the UK and arrives quickly?

Thank you so much!

What do you mean by lithium paper? Are you talking about the paper that changes color when wet?

Fish paper I think

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You should have the appropriate fish paper and shrink wrap, it helps hold the pack together which prevents stress on the weld/solder joints and protects it from shorting out on anything inside the enclosure when it shakes around

I think Fogstar is the preferred cell and battery building supply company in the UK?

https://a.aliexpress.com/_EJFeNFb

This is the stuff I’m using. Passed the salt water test and have had zero problems welding.

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Is it true that some LLT BMSs have higher idle drain rates than others?

^^ Is this BMS one of them? I’m looking for one that’s 20s+, so the links posted by Artem above aren’t applicable unfortunately…

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is this a bad bms? After connecting the unit one group shows much higher than the rest, i confirmed with a meter and there’s no pack with this voltage.

I set the pack to static balance but idk if its doing anything. I also don’t have the correct charger to give this pack some juice at the moment, can i use another charger, or does the voltage have to match even though I’m not charging to full?

I was able to manually set the correct voltage in this menu, is this a fix or will it there be issues going forward with this more than likely bad bms?

I have never used that one

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The LLT BMS I just installed is off by something like 0.15 - 0.165v per p-group, resulting in nearly 2 volts in total deviation across the entire pack. Is there a way to calibrate these things?

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I haven’t messed with it but you should be able to set offsets in the voltage calibration menu to correct for that

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That worked perfectly. I was expecting 41.92v after calibration, and got exactly that. Thanks.

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