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Apr 03, 2019, 03:00 AM
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Quote:
Originally Posted by miky94
Ok, I thought about hot glue because I've seen use it to cover solder joints the DJI's video on how to assembly flame wheel arf kit.
having the cells inside the arms I think this would be the best solution for the wiring diagram, what do you think about it?
That may have been silicone. There are certain types of "hot glue" used for different applications. My dad for instance uses some industrial "hot glue" spray gun for working on shoes. The glue comes in a tube, I don't know much about it but he says it's expensive. It can be used, you can get away with it, but I would call it hacky, along the lines of duct tape. Great for quick repairs of noncritical things tho!
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Apr 03, 2019, 06:21 PM
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is there some difference in batteries storage between LiIons and LiPos?
Apr 13, 2019, 10:46 PM
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Quote:
Originally Posted by miky94
is there some difference in batteries storage between LiIons and LiPos?
You can find documents on best practices for lithium ion pretty easily. And as I have said, "LiPos" are actually lithium ion cells. The exact chemistry is generally a trade secret, however. I think they are similar enough. Just keep them in a safe place, don't keep them under your pillow, be reasonable. Keeping them fully charged is "bad" although damage from keeping them at 4.20v, you might lose tens of mAH over the course of years.
Apr 14, 2019, 04:18 AM
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Quote:
Originally Posted by Power Max
You can find documents on best practices for lithium ion pretty easily. And as I have said, "LiPos" are actually lithium ion cells. The exact chemistry is generally a trade secret, however. I think they are similar enough. Just keep them in a safe place, don't keep them under your pillow, be reasonable. Keeping them fully charged is "bad" although damage from keeping them at 4.20v, you might lose tens of mAH over the course of years.
yes of course Li is always Lithium.
I found conflicting information on internet about minimum voltage, it probably depends on the chemistry and therefore on makers.
as far as I know the advantage on LiIon is that you can safely discharge them to 2.8V (dead point 2.5V) vs LiPos 3.3V (dead point 3.0V).
I think the minimal voltage increase with the number of cells in series, because of the unbalanced discharge.
LiPos storage voltage is 3.8V, a bit higher than nominal voltage probably because of self-discharge, so I think for LiIon is the same.
since I read they have a shelf life that worsens with high temperature and voltage of storage, wouldn't be better to store them in a cool place to a lower voltage? or this would increase the self-discharge and the frequency of recharge to maintain a safe voltage so, that also degrade the batteries, and so 3.8V is a compromise?
one thing I never understood is if I fully charge a battery but then I don't use it, should I discharge it to storage voltage and then the day after charge it again or the charging/discharging is worse than keep it at 4.2V for a day? because a week at maximum voltage kills batteries but I don't know how long can I safely keep it to that voltage.
Apr 14, 2019, 01:52 PM
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Quote:
Originally Posted by miky94
yes of course Li is always Lithium.
I found conflicting information on internet about minimum voltage, it probably depends on the chemistry and therefore on makers.
as far as I know the advantage on LiIon is that you can safely discharge them to 2.8V (dead point 2.5V) vs LiPos 3.3V (dead point 3.0V).
I think the minimal voltage increase with the number of cells in series, because of the unbalanced discharge.
LiPos storage voltage is 3.8V, a bit higher than nominal voltage probably because of self-discharge, so I think for LiIon is the same.
since I read they have a shelf life that worsens with high temperature and voltage of storage, wouldn't be better to store them in a cool place to a lower voltage? or this would increase the self-discharge and the frequency of recharge to maintain a safe voltage so, that also degrade the batteries, and so 3.8V is a compromise?

one thing I never understood is if I fully charge a battery but then I don't use it, should I discharge it to storage voltage and then the day after charge it again or the charging/discharging is worse than keep it at 4.2V for a day? because a week at maximum voltage kills batteries but I don't know how long can I safely keep it to that voltage.
Yes, there is plenty of misinformation out there. Your best bet is to consult the original manufacture for the cell. For 18650's, you can easily find model numbers and refer to the corresponding datasheet. The worst that can happen with a couple of 18650s is they pop, fizz, and maybe shoot out some flames. A huge group of them is more dangerous, but still manageable .

Also what exact voltage you are talking about? The open-circuit voltage (no load)- is very different than the voltage of the cell with load. You can probably use a cutoff voltage of 2.5V under heavy load, but as soon as the load is disconnected you will observe the voltage rebound. My LiPos will eventually rebound to ~3.6V even after a full discharge, making it seem they still have some juice left.

Will keeping the cell fully charged damage it well the answer is not really. Technically yes, but not noticeably. Good quality cells will lose about 50mAH per year left fully charged.

The reason for the 3.8V charge is that it supposedly keeps the very reactive lithium ions evenly distributed on both sides of the separator, thus reducing corrosive reactions with either the anode or cathode material. When you over-discharge and especially reverse charge the lithium ion cell, bits of copper (copper ions) begin to try and penetrate the separator, and small bits will pierce it, shorting the cell internally. Now the cell is compromised, and will not hold a charge. (It's "leaky.") If it's in series with other cells w/o cell balancing or a BPS/BMS, this turns into a runaway effect as each discharge cycle further reverse-charges the internally shorted cell, further damaging it. It will fail catastrophically when you attempt to recharge it due to the internal short.

This video is pretty good ELI5 of how lithium ion cells work.
Apr 14, 2019, 02:44 PM
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Quote:
Originally Posted by Power Max
Yes, there is plenty of misinformation out there. Your best bet is to consult the original manufacture for the cell. For 18650's, you can easily find model numbers and refer to the corresponding datasheet. The worst that can happen with a couple of 18650s is they pop, fizz, and maybe shoot out some flames. A huge group of them is more dangerous, but still manageable .

Also what exact voltage you are talking about? The open-circuit voltage (no load)- is very different than the voltage of the cell with load. You can probably use a cutoff voltage of 2.5V under heavy load, but as soon as the load is disconnected you will observe the voltage rebound. My LiPos will eventually rebound to ~3.6V even after a full discharge, making it seem they still have some juice left.

Will keeping the cell fully charged damage it well the answer is not really. Technically yes, but not noticeably. Good quality cells will lose about 50mAH per year left fully charged.

The reason for the 3.8V charge is that it supposedly keeps the very reactive lithium ions evenly distributed on both sides of the separator, thus reducing corrosive reactions with either the anode or cathode material. When you over-discharge and especially reverse charge the lithium ion cell, bits of copper (copper ions) begin to try and penetrate the separator, and small bits will pierce it, shorting the cell internally. Now the cell is compromised, and will not hold a charge. (It's "leaky.") If it's in series with other cells w/o cell balancing or a BPS/BMS, this turns into a runaway effect as each discharge cycle further reverse-charges the internally shorted cell, further damaging it. It will fail catastrophically when you attempt to recharge it due to the internal short.

This video is pretty good ELI5 of how lithium ion cells work.
not sure about the voltage, with LiPos I use to balance charge them to 4.2V per cell and I use them till the buzzer beeps at 3.3V. then I recharge to 3.8V to storage, even if I'll use them the day after.
so for LiIon I'd do the same except for discharging up to 16.8V (2.8V x 6S), because single cells voltage could be lower so I'd stay a bit safer.
I found this HG2 datasheet specs which confirms this voltages, 4.2V max and 2.5V min. https://cdn.shopify.com/s/files/1/06...spec-sheet.pdf
so if keeping the battery fully charged won't damage it, for storaging I only have to charge it when is below to which voltage? and to what voltage should I recharge it?
Apr 14, 2019, 11:10 PM
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Quote:
Originally Posted by miky94
not sure about the voltage, with LiPos I use to balance charge them to 4.2V per cell and I use them till the buzzer beeps at 3.3V. then I recharge to 3.8V to storage, even if I'll use them the day after.
seems reasonable. You treat your cells better than I do mine!

Quote:
Originally Posted by miky94
so for LiIon I'd do the same except for discharging up to 16.8V (2.8V x 6S), because single cells voltage could be lower so I'd stay a bit safer.
I found this HG2 datasheet specs which confirms this voltages, 4.2V max and 2.5V min. https://cdn.shopify.com/s/files/1/06...spec-sheet.pdf
so if keeping the battery fully charged won't damage it, for storaging I only have to charge it when is below to which voltage? and to what voltage should I recharge it?
You can treat 18650s the same as you do the previous flat cell packs, but they can be pushed a bit harder as well, and they are rated for it. Everything about cells is a bit grey and soft, there is no hard limit on anything. The nicer you treat your cells, the longer they will last, to a point. I would probably treat 18650s as you describe here. The old UR18650 tesla cells I came shipped at 3.8V, you can just measure your cells to see what voltage they arrived at.
Apr 15, 2019, 06:53 AM
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Thread OP
Quote:
Originally Posted by Power Max
seems reasonable. You treat your cells better than I do mine!


You can treat 18650s the same as you do the previous flat cell packs, but they can be pushed a bit harder as well, and they are rated for it. Everything about cells is a bit grey and soft, there is no hard limit on anything. The nicer you treat your cells, the longer they will last, to a point. I would probably treat 18650s as you describe here. The old UR18650 tesla cells I came shipped at 3.8V, you can just measure your cells to see what voltage they arrived at.
the last thing I'm a bit undecided of, is when should I charge/discharge to storage voltage, because since I'm still testing maybe I full charge the battery but then I can't fly for a problem and I don't know how long it will take to solve it so I discharge to storage voltage.
this continuous charge/discharge sounds to me a bit stupid and maybe instead of preserving battery life it has the opposite effect, is more harmful than useful.
I'm not paranoid, I just want to know what is best practice, because of endless delivery time to receive new cells and
lot of work for this custom-built battery, even if probably once the first is built the next ones will be easier
Apr 15, 2019, 09:55 AM
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Quote:
Originally Posted by miky94
the last thing I'm a bit undecided of, is when should I charge/discharge to storage voltage, because since I'm still testing maybe I full charge the battery but then I can't fly for a problem and I don't know how long it will take to solve it so I discharge to storage voltage.
this continuous charge/discharge sounds to me a bit stupid and maybe instead of preserving battery life it has the opposite effect, is more harmful than useful.
Hence why I don't bother. I just keep my battery charged. The convenience of having them available on standby at a moment's notice is worth the 50mAH/year cost in capacity, especially if you do a lot of flying.

Quote:
Originally Posted by miky94
I'm not paranoid, I just want to know what is best practice, because of endless delivery time to receive new cells and
lot of work for this custom-built battery, even if probably once the first is built the next ones will be easier
I think the military spec is to charge lithium ions to a peak voltage of 3.9V instead of 4.2V, although I don't have a source for that. You can also do some research on the topic if you are really want to know this stuff. https://batteryuniversity.com/learn/...ased_batteries

Your cells are going to end up damaged more likely due to a crash rather than electrical stress.
Jul 19, 2019, 01:22 AM
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Quote:
Originally Posted by miky94
what about buying cells with presoldered nichel strips and solder them toghether using a normal iron soldering?
Hello, Do you have a demo video on how to solder them using a noral iron solder? Thanks.


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