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balancing
#11
The replies above are great & I wanted to add a bit about these two parts:
(08-09-2019, 06:48 PM)100kwh-hunter Wrote: My packs will be running between 3.1v and 3.9 volt (80%????)
All my cells in my packs are above 92% soh.
The reason you run a pack at say 3.1 to 3.9V & only over 80% of the full SoC range is to extend the cell life.
This also means you are less likely to hit voltage extremes with some cells going too low or too high voltage. Ie the lights won't cut off, keeps the wife happy!
Note that 3.9V/cell may be unnecessarily low for the top end, you could easily run up to 4, 4.05 or 4.1 like most on the forum do.

Re the cells having >92% SoH is great, it means you have cells which have only been lightly used & have most of their life to go!
It means you have approx 92% of the original manufacturers stated capacity available.
Over time & with use, this SoH number will drop, reducing the available capacity in your system.
The SoH (& available capacity) will drop faster if you push the cells harder eg use over a wider SoC range &/or draw/charge at higher currents.
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#12
Thanks for your replays,

With a overfilled barrel you mean, cells above 4.20 volt?
Makes sense, cause they keep on charging till they are all at(in my case) 3,9v.

The longmons make sure that the 250ah pack will not overcharge but give some more to the other packs or starts to bleed some energy.
Except when the charge is to much for them?, then the pack will be flooded?

So in both ends, you would have some energy in storage that is useless?
At the top end it could be even risky to have pack's that are so far away from each other?

Thanks
Still learning English. Learning Li ion and solar technology.

4200 cells in packs Exclamation above 2500mah and 90%soh.
1500 waiting for testing.

Saving for 3 times phoenix inverter 48/3000 230v to gain also 380v
3 chargers?

Time is our enemy, must work to, the sun is our friend, must relax to.
With best regards
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#13
(08-18-2019, 08:56 AM)100kwh-hunter Wrote: With a overfilled barrel you mean, cells above 4.20 volt?

No, not necessarily 4.2v - that's the very top end of the charge target range, where you need to think about setting your critical cell voltage at (in order to prevent over charging and hence damage)

In the context of this conversation overfilled means reaching a voltage above that which you've set the bypass voltage to - whatever that might be (upto a max of 4.2v dependent on chemistry etc)

(08-18-2019, 08:56 AM)100kwh-hunter Wrote: The longmons make sure that the 250ah pack will not overcharge but give some more to the other packs or starts to bleed some energy.

Bypassing = energy wasted, so the aim should be to minimise it (hence being able to set a lower charge rate when in bypass with a compatable charger) - when some cells are in bypass, the charge rate for all other cells does not increase, so no the system will not "give some more to the other packs"

(08-18-2019, 08:56 AM)100kwh-hunter Wrote: Except when the charge is to much for them?, then the pack will be flooded?

The mons can only bypass a fairly limited, but more than adequate current, that's assuming you thermally manage them by either active cooling or current limiting (either the overall charge rate, or the mons bypass current from within the toolkit) - or both.

(08-18-2019, 08:56 AM)100kwh-hunter Wrote: So in both ends, you would have some energy in storage that is useless?
At the top end it could be even risky to have pack's that are so far away from each other?

I'm not entirely sure what this means - but no energy stored (in a system designed to store energy) can be deemed "useless" - unless you've allowed cells to reach a terminal voltage above your bypass limits, or out with it's safe working parameters - perhaps pointless or dangerous is a better word than useless in that scenario.

If you've got cells "at the top end" and others that are "so far away from each other" - I'll assume you mean in terms of states of charge - in that situation the role of the BMS is to manage the charging system such that those cells which are "at the top" stay exactly "at the top" while allowing all remaining cells to catch up "at the top"
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#14
Any system like longmons will not stop the cells overcharging (going too high in voltage) or being over discharged.
But they will tell you about an issue (cells gone high or low) and help maintain balance with other cells.

If cell voltage goes too high, you need the Watchmon to trigger "stop charging" or even disconnect the battery via a shunt trip breaker.
Similarly if a cell goes too low voltage, you need the Watchmon to trigger "stop discharging" (eg switch off the inverter) or also disconnect the battery via the shunt trip breaker.

Don't worry about the energy lost in bypassing - it's small compared to everything else but essential & the simplest way to do it.
Running off solar, DIY & electronics fan :-)
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#15
(08-18-2019, 12:54 PM)Redpacket Wrote: Any system like longmons will not stop the cells overcharging (going too high in voltage) or being over discharged.
But they will tell you about an issue (cells gone high or low) and help maintain balance with other cells.

If cell voltage goes too high, you need the Watchmon to trigger "stop charging" or even disconnect the battery via a shunt trip breaker.
Similarly if a cell goes too low voltage, you need the Watchmon to trigger "stop discharging" (eg switch off the inverter) or also disconnect the battery via the shunt trip breaker.

Don't worry about the energy lost in bypassing - it's small compared to everything else but essential & the simplest way to do it.

Batrium mons, or any other competently designed cell monitor will prevent a cell being charged to a voltage deemed to be excessive - that is one of their main design criteria, but they'll only be able to do that in a correctly configured system.

My comments regarding bypassed energy being wasted energy are correct, but you are right to point out it's a relatively small amount in the scheme of these things - however it's been mentioned elsewhere that stacking multiple mons in order to achieve 10A and above is a practical solution - bypassing that amount of current really is wasteful, the point at which bypassed charge current becomes wasteful is obviously somewhat subjective.
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#16
(08-18-2019, 01:08 PM)Sean Wrote: .... stacking multiple mons in order to achieve 10A and above.....
If high bypass currents are wanted, maybe active balancing units would be a better answer, although they can tend to mask issues. 10A long term bypassing with stacked longmons is highlighting bad design of something!

(08-18-2019, 01:08 PM)Sean Wrote: Batrium mons, or any other competently designed cell monitor will prevent a cell being charged to a voltage deemed to be excessive - that is one of their main design criteria, but they'll only be able to do that in a correctly configured system.
Yeah that's what I was pointing out, unless the Watchmon can trigger something else, a longmon won't protect a cell by itself.
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