Beginners Guide to Processing 18650 Cells | Cell Database



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HBPowerwall (Official)
Its also the Limitation of the Longmons to dissipate enough energy. too large of a single cell in Ah it would take too long to balance. Also what Korishan said
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(02-18-2018, 01:48 PM)Korishan Wrote: 1)The logic behind it is if you have to take a string out of service for some reason, you don't have an imbalance....
2)The other reason is you can't get away from needing a balance board for each pack....
3)it would take it waaaay longer and harder to keep that pack in balance.
4)it would make it super hard to find a problem cell.
5)It would just need to add a lot more hardware/monitoring to be able to keep an eye on all the packs.
6)You would need for sure to add a current shunt on each pack, and probably have one between packs....

I am one of those who did it the "other" way... Big Grin
my setup has a connection in between each pack in serie's, so every pack are realy 3 packs of 90p in parallel

Soooo, my thinking on Korishian's thinking:

1) Same if you have a setup with 4 strings of 14s80p (like Peter), if you take out 1 pack for service, that whole string is out of service...
if you have packs in parallel and draw is low, you can take 1 pack out for inspection ( few minutes ) and put it back, i do this often. For a big repair, just have to take out 14 packs at once.

2) only need for 1 longmon for each "pack" in series, no more than 14 in my case.

3) initial balancing will take long, yes, but once balanced, the longmons have no problem to topbalance (again, in my case...)

4) True, but with a bit of a elimination proces, it wont be a problem.

5) shunts between the packs?.. they have no use on this setup , the packs in parallel have always the same voltage, as cells in parallel have... never more than 14 "packs" to monitor ... so, less hardware needed. 
A fuse on each pack might be a good idea... but is it not always?

6) As sayd, packs in parallel have same voltage, so no currents should be possible in between them, if there is, ie after a high current draw, a difference between the parralel packs, they will simply balance, as cells in parralel  in a pack will do.

The longmons have a max balancing current of Max 2A (if cooled), so they are limited... on this part i aggree, but if your packs are well balanced in capacity, in sets of 14, from the start ... they can handle pretty big packs.

The pro's are : 
- way less "big, heavy duty" cables / connections needed.
- Only 14 "packs" ever to get out of balance.
- No inbalance inbetween the strings of 14s.

The con's :
- Maybe, when the cells are getting older, there will be to much of a inbalance for 1 longmon to handle... possible...

This is why i have a interest in that "flying pack" thing, to do kind of continius balacing ... or i might just add a longmon  Wink

I am using my system for 10 months now, never got a problem with balacing (even after adding packs) . 
The longest balancing session took about 24h and this after not balancing for 3 months... 

So yes, you can do it, but instead of 1 super big pack, it is better to build a few smaller packs and connect them in parralel... more options this way.
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18x 300Wp solar off grid and 10x 180Wp solar tracker grid-tie
10KW 3phase hybrid inverter. 40Kwh 18650 storage (for now)
My setup: http://www.diypowerwalls.com/t-Instant-powerwall
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5) shunts for each pack was to see which direction the current was flowing to help in narrowing down the leaking pack. If you only have 3 strings, this may not be a problem. But if you have 5 or more, it gets increasingly difficult and the shunts could help narrow down the troubled pack. If string 2 pack 3 has a leaker, then all the other shunts will show current flow going towards string 2 pack 3.

I'm all about super automated and super data collection. So in my packs I'm going to have monitors on each pack as well as each string. I will be able to find the troubled cell relatively easily/quickly. But, I like knowing everything little thing goin on and micro-managing. (this is why I like sim games like SimCity, Civilizations, Settlers Online, etc)

It is doable. Just needs a little more attention to keep it all balanced. Which wim alluded to above Wink

Not saying to not do it. It just takes a bit more forethought to put it all together.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
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Certified 18650 Cell Reclamation Technician
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(02-18-2018, 04:45 PM)wim Wrote: So yes, you can do it, but instead of 1 super big pack, it is better to build a few smaller packs and connect them in parralel... more options this way.

Pretty much just like I thought it, smaller packs but connected in parallel on every potential/voltage -level.

Was also thinking, maybe connect the parallel packs with some small resistance/resistor, to limit balancing cross currents between packs, or am I thinking too much already?
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The resistance between the packs should be low as possibele.... or they are not realy in parralel....
If there is no resitance, there wil be no voltage difference and no currents between the packs.
A bad "draining" cel wil blow its fuse or drain the packs down enough to show on batrium. 

That sayd, a resistor between the packs instead of a wire ( so no packs in parralel ) is a interesting idea ... hmmm ... needs some thinking  Smile
___________________________________
18x 300Wp solar off grid and 10x 180Wp solar tracker grid-tie
10KW 3phase hybrid inverter. 40Kwh 18650 storage (for now)
My setup: http://www.diypowerwalls.com/t-Instant-powerwall
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A resistor between packs will give you the worst of both worlds.
Resistance will be too high to add any currency carrying capability under load or charging.
Even the smallest resistor will give some balancing effect between packs and allow a bad cell to sligty draw down all the parallel packs it’s coonected too.

Working in the industry with telemetry for the last 30 years, some monitoring is essential but you very quickly reach the point where more monitoring doesn’t pay for itself.
E.g I’m building a parallel busbar type system, I wouldn’t run it without a batrium or similar to balance and monitor, if a bad cell is pulling a pack (made up of sets of packs to a common busbar) down I’ll know which set of packs to start checking. The added expense and complexity of knowing which one of the 3-5 sub packs to check won’t pay for itself in my opinion.
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