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Off grid fridge project in west africa
#21
(01-20-2019, 10:47 PM)babish Wrote: at what voltage should I charge them? should I try a lower voltage first, eg 12 or 24V?

It's not so much what voltage but the current you push into them - you have to limit the input current eg set the charger current or put some DC lamps in series so the batteries only see 1A or so until they recover in voltage, then you can go back to "normal charging".
Running off solar, DIY & electronics fan :-)
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#22
I only have the solar charger where the max current setting starts at 10A. So I will try with 24V just before dusk first, and check that I have less than 20W from the panels.
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#23
Ouch. Touch lesson but 1.5kwh aint much and 6 weeks is Long time. Thats what you need the disconnect for.

Disconnect the wm from the battery first then Connect to your computer
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#24
The actual time they've been "badly discharged" might only be eg 2 weeks, not the whole 6, ie:
- they started with some charge in them,
- got slowly discharged to the point the electronics draws even less power, eg CPU not runnin g (maybe ~4 weeks or so)
- then dropped to now.

With care you'll probably get them back to some useful capacity.
Running off solar, DIY & electronics fan :-)
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#25
I could not initiate the charge with the solar charger, the battery is too weak (and after a few seconds when I tried to switch it on, some of the bad cells went to almost 0V, though it came back higher later)
The only solution would be to directly wire one of the 30V PV, I could try just before dawn to have a very small current.
Though the http://nordkyndesign.com/lithium-battery...egradation paper is quite scary, I will need to carefully monitor the cells voltage during the charging.

edit: maybe not a good idea, as it is more the voltage than the current that would drop with low light?
 
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#26
Actually the charging with the solar panel was fine, at 30V with low current. I charged for about 30min before the night and now the voltage per cell is:
1 0.84
2 0.69
3 1.52
4 1.56
5 0.97
6 2.08
7 2.08
8 0.33
9 0.36
10 2.2
11 2.41
12 2.51
13 2.6
14 2
15 2.63
16 2.65

hopefully the ones that got back above 2.5 or 2 will be fine, I will try again tomorrow morning until the current get a bit above 0.5A.

Also should I disconnect the blockMon? they start to blink red above 2V and solid green above 2.5V
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#27
I'd suggest to keep going, looks like the cells are coming back OK so far.

If you cannot keep charging, then remove the cellmons, otherwise you can leave them attached.

Try to get some more charge into the cells under 2V. Make sure all the cells measure a positive voltage & none measure a reversed voltage.

You could even connect the solar panels (at low light time) directly to the cell - the solar voltage will drop & just push some current into the cells.

Keep charging gently until you have all cells at or above about 2.9V, then you can start normal charging again.
Running off solar, DIY & electronics fan :-)
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#28
So I managed to slowly charge yesterday (<0.5A), using 2 panels in series and partially shading them.
I ended up with the voltage:
Yesterday 6pm Today 6am Diff
1 2.99 2.94 -0.05
2 2.97 2.92 -0.05
3 3.06 3.03 -0.03
4 3.08 3.05 -0.03
5 3.03 2.99 -0.04
6 3.11 3.08 -0.03
7 3.1 3.08 -0.02
8 2.89 2.77 -0.12
9 2.9 2.8 -0.1
10 3.1 3.08 -0.02
11 3.13 3.11 -0.02
12 3.12 3.1 -0.02
13 3.14 3.12 -0.02
14 3.11 3.08 -0.03
15 3.15 3.14 -0.01
16 3.14 3.13 -0.01

Also the shunt at rest is showing ~-0.004A, I guess from the self discharging of the cells?

Cells 8&9 and then 1&2 were the most damaged, so I probably want to replace them, though I would like to test them first and also test the other ones.

I am quite scared about "The first consequence of dendrite formation is increased self-discharge through internal micro short-circuits; those also induce cell heating during recharging. A cell that has faced such treatment can potentially fail at any time afterwards and there is no assurance any more that it might fail “nicely”" (http://nordkyndesign.com/lithium-battery...egradation).

I plan to keep charging them slowly until they are all above 3.2V, then I will try higher current charge and discharge while monitoring the temperature, and also monitor the self discharging.
Any other things I should do?
thanks for the help!
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#29
OK that's looking much better! Good job there.
re the dendrites, I'm not sure you'll have much if any of those because your cells will not have been totally dead flat for a long time (eg months).
I'd go ahead & start normal charging from here & watch them carefully.
I would be charging to about 3.40V per cell, not more (good value long term anyway).
Watch for:
- any cell going high voltage way too soon when charging (that's a definite immediate "remove it now"),
- out of balance as they get toward full & you may need to stop charging the whole pack & manually balance low cells to equalize them.
- any self discharging overnight (may still recover to normal with a few cycle/discharge cycles),
- any further bloating (that's a definite immediate "remove it now"),
- anything else obvious like heating.

After you've balanced the pack & let it sit full for a day or so (& all else is good) eventually you want to do a capacity test - run a known "moderate" load on the pack & time how long it takes to hit the bottom (any cell goes below about 2.90V).
I would not do anything more than a quick 1-2mins medium higher current test with them yet.
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Running off solar, DIY & electronics fan :-)
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#30
ok thanks, I will do.
what do you call "moderate" and "medium higher" current?
I usually have 2 loads, one ~ 50W and one 80/120W, so between ~ 1 and 4A, so I guess pretty small.
I will run only the 50W load first.
Also about charging should I still limit to low current for now, eg max 2A? Or how high can I go if I do not see overheating?
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