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J-Mans project
#31
(05-24-2017, 08:51 PM)Korishan Wrote: Looks good.
You can heat your bus bar pretty hot if need be. Its not transferring heat to the cells like you'd have if you're directly on the cells.
Make sure you have plenty of flux. It's possible your solder you are using isn't flowing the flux fully.
It's possible your multimeter isn't fully calibrated, or the iMax isn't. If you can get another MM to test to the voltage, that could help you zero in the true voltages.

Some MM's have an adjustment resistor inside to fine tune the voltages.

You could name your build the Purple Power Eater  Tongue

ah ok thats good to know. Ill try with some more flux next time 

Definitly the iMax, I noticed before that when i did the very first discharge tests it shows 0.2V below the actual cell voltage. Not really a problem when charging my packs, ok at the end it might be slower as is lowers the current earlier. I was reading about calibrating the iMax, the thing where you get one chance to do it and then the menu disappears for ever :Big Grin Ill try it out maybe in the next days. 
Ill check my MM as well, wasn't exactly an expensive one but it seems accurate 

hahahahha I like it!
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#32
(05-24-2017, 09:29 PM)The-J-Man Wrote: ah ok thats good to know. Ill try with some more flux next time 

Definitly the iMax, I noticed before that when i did the very first discharge tests it shows 0.2V below the actual cell voltage. Not really a problem when charging my packs, ok at the end it might be slower as is lowers the current earlier. I was reading about calibrating the iMax, the thing where you get one chance to do it and then the menu disappears for ever :Big Grin Ill try it out maybe in the next days. 
Ill check my MM as well, wasn't exactly an expensive one but it seems accurate 

hahahahha I like it!

Hi The-J-Man,

to know the correct voltage is extremly important. To set the cells on overvoltage is deadly - it destroys the chemistry.
I have also two i-Maxes ( should be genuine because of hologramm on bottom plate) but every one shows his own "measured" voltage.
I have had to buy a real DMM tool - Fluke and since then  I do not have any worries. It is callibrated and shows very precise the voltage.

Best regards
BigBen
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#33
(05-25-2017, 01:55 PM)BigBen Wrote: Hi The-J-Man,

to know the correct voltage is extremly important. To set the cells on overvoltage is deadly - it destroys the chemistry.
I have also two i-Maxes ( should be genuine because of hologramm on bottom plate) but every one shows his own "measured" voltage.
I have had to buy a real DMM tool - Fluke and since then  I do not have any worries. It is callibrated and shows very precise the voltage.

Best regards
BigBen
thanks for your help.
I have accessed the calibration menu and calibrated the voltage reading as close as possible with a cell at 4.21v. It worked so far but when im charging its still off. 
Im charging my 120p pack and when pack voltage is 4.11 the imax is reading 4.2, the lower I set the charge current the more accurate the reading is. Am I getting some resistance some where or what could cause this?

cheers
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#34
One of the reasons i dont use an imax Smile Note that you get voltage drop on the wires when actually doing charge/disharge and its normal on those thin wires and solder points inside since it does the meassurement at same time as it do pull current through it.
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#35
Newest addition: 120 NCR18650PD /F cells out of practically new e-bike batteries. It was actually 160 cells but the connectors were spot welded so damn good that the cells tore open when trying to tear off the connectors. So I lost 25 cells that way.... I ended up leaving the connectors on at the negative end after that. 
One of the packs of 50cells was super discharged over the course of 4 days I was told, to purposely render it broken. This is the first pack I took apart and lost 15 of those cells due to the reason above. Voltages were at about 0.6, I revived them and most ended up at 2700+ (on the opus) as opposed to 2900+ for all other cells. A couple of the revived cells are down at 2500 so they are being put aside since they probably took some damage of some sort.

This will probably be my 14th pack as I currently dont have enough cells from the hoverboard packs for 14 x 120, ( have 1560cells atm)

Also have another ebike pack sitting here with a broken bms it seems. Pack voltage 40.1 at the moment, cells are NCR18650A and 40 of them! Also barely used! 

Hard to include these in my build which will be 90% out of the 2200mAh hoverboard cells but who knows how this project will end up going.. Wink

Slowed down a bit as I am super usy with work at the moment and have not found the time to take apart my remaining 30 odd hoverboard packs.

(05-30-2017, 04:39 PM)daromer Wrote: One of the reasons i dont use an imax Smile Note that you get voltage drop on the wires when actually doing charge/disharge and its normal on those thin wires and solder points inside since it does the meassurement at same time as it do pull current through it.

Ahh ok that makes sense then. Its more accurate then it was and it still charges to 4.2 in the end, it just slows the charge current earlier


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#36
Still testing cells here, but things are progressing Smile

Got another question. The test pack I soldered together has been sitting here for like what 2 weeks now, maybe longer I cant remember. Well I charged it fully back then and it was at 4.2V, yesterday I measured it and it was 4.13V. I plugged the iMax in last night and up until now it has put nearly 8000mAh back into the back. There arent any warm cells or alike so hows this possible? Anyone know?

cheers


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#37
Cells will self-discharge. Did you check self-discharging before putting the pack together? If not, you may have 1 (or more) cells that are discharging faster than the others and it's sucking the power from the others. You want to let cells sit for at least 2 weeks (mine sit for at least a month or more) to test their self-discharge rate. There's several threads that talk about this and help to clarify the mud a bit. But you definitely don't want to just charge and capacity check the cells and then just throw the similar ones in a pack. You need to let the cells sit unattached to anything.

.7V in 2 weeks does seem a lot to me. I'd gather you have a cell or more that are not holding charges.

Also, 4.2V is not your normal running operational voltage. You want to stay around 4.1V anyways as this increases cell life.
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#38
(06-15-2017, 04:27 PM)Korishan Wrote: Cells will self-discharge. Did you check self-discharging before putting the pack together?  If not, you may have 1 (or more) cells that are discharging faster than the others and it's sucking the power from the others. You want to let cells sit for at least 2 weeks (mine sit for at least a month or more) to test their self-discharge rate. There's several threads that talk about this and help to clarify the mud a bit. But you definitely don't want to just charge and capacity check the cells and then just throw the similar ones in a pack. You need to let the cells sit unattached to anything.

.7V in 2 weeks does seem a lot to me. I'd gather you have a cell or more that are not holding charges.

Also, 4.2V is not your normal running operational voltage. You want to stay around 4.1V anyways as this increases cell life.
thanks for your reply mate

I just checked, its been just above 3 weeks actually. 
I didnt check self discharge no. each of my 120p blocks is made from 6 hoverboard packs. this block was made from 6 pretty much perfect packs, that were sat idle at my recycler for several weeks, and they were all at about 4V when I got them, between charging and discharging was 1-2 days and the cells all went into my opus at minimum 4.18V. 
Once its charged again I will let it sit again and see what happens. 
Can 1 cell cause this? Wouldn't there be a hot cell then? --- Thats a lot of energy to be dissipated by 1, even if its 5 cells. 

Ill definitely use my packs at 4.1V once its all set up.
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#39
if 1 cell is has a higher IR and is discharging faster than the others, then it'll pull the other down, yes.
That 1 cell won't necessarily get hot. If it's only burning 100mW, then it can take awhile for it to pull the pack down, and that little bit of heat can dissipate faster than what it's being produced. There's some math wiz's on here who can better explain it than I can. But I do know that 1 cell can bring the whole pack down.

It's kinda like self-balancing a pack. Several ppl on here will allow a pack to balance itself when all the cells are in parallel. Now, there may not be anything inherently wrong here. The one cell that's causing an issue could just be wanting to be at 4.15V and not want to stay any higher. Anything over that, it'll burn off till it reaches "its" top-end mark.

Just charge them up again, let 'em sit for a month or so, and then recheck them. If they went down to 4.13V again and not any lower, then you know what that packs' stable max voltage is. Which, is still fine as long as it's over 4.1V. If they want to stay lower than that, you might wanna pull them apart and find out which cell is killing the pack.
Proceed with caution. Knowledge is Power! Literally! Cool 
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#40
(06-15-2017, 06:56 PM)Korishan Wrote: if 1 cell is has a higher IR and is discharging faster than the others, then it'll pull the other down, yes.
That 1 cell won't necessarily get hot. If it's only burning 100mW, then it can take awhile for it to pull the pack down, and that little bit of heat can dissipate faster than what it's being produced. There's some math wiz's on here who can better explain it than I can. But I do know that 1 cell can bring the whole pack down.

It's kinda like self-balancing a pack. Several ppl on here will allow a pack to balance itself when all the cells are in parallel. Now, there may not be anything inherently wrong here. The one cell that's causing an issue could just be wanting to be at 4.15V and not want to stay any higher. Anything over that, it'll burn off till it reaches "its" top-end mark.

Just charge them up again, let 'em sit for a month or so, and then recheck them. If they went down to 4.13V again and not any lower, then you know what that packs' stable max voltage is. Which, is still fine as long as it's over 4.1V. If they want to stay lower than that, you might wanna pull them apart and find out which cell is killing the pack.

Awesome thanks, I understand the concept now Smile
ill do that, nearly charged, 9000mAh went into up until now
12000mAh now  Dodgy
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