GoldenMotor.com Forum
General Category => General Discussions => Topic started by: GM Canada on April 02, 2012, 08:27:03 PM
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Hey All!
Recently I was asked about the cells in a LiFePO4 Battery. Are the cells really Square? Do they really have the screw on tops for joining the batteries? Or are they like the older style lithium batteries we used to sell. Machine soldered together in groups. Almost impossible to repair.
Well lets take a look.....
First here is one of my batteries in current daily use.
(https://arhservices.co.uk/GoldenMotorCanada/001-4.jpg)
First I remove all the screws from both ends. Make sure yo have a good fitting screwdriver so you don't strip the screws.
(https://arhservices.co.uk/GoldenMotorCanada/002-2.jpg)
This is a look in the keyswitch end. Seems like nice heavy gauge wires!
(https://arhservices.co.uk/GoldenMotorCanada/003-1.jpg)
Now the charging end. Thinner wires but fine. I also notice some sealant and you can see the BMS.
(https://arhservices.co.uk/GoldenMotorCanada/004-1.jpg)
Next to slide it out you tuck in the end cap on one end and push everything through. Be careful you don't damage anything.
(https://arhservices.co.uk/GoldenMotorCanada/005-2.jpg)
Now its all out of the case.
(https://arhservices.co.uk/GoldenMotorCanada/006-4.jpg)
Now let's cut it open.
(https://arhservices.co.uk/GoldenMotorCanada/009-2.jpg)
16 nice big square cells with a black foam cover over the wiring.
(https://arhservices.co.uk/GoldenMotorCanada/010-3.jpg)
Peel the foam back an we find this.
(https://arhservices.co.uk/GoldenMotorCanada/011-4.jpg)
Screw on terminals, I like it!
(https://arhservices.co.uk/GoldenMotorCanada/012-5.jpg)
Looks pretty Impressive. seems like replacing cells is possible if necessary.
(https://arhservices.co.uk/GoldenMotorCanada/013-4.jpg)
The little black bits are just foam that still stuck to the cells when I peeled it back.
(https://arhservices.co.uk/GoldenMotorCanada/014-1.jpg)
There was no writing on any of the cells I could see. I did not want to cut the shrink wrap any more then I already did as I still want it to hold together nicely.
So for now its back together again and I used it to go to work today. What a nice ride it was coming home. Summer is coming!
Gary
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Hi Gary.
Thanks for the great photos. I'm wondering how the cell sense wires for the BMS are attached to the cells? Solder? just stripped and slipped under the buss straps?
TTFN,
Dennis
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lol
I was thinking as I was putting it back together everyone will want me to open it again :)
Once I opened it I thought I will have to do this again in the near future when I have more time. I want to see if the cells have writing on them in an area I didn't remove the wrap. Also see if the cells are attached together or if they can e removed easily.
This was just a very brief moment in a busy life and I had to get it back together again to charge for work again. For now we will have to scrutinize the pictures for more details.
If anyone else want me to look at something the next time I open it let me know.
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I was hoping the cells would look like this.
(https://arhservices.co.uk/GoldenMotorCanada/LargeLiFePO4Cells.jpg)
Now that I look at the pictures they do seem to be individually shrink wrapped. I want to see a cell individually. I also want to see if there is any matching numbers to this info.
(https://arhservices.co.uk/GoldenMotorCanada/LiFePO4Cells.jpg)
Gary
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Nice one Gary,(http://www.arhservices.co.uk/GoldenMotor/emoticons/everyday_thumb_up_230608.GIF)those pictures should provide the answer to many of the questions that have been asked.
I counted 16 cells (51.2V nominal @ 3.2V/cell), which should give a fully charged voltage of 57.6V @ 3.6V/cell (or 58.4V @ 3.65V/cell).
What voltage is stated on the charger?
I'm wondering how the cell sense wires for the BMS are attached to the cells? Solder? just stripped and slipped under the buss straps?
Dennis,they appear to be soldered to the centre of the links and the hot melt glue should do a good job of holding them securely in place so they don't move and fatigue at the soldered joint causing possible failure.
Also see if the cells are attached together or if they can e removed easily.
If anyone else want me to look at something the next time I open it let me know.
The typical assembly technique for assembling the soft pouch cells is to use double-sided tape between the cells to hold them in place before the shrink-wrap is applied:
(http://www.arhservices.co.uk/GoldenMotor/P1010976.JPG)
So it's possible that this method has been used with these rigid cells too.
I had to use some strong nylon fishing line to carefully cut through the sticky tape between the cells on my LiPo pack when I had to remove a faulty cell from it.
The fishing line worked like a cheese wire and has no sharp edges which might otherwise damage the cell's outer wrapping.
It would be nice to see what the BMS looks like next time you open it up. ;)
I was hoping the cells would look like this.
(http://www.arhservices.co.uk/GoldenMotorCanada/LargeLiFePO4Cells.jpg)
Now that I look at the pictures they do seem to be individually shrink wrapped. I want to see a cell individually. I also want to see if there is any matching numbers to this info.
(http://www.arhservices.co.uk/GoldenMotorCanada/LiFePO4Cells.jpg)
It looks very similar to the 10Ah version of those cells, and the corners inside the shrink wrap appear to be well formed (not soft rounded edges like the typical pouch cells have).
Alan
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Thanks Gary this is great. There was a question about GM LiFePo4 batteries on the TERA board today and both myself and lock put out what we knew and then I came here to see you had already done a picture laden report.
Doug
PS, yea I did and update for TERA
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What voltage is stated on the charger?
Originally the liFePO4 Chargers were marked at only 48 volts but they did bring the batteries up much Higher then that. Around 56 volts I think. Gawd my memory sux sometimes. My latest Chargers are now marked 58.4 volts. So maybe they have already improved the LiFePO4 Batteries, Chargers or both.
Gary
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Thanks Gary this is great. There was a question about GM LiFePo4 batteries on the TERA board today and both myself and lock put out what we knew and then I came here to see you had already done a picture laden report.
Doug
PS, yea I did and update for TERA
Yay TERA!
First meetup this year April 15th 2012!!
See you on Sunday!
Gary
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They look awesome Gary. And no don't remove any more shrink wrap. Other members here please do not do this to your New LiFePo4 packs. NO NO.
LOL you take a risk removing the first lot Gary. This adds back pressure, to a pressure that can increase inside the cells when you push them, the cells get warm, and the electrolyte can un-precipitate causing slight puffiness, this then increases the distance between electrodes and significantly decreases the capacity.. Sure they are dry cells, NOT! Just not water based as in Dry. Without mechanical pressure and the vacuum created between electrodes when the roll them tight, Lithium electrolyte evaporates at room temperature and stinks to high heavens..
I suspect the added shrink wrap helps increase its C rating. I had these old puffy 5Ah cells in aluminium cases, and they were pretty useless, I compressed them together in G clamps between wood, and they regained almost full capacity. Inside those cases are just LiFePo4 pouches and will perform better with the shrink wrapping.
This is why often round cells usually have better C rating because the round cells have less chance of bulging under high stress and can get a lot warmer, the flat cells flat sides can expand out more easily, and it is imperative they are held together like a brick sh!t house..
But the only issue now is, a spot weld can fail hurting the cell, so can a battery lug not tightened up with the correct torque applied to the nut. If a lug is loose it is bye bye battery cell.
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And if I was you Gary I'd pack them back up solid as, before you try 3C from them. Even if you can improve on the original job would be nice.. The pressure should be even over each face of the cell block.
The packs look very well constructed, and thank you very much for sharing.
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Two cells,a yellow cylindrical cell, a blue rectangle cell.
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And BMS.
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Two cells,a yellow cylindrical cell, a blue rectangle cell.
Henry,
I assume the yellow cell is a 26650 4Ah LiMn2O4, but is the LiFePO4 cell in the picture a 10Ah or 12Ah one?
Also, is the 60Amp BMS shown in your picture the correct one for a 10Ah pack? because I see that the 10Ah pack is only rated as 50Amp max.
Alan
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Hi Alan.
You are always right, that cell is 12 AH. 10 ah cell and 12 ah cell size are almost the same. I think that 48v BMS is for 10 AH pack, due to the lack of care found and I'm not sure, I also don't quite understand why is 60 amp, it is the equilibrium current ?If it's max discharge current , that becomes 48/20's?
You know I am utterly ignorant of technology,I have to go back to have a look.
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Two cells,a yellow cylindrical cell, a blue rectangle cell.
Henry,
do you know where I could purchase 3 of the orange cylindrical cells (for repair of my 48V pack) ?
Any information appreciated, many thanks.
Pavel
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Two cells,a yellow cylindrical cell, a blue rectangle cell.
Henry,
I assume the yellow cell is a 26650 4Ah LiMn2O4, but is the LiFePO4 cell in the picture a 10Ah or 12Ah one?
Also, is the 60Amp BMS shown in your picture the correct one for a 10Ah pack? because I see that the 10Ah pack is only rated as 50Amp max.
Alan
The round one you are correct. The square one is a 12 ah cell. You can tell by the battery connection points. For some reason the 10 amp hour cell has pins the 12 amp hour has flats. Could they just be inverted to prevent mixup? Please forgive my tech talk.
The 60 amp bms is for the 40v30ah battery. I recently had one open and took some pictures. I will upload them to the forum soon. The 48v10 amp bms is 30 amp. I have not opened a 48v20 yet but will soon.
Gary