Author Topic: Lifepo4 charging  (Read 101 times)

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Offline CG

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Lifepo4 charging
« on: December 07, 2020, 11:22:01 am »
« Last Edit: December 10, 2020, 08:46:02 am by CG »

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Offline CG

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Re: Lifepo4 charging
« Reply #1 on: December 09, 2020, 06:20:59 pm »
So ....after charging and discharging this LiFePO4 cell a few times I'm starting to become a fan.
Not for cells in series though. They still require balancing and if not balanced one cell could be charged backwards. You could use them in series with balancing boards connected.
Still running tests on the one I have.

Offline CG

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Re: Lifepo4 charging
« Reply #2 on: December 10, 2020, 08:40:09 am »
I've been charging this 3.2v cell with a 7 v power source. Which produces about 280 mA.
The 'cell' itself controls the voltage in the beginning, turning the 7 volts into charging current. But it requires some baby sitting near the end as cell voltage rises and current goes down.
I'm looking for a wall wart supply that will charge the 3.2 volt LiFePO4 cell  with 12 volts. That way I'll get the 1/10th C charging current I need. Just need to turn it off when the voltage gets to about 3.6  volts. (Using the Triac circuit).




To eliminate the cell balancing act using multiple LiFePO4 cells in series, we could just use a single 3.2 volt cell and a dc-dc converter.
My single LiFePO4 cell is rated at 6000mAh and as the link below shows , the LiFePO4 cell has very high discharge rates.

It would be great if they could make the LiFePO4 cell in a 'flat pack ' shape , like cell phone Liion cells.

https://endless-sphere.com/forums/viewtopic.php?t=1773



FOUND IT>>>>>>>>     https://overkillsolar.com/product/lifepo4-cell-100ah/
« Last Edit: December 10, 2020, 09:01:59 am by CG »

Offline CG

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Re: Lifepo4 charging
« Reply #3 on: December 10, 2020, 10:15:45 am »
Another solution.
A cheap BMS for series connected cells.
It could be as simple as 6 dpdt switches with their toggles bolted together.
This will charge three cells "IN parallel" which will auto balance the cells. Then switch to "in series" to get higher voltage in discharge mode.

https://drive.google.com/file/d/1jsUqN_ju3MeCcUhk18xyG6ffMNqdyVcb/view?usp=drivesdk

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« Last Edit: December 11, 2020, 08:05:38 am by CG »

Offline Caleb

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Re: Lifepo4 charging
« Reply #4 on: December 10, 2020, 07:36:29 pm »
I can't access Googledrive files, but your description is pretty good.

Offline CG

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Re: Lifepo4 charging
« Reply #5 on: December 10, 2020, 08:02:09 pm »
Try the one above again. Does it work? Google keeps changing things. Drives me nuts.

Offline Caleb

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Re: Lifepo4 charging
« Reply #6 on: December 11, 2020, 07:28:00 am »
No, it still doesn't work.  I have to be signed up with an account that has access, but I don't have one of those.  I'm trying to avoid Google as much as possible.  :-\

Offline CG

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Re: Lifepo4 charging
« Reply #7 on: December 11, 2020, 08:09:55 am »
Ok. Darn Google.
I attached an image to the post. Just click on it to expand it. You can pan the image also.
This makes more work for me as administrator because we have limited space on the 'free' forum . I will have to start 'pruning " older images which ruins the archival aspects of the forum.
I need to find a 'free' image hosting sight like 'photo bucket' used to be. before they screwed everything up.
If you want to see any other images let me know.

try this>   https://www.dropbox.com/s/pj84x494bhbj92l/IMG_20201210_101105_630.jpg?dl=0
« Last Edit: December 11, 2020, 09:22:45 am by CG »

Offline CG

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Re: Lifepo4 charging
« Reply #8 on: December 11, 2020, 02:58:40 pm »
I wonder if this will turn off the charger when the battery reaches a set voltage?

https://www.dropbox.com/s/7l8od1il0s03tp2/IMG_20201211_145510_163.jpg?dl=0

Offline Caleb

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Re: Lifepo4 charging
« Reply #9 on: December 11, 2020, 08:25:03 pm »
It might, but I don't think the voltage level will be all that precise.  Maybe adjusting it will make it work, but I don't think the triacs are made to turn on a precise voltages.

Offline CG

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Re: Lifepo4 charging
« Reply #10 on: December 12, 2020, 06:32:05 am »
Yes, thats why I put in the potentiometer. It won't be exact but will be good enough to stop it from overcharging.

Offline CG

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Re: Lifepo4 charging
« Reply #11 on: December 14, 2020, 06:05:31 pm »
Okay, that design didn't work, because I couldn't get enough current through the collector to emitter.




I built this and it works>>>>>>>https://www.dropbox.com/s/eq5shrh7ctbx41h/IMG_20201216_085335_518.jpg?dl=0
« Last Edit: December 16, 2020, 08:55:49 am by CG »

Offline CG

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Re: Lifepo4 charging
« Reply #12 on: December 17, 2020, 02:44:12 pm »
The BJL_LED is running wide open at 168 mA off of the LiFePO4 cell. It has run 14 hours so far (2350 mAh). I'm hoping it gets close to the 6000 mAh rating.

Offline CG

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Re: Lifepo4 charging
« Reply #13 on: December 18, 2020, 09:22:37 am »
4025 mAh so far. Hooowee

Offline CG

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Re: Lifepo4 charging
« Reply #14 on: December 18, 2020, 04:48:00 pm »
5000 mAh
Almost there.