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Battery bank charger build

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fbeans

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A few months ago I purchased a 3.7v - 10,000mah LiPo battery and project case from ebay. The battery came with a pcb installed and the case came with a pcb to attach to the battery and mount to the case. I did that and then charged it. It displayed 100% and I was excited. I let my S3 discharged to about 25% remaining and plugged it into my new charger. My oem phone battery is 3.8v - 2,100mah so if I understand the math, my new charger should be able to charge my phone from say 10% to full at least 4 times before needing to be recharged itself.?

So my phone at 25% is plugged in to the new charger and in about 20-30min the charger is displaying 76% and the phone is not even close to full charge. So after a while I decide that perhaps the pcb boards on both the case and the battery are fighting each other, is that possible.? Yesterday I took the yellow cellophane tape off the top of the battery to expose the pcb. I then removed it with the help of my soldering iron. I cleaned up the battery tabs and soldered the case pcb to the battery.

All day yesterday I monitored the battery during discharge (charging my phone) and charging for any heat issues because I know LiPo batteries are no joke. So far there haven't been any heat issues and the discharge rate seems to be inline now with my math because it only discharged 4% to charge my phone from 96% to full in just under 10 minutes.

Any here's a picture (I hope) of my project and let me know what you think of my ramblings. (I couldn't find the "advanced editor" button so I clicked on "upload a file" let me know if you see my picture)
charger3.jpg
 
I have removed the black tape and have applied plasti coat to the battery connections (if you were wondering).
 
You might have fixed it when you re-soldered on the connections. Residual heat might have burnt off some flux that was on a connection inside the board. The batteries shouldn't fight each other if the circuit was properly designed, they hopefully made use of a diode or high side PFET.

The battery itself should have a protection board on it, outside of the boost/LCD driver.
 
I think you are overlooking the actual battery charging efficiency losses plus the losses from the two stages of power conversion and control between the batteries.

Figure about 60 - 70% charging efficiency plus you have a 3.7 volt to 5 volt boost converter that is maybe 85% followed by a charging controller that is then taking the 5 volts back down to the 4.2~ volts the battery needs to charge which maybe 85% efficient at best as well.

All things considered if you get anything above 50% (2:1) charge transfer efficiency consider your battery to battery charging system to be working pretty well.
 
It's one LiPo pack and I took the pcm/pcb board off the battery and direct connected the battery to the project cases' pcm/pcb board that came with it. It appears that the board on the battery was fighting the board on the case. I refer back to my original post and I clearly stated that. Thanks though.
 
How are you measuring the heating given your system could easily be loosing 50% of it transferred power and still never break the 2 watt level on heat loss which if spread out over two batteries two control circuits and wheat ever else could easily be below the threshold of human perception by touch at any single point on the devices involved.
 
There are always power losses. You may not feel them but they're there.

I use an excellent iAnker 12,800mAh battery pack and it gets noticeably warm charging my iPad. iPad gets warm too. That's normal.
 
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