Begginers Guide to Processing 18650 Cells | Cell Database


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TP4056: Is the series shorting problem fixable?
#21
Thanks for catching that. Fixt it. Smile
-Mike G
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#22
Just a idea,
100% isolated...
http://www.benl.ebay.be/itm/Wireless-Pow...SwiDFYNxcd

i have used these ones before to charge a wireless display.
http://www.benl.ebay.be/itm/5V-2A-Wirele...SwtfhYqLoL

works perfect, no need for charging wires anymore.
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#23
Did some experimenting to confirm the isolating effect of using individual power supplies for each TP4056:


-Mike G
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#24
I fully charged two cells in series with the isolated converter boards today.
[Image: a9e046ca4f99e486b90d9d2f78a6c827.jpg]

While they were charging, I played around with a Volt and Amp meter at various points in the circuit. What I found is that with both TPs running, the center green wire doesn't seem to do anything. I think what is happening is that with the boards hooked up like this, they are effectively sending 8.4V 1A to the whole battery.

The green wire becomes important once either of the boards finishes before the other. If for instance, the top board finishes first, the green wire becomes the positive for the second board, and the red wire is no longer in use. Or if the bottom board finishes first, the green becomes the top board's negative, and the black wire is no longer in use. Neither board got any hotter than they normally do. So, I think this can be scaled up to the 7s batteries I want to charge.
grgdgreek and Korishan like this post
-Mike G
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#25
Very Nice setup. have you measured any drain from the tp that stops to the other battery?
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#26
another thing to consider, though I don't know if it'd effect the TP's sensing ability, is put a diode between the TP and the junction of the green wire. But that might cause too much of a voltage drop and cause overheating. Hrmm, maybe not a good idea then *ponders*
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
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Certified 18650 Cell Reclamation Technician
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#27
I don't know enough about electronics to tell if a diode would be good or bad.

As far as I can tell, the charged cell has no effect on the cell still charging. Once the TP decides its finished, it seem to completely remove itself from the circuit. As far as the additive voltage between the two, I think that's what is happening. What makes me think so, is that I know a single TP4056 board will read around 4.2V when its in constant voltage mode, but when I put the probes directly on the cell being charged, it is typically less than 4.2V until its close to the end of its charge. With the TPs in series like this, I measure 8.42V from the + out on the top one to the - out on the bottom. When I measured the cells while they were charging, I got less than 8V.

Unfortunately, both cells finished their charge while I wasn't watching, so I missed the behavior with one finished first. Both cells finished with a voltage of 4.18V independently. Maybe I'll try charging unbalanced cells next. Maybe one at 4V and the other at 3.7V. Hopefully, they would end at the same voltage but at different times.

I just got it fixed up a little so as to be a bit more compact and less clumsy looking.
[Image: 98eaca55feee277bc15f6d1d08e168e1.jpg]
Korishan and jdeadman like this post
-Mike G
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