I built a battery bank with 7 Panasonic 3400s. I tested them for capacity before using them and all were as rated.
I have a Samsung J3 phone, and when it has a low charge, I connect the bank, and it goes to 50-60 percent power before the phone is fully charged.
I would think a bank with 7 Panasonic 3400s would last a lot longer. I’m not sure I could charge the phone twice.
Am I missing something, or am I expecting to much?
Where did you get 7x Panasonic NCR18650Bs?
What is your DIY powerbank?
Did you charge the 18650s before using the powerbank?
What is your USB cable?
How are you determining that the bank is at “50-60 percent power”?
The bank has a percentage light showing remaining power.
Ordered them form a reliable dealer some time back. And yes, I charged, and checked for capacity. All checked out.
Not sure of the bank brand, it isn’t on the case. And used several cables.
The only way to truly know the total capacity is to get a USB tester and a USB load device — Usually the capacity is around 40-50% of the cells —- Then use the same USB tester when charging your phone to get an acurate consumption mah
Make sure that’s actually an accurate “gauge”. Some go only by voltage on the cells, which can hold most of their SOC at higher voltages, then drop like a rock once they get into the 3s.
Either way, charging circuits can be rather inefficient, taking the bank’s cell voltage and stepping up to 5V, which goes to the phone and then gets stepped down to whatever feeds the its cells, etc. Losses in the cable, connector, etc., can all add up. Fast-chargers are worse, as they’ll suck down more current and generate more I²R losses everywhere along the way, more voltage-sag in the bank’s cells, etc.
If you’re so inclined, measure the charging current to the phone (eg, one of those in-line usb thingies) and “log” it for however long it takes before the current starts dropping. Then compare with the phone’s cell and bank’s cells.
This is something I didn’t know… which is why you guys who know, are much appreciated.
Most powerbanks have efficiencies in the 80-90% range.
Could you show us a picture of the top of the 18650s, and the powerbank?
Thank you.
The bank snapped shut and can’t get it apart. I have other batteries, but am leaving for work, will try to post pic when I get home.
“DIY use-your-own-18650” powerbanks have poor efficiency most of the time, combined with extremely high LVP trigger the capacity % can be way off.
But for 7 genuine NCR-B I’d expect at least 45Wh of output energy, that should translate into at least 2 full charges. Definitely something wrong with the batteries or powerbank.
These did have protection on them but I removed them to fit in case. I may run phone all the way down till it shots off, and then charge it, then run it down again and see what happens that way.
I don’t share your optimism….
Sure good powerbanks have that efficiency, even higher.
But I’ve seen tests of powerbanks that only deliver 40%.
But I must admit that weren’t DIYs. So the cells could be crap and not just the conversion electronics.
I must say I see the same thing regarding flashlights. The focus is on the lumens (mAh for the powerbank) and the modes (slots of the powerbank) but far less focus on the efficiency.
I’m not claiming I’m a powerbank expert, I’m not, but as a user I can say from experience a good 10,000 mAh bank has more (usuable) juice than a bad 15,000 mAh one.
Just my 2 cents…
I’m starting to think the bank kit and electronics are not up to par, so I may look for another case from a more well known maker.