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Dual charging

Drake2312

Oct 9, 2017
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Hello i am in the process of building a manual charger for use as both an average battery charger e.g. AA, AAA, 18650 etc. as well as power bank charger and I am trying to figure out a circuit design that will allow me to have them both connected to the power generator, but a switch will decide which will receive power e.g. switch is in position one the battery(s) will be charging and in position two it will charge the power bank, but i am having trouble figuring it out.
 

73's de Edd

Aug 21, 2015
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You are doing fine 'til you included the "18650"

They are a whole different story in the precise control needed for them
 

Drake2312

Oct 9, 2017
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aren't a lot of 18650 batteries just similar to most li-ion type batteries or is there something i am missing about them?
 

73's de Edd

Aug 21, 2015
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You started with the Ni-Cads or Ni MH and then also included the Li Ion family.
The latter needs critical current and voltage monitoring.
They are rated at 3.6 VDC but will creep up slowly from lower than that nominal value whle charging.
If they happen to reach somewhat above their critical threshold of ~4.3 Vdc you should find yourself with an open cell never-never-never to operate again.
In all of my different Li-ion units . . . I am NOT being in a hurry . . . so I charge them slowly at 1/10 current capacity and never let them reach a charge voltage level above 4.25 VDC . I still have some 18650 cells that date back to 2007 that I am still using.
 
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Drake2312

Oct 9, 2017
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ok well thanks for the info, but still even after removing the 18650 charging capability, i'm still a bit lost as i'm a bit new to circuit designing
 

BobK

Jan 5, 2010
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The question you are asking is the least of your problems. A simple SPDT switch is all you need to switch from sending power from one type of battery to another.

But, there is a lot more to this project than you realize. Lithium cells are actually easier than NiCd and NiMH to charge properly. All three of them need a different charging regimen, particularly in determining the end of charge condition. All three of them need special attention when they are overly discharged at the start. You do not simply connect a voltage source, or even a current source to the batteries to charge them, although you can do this if you are only interested charging at a rate that will take about 24 hours to charge them. And different capacity batteries require a different charging current.

For a power bank, you DO charge it using a voltage source (5V) because the charging smarts are inside the device.

A general purpose charger like you are describing is not a simple project.

Bob
 
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