Charging two 3.7v Li-Ion Cells

So for a portable project, I will be using two lithium ion 2200mah 3.7v batteries in series to give me 7.4v. I have a USB powered 3.7v Lithium Ion charger found here https://www.adafruit.com/products/1905 . How could I charge both the batteries in parallel and then use them in series for 7.4v?

All help is greatly appreciated.

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michaelkellett over 10 years ago in reply to dougw +2

I see some problems with this idea - if one battery is at a significantly different state of charge and thus voltage form the other (and this happens as the batteries age) then a huge current will flow…
Kilohercas over 10 years ago in reply to derkarhu +1

You can also make very expensive circuit for battery charging, with CCCV push/pull 3A converters, just treat them as capacitors http://cds.linear.com/docs/en/datasheet/8052ff.pdf Super-capacitors are equivalent…

lz1ppl over 10 years ago

You ca just use something like that:
http://www.ebay.com/itm/2pcs-2-Cell-Lithium-Battery-Charging-Board-Charger-Module-Protection-DC-7-4V-3A-/151715735343?pt=LH_DefaultDomain_0&hash=item2352f6672f
or that:
2 Cells Single Lithium ion Battery Charger Module 1 2A PCB 18650 TP5100 iPhone | eBay

Or if you want to do it yourself you can use MCP73213 http://ww1.microchip.com/downloads/en/DeviceDoc/20002190C.pdf or some similar product.
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Former Member over 9 years ago in reply to lz1ppl

i know this is a little old now but does anyone know if this is balancing?

2 Cells Single Lithium ion Battery Charger Module 1 2A PCB 18650 TP5100 iPhone | eBay
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mkhanemkay over 7 years ago in reply to Former Member

Hi,

I have the same question, did you ever find the answer, could you kindly reply if you figured out if it balances or a Balance board is necessary.

Also, do you happen to know if we can charge 2s @ 5v input with this? , as this one seems like a switching type module (probably doing buck ,maybe)...

Thanks,
Khan
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zagene over 6 years ago in reply to lz1ppl

Hi, I purchased 10 of TP5100 modules trough Banggood and already six of the TP5100 failed miserably. (With all of them the TP5100 IC failed)
The problem seems to be with some sub standard components and I studied the circuit and the badly translated document so I redid the document as well as I could.
The main problem seems to be with the Schottky, the SS34’s reverse leakage current maybe just to high for the IC.
Im ordering MBRS540T3G (RS-Components number 688-0512) with an reverse leakage of 300uA as a replacement for the four that survived. Im also going to replace the remaining 10uF caps for just in case and also the 100nF cap. I’m going to use a low ESR 10uF cap from TDK with a 10% tolerance (RS-Components number 903-9170). All the components footprint is the same as the current. I’m also thinking about replacing the two 100 mili ohm resistor with a 1% tolerance 50 milli ohm 1W resistor (RS-Components number 126-0398) that is specifically for current sense purposes just to be on the safe side (The items takes way to long to reach me to risk the remaining four and with sensitive devices like the LiPo batteries high risk)
I have improved the translated document on the TP5100 and made some notes in PDF format If you are interested.
Hope this help
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