Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Lithium cell observation

Status
Not open for further replies.

WTP Pepper

Active Member
Hi
This is an observation that appears to go against general understanding everywhere of how these cells operate.

Firstly, charging these cells at constant current to a constant voltage (4.2v) then cutting off at a pre-determined current depending upon C of the cell is my general understanding. The constant current and cut off is controlled by the device being charged in combination with the current limits of the charger.

I have a Nexus 4 phone, a Nexus 7 pad and an eCig that are regularly charged.

e.g. When I charge with the cheap wall plug USB adaptor supplied with the phone, it will eventually show 100% charge after a period.
When I charge from a higher power charger (but the current should still be controlled by the charging device - the phone in this case) it also shows 100% after time.

However, when discharged through use, the device runs down quicker when charged to 100% from the wall power thing compared to being charged to 100% by my in-car USB charger.

I am aware some chargers charge to 4.1v to prolong life, but even taking that into account, it doesn't add up. I am talking about 50% reduction of use timewise.

A different chemistry I know, but I have some 2800mAh AA NiMh cells where it said in the instructions that you need a heavy duty charger to charge them and not a cheap Supermarket NiMh charger to maintain their capacity. I have a Revolex charger and this seems a correct statement as I get the best out of them charging them at C/2 as opposed to C/10.

Our battery experts at work say this isn't possible, but this doesn't seem to be the case. I am using experience against so called science.

No detailed solutions but would be interested in a basic explanation or observations from others.
 
I think I know what's happening. Based on the service manual for the RAZR V3. there were three different charging level implemented IN THE PHONE. This was before there was any defined system. Resistors to the data lines in the cable or OEM charger defined this. You got stuck charging at a low level UNLESS you had the OEM charger or cable.

There is now a "charge only" mode which can supply like 1A of current and, I think, the USB standard can support something like 2A for Ipads etc.

Your "Experiment" has to have measured charing current in the equation.

Look **broken link removed**

and on the left side bar for "Charging Lithium Ion"
 
Hi,

To see if there is a difference in chargers, measure the final voltage of the cells once they are done charging.

Also, for NiCd and NiHM cells the charge acceptance factor is not as high for lower current charge rates than for higher current charge rates. For Li-ion though there should not be as much difference, although i myself have never attempted to measure this for those cells.
 
There are two different questions in your post.

First about LiPo (Lithium Polymer) battery. Easy to charge, more complicated to do safely.

1) If battery voltage is less then about 1.5v then it is damaged and may contain metal dendrites, attempting to recharge can result is cell bursting. The cell bag will enlarge like an inflated balloon under internal pressure.
2) If battery is less then about 2.7 vdc then only a trickle charge of less then 0.05C is applied until voltage rises above 2.8v or 30 mins. to 60 mins. pass where battery is then declared defective.
3) If battery is or rises above 2.8v then the full constant current charge rate may be applied. This is normally a maximum about 60% to 75% C rating in current. There should be about a 120-150 min. safety timeout to terminate charge if 4.2v is not reached by that time.
4) When battery reaches 4.2v +/-50 mv. the charger enters constant voltage charging. This is the last 15% restoration of capacity and charge is terminated when current drops to less then about 3% to 5% C rate or safety timeout expires (about 2 hrs.).

All of these rules get difficult to follow when the phone is ON during recharge.

Second about USB charging.

There is a lot of variance on how a phone react to USB charging. Per the official USB standard it should only draw a max of 100 mA from source until it negotiates with host to allow it to go to a maximum of 500 mA. Newest USB specs allow for higher charge current but few manufacturers are presently following the rules.

Most smart phones have battery of 1200 to 1800 mAH, meaning that they can take significant over one amp during constant current phase of charging. USB 2.0/1.1 rev computer ports are designed for maximum of 500 mA's. Charger that come along with phone have varied and unique ways of determining it is their matching and unique charger that allows full charge current to be drawn. iPhone has resistor divider network fed back into USB data lines. Some USB chargers just tie D+ and D- together. Motorola uses ID pin 5 of USB. Bottom line is unless you use their unique charger it is often unlikely you will get full recharge current.

Many of phone's unique chargers have current limit function that sets the constant current phase of charging. This is advantage as the phone only needs to switch on and off the charging path to manage constant current charging thereby reducing heating of a linear regulator in the phone during high current recharging. When phone determines its a generic computer or unknown charger type it will enter linear regulation mode at a lower charge current then full rate. This is why it doesn't charge very fast. If you have the phone ON drawing higher current for its internal circuitry it may actually be net negative (discharging) of the phone's battery.
 
Last edited:
This is why it doesn't charge very fast. If you have the phone ON drawing higher current for its internal circuitry it may actually be net negative (discharging) of the phone's battery.

I had this happen when trying to use the phone as a modem and charging at the same time, A Mororola RAZR and the V3 worked fine. A Motorola Backflip did not. For the Backflip, I actually tried to power the phone through an isolated USB adapter and still had issues. I used the specific USB cable but not sure exactly what the cigarette lighter charger parameters were.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top