Guido update laptop battery.

Geo-TH,In

Well-known Member
The laptop cells are 3.7v. I decided to charge the two cells that were only 2v at 50 ma rate. Well they are up to 3.65v and holding. I'm slowly charging the other pairs of cells at a slow rate too. Voltage is increasing too.

I don't fully understand the electronic chargers inside battery, but I'm guessing my cells are good, just a screw up with the electronic charging system. If I had another laptop battery, I would be tempted to make an 18v battery for my dewalt tools and make a charger to slow charge them, say 100 ma.

BYW, my cells show no signs of getting warm. Been charging for a few days, no fires.

From what I've read, Li batteries catch fire when discharging, thermal runaway.

What do you think?
geo
 
Hello Geo-Th,In,

Thermal runaway usually is the result on an internal short. Chargers can fail and the heat generated above saturation will expand the separation between the negative and the positive. They will kiss hard and make fire as well. Charge all the cells as you are doing, then use the pack without the charger cord. You will know then which is the culprit. My guess in your case is a bad charger balancing circuit on the low cells. Not usually the case though, heat is the killer, no matter how administered. The 3.7 volt cells are the higher MA rated 2.4 amp hour or more. I have some 2.7 volts rated at 2.8 amp hour. Same setup as your laptop,

Guido.
 
Guido,
Didn't the hover boards catch fire when discharging, thermal runaway??

So there is a way for my batteries to burn if I'm only 50-100ma? Nothing is getting above room temp.

From what I've read there are 3.3v, 3.7v and some at 4 v. I've never read anything about 2.7v Li.
geo
 
Hello Geo-TH, In,

That should have read 3.7 volts. Lots of these fires are started while the batteries were charging. Cheaply designed chargers, with poor quality conponents? A recipe for disaster! You are charging at a very low rate, no reason to do it, unless the battery won't take a regular charge rate. Some cells have a cutoff voltage of 2.7. Volts,it then will read zero, so smart charger will not charge them. Rule of thumb is that you can charge a battery in one hour at its rated capacity. Best gauge to use to determine battery full charge is you vom meter. When voltage starts to drop, STOP charging! charging after peak voltage will produce heat, it will eventually go boom! 86*F. Is considered hot for Lithium cells. There are no 4volt Lthium batteries that I know of, they are normally said to be fully charged @ 4.2volts. I have charged them to 4.4v with no heat built up, but they unusually settle back to 4.2 volts. So that is were I stop charging with my manual charger when I'm making a lose pack. Heat control is the key. Guido.
 
Guido,
This sounds crazy. Sounds to me like they don't know what to call the voltage.

The nominal voltage of lithium-ion is 3.60V/cell. Some cell manufacturers mark their Li-ion as 3.70V/cell or higher. This offers a marketing advantage because the higher voltage boosts the watt-hours on paper (voltage multiplied by current equals watts). The 3.70V/cell rating also creates unfamiliar references of 11.1V and 14.8V when connecting three and four cells in series rather than the more familiar 10.80V and 14.40V respectively. Equipment manufacturers adhere to the nominal cell voltage of 3.60V for most Li-ion systems as a power source.

How did this higher voltage creep in? The cell manufacturer plots the voltage of a fully charged cell that measures 4.20V, discharges it at 0.5C to 3.00V and takes the mid-way point. For Li-cobalt the mid-way point is about 3.60V. The same scan done on Li-manganese with a lower internal resistance gives an average voltage of about 3.70V. It should be noted that the higher voltage is arbitrary and does not affect the operation of portable devices or the setting of the chargers.

The phosphate-based lithium-ion has a nominal cell voltage of 3.20V and 3.30V; lithium-titanate is 2.40V. This voltage difference makes these chemistries incompatible with regular Li-ion in terms of cell count and charging algorithm.

Last Updated 2016-02-21
 
Hello Geo-TH,In


Cell ratings are OEM specs. like I said @3.7 volts the Lithium cells are the higher MAH rated. You did not mention Lithium Polymer, now they are a different breed! Check them out.......

Guido.
 
Guido,
From what I read, 3.7v is the average between the low of 3v and the high of 4.4v. Sounds crazy to call them 3.7v. geo
 

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