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Old 11-08-2010, 09:51 AM   #60 (permalink)
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Join Date: Nov 2010
Model: 9700
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Default 9700 alternating between Red LED & Charging Icon

I had the same problem with my 9700 when I allowed the battery to run flat
it refused to boot and alternated between showing a red led and a white screen with the charging icon displayed. No helpful messages or indication that it was doing anything. After 4 hours it finally booted. It could be that if you let it run completely flat the charger enters a battery precondition mode. The following info is taken from the datasheet of a typical chip that performs the charging function. I have edited some sections to explain in simple laymans terms for those of you that dont have technical knowledge. The majority of charge systems for lithium polymer batteries follow this scheme

Charge Qualification and Preconditioning
"Upon application of an external supply, the charge controller automatically performs a series of safety checks to qualify the charge. The input source voltage must be above the undervoltage lockout threshold, "

Basically this check is for the output voltage of the plugin adapter or usb voltage. it must 5v to begin charging. Some USB ports are not capable of supplying the required current so always try with your supplied wall charger if you have problems. If the voltage is too low charging will not proceed

"The cell temperature monitor must be within the upper and lower thresholds."
This check measures the temperature of the battery. Each battery has a temperature sensor built into it which the charger chip reads. If the battery temperature is too high or too low charging will be suspended. This may be why some posts refer to freezing the battery being a solution. The reason for the temperature sensor is that the battery chemistry can get unstable if there is a fault or if it is being overcharged. This can lead to exploding batteries! hence this safety feature to suspend charging if the battery temperature is outside its normal limits. My advice is not to freeze the battery. If it feels like it is at room temperature then all should be okay and freezing will not work. If it feels hot do not attempt to overide this safety feature by cooling the battery and attempting to fool the charger into charging the battery

If the checks of the plug in adapter voltage and the battery temperature have passed. The charger chip in the phone then attempts a charge cycle as follows

"If the battery voltage is below the preconditioning threshold, the battery is first preconditioned with a tricklecharge. The preconditioning current is set to approximately 10% of the fast charge regulation current. The preconditioning trickle-charge safely replenishes deeply depleted cells and minimizes heat dissipation in the external pass transistor during the initial charge cycle. If the battery voltage has not exceeded the preconditioning threshold before the preconditioning timer has expired, a fault is indicated and the charge cycle is terminated."

What happens in this step is that the chip first measures the voltage of the battery. If it is very deeply discharged it does a pre-charge of only 10% of the normal chargiing current. The reason for this is that the heat generated from the charging process is greatest when the battery is flat. So a small charge is first applied to reduce the heat generated in the phone, wall charge adapter and the battery. This reduces the cost for the manufacturer of the various components in the product. An important point to note is that its only a 10% charge current so If your battery normally charged in 1 hour. The pre-charge current level would take 10 hours to charge. Of course the pre-charge cycle is not intended to charge the battery fully. The charger chip will check the battery voltage periodically and when a threshold is reached it steps on the gas and applies full charging power to the battery. If this threshold is not reached in a preset time the charger chip suspends charging. The charge cycle can only be restarted by power cycling the device. So if you have no luck after a few hours try unplugging the charger for 30 seconds and plug back in to attempt another cycle

I dont know if the above is what is happening but I suspect it is. Only RIM can answer that one. I could measure the battery voltage and the charging current the next time this happens to me to confirm that its using a low current when it displays the charge screen and red led. This is such a PIA that I will try to avoid running the battery flat again, but if it does happen I will post an update. Hope this post is helpful if a bit long winded

Last edited by Canalcop : 11-08-2010 at 10:04 AM.
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