1
\$\begingroup\$

I want to replace my 300 mAh Chinese tablet battery with a 3000mAh new one, My old battery has 3 wires red , black and White, the white one connect to a point on tablet board named "T" which I have been told is a temperature measuring thermistor connection.. but my new one has only 2 black and red.. I connected the red and black wires of the new battery to + and - poles .leave the "T" pole on the board unattached .. The tablet worked with the new battery just fine .. BUT the problem is that I can not charge the new battery .. I connected the charger for one hour but the battery charge level never increase even 1% I think this is because the "T" spot on the board is not connected to battery .. what can I do ?

\$\endgroup\$
  • \$\begingroup\$ Note This is the next stage of the series after this question from yesterday \$\endgroup\$ – Russell McMahon Feb 2 '15 at 9:12
  • \$\begingroup\$ How do you know that the charge level did not increase? What are you using to measure charge level? What charger are you using? What is the charge level of the battery at present? How did you "introduce" the battery to the system? If you are using the original charger it will take 24 hours + to fully charge. Even when the level is low you will only get 10% charge in 1 hour. So your measuring system may be missing this. If you charge it for say 12 hours you certainly should see a change. The battery may need to be "in-sync" with the tablet's charge controller to work properly. \$\endgroup\$ – Russell McMahon Feb 2 '15 at 9:17
  • \$\begingroup\$ If you answer the above questions we can probably help you. Failure to answer makes a good answer unlikely. \$\endgroup\$ – Russell McMahon Feb 2 '15 at 9:18
  • \$\begingroup\$ The chrge level now is only 1% and still 1% after 3 hours charging with the orginal charger of the tablet, and the tablet is turnning off few seconds after discconnecting charger , "The battery may need to be "in-sync" with the tablet's charge controller to work properly" what that means? and how to do that ? thank you vey much" \$\endgroup\$ – Marah Ali Feb 2 '15 at 11:18
  • \$\begingroup\$ Have you followed any of other suggestions (Michael's below or elsewhere) re what to do with the extra lead? If you leave it open or connect it wrongly the charger and tablet will think that the battery is faulty and will not charge it. \$\endgroup\$ – Russell McMahon Feb 2 '15 at 11:23
2
\$\begingroup\$

There is a convention that the "T" wire is connected to ground via a 10kOhm NTC, as mentioned for example on this thread on AnandTech. Replacing it with a 10k fixed resistor should enabling charging, but on your own risk. The sensor is used to prevent charging when the battery is too cold or too hot (possibly caused by environment temperature) to avoid damaging the battery. Also it can be used as an emergency cutoff if the battery gets too hot during charging. A fixed resistor will disable these safty functions.

\$\endgroup\$
  • \$\begingroup\$ Where is the risk ?! I think The battery comes with "protection circuit " which supposed to protect it from overcharging , overdischarging , and other dangers.. am I right ? \$\endgroup\$ – Marah Ali Feb 2 '15 at 14:50
  • \$\begingroup\$ The protection circuit inside the battery is typically meant as second layer of security if the regular charge controller failed. It's limits for overcharging and overdischarging are commonly chosen in a way that they make sure the battery doesn't burst or catch fire, but they still allow significant shortening of the battery life. Furthermore, integrated protection circuits might not have temperature sensing at all. \$\endgroup\$ – Michael Karcher Feb 2 '15 at 14:54
  • \$\begingroup\$ What about the tablets and / or batteries which come with only +/- poles are these unsafe ? \$\endgroup\$ – Marah Ali Feb 3 '15 at 7:33
  • \$\begingroup\$ Tablets and / or batteries only use two wires are indeed less safe (I wouldn't necessarily call it unsafe) than a three-wire system, if they don't compensate the missing thermal sensor in the battery (for example by an on-board thermal sensor, mounted near the battery). A system completely without thermal sensing can not avoid applying charging current to the battery while the temperature is outside the specified range (typically 0°C..40°C). You have to decide yourself whether this is an acceptable risk. \$\endgroup\$ – Michael Karcher Feb 3 '15 at 20:39
  • \$\begingroup\$ I used a 10k fixed resistor with this new 2 wires battery .. now I can charge this battery .. but I'm concerned about this "risk" .. I charged this battery to 90% -it took about three hours - with tablet open And touched the battery, which remained totally cool Does this mean it's safe ? dose the "risk" include both charge and discharge .. thank you very much \$\endgroup\$ – Marah Ali Feb 4 '15 at 7:04
1
\$\begingroup\$

I know this is an old topic, but I thought I would throw this in so that those who stumble on this topic through Google have a solution. I had the same problem. I purchased a two wire battery, installed the battery, then found that the tablet ran fine but would not charge. To solve this, I soldered the white wire to the black wire. Seems to be charging now.

\$\endgroup\$

protected by Dave Tweed May 10 '15 at 10:46

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.