Thread: hotswap of battery possible!
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zimon is offline zimon
2010-08-25 , 15:28
Posts: 1,341 | Thanked: 708 times | Joined on Feb 2010
#17
Originally Posted by joerg_rw View Post
Q:Why do we need all that 'stop bme' obscure stuff? A: bme (the battery management entity) seems to check for existence of a correct battery, by probing the 3rd contact of battery (the BSI indicator contact). If bme detects the battery is missing, it shuts down N900 in <1 second. (that's what I gathered on unconfirmed facts so far). Probably this is done to switch off system gracefully and not corrupt filesystems or whatever evil may happen when you pull the plug of any computer system.
Howabout a hardware hack, where small resistor is connected parallel between 3rd and 2nd (?) contact of the battery socket, so bme would be fooled to think the battery is still in place although would be quickly changed to a fresh one?

At least, with Mugen 2400 mAh battery, which has thermistor instead of resistor there, seems to fool BME correctly to think the battery is there all the time although the resistance is changing with the inner temperature. I mean, BME seem not to be too picky about the resistance and some resistor parallel to battery and without a battery could fool it.

What I am (would like) to experiment, is how to make bigger 2640 mAh battery from two original BL-5J batteries. I have extra bigger back cover, which came with Mugen Power battery. Under this bigger back cover I can have two BL-5J batteries currently, but nowadays I have to reboot to use (switch) both of them during the day. (My original Mugen 2400 mAh battery was stolen with my previous N900 in Lisbon last month.)

I wonder, if just connecting the two BL-5J batteries parallel on their [+] and [-] pins would work? The internal resistance of the battery system then would be half of that of the single battery. I wonder would that be a problem or break something?
Last edited by zimon; 2010-08-25 at 15:36.
 

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