Adapter to PENTAX camera charger for cell phone Li-ON battery  - Page 1
Forum section: electronics / projects

author: eneuro
author_rank: Super Contributor
timestamp: January 11, 2015, 10:10:41 am
content: Hello,Just designed PCBs for adapter to PENTAX camera charger for cell phone Li-ON battery which is marked 3.7V. It is from old crappy Siemens phone which refuses to recharge itself from external power sourceHowever, when measured this voltage between --/T connectors marked in green it shows 4.9V without any loadAnyway, oryginal PENTAX Li-ON battery is charged without any problems.I've made direct connections between (+ +) and (- -) as well as this center connector marked by (T) in Pentax charger with center pad of Li-On battery.How do you think this PENTAX camera charger can be used to charge Siemens Li-ON cell phone battery or some tricky things are made by manufacturers to prevent this?

author: eneuro
author_rank: Super Contributor
timestamp: January 13, 2015, 09:58:52 am
content: Nope,Checked Pentax Li-ON oryginal battery 3.7V 700mAh and between (-) and (T) middle terminal is as expected termistor which at room temperature has about 10k Ohm resistance, while Siemens cell phone battery has between this (-) and middle pin very low resistanceTermistor resistance goes down when heated this Pentax battery in hand easy below 8k Ohm.Maybe it will be good idea to put in this adapter 5k Ohm or less resitor (10k potentiometer) in place of thermistor to let know Pentax charger that battery temperature is high (battery is hot) , so it will provide lower current and quite safelly charge this cell phone battery?Probably leaving (T) terminal not connected at all is bad idea.Or lets wait... something more fancy add to this adapter external termistor (I guess 10k) and put it close to battery case and compare its resistance with oryginal Pentax Battery builtinDoes it mean that this crappy old Siemens phone charger do not care about Li-ON battery temperature at all or this battery is damaged?

author: amyk
author_rank: Super Contributor
timestamp: January 13, 2015, 03:50:17 pm
content: According to the specs, the charger will charge at 630mA which could be far too much for a smaller battery. Put a slight bit of load on the charger (few mA) and measure the voltage again.

author: eneuro
author_rank: Super Contributor
timestamp: January 13, 2015, 04:41:04 pm
content: Thx for those hintsFor the moment trying to figure out why this resistance in this old Siemens cell phone battery between (-) and middle pin is very low close to conductorThere are no termistor (T) in this battery and is shorted to tell somehow charger about it or this is Siemens knowhow?Anyway made also PCB adapter for cell phone to put in place of removed battery and power phone with external power source, but unsure for the moment what can be maximum power needed to make a call-it is old Siemens phone.I guess that 4.0V in such power supply in place of battery should be fine, while charged Pentax Li-on have about 4.15V now.Cell phone battery has now 3.66V and phone is dead at this voltage level.Need to figure out which is the current needed for this phone to work (make calls nothing else), so probably will use my new PCB cell phone power adapter and connect this fully charged Pentax Li-on battery (+) (-) pins only-and lets see how much current is needed for my external power supply as another option to make calls in emergency using custom 12V car battery -> 4.0V PSU...It could be nice make such small PSU for this phone and... use PV solar energy to make calls etc...

author: eneuro
author_rank: Super Contributor
timestamp: January 14, 2015, 09:48:56 pm
content: Yep, it looks like cell phone is fine and draws from replaced Pentax Li-on battery 100mA-150mA @ 4V during voice call and about 50mA with display enabled and menu options visible.Probably even LM317 could be fine but LM350 3A in aluminium pipe as heatsink cover could be better to power this old Siemens phone without oryginal Li-On battery-connect to solar panel, even... bike alternatorLets forget about crappy 230VAC chargers and flammable Li-ONs while this phone is only to make emergency/short calls, so more important is to be able connect it to any low voltage power source and make call if needed, so those a few wats of power needed can be generated even by human somehow...in car its 12V battery will be good source of power

author: eneuro
author_rank: Super Contributor
timestamp: January 21, 2015, 03:59:03 pm
content: Proof of concept made on 1inch2 PCB and changed Li-On battery to... much bigger 12V L4 old car battery and now this 4.14V PSU is fine - no need to use Li-On no moreMade a lot of cell phones calls to see if this thing will get hot, but it is notLM350T at 15*C ambient temperature isn't even warm during old cell phone calls (classic Siemens) with this small radiator and a few resistors define its output voltage to simulate good charged Li-On 14.14V -3rd resitor is to make some load - 4mA in this caseJust thinking on submerge this 0.5inch x 2inch 4.14V PSU into something which could absorb some amout of heat and put everything into copper pipe with input on one cylinder side and output on another.Any ideas what kind of cheap refrigerant it could be to glue everything together, but still be able to melt and change electrolytic capacitors when needed?Maybe even some kind of paraffin composite?Thermophysical Comparison of FiveCommercial ParaffinWaxesas Latent Heat StorageMaterialsQuote