Mobile Charger...Slow Charging problem..

Thread Starter

qaisershah

Joined Nov 21, 2014
18
Respected friends!
I have little bit knowledge of Electronics, i have built a mobile charger but it is charging the smart phone very slowly...what to do for fast charging...details are as below:
Smart phone = Nokia lumia 520 (1430mAh).
homemade charger=
Transformer = 2Amps (12V)
Bridge= 5 Amp
Capacitor= 4700uF 35V
Transistor= 7805 ( for output 5V).
plz reply me any suggestions for improvements in circuit...
this charger gives only 120mAh charging and mobile phone takes too long to charge...
help me out plz friends..
thanking you in anticipation.
 

AnasMalas

Joined Nov 27, 2015
66
Sometimes its the phone that limits the charging for safety! Iphones for example need 2 volts through the data pins. some androids need data pins to be shorted.
I have no idea about the lumia phones however...
 

KJ6EAD

Joined Apr 30, 2011
1,570
On a side note and in deference to the foregoing comments regarding data pin requirements, often when a dedicated fast charger starts acting like a generic slow charger, it's due to a break in the wire or connector on one or more of the data pins.
 

GopherT

Joined Nov 23, 2012
8,012
Respected friends!
I have little bit knowledge of Electronics, i have built a mobile charger but it is charging the smart phone very slowly...what to do for fast charging...details are as below:
Smart phone = Nokia lumia 520 (1430mAh).
homemade charger=
Transformer = 2Amps (12V)
Bridge= 5 Amp
Capacitor= 4700uF 35V
Transistor= 7805 ( for output 5V).
plz reply me any suggestions for improvements in circuit...
this charger gives only 120mAh charging and mobile phone takes too long to charge...
help me out plz friends..
thanking you in anticipation.
So, let's analyze this using math.

You have a 12 V source and a 5 volt regulator. That means the regulator drops 7 volts at 150 mA = 1 watt.

These little 7805 regulators have a thermal shutdown. So it is likely throttling back the current as it heats up. 1 watt is a lot for a 7805 without a heat sink. If you are expecting a full 2-amp charge rate (based on transformer rating), then the little 7805 would need to dissipate 14 watts. You need better heat sinks and maybe a purchased charger based on a switching power supply.
 

AnasMalas

Joined Nov 27, 2015
66
So, let's analyze this using math.

You have a 12 V source and a 5 volt regulator. That means the regulator drops 7 volts at 150 mA = 1 watt.

These little 7805 regulators have a thermal shutdown. So it is likely throttling back the current as it heats up. 1 watt is a lot for a 7805 without a heat sink. If you are expecting a full 2-amp charge rate (based on transformer rating), then the little 7805 would need to dissipate 14 watts. You need better heat sinks and maybe a purchased charger based on a switching power supply.
this may be the case(i dont know much about voltage regulators). if it really is wouldn't a 12 v to 5 v transformer work? these typically aren't that big... and not that expensive.
 

Thread Starter

qaisershah

Joined Nov 21, 2014
18
i have added four 7805 and all are connected with heat sinks...actually i have four smartphone at home (family), i want to charge all of them through single charger....let me add the the above mentioned 120mAh charge rate was from one port while other port where not connected with load (phones).

Can i use computer power supply as it has 3.3V,5V and 12V output for phone charging?
 

Dr.killjoy

Joined Apr 28, 2013
1,196
I didn't see anyone mention it but in the past for me I get different charge rate depending on the wire diameter of the USB cord..
 

Willen

Joined Nov 13, 2015
281
Or add a current booster transistor too to divide down the the huge power dissipation/heat or to boost currents. Search for 'current booster circuit for 7805'. However it wastes lots of power if you are using 12V battery as power source.
 

marcf

Joined Dec 29, 2014
257
I probably do not need to point out that there is a big difference between a charging circuit and a power supply. Connecting a PS capable to supplying 20 Amps at 5v to a battery could have bad results.
 

marcf

Joined Dec 29, 2014
257
I understand that point, but I just thought it would be good to point out that it can be a very bad idea to charge a battery with a power supply. A battery charger is not a power supply, it is a device for charging batteries that contains a power supply and is designed to properly charge batteries. Some of the designs in this post do not seem to take this into account.
 

AnasMalas

Joined Nov 27, 2015
66
I understand that point, but I just thought it would be good to point out that it can be a very bad idea to charge a battery with a power supply. A battery charger is not a power supply, it is a device for charging batteries that contains a power supply and is designed to properly charge batteries. Some of the designs in this post do not seem to take this into account.
But the battery charger circuits are in the phone itself. and even in the battery in some cases. you dont pump 5 volts to the battery. you regulate the voltage down...
 
Top