cell phone charger on motorcycle

[cakrawibawa]

motorcycle cell phone charger

Dear all,

I wanna make a cellphone charger using LM317 or 7805 regulator to generate 5V, 800mA output. The circuit will charge my cellphone when I'm driving. Input source come from my motorcycle battery which supply 12V 5A max. The circuit is basic circuit.

The problem is, when the motorcycle machine turning on (or when I'm driving), the 7805 IC is getting hot, only in seconds!. If the machine turning off (source only come from the accu), the IC calming down. (this condition when i charging my cellphone)

Is it caused from the coil of my motorcycle?
As I knew, every car/motorcycle have a "kuproks" as the rectifier to charge the accu. And when I measure on the accu terminal, the voltage arise between 12 to 16V when I arise the speed.

According to datasheet, 7805 IC can accept max 40V voltage input. Why it's getting hot?? is this caused from high current from the alternator/coil?

Any advises is higly appreciated.

Thanks
Tono

 

[timpati]

motorcycle phone charger

add a nF condenser for high frequencies to the reg IC's front and you must eliminate extra voltage to 7805 or 317 by adding a resistor (low value but high wattage i.e 4.7 ohm/5W). reg IC require 3V+ than outputs at least. however, if the output current is more than 0.3-0.5A, then it must have a cooler plate like a Al bar.

 

[pranam77]

motorbike phone charger

Hai cakrawibawa
When the alternator is running, the voltage on the battery terminal rises up to 14-15 volts which is not a pure DC source. You may use a 2200Mfd/ 50 volts capacitor across battrey to filter the output. On the other hand the voltage available at the input is 14-15 volts whereas the output of the regulator is 5volts and thus it creates a drop of average 10 Volts which is generating the heat. Also i coudnt get why are you using LM317 and LM7805 to get 5 volts? You can directly get 5 volts dc from any input on the bike with the LM317 regulator circuit given here. Just Adjust the variavle resistor to get the required output.
Hope this helps. Good luck

 

[cakrawibawa]

mobile phone charger in motor cycle

thanks pranam and timpati,

btw, i was try using 1000uF as the filter on 7805 input and using 4, 27ohm 10W in paralel (so i get about 6ohm and 40W resistor). with this, these 4 resistor getting hot, but the IC calm down.

I was tried using 7806, 7805 and L200. Is pranam circuit would be the same like mine? I mean without using the 4 resistors I mention above, the IC will getting hot?

Thanks

Cakra

 

[pranam77]

charging cell phone on motorcycle

Practically speaking we have to reduce heating as the power will be lost in the heat. Using resistors of 40watt for charging a mobile phone, is not a good idea, and a stright approach. The given schematic should work fine. Connecting it to a input source and keeping the output open without any load shud keep the LM317 cool. When you connect the mobile, the LM317 will be warm in proportion to the consumption. Also do measure the current consumption after the regulator and the phone. Good luck.

 

[Tahmid]

Hi,
Since 5v 800mA is required from a source of greater than 12v, switching regulator will be best in terms of efficiency.
Look at L4960, L4962, L4971(8-pin DIP).
http://www.datasheetcatalog.org/datasheet/stmicroelectronics/1356.pdf (L4960)
http://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXqqwtt.pdf (L4962)
http://www.datasheetcatalog.org/datasheet/stmicroelectronics/5598.pdf (L4971)

I have a 16v to 5v regulator 1.5A with L4960. It runs continuously for more than 3 to 5 hours with almost no heat at all. I just provided a small aluminum heatsink.

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