# 14.4v reduced

Discussion in 'General Electronics Chat' started by drabking, Feb 10, 2013.

1. ### drabking Thread Starter New Member

Feb 10, 2013
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0
Hey guys

My name is Roy I'm new here and kinda new to electronics (although I've done things using arduino and leds).
So i'll get to the point:

I want to make a USB charger that delivers 5V 1amp that will be juiced from a 14.4v battery that I have.

This is a very nice tutorial : http://www.instructables.com/id/EO7VZ73NWXEP286ZV3/?ALLSTEPS
that takes a 9v battery and delivers a 5V but I'm not sure what are the amps and is it possible to use instead of 9v a 14.4v battery without getting to much excess heat.

So if you know how to use the same setup for a 14.4v battery with some alterations, or have a better idea write me.

Thanx
Roy

2. ### ScottWang Moderator

Aug 23, 2012
4,925
777
If you want to do that, there are some questions here:
1. How's the current of your 5V battery?

2. Assuming that the current of your 5v battery is 1A, then you can't use 1A to charge the battery, probably it's using as 1/3~1/5A.

3. If using 1/3A=333mA from 7805(1A), and then plus a sink for 7805 then it's ok.

4. You can't just using the 5V to charge the battery, because if there is no charging protection, that is very dangerous, it "could be" cause the battery "explosion", unless you using a voltage meter to monitor the voltage, and you watch it all the time, but in this way still not safe.

I have been used less than 20mA to charge the battery for repairing, it took me over 20 hrs.

3. ### Audioguru New Member

Dec 20, 2007
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896
The 7805 voltage regulator IC produces an output of 5V with up to at least 1A but some can produce 2.2A.
It gets hot. The heating is the current in it times the voltage from its input to its output.

14.4V - 5V= 9.4v. 9.4V x 1A= 9.4W which is a lot of heat. It will need a pretty big heatsink. Here is a little anodized aluminum heatsink:

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4. ### drabking Thread Starter New Member

Feb 10, 2013
3
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hey ScottWang

maybe I wasn't clear enough

I want to make a USB charger that charges a 5v 1amp device from a 14.4V battery.
So the question is what sort of voltage regulator I need.
AudioGuru answered that, but I've got a following question

How can I deminish the excesive heat?
I have a posibility of having two USB ports.. Will that help to reduce the heat? and if so how do I assemble everything together.
If it won't help, how can I reduce the heat in another way? can I use some kind of Electrolytic Capacitor or is it used for entirely something else..

Isn't there a way to reduce heat without a bulky heatsink?

5. ### tubeguy Well-Known Member

Nov 3, 2012
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You are saying you want to 'charge' a 1 amp 5 volt device.
Charge implies charging a battery. Do you mean you want to power a 5V device?

6. ### Audioguru New Member

Dec 20, 2007
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There is a switching voltage regulator module made by somebody that has the same shape and pins as a 7805 linear voltage regulator. It switches on and off very quickly so it does not get hot. It is fairly expensive but you can make your own.

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8. ### drabking Thread Starter New Member

Feb 10, 2013
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hey TubeGuy

there's a good chance I'm wrong.

I want to charge cellphones that need 5V 1A with a 14.4V battery.. Is it charging or powering? I think its charging..

Bertus, what does it mean "It only needs 4 external components to make a DC-DC converter from 5-40 volts input to 5 Volts output."

What are external components?

Could someone explain to an Industrial designer (no skill in reading schematics) how to hookup this LM2575 to a USB port?

Apr 5, 2008
15,799
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Hello,

In the data sheet this schematic is given:

There are two capacitors a coil and a diode extra needed.

Bertus

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10. ### Audioguru New Member

Dec 20, 2007
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The lithium rechargeable battery in a cell phone is 4.20V when fully charged. The charger circuit in the phone limits the charging voltage and limits the charging current. It also disconnects the charger when the battery is fully charged to prevent over-charging (a fire hazzard).

The "charger" is just a 5V power supply for the charger circuit.

11. ### ScottWang Moderator

Aug 23, 2012
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777
When you say that you want to design a charger to charge something, it means that you want to charge a battery not a device, saying charge a device is the way from sales talking to the consumer, because the charger is one kind of device, but battery is not a device, battery is one kind of component.

So if you don't know the voltage and current of battery, how can you design a charger to suit the battery needed.

12. ### t06afre AAC Fanatic!

May 11, 2009
5,939
1,222
You can get an car cigarette lighter receptacle that convert to 5 volt for cell phone charging. Quite cheap in many stores. Should fit your needs quite good. Regarding polarity. The center is positive on ALL automotive cigarette lighters as a industry standard