# How to modify 12-24v car phone charger?

May 9, 2016
77
Hi!
Dear All,
I need and step down converter from 12-24v to 9v exact to run a router on 12v battery. As I have extra car phone charger that is a step down from 12-24v to 5v. Is there any way I can modify it to provide 9v? Amp usgae will be only 0.6A. Please see the attached pictures of its circuit. I am very begineer, so I will need a detailed guide! Thanks!

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
On that, possibly not.

Some have a pair of resistors used to set the voltage and you can vary one of these to change the voltage. This does not appear to be amenable to such a simple modification.

The AD85063D seems to have datasheets in Chinese only and also appears to have a fixed 5V output. Maybe it can be hacked, and maybe someone here knows how. Let's wait and see.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Oh, 9V at 600mA is 5.4W, while 5V 1A is 5W -- you're actually asking for more power, not less.

May 9, 2016
77
Oh, 9V at 600mA is 5.4W, while 5V 1A is 5W -- you're actually asking for more power, not less.

Oh I see.. So it means its totally impossible?

May 9, 2016
77
Oh I see.. So it means its totally impossible?

I have one more car charger, also please check if there is any possibility it. It has one more issue that it has only input of 12v but I will need upto 15v as I will connect charger for 12v batteries to it. The output of this one is 6v 500mA. My requirements are 9v 600mA

#### 73's de Edd

Aug 21, 2015
3,636
Sir Nauman Muhammad . . . . .

Much better choice . . . . as being compared to the latter unit.

Change that upside 3 terminal regulator from a LM7806 to a LM7809.
The input of the charger will accommodate your potentially higher DC input as it is.

I see that your slow boat / or / camel caravan finally arrived , and you now have your meter.

73's de Edd

Last edited by a moderator:

May 9, 2016
77
Sir Nauman Muhammad . . . . .

Much better choice . . . . as being compared to the latter unit.

Change that upside 3 terminal regulator from a LM7806 to a LM7809.
The input of the charger will accommodate your potentially higher DC input as it is.

I see that your slow boat / or / camel caravan finally arrived , and you now have your meter.

73's de Edd

Yeah Sir it finally arrived in the camel caravan

Can I find the regulator in any old devices like printer, toys etc?

Furthermore what to do for 9v 600mA output instead of 6v 500mA output.

Last edited by a moderator:

#### CDRIVE

##### Hauling 10' pipe on a Trek Shift3
May 8, 2012
4,960
The LM78xx series regulators can output up to 1A with proper heat sinking. Keep in mind that the heat dissipated by these regulators is related to both the input voltage and the output current. The max input voltage of the LM78xx is 35V with the exception of the LM7824 that has an input max of 40V.

Since your input voltage will be about 14.5V max (13.8V nominal) the voltage drop across the regulator will be about 5.5V max. This equates to about 3.3 Watts that the 7809 will dissipate.

Chris

#### CDRIVE

##### Hauling 10' pipe on a Trek Shift3
May 8, 2012
4,960
I just noticed that your board employs 5 series Diodes that drops the input voltage to the regulator by (.7V * 5) = 3.5V. Therefor if the battery voltage is at 12 volts then 12 - 3.5 = 8.5V inputted to the regulator. You will probably have to jump some (possibly all) of these diodes to keep the input voltage to the 7809 above its minimum input voltage that it needs to properly regulate 9V output.

Chris

#### 73's de Edd

Aug 21, 2015
3,636
.

Sir Bauman Muhammad . . . . .

Oh NO! ! ! . . . . .we forgot the parts procurement situation.
It looks like the large diodes in series are being 1N4001's
What we will do, is only use the first series diode from the
battery line to provide isolation and then we will surgically cut
apart the other units, plus the inserting of some added ones to
act as individual .7 v " Zeners " as we then use their junctions
backwards.

We will lift the center terminal of the present five volt regulator
and insert the diode series string to ground.
We will also need a small .1 uf ceramic or poly/paper bypass
capacitor.
we will need a 5 watt 15 ohm resistor, OR, a mix / cluster of resistors, to create
that equivalent value.
Can you come up with these ?
Then, I can show you where to surgically cut the boards foils to insert
these extra parts .

73's de Edd

.

Last edited:

May 9, 2016
77
The LM78xx series regulators can output up to 1A with proper heat sinking. Keep in mind that the heat dissipated by these regulators is related to both the input voltage and the output current. The max input voltage of the LM78xx is 35V with the exception of the LM7824 that has an input max of 40V.

Since your input voltage will be about 14.5V max (13.8V nominal) the voltage drop across the regulator will be about 5.5V max. This equates to about 3.3 Watts that the 7809 will dissipate.

Chris
I just noticed that your board employs 5 series Diodes that drops the input voltage to the regulator by (.7V * 5) = 3.5V. Therefor if the battery voltage is at 12 volts then 12 - 3.5 = 8.5V inputted to the regulator. You will probably have to jump some (possibly all) of these diodes to keep the input voltage to the 7809 above its minimum input voltage that it needs to properly regulate 9V output.

Chris

Oh I see.. So first of all I need to find LM7809.. Then I will have to jump all diodes..

May 9, 2016
77
.

Sir Bauman Muhammad . . . . .

Oh NO! ! ! . . . . .we forgot the parts procurement situation.
It looks like the large diodes in series are being 1N4001's
What we will do, is only use the first series diode from the
battery line to provide isolation and then we will surgically cut
apart the other units, plus the inserting of some added ones to
act as individual .7 v " Zeners " as we then use their junctions
backwards.

We will lift the center terminal of the present five volt regulator
and insert the diode series string to ground.
We will also need a small .1 uf ceramic or poly/paper bypass
capacitor.
we will need a 5 watt 15 ohm resistor, OR, a mix / cluster of resistors, to create
that equivalent value.
Can you come up with these ?
Then, I can show you where to surgically cut the boards foils to insert
these extra parts .

73's de Edd

.

Yes sure, I will come up with these from probably old devices or from market..

#### 73's de Edd

Aug 21, 2015
3,636
.

Sir Nauman Muhammad . . . . . . .

You say:
Furthermore what to do for 9v 600mA output instead of 6v 500mA output.

When I reread my earlier supplied text . . . .I don't know if you interpreted it correctly, but the idea now is to modify the EXISTING LM7805 regulator to make it regulate to 9 volts.
However, when you mentioned the possibility of obtaining parts in Islamabad, I checked their " PREMIERE " mail order supplier and found no LM7805's or LM7809's were even being stocked.
HOWEVER, I did see the LM7817, which is an ADJUSTABLE regulator, using two resistors to set the voltage desired .
Their price is being right . . . . . . . . at 0.40 Pak Rupee.
BUT, DO check their stock level:

So o o o o o o o, do you want to get "the" LM7817, or shall we reuse the existing LM7805, by altering its voltage upward in .7 volt step increments, by the use of common series inserted diodes ?

We are already 2.8 volts in that direction, if we use the 4 spare 1N4001 diodes already being on the board.

What say you?

73's de Edd

.

Last edited:

#### cjdelphi

Oct 26, 2011
1,166
Data sheet says 1.2a max for the switcher ic, yet the usb outputs are 1a/2a lol

May 9, 2016
77
OMG thatswhy it never charged my quickly!

Data sheet says 1.2a max for the switcher ic, yet the usb outputs are 1a/2a lol
y

May 9, 2016
77
.

Sir Nauman Muhammad . . . . . . .

You say:
Furthermore what to do for 9v 600mA output instead of 6v 500mA output.

When I reread my earlier supplied text . . . .I don't know if you interpreted it correctly, but the idea now is to modify the EXISTING LM7805 regulator to make it regulate to 9 volts.
However, when you mentioned the possibility of obtaining parts in Islamabad, I checked their " PREMIERE " mail order supplier and found no LM7805's or LM7809's were even being stocked.
HOWEVER, I did see the LM7817, which is an ADJUSTABLE regulator, using two resistors to set the voltage desired .
Their price is being right . . . . . . . . at 0.40 Pak Rupee.
BUT, DO check their stock level:

So o o o o o o o, do you want to get "the" LM7817, or shall we reuse the existing LM7805, by altering its voltage upward in .7 volt step increments, by the use of common series inserted diodes ?

We are already 2.8 volts in that direction, if we use the 4 spare 1N4001 diodes already being on the board.

What say you?

73's de Edd

.

Sir,

Yup I interpreted it that we are going to modify our LM7805...

Finally I now know abou good local site for electronic supplies but they only checkout on purchase of items of Rs. 500.

So my idea is to modify our current regulator as it will be fun and challenging for me.

May 9, 2016
77
Sir,

Yup I interpreted it that we are going to modify our LM7805...

Finally I now know abou good local site for electronic supplies but they only checkout on purchase of items of Rs. 500.

So my idea is to modify our current regulator as it will be fun and challenging for me.

Sir,

I just saw that it has 7806 not 7805 if I am not wrong.

#### 73's de Edd

Aug 21, 2015
3,636
.

Sir Nauman Muhammad . . . . . . .

Yes, that regulator is indeed being a 6 volt unit, so that is just less voltage that we will have to drop.

Consulting the mark up:

It will need 4 foil paths to be cut enough to leave gaps. they are being marked in PINK
I just color coded the diffferent wires for clarity.
It will need one RED jumper wire to get raw 12V + DC over to the input terminal of the 3 terminal regulator, since we have cut open that series diode string path and are now going to use them in another manner.
We need the BLUE jumper wire to make connection to one end of our new repurposed series diode path.
We need two BLACK jumper wires to carry ground connections to newly created positions.
Scrape the green resist from the foil to solder tin those areas initially.
We need the 0.1 ufd for HF filtering bypass.
When you get this done, load the supply with the previously mentioned load resistor, you should come up with less than the full 9 volts.
Then, that will let us see how many more series diodes need to be added in the string to trim on into 9 olts..

Here's . . . . . The Plan . . . . . .man . . . .

73's de Edd

.

May 9, 2016
77
.

Sir Nauman Muhammad . . . . . . .

Yes, that regulator is indeed being a 6 volt unit, so that is just less voltage that we will have to drop.

Consulting the mark up:

It will need 4 foil paths to be cut enough to leave gaps. they are being marked in PINK
I just color coded the diffferent wires for clarity.
It will need one RED jumper wire to get raw 12V + DC over to the input terminal of the 3 terminal regulator, since we have cut open that series diode string path and are now going to use them in another manner.
We need the BLUE jumper wire to make connection to one end of our new repurposed series diode path.
We need two BLACK jumper wires to carry ground connections to newly created positions.
Scrape the green resist from the foil to solder tin those areas initially.
We need the 0.1 ufd for HF filtering bypass.
When you get this done, load the supply with the previously mentioned load resistor, you should come up with less than the full 9 volts.
Then, that will let us see how many more series diodes need to be added in the string to trim on into 9 olts..

Here's . . . . . The Plan . . . . . .man . . . .

73's de Edd

.

Oh thats great!

I am starting work on it. But before it I need to clear that?

I need to break the circuit at pink marks?

I did not understand this point "Scrape the green resist from the foil to solder tin those areas initially.
We need the 0.1 ufd for HF filtering bypass."

Thanks..

#### 73's de Edd

Aug 21, 2015
3,636
.

Sir Nauman Muhammad . . . . . . .

I need to break the circuit at pink marks?

Yes, use a single edge razor blade, Exacto hobby knife, surgical scalpel or SHARP pocket knife and cut two lines, side by side, in the copper foil, about the width of a metal paper clip and then peel the strip out. It will then leave a small gap in the copper foil.

I did not understand this point "Scrape the green resist from the foil to solder tin those areas initially.

You can not solder to a point that is covered with that green resist, until you scrape it off enough to reveal the bare copper foil that is beneath it.

We need the 0.1 ufd for High Frequency filtering and bypassing."

That is just an added part that we need to place in the circuit, it is the round orange capacitor, old equipment has MANY of these being used in their circuitry..

73's de Edd

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