How to charge a 9 volt from a 5 volt

[josephm]

How to charge a 9 volt from a 5 volt supply

do i just connect a 9volt to a 5volt supply..

how would a 9 volt rechargable battery get the power from a 5volt
like a phone charger how do the batteries charge if you plug it in how does the schematics/system work..

 

[tgootee]

Re: How to charge a 9 volt from a 5 volt supply

In order to charge a battery, the charging voltage must be at least as high as the desired battery voltage, and not too much higher. Usually, you would also need to limit the current flowing into the battery, during charging, so the battery wouldn't get too hot, so it wouldn't be damaged or explode.

You will need to know what voltage the battery should be charged from (it is always a little higher than the desired final battery voltage), and what the ideal charging current might be.

There are also dedicated battery-charging circuits, with features such as automatically stopping charging when the battery is fully charged, and contouring the voltage and current levels during charging.

In this case, you are wanting to charge a higher-voltage battery from a lower-voltage supply. To be able to do that, you would need a circuit to raise the supply voltage to at least as high as the desired battery voltage. (You will probably also need to have a resistor in between the charger and the battery, to limit the current to a level that is safe for the battery.)

For methods and circuits to raise the supply voltage, from 5 Volts to about 9 Volts, do a search for "boost converter" or "boost mode" smps.

It is usually done with a "switch-mode power supply" (smps) circuit.

Edit: OK, you can raise 5 Volts to 9 Volts very, very easily, using the MC34063A chip, if you don't need more than about 300 mA of current.

Here is a web-based tool that will give you the schematic and will calculate the component values, automatically:

**broken link removed**

You need to enter:
1) Vin = 5
2) Vout = a little higher than 9 Volts
3) Iout = the current you need, in mA
4) Vripple = the peak-to-peak output voltage ripple that you can tolerate
5) Fmin = the desired switching frequency (up to 100 kHz).

You can play with the values above and see how they affect the component values that result.

Using a higher frequency would allow using a smaller-value (and probably smaller size and cheaper) inductor.

Here is the Fairchild datasheet for the MC34063A:

https://www.fairchildsemi.com/ds/MC/MC33063A.pdf

And here is the Texas Instruments datasheet for the MC34063A:

https://www.ti.com/lit/ds/symlink/mc34063a.pdf

 

[josephm]

so probably not a good idea to charge it with a small amount..

maybe from a twelve volt dc charger (an old wifi/router connector) i found around lying,
could i convert it to a rechargable 9 volt battery?

 

[PA4TIM]

What type of rechargable 9V battery you try to charge ?

If it is a nimh or nicd you need to look the capacity of the battery and limmit the charge current to 1/10th of that capacitie. So if it is a 1000 mAh battery, you can charge it save with 100 mA. You can charge it witth 1000 mA but then it will be charged in one houre and if you do not stop on time it can explode or get very very hot.
If your adapter is 12V and capable to deliver 100 mA then you need to select a current limitting resistor. Your battery is 9V so you have 12-9=3V over. 3V / 0.1A = 30 Ohm. So a 27 Ohm will do. 3V x 0.1A = 0.3W so take a 0.5 or 1W resistor.
Now you can charge it for 10 hours. In practice this will be not exact what happens because the battery will start around 7V so at the start more current will flow.
You can also use a 12V car headlight in seruies with the battery.

If you want more control you can use a LM317 as a current source.

But if you are talking about lion or lipo batterys I have one advise, forget it or be shure you have a good health insurance

 

[tpetar]

Re: How to charge a 9 volt from a 5 volt supply

do i just connect a 9volt to a 5volt supply..

how would a 9 volt rechargable battery get the power from a 5volt
like a phone charger how do the batteries charge if you plug it in how does the schematics/system work..

If you want to charge 9V from 5V power source you need to boost voltage from 5V to higher voltage level needed for charging purpose. Depending from battery chemistry and from choosed charging method you will determine charging voltage and charging current. For sure respecting battery charging recommended current ratings and voltages are always good choice.

What rechargable 9V battery you want to charge ?

so probably not a good idea to charge it with a small amount..

This is not smart for sure, battery will be discharged completelly.

maybe from a twelve volt dc charger (an old wifi/router connector) i found around lying,
could i convert it to a rechargable 9 volt battery?

Probably yes. But zou didnt say nothing about battery, what chemistry ?

9V battery contains 6 cells and usually have smaller capacity then single cell battery, pay attention on charging current.

See this simple circuit:
http://www.circuitdiagram.org/nicd-nimh-battery-charger-circuit.html

Best regards,
Peter