Continue to Site

# [Moved] Reduction of power supply voltage

Status
Not open for further replies.

#### M.Imran Ali

##### Member level 5
Hi
I am facing a problem i have a 12V 7 amp battery .
I have power supply of 16v 7.5A . I want to reduce its voltage to 13.8V what is simple way to do it so that i could not lose maximum current rating?
basically i have to charge the battery.
I dont know internal resistance of battery

Re: Reduction of power supply voltage

a common way is to use a voltage divider. it's pretty simple just calculate the resistances' values to suite you.

Re: Reduction of power supply voltage

Drop voltage over 3 (power) diodes connected in series, each will reduce voltage by roughly 0.7-0.9V at full load ..

:wink:
IanP

#### Attachments

• diodes in series ex0.png
1.4 KB · Views: 138
Last edited:

Re: Reduction of power supply voltage

Prince i dont know the resistance of battery ? How can i use voltage divider?

- - - Updated - - -

Prince i dont know the resistance of battery ? How can i use voltage divider?

Re: Reduction of power supply voltage

You can't - shouldn't even attempt to - use a voltage divider for such high currents for charging the battery. Overall, it would be a poor method.

Use the diodes as shown by IanP. That is the simplest reliable method for you.

Just for constant voltage charging, you don't need to worry about the battery's internal resistance. However, the internal resistance can be found experimentally.

Hope this helps.
Tahmid.

Re: Reduction of power supply voltage

Ianp
I used power diode but these are very much heated . I what type of heat sink should be used if w want to use these in series with wire bcoz i have no spare place in body of my power supply?

Re: Reduction of power supply voltage

but will 0.9v be enough to charge a 12v battery?

Re: Reduction of power supply voltage

Hi
I am facing a problem i have a 12V 7 amp battery .
I have power supply of 16v 7.5A . I want to reduce its voltage to 13.8V what is simple way to do it so that i could not lose maximum current rating?
basically i have to charge the battery.
I dont know internal resistance of battery

You should not try to charge 12V 7Ah battery with current of 7A !!!. That small gel batteries is charged with current around 0,7A-1A. You can check manufacturer datasheet for battery.

Use some LDO voltage regulator to decrease 16V to stable 13,8V and current should be limited around 0,7A not more.

Starter Lead Acid batteries should be charged with currents at C/10 and this gelled batteries even with C/20.

If you dont accept manufacturer suggestions and recommendations about charging and discharging of batteries, you will for sure reduce battery life and capacity, maybe you will kill battery like rabbit.

Your charger should have around 1A-2A max, no need for 7A. Its no problem at all to have stronger psu.

If charging process is in very warm environment, reduce voltage from 13,8V to 13,5V or lower according to voltage/temp table. I suggest reading mannufacturer battery datasheet.

When lead acid battery is discharged a lot, battery knows to pull lots of current when charger is connect, because of that you must limit current to recommended range. For that reason in almost each car manufacturers implement power resistor in serie with car battery.

:wink:

Status
Not open for further replies.