how do i drop voltage of a power supply

[daniel barter]

Hi I am new to electronics so go easy on me. I am trying to drop to voltage of my power supply / battery charger from 29v 5a down to 25v 5a. Is there a easy way of doing this? can I just use a diode and resistor on output? any advice regards dan

 

[Colin Mitchell]

Just use some 10 amp diodes.

 

[shrtrnd]

I'm going to stick my 2-cents worth in here.
I don't know your battery charger circuit, but some of them indicate a higher voltage when unloaded, than they do with a load. Just suggesting you verify that your power supply output with it's load, is still higher than you want, if you haven't done that already.

 

[daniel barter]

Just use some 10 amp diodes.

Thanks for your reply, how many 10 amp diodes would I need?

 

[daniel barter]

I'm going to stick my 2-cents worth in here.
I don't know your battery charger circuit, but some of them indicate a higher voltage when unloaded, than they do with a load. Just suggesting you verify that your power supply output with it's load, is still higher than you want, if you haven't done that already.

I have already checked that and as the charger is designed for lion batteries it will not drop below 29v

 

[hevans1944]

Thanks for your reply, how many 10 amp diodes would I need?

The forward voltage drop across each diode will be approximately 0.6 V to 0.7 V at 5 A current. So to drop 29 V to 25 V you need to drop 4 V across the series-connected string of diodes. Do the math: 4 / 0.7 = 5.7 ==> six diodes, or maybe seven diodes if 4 / 0.6 = 6.6.

This is a "quick and dirty" way to drop power supply voltage. If you need a precision reduction, use a three-terminal voltage regulator with an external transistor to carry the 5 A. Many circuits available to search for and try out on the Internet.

 

[BobK]

And, no matter how you do it, you will need a heat sink since there is 20W to dissapate.


Bob