Help from an electrical engineer

[seneka]

I really am not sure as to what to ask for...

Here is the scenerio. I have a 13.8v 20 amp power supply. I need to regulate this to 12.0v 20 amps, with clean enough power to supply even the most sensitive lipoly chargers.

I will also be using this supply for various other projects, and require this device.

Not sure if there is anything available pre-made, but i would like to build it myself. So i was wondering if anyone has seen schematics, or could create one that meets the following:

1. Input voltage 13.8v 20 amps (variable from 0-20 depending on load)
2. Output voltage 12.0v 20 amps (variable from 0-20 depending on load)
3. Dual channel, as the power supply has dual outputs, so i would need dual outputs as well.
4. Power LED's
5. Drawing of circuits (schematic)
6. Parts list (including a good supplier of said parts)
7. **optional** overload protection to save charger/supply

I was running a thermovoltaic cell at 13.8v (when it was 12v rated) pulling 18 amps when after around a day it gave up the ghost. I also know that most chargers that have circuits to accept anything from 11-15v, but i would like it to be a consistant 12.0v.

Any help you can give me would be much appreciated.

i am super new to this kind of stuff, but am a fast study. I can read a schematic fairly well.

Thanks!

[Chippie]

IMHO....there is insufficient headroom for regulation....

13.8v in to 12v out........

[vintage1]

13.8v is perfect for LIPO chargers. I assume its some kind of 12v battery emulating power supply.

Just hook it up.

[GlowFly]

13.8v is perfect for LIPO chargers. I assume its some kind of 12v battery emulating power supply.

Just hook it up.
I agree. Just about all 13.8v supplies I know of are already regulated and intended to replace a 12v lead acid accumulator. Our R/C chargers are designed to use a ... 12v lead acid accumulator! Also many 13.8v supplies are internally adjustable within small limits and may well spread to 12v.

If you really have to have 12v it may be easier to modify a fixed 13.8v supply for 12v. Depends on the circuit...
--
Steve

[Chippie]

I think the thread starter needs to clarify his requirements...

[seneka]

Dont really know how to clarify much more than i already have...

The power supply will NOT be used specifically for a lipo battery charger. 12v is required... as that is the maximum voltage of some of the devices i will be powering. I have already fried a few things using this supply.

I understand it is perfect for a battery charger.. yes.. but not perfect for 12v max rated devices... such as the TEC described in initial posting, as well as brushless fans.

Burned up 125w 12v TEC (with tvc capability).
Burned up 2 12v fans
Burned up a 12v audio amplifier (which i built)

But i have spoken with another engineer via PMs, and recognize the problems with what i want to do. Its just not economical or practical to modify what i have, to what i need. I said "lipo" charger in my original posting, as that was the most sensitive device in regards to power signals (and how clean it is). Sorry for the confusion.

I feel that i will most likely be building my own power supply that supplies a maximum of 12v. I will look into modifying the power supply i currently own, internally with its own circuits first tho.

Thanks!

[seneka]

By the way.... this is the power supply i am talking about.

http://www.rchover.com/inc/sdetail/86590

[vintage1]

anything that is designed to work on a 12V accumulator should work fine on that.

I cannot understand why things have burned up, unless you had 'finger trouble'

It should be easy enough to get it to regulate to 12v instead of 13,8v. In gfact I wouldn't be surprised if it didn't have an internal sjustememt.

But first, stick a meter on its output.

Could be its giving e.g. 16v!

you never know.

[Probedude]

I agree with Vintage1. Open the case and look at the supply inside - likely there is a adjustment pot to trim it down to +12V, and maybe right now it isn't even set to 13.8V. If there isn't a pot to trim it down, I think it would be simpler to tweak the voltage divider resistors in the feedback loop than to build an external regulator capable of 20A.

Dave

[alexcmag]

Another good choice if your power supply has no adjust is is to modify a good ATX PC power supply, changing the Vref from 5V output to 12V output and using a multi-turn 10K trim-pot to got fine adjust.

There is an excelent tutorial (in spanish, but have pictures) in http://picayzumba.com/contentid-68.html

In my case instead of searching for resistor I simply used a 10K pot so I can adjust.

[nick_cool]

Not the best but a good a approximation, assuming that the 13,8v are constant, could be put 2 30A diodes in serial with the output. It will give 13,8-0,7-0,7=12,4V aprox.

With this little voltage margin and a 20A load calculate a regulator based in a power transistor will be difficult and expensive.

[nick_cool]

Te best option, and the most expensive too, is to put a DC-DC converter in the output. Converter are based in switching technology and can handle this spec.