Damn it. Voltage on 13.8v PSU too high...
 

Does anyone know of a good part or design of a 13.8v voltage regulator?

I got a 13.8v PSU off of ebay but its putting out 14.8v-14.9v... I want to power my two 50Zs. If I can't come up with a good solution I guess I'll return it :(

Re: Damn it. Voltage on 13.8v PSU too high...
 

Did you put a load on it? It might come down to 13.8 .

Re: Damn it. Voltage on 13.8v PSU too high...
 

I have a meanwell 13.8V Psu and it allows adjustments from 12 to 15 volts. Maybe that is why you are at 14.8-14.9V.

Re: Damn it. Voltage on 13.8v PSU too high...
 

No, I cant think of anything I have that is supposed to take over 12v that I can load it with. Does the avg 12v fan handle 14-15v for a min? I probably have one or two I can gamble with that I wont care about frying. Even if that pulls it down how afraid should I be of how it initially starts at 15v and goes down to 14v even in a second?

Re: Damn it. Voltage on 13.8v PSU too high...
 

A 1k resistor would be perfect. Too bad you're not here, I have a bunch.

The fan is probably ok until 13.8; at your own risk above. The voltage normally drops significantly with the smallest load.

Re: Damn it. Voltage on 13.8v PSU too high...
 

Think I actually have a few left over. Not 50w ones though :( If it doesnt dip I'll just buy a tripp-lite one...

Re: Damn it. Voltage on 13.8v PSU too high...
 

You don't need a powerful resistor.

V = R * I
P = V * I

Let's use:
V= 15 volts
R = 1000 (1k)

"I" resolves to 0.015 Amps (aka 15 mA)
"P" resolves to 0.225 Watts

A standard quarter watt resistor will do just fine.
;)

Re: Damn it. Voltage on 13.8v PSU too high...
 

That's not a PSU, it's a car battery. :ha:

Re: Damn it. Voltage on 13.8v PSU too high...
 

Unless its a really cheap psu I can't see why you can't crack open the psu case and make voltage adjustment. Manual might help.

Re: Damn it. Voltage on 13.8v PSU too high...
 

Its a darn cheap psu. I can take pics later. Its old and beatup also.

Re: Damn it. Voltage on 13.8v PSU too high...
 

suggest something like:

http://www.xtremesystems.org/forums/...ad.php?t=37574

?

Re: Damn it. Voltage on 13.8v PSU too high...
 

Awesome guide but Im working with a little bench power supply. Not a PC PSU.

I'll post pics of the innards when I get home. Hopefully someone knows how to modify the PCB to change the regulated value. The PCB is pretty simple, only a handfull of components on there.

Re: Damn it. Voltage on 13.8v PSU too high...
 

Try the resistor first.

Re: Damn it. Voltage on 13.8v PSU too high...
 

Tried the 1k resistor. On the pumps it dropped the voltage so low they wouldnt spin at all. 5v IIRC. Same for the fan I had. Dropped it to 8a with a fan that pulls 1A at 12v.

Here are some pics of the PCB.

http://filebox.vt.edu/users/jtorres/...%20(WinCE).JPG
http://filebox.vt.edu/users/jtorres/...%20(WinCE).JPG
http://filebox.vt.edu/users/jtorres/...%20(WinCE).JPG

In the first pic:
The two black leads coming from the bottom left come from the transformer.
The white lead that comes from the bottom left feeds ~1v to an LED thats not working
The black lead that comes from behind the PCB comes from the same solder joint that the white and black wire come from, from the bottom right corner.

The white lead that comes right off the bottom of the big white resistor is the +15v output. The white lead that comes from the bottom right corner is the GND.

Chip markings:
The mosfet looking one - TIP29 A7711
8 legged IC - MC1741CP 1 "Motorola insignia" 7707
3 legged diode - 2N 5172
The three black rectangle tab looking ones all have "100" then something that looks like omega then maybe an S. Act like caps.
Had to unsolder the last pic to get it unmounted just to take a pic. - "Motorola insignia" 2N5877 7626

Re: Damn it. Voltage on 13.8v PSU too high...
 

TIP's arent mosfets. switching transistors.
Used a few for a PWM controller (TIP32c).
the MC1741 -> op amps.
the 2N 5172- > NPN Darlington Transistor not diodes.

that's a pretty simple psu.

Re: Damn it. Voltage on 13.8v PSU too high...
 

Any chance you can get me wearing gold plated diapers and tell me how to modify the board to lower the output voltage? :D

Re: Damn it. Voltage on 13.8v PSU too high...
 

No adjustments here.

The 1K resistor wasn't meant to be put in series. I was trying to point out that a PSU without a load can put out higher than normal voltages, and meant to suggest that you put the 1k resistor as a load (parallel, not series) by itself, then see if the voltages drop back down to something expected. If it does, then you can add another load (i.e. a fan) and see if it drops further.

13.8v PSUs are simple circuits, usually meant to replace/simulate a car battery. Heck I need one of those; I have a CD stuck in my old CD player!

Re: Damn it. Voltage on 13.8v PSU too high...
 

I was wondering if you meant parrallel. You think it would drop the voltage more than a normal 12v fan would? I'll try it when I get home. Hey I'll sell you this one for $12! :banana:

Re: Damn it. Voltage on 13.8v PSU too high...
 

With the shipping and $12 for PSU I dont that CD is worth that much....

He meant not to place the resistor inline in a series circuit with the pumps or the fan. With the resistor in inline, the current is the same for both the resistor and pumps. That is why you got a big drop in current.

Place it in parallel and the current through the pump and resistor varies based on their resistance but voltage is the same for both. All you need to do is build another circuit to the pump like how you did exactly with the resistor.

Re: Damn it. Voltage on 13.8v PSU too high...
 

You know I was joking about selling it for the amount I bought it for, right? Sorry, hard to detect sarcasm, I should have used tags.

What do you mean I have to build anothe circuit to the pump? Are you just talking about putting the pump and resistor in parrallel?

Re: Damn it. Voltage on 13.8v PSU too high...
 

Yeah, the sarcasm was hard to detect. It sounded more like desperation.:doh:


Just think of it in WCing loop in parallel with two block. You have Y and split into 2 inputs in the two blocks and have the 2 output of the blocks combine into Y.

PSU positive terminal < Resistor | Pump > ground terminal of psu.

----------PSU---------
----------- ^----------
-----------|--|---------
-------Res Pump----
-----------|--|---------
------------V---------
----------PSU---------

From positive terminal of PSU, you split into resistor and red molex of pump. Then you have the black ground terminal from pump and resistor connect into another Y before you finish at ground connection of psu.

You don't connect the resistor to pump but keep them seperately.

Re: Damn it. Voltage on 13.8v PSU too high...
 

lol thanks I know what parrallel and series circuits are :D I'm no EE but took enough electronics classes to understand the basics. I just don't recognize components.

I put the 1k resistor and fan in parrallel and it still gave 15v. I just don't understand why increasing the load a little with a resistor was supposed to do anything? Voltage is constant across a parrallel circuit so if the fan was getting 15v why would putting a resistor in parrallel with it change anything other than the total current? I guess if the more load I put on it the voltage would sag but I put up to 35-40w and it still was above 14.8v.

Re: Damn it. Voltage on 13.8v PSU too high...
 

If you still have the exact same voltage after that; then it won't change.

Let us know the color codes on the resistors (and the pins that they're connected to); there might be a way to adjust it.

Note: http://www.national.com/ds/LM/LM107.pdf

Re: Damn it. Voltage on 13.8v PSU too high...
 

how many watts is it supposed to provide? 50W?
Lets just say yes, and do the math. At 13.8 V that gives about 3,6 Amp. Lets leave a margin, say 4.

Then, LM338 - 5A, voltage regulator.
http://www.national.com/pf/LM/LM338.html
can regulate from 1,2 V to 32 V .
Circuits in the PDF (including specs).
Just connect the psu output to the regulator circuit.
done.
drink coffee.

Re: Damn it. Voltage on 13.8v PSU too high...
 

Thanks TerraMex