Need to get 15vdc power supply down to 12vdc

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bmklawt

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I need to power a picoPSU-160-XT ATX Power Supply.
https://www.mini-box.com/picoPSU-160-XT off a 12 volt source.
The PicoPSU has over voltage shut down at 13vdc,

I would like to power this from the power supply I currently have, which is putting out 15.4vdc. I am assuming I can put a resister in there but I can figure out what size I would need.

The power supply is for my mill and I don't have room to add another power supply and a new one is to expensive. The current power supply puts out -5v, +5v, -12v, +15.4 (its suppose to be +12v) -24v and +24v.

Your help in this matter is greatly appreciated,
Bruce
 
Hi Bruce,

that power supply has a total power of 160W. There is no (known to me) resistor dissipating ~34W to get rid of the extra 2.5V (14.5V-12V).

I suggest you use an appropriate power supply to connect directly to the mini-psu.

Boncuk
 
That Pico unit is rated 200W peak. Can your present supply handle 200W? If not, it won't be suitable.
Even if it can give 200W, I doubt the output would be 15.4V at that power: it will probably drop to around 12V. So a simple resistor can't be used to drop the volts. A power mosfet might do the job, however.
 
You might try several (maybe 4) automotive diodes (about a 35 amp diode) in series with your load. Figure roughly a .65 volt drop for each diode. That should give you about a 2.6 volt drop across the diode string. This assumes your 15 volt supply has the needed current to drive your PSU.

Ron
 
The power supply is a Sorensen or maybe a KYOSAN Model SCB306A-02, I can find no information on the web about it. I just figured it could handle whatever I through at it.
Any one possibly know if there is a way to adjust this down to 12v where is is suppose to be.

Thanks much,
Bruce
 

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Try running your supply with a ~ 5A load on the +5V line (a fair-sized load may be needed for proper regulation) and a ~ 10A load on the '15.4' V line and let us know the measured voltages across both loads. That may give us a clue as to the feasibility of this project.
 
Ok I should have stated I know very little about electronics, when you say to add a 5 amp load to +5v line I am lost, but I will figure it out.

What is a buck?
 
A 1 Ohm resistor will draw 5A (so it's a 5A load) from a 5V source and dissipate 25W. That is probably a greater load than you need to check the regulation. Do you have any low (< 10 Ohm) value high wattage resistors to hand?
 
I do have some of the following:
8 ohm non inductive - I have no clue what this is
10 ohm 10W
1 ohm 10W
.47 ohm 5W
 
Try a 10 ohm 10W on the 5V line and see what the '12V' voltage is.
If the 8 ohm is similar in physical size to the 10 ohm it may have a similar rating. If so, you could try connecting the 8 and 10 ohm (or better still 2 x 10 ohms if you have them) resistors in series, connect one end of the combination to ground and then briefly (no more than a second or two to prevent the resistors getting hot, as they will be running at or above their maximum rating) touch the other end to the '12V' line and see what the voltage is.

WARNING: when the resistors are drawing current keep them away from anything inflammable and don't touch the resistor bodies!
 
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Readings I get on the 12v line:
15.3v no load
15.6 with 10 ohm on 5v line
14.6 with 2x10 ohm in series on the 12v line
The resistors only got slightly warm if that matters

Thanks,
Bruce
 
i understand it as an SMPS managed with a initial step-down transformer for isolation.

it has multiple outputs.
while loading 5V supply (being in control loop ) and managing 15V is correct,
perhaps it could be done this way.
try to manage to change the control loop from 5 V to 15V line, change the resistor divider to get 12V output. Generally they use TL431 as controlling element. Then on, on it works with 12V perfectly regulated. Other voltages would reduce to the proportion.

BTW, can you check what switch mode IC they used as per the unit by physical check and identify the feed back section?
Any schematic or block diagram, in the user manual that you may have?
 
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Interesting that the 12V line actually rises slightly when the 5V line is loaded. Both that, and the fact that the 12V line drops when loaded, suggest the regulation is done on the 5V line only.
So with only a ~11W load (20 ohms, 0.73A) on the 12V line it drops from 15.6V to 14.6V. I would expect it to drop a lot more if you increase the load significantly. That confirms a simple resistor won't be the best solution to getting a target voltage of 12V, and an active component (e.g. FET) will be needed. However, I'd be very surprised if the 12V line can provide enough current for driving the Pico. At a peak power of 200W you need ~ 16.7A from that 12V line !!!
 
In multiple output power supplies, it is but natural. the one which controlls the loop like 5V or 3.3V in pc psu, remains stable under control, other voltages change slightly.
In general, such PSUs are designed for slightly less than the actual voltages on auxulary supplies. Once the main voltage is loaded, others boost up high and come near to needed values.
 
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