Modifying SMPS from 12 volts to 13.6 volts

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,091
I have a few extra - laying around - power supplies that once were used to power cable boxes and the likes. they're in-line boxes that plug into 120 VAC and provide a steady regulated 12 VDC. One I have in hand at this moment is rated 100 ~ 120 VAC input; 12 VDC @ 2.67 amps Output. Amperage is not going to be my concern here. I want to provide 13.6 volts to maintain a car battery at float voltage.

I'd like to modify this by doing something to the circuitry. But have no idea (first) if it's easy enough to do and (second) if it's wise or unwise.

The box does not have screws, so I'll need to crack the case open one way or another. Haven't done that yet, but am willing if y'all think this is a possibly worth while endeavor. If not - I have a couple 18 VDC 1.1 amp boxes (comes from old printers) I suppose I could regulate down to 13.6 volts if need be. But I'd rather go with the higher amperage unit. Likely changing the voltage will lower the amperage, again, this is not the most important part of this project.

My goal: To keep a bench top car battery (in the garage) charged to normal operating voltage. I may run a car radio off of it - I may run some other electronics meant for automotive use. Having the necessary voltage would solve the problem of throwing a car battery charger on the battery and charging it up then disconnecting when done.
 

R!f@@

Joined Apr 2, 2009
9,734
Probability is high that it can be done but how it can be done can only be by checking the feedback circuitry
 

Dodgydave

Joined Jun 22, 2012
9,468
Easy to do, you need to find what chip it uses, then download the datasheet, the chip will have on board uvp protection (under -over -voltage) and can be overridden to make it variable, i made mine go from 4.5V to 28V @22amps. See if it has a voltage preset inside first.

Here are some common chips...

TL494, SG6105, KA3511, KA7500, WT7520
 
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Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,091
Working on getting the casing open - WITHOUT cutting flesh. Will know more when I have some actual circuitry in hand.
 

Ylli

Joined Nov 13, 2015
978
Careful here. You are probably looking at a power supply that is connected directly to the line. Use utmost caution when making any adjustments or part changes.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,091
Photos as requested:

On the solder side there's a chip: NE1190F. One transistor (Q1) and the rest are resistors or capacitors. Maybe a diode or two, I didn't look that closely.

On the component side there are two heat sinks along the length, one on each side. there's a glob of some kind of black stuff - I don't YET know what's under that. And the black glob adjacent the (I'm calling it an) output transformer. So far I haven't spotted anything that looks like a trim pot. if I come up with something I'll be quick to let you know.

In the pictures you can see the plug end by the heavier input cable. That small transformer and FW Rectifier and large cap are the input side of this bugger.
 

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Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,091
There are no trim pots anywhere on the board. Even underneath the black globs I can absolutely identify what's there - and that precludes the possibility of a trim pot. On the solder side there are three pads spaced the spacing of a regulator. Opposite that "Regulator" is something hard connected to the heat sink. Pealing just a little off the top I can see it IS a regulator. One more glob covers a coil of some unknown value. Having looked at this I'm not sure what type of PS this is. It MAY be s SMPS, it may be something else all together. Under the black I DO see what appears to be a four lead IC. Nomenclature APPEARS to say:

1217
817CN

That's best I can make of this four legged chip.

The one regulator type device that is NOT covered with black is a:

FTA06N60D
IPS(logo) YKL2
7453MH

The covered regulator I have yet to de-goup it. I'll post more about that when I find its VIN#
 

RichardO

Joined May 4, 2013
2,271
There are no trim pots anywhere on the board. Even underneath the black globs I can absolutely identify what's there - and that precludes the possibility of a trim pot. On the solder side there are three pads spaced the spacing of a regulator. Opposite that "Regulator" is something hard connected to the heat sink. Pealing just a little off the top I can see it IS a regulator. One more glob covers a coil of some unknown value. Having looked at this I'm not sure what type of PS this is. It MAY be s SMPS, it may be something else all together. Under the black I DO see what appears to be a four lead IC. Nomenclature APPEARS to say:

1217
817CN

FTA06N60D
IPS(logo) YKL2
7453MH
The "1217" is likely an opto-coupler. These are used as part of the isolated feedback in a SMPS.
The "FTA06N60D" is likely the switching transistor driving the inductor.

From here: http://www.inpowersemi.com/productshow.aspx?cateid=52&productsid=166

Part Number FTA06N60D
VDss(V) 600
ID(A) 6
RDSON(ohm) 1.7
RDSON(ohm) 1.5
Qg(nC) 18
Ciss(pF) 720
Package TO-220F
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,091
The unknown is now known. Gloop removed, it's a:

DII (possible logo) SBR
10U100CT
1119
With what appears to be 2 diode symbols Cathodes facing the middle. I've done some paintbrush touchup to bring out what I can see that the camera is having difficulty picking up:

Diodes.jpg
 

#12

Joined Nov 30, 2010
18,210
Image1 3.jpg
There we go. The goodies are on the back-side. Hope your eyes are good because that's where you're going to be working.;)
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
5,091
Is it an optocoupler between R20 and C4?
No, those are rubber pads meant to keep the board off the plastic.
Oh, wait a minute: Actually U2, as it is labeled IS

1217
817CN

There are rubber pads on the back of the board. Just happens one is sitting very closely to where you stated: R20 and C4. On the component side - yes, it's the device above named.
 

Dodgydave

Joined Jun 22, 2012
9,468
There are no trim pots anywhere on the board. Even underneath the black globs I can absolutely identify what's there - and that precludes the possibility of a trim pot. On the solder side there are three pads spaced the spacing of a regulator. Opposite that "Regulator" is something hard connected to the heat sink. Pealing just a little off the top I can see it IS a regulator. One more glob covers a coil of some unknown value. Having looked at this I'm not sure what type of PS this is. It MAY be s SMPS, it may be something else all together. Under the black I DO see what appears to be a four lead IC. Nomenclature APPEARS to say:

1217
817CN

That's best I can make of this four legged chip.

The one regulator type device that is NOT covered with black is a:

FTA06N60D
IPS(logo) YKL2
7453MH

The covered regulator I have yet to de-goup it. I'll post more about that when I find its VIN#
That's not an atx psu its a cheap switchmode psu, probably using a UC3845 series, what is the number of the chip U2 (8pin) surface mounted, it can be controlled by the Zener Zd1 and resistors to feed the opto-coupler on pin2.



R5oaW.png
 
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