Help: Need +12V to +13.8V mod.

[maxbarjr]

I am new here. I was searching for a schematic diagram for an ENERMAX EG651P-V when I came across this forum. Been reading this thread and I found it really interesting. The EG651P is an old PSU, but it's still working. I would like to use it for my ham radio power supply. How can I crank up the +12V to +13.8V? This SMPS is using the LM339N Comparator not the usual TL494 chip.

See attached pix.

Looking forward for any help out there.

Thank you in advance.

Max

[keeney123]

Re: Help: Need +12V to +13.8V mod.

It would help to have a schematic of the board to even see if that is possible. You would need to know what is the maximum voltage that is driving the comparator. Is that voltage above the 12 volts and can a just simple different resistor combination drive that to a higher voltage. On pulse modulated power supplies there is a feedback circuity to control the duty cycle. Unless a person is very familiar with this particular supply they would have to have a schematic of the circuitry to tell if the original design would allow for such an alteration. They would also need to know the power supply specifications of your ham radio to determine is this supply would work.

[stj]

Re: Help: Need +12V to +13.8V mod.

i wouldnt try that, the primary output is 5v, that is the one the feedback will track.

[japlytic]

Re: Help: Need +12V to +13.8V mod.

In an number of cases, comparators (usually ICs; sometimes transistors and zeners in old units) can act as overvoltage shutdown protection devices, from a number of computer power supplies I have examined.

[Behemot]

Re: Help: Need +12V to +13.8V mod.

Such incredibly +5/+3.3V heavy unit will not work anyway as long as you'll draw more than a few amps from the rail. You'd need to draw heavy power from them in order to keep +12V high. Sell it to somebody with powerfull dual PIII or similar system as such units are hard to get, and get 13.8V unit for that money.

[noppa]

Re: Help: Need +12V to +13.8V mod.

look if this may help

http://www.chirio.com/atx_14_volt.htm

[Stefan Payne]

Re: Help: Need +12V to +13.8V mod.

I wouldn't do it. Because it's a working, decent older unit wich aren't found that often and needed for some 'special purpose' things. Like an ASUS A7V266-D...

Besides that:
This is a group regulated unit. Means that you nead load on at least the +12V _AND_ +5V rail. You have to load it according to the loads of the time -> +5V heavy and not so heavy on the +12V rail.

Thus this unit is just bullshit for this project because of that...


Second:
ATX units have protection ICs, even with the worst possible protection chips, almost 14V is in an area where the OVP will kick in. So no chance whatsoever...

So in the end, your modification will not work!
All you could do is to put a Buck/Boost converter inside the PSU that you'll adjust to 13,8V...

But it's probably better to use a board for that and PCIe connectors as interface...

BUT:
You will need a modern ATX PSU for that wich is designed for heavy +12V loading and light +5V loading.

So in the end, isn't it better to get a 13,8V Powersupply?

I've taken a short look on what's available in my region (google shopping) and found something like cheap/2nd hand notebook power bricks for under 15€ as well as a MEANWELL PSC-60A for under 25€ (+ shipping).
So I don't think it's worth modifying this ATX PSU that isn't made for ~14V...

[maxbarjr]

Re: Help: Need +12V to +13.8V mod.

Thank you all for your comments and suggestions. All of you hit the nail on the head. I have decided to just use the power supply for a Linux Server project.

Again many thanks.

maxbarjr