I am building Manson EP-925 power supply

DigiSoft · Jan 17, 2008

Hi. I am building Manson EP-925 power supply. What do you think about this supply. Does anyone have experience with it?
I've build myself the PCB ant the BOX. I'll post pictures.

Thanks for the info.

Here are some pictures:
https://www.xs4all.nl/~pa0fri/Diversen/EP925/ep925.htm

**broken link removed**

Here is the schematic:
**broken link removed**

Damo666 · Aug 23, 2009

I have one of these that's faulty. Has anybody got the schematic for it please?

Nigel Goodwin · Aug 23, 2009

That's why you should post any attachments HERE, and not on a third party site.

Damo666 · Aug 23, 2009

My thoughts precisely Nigel. I was looking forward to viewing the schematic, but when it was a dead link i was rather brassed off. Ah well, the search continues.

mneary · Aug 23, 2009

I think I found it.

bountyhunter · Aug 23, 2009

DigiSoft said:
Hi. I am building Manson EP-925 power supply. What do you think about this supply. Does anyone have experience with it?
I've build myself the PCB ant the BOX. I'll post pictures.

Thanks for the info.

Here are some pictures:
ep925

**broken link removed**

Here is the schematic:
**broken link removed**

Wow, that is serious ambition.... I had almost forgotten what it's like to be young and full of energy.

Good luck.

Damo666 · Aug 24, 2009

Mneary - You're a good man. I know the psu says it's capable of 25A continuous, but realistically what would you say its safe operating parameter are for 12V use?

mneary said:
I think I found it.

Nigel Goodwin · Aug 24, 2009

mneary said:
I think I found it.

Thank you very much for that.

Nigel Goodwin · Aug 24, 2009

Damo666 said:
Mneary - You're a good man. I know the psu says it's capable of 25A continuous, but realistically what would you say its safe operating parameter are for 12V use?

It's mainly down to how much heat it can dissipate, and how large the heatsinks are. I see it has fan cooling as well.

But assuming there's 32V going in the regulators, and 12V out, that's 20V at 25A, which is 500W to dissipate, and 2N3055's are rated (absolute max) at 115W each. Assuming there's only 22V going in, then it's still 250W heat to lose.

fernando_g · Aug 24, 2009

Looking at the schematic threw me back into the late 70s electronics...you know an LM723 regulator and 2N3055 metal can transistor and such.

I'm not saying this in a scornful way, quite the contrary. I consider the late 70's to be a very happy marriage between discrete semiconductors and quite simple analog ICs. (simple for today's standards). It required a high level of design skills, and thorough undertanding of component limitations.

Nigel Goodwin · Aug 24, 2009

fernando_g said:
Looking at the schematic threw me back into the late 70s electronics...you know an LM723 regulator and 2N3055 metal can transistor and such.

Has anything ever replaced the LM723?.

Damo666 · Aug 24, 2009

Nigel Goodwin said:
It's mainly down to how much heat it can dissipate, and how large the heatsinks are. I see it has fan cooling as well.

But assuming there's 32V going in the regulators, and 12V out, that's 20V at 25A, which is 500W to dissipate, and 2N3055's are rated (absolute max) at 115W each. Assuming there's only 22V going in, then it's still 250W heat to lose.

Hi Nigel. I've opened the psu and noticed that the fan cooling is utterly pointless. By this, i mean that the huge transformer is actually blocking the fan from cooling the horizontal heatsinks that hold the bridge rectifier and the 5 x 2n3055 transistors. I've actually diagnosed the fault. All 5 of the pass transistors have become open circuit for some reason, yet the most i've ever drawn from this psu is 15A intermittently for running a cb and linear amp. I've now decided to put a fan on either side of the metal enclosure in the hope it doesn't break again. If you look at the images that the op posted, you'll see that the fan mainly on blows on the trafo rather than on the pass transistors. Very bad design ultimately.

bountyhunter · Aug 24, 2009

Nigel Goodwin said:
But assuming there's 32V going in the regulators, and 12V out, that's 20V at 25A, which is 500W to dissipate, and 2N3055's are rated (absolute max) at 115W each. Assuming there's only 22V going in, then it's still 250W heat to lose.

You have to calcultae the thetas to get the junction temps: ThetaJ-C on the 2N3055 is 1.5C/W, and if you use a typical mica/grease mount add about another 0.4C/W. That means you have about 2C/W from junction to heatsink. If each 2N3055 is dissipating 20W, the transistor junction temp will be 40C higher than whatever the heatsink temp is right beneath the transistor case.

A hefty heatsink with a fan blowing on it can attain theta (S-A) values under 1C/W, not sure exactly what yours is.

bountyhunter · Aug 24, 2009

Nigel Goodwin said:
Has anything ever replaced the LM723?.

Discrete circuitry. Never been a big fan of that IC, performance is pretty mediocre but the military uses it a lot because it is JAN qualified.

bountyhunter · Aug 24, 2009

Damo666 said:
I've actually diagnosed the fault. All 5 of the pass transistors have become open circuit for some reason,

Maybe it's my eyes, but I didn't see any current limit protection built in on the schematic? That would explain the five blown transistors.....

ADD: the current limiter is IC2D. A really klugy circuit using a comparator and a screwball level shift. Note that the current limit changes both with temp and output voltage. Higher outputs allow more current, looks like they are trying to follow the SOA for the transistor somewhat.

mneary · Aug 24, 2009

the huge transformer is actually blocking the fan from cooling the horizontal heatsinks

Maybe the transformer requires more cooling than the heatsinks.

bountyhunter · Aug 24, 2009

From what I can see from the picture, it looks like the fan is set up as a "pusher" to suck air out of the box and push it out the rear. That draws cool air into the front of the unit from outside. If so, you want the transformer near the fan so it doesn't "pre heat" the air passing across the heatsink. The cool air inlets are all at the front around the heatsink assembly.

Damo666 · Aug 25, 2009

bountyhunter said:
From what I can see from the picture, it looks like the fan is set up as a "pusher" to suck air out of the box and push it out the rear. That draws cool air into the front of the unit from outside. If so, you want the transformer near the fan so it doesn't "pre heat" the air passing across the heatsink. The cool air inlets are all at the front around the heatsink assembly.

i'll check to see if it's blowing or sucking air next time i draw a significant amount of current from it, as it only comes on intermittently when drawing a large current. One other question i have is this - with regards the series pass transistors, are they classed as common base configuration? I'm slowly trying my hand at electronics again after a 15yr break. Cheers.

Nigel Goodwin · Aug 25, 2009

Damo666 said:
One other question i have is this - with regards the series pass transistors, are they classed as common base configuration?

No, common collector (also known as emitter followers).

bountyhunter · Aug 25, 2009

Damo666 said:
One other question i have is this - with regards the series pass transistors, are they classed as common base configuration?

The pass transistor is an NPN darlington connected as emitter follower, which gives a voltage gain of approximately one but has huge current gain. It also has an extremely low output impedance off the emitter drive point.

I am building Manson EP-925 power supply

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