3.5kV power supply teardown

[rolycat]

I recently acquired a Pharmacia Biotech EPS 3500 XL power supply for 'next to nix' and thought a mini-teardown might be of interest.

It can generate up to 3500V at 100W and monitor the current to within a microamp. Unfortunately the shrouded 2mm connectors for the outputs are expensive unobtainium, so I haven't (yet) been brave enough to run it up to its full capacity. Fortunately some multimeter probes reach nicely, so its good up to 1000V.

The instrument was designed and built in Sweden and dates from the mid nineties. Apparently it was designed principally for 2D electrophoresis using isoelectric focusing.

I also have an EPS 300 from the same manufacturer. With a 300V maximum output it is rather less exotic, although I could probably do a teardown if anyone is interested.

Here is the EPS 3500 XL feeding 1000V to a multimeter. Meter input impedance is 10 megohms, so the 100uA measured draw is spot on:


The back of the unit. The fan is a Panaflo FBA08A12W, curiously the exact model used on an HP E3631A PSU which I am currently attempting to repair:


The main PCB, proudly designed by Kenneth Lindh. The large power MOSFET at the back is a 2SK1359:


And the backside, with some appropriately tall standoffs:


The processor, a Hitachi (now Renesas) H8/532. The 8 pin chip is a TL7705ACP voltage supervisor. Other ICs on the board are the firmware ROM, an LT1244 switching controller, an LM339 comparator and two TL074 op amps:


The voltage multiplier section. The diodes are BYV26E 1000V ultra fast avalanche types. Electrolytics are all Nichicon 400V 10uF:


The final output stage, linking -1750 and +1750 volt sections with a 4kV 3n3 ceramic. The wires to the output terminals with the ferrite beads attached are stiff and somewhat springy:

[rsjsouza]

Thank you for the teardown. I have a special attraction to high voltage design, and this one is really nice.

BTW, you have a nice probe insulation tester in your hands... Simply grab some el-cheapo probes and start increasing the voltage to check their insulation... I have not seen any probes to fully break through the insulator (even some terribly cheap ones), but you can see the glow around them in a dark room...

[PedroDaGr8]

NIce, this is a high voltage gel electrophoresis power supply (considering the voltage it might even be used for capillary electrophoresis as 3.5kV is too high for most gels).

A bit about the company. Pharmacia is famous for making the Äkta brand of FPLC machines. If you have worked in a biological lab where you purify biological compounds you know about Äkta's. Pharmacia was acquired by Amersham Biosciences which was subsequently acquired by GE Healthcare Life Sciences. I have an old board out of a Pharmacia Äkta. It shares a lot of the same parts with this one (minus the high voltage rated ones). The blue box caps, the whole power switch, power input and connector next to it, the microcontroller, etc. are the same.

[TerraHertz]

Nice looking board. You don't happen to have a schematic?

It is quite amusing that the 'STOP' button is closest to the output terminals. Sort of 'I *dare* you to stop me!'


You should be able to improvise a shrouded connector using some PVC tubing of appropriate size, bits of wire, gold-plated pins from D25 connectors, and silicone glue?

[nathanpc]

"Made in Sweden"

That's something you don't see very often.

[rolycat]

NIce, this is a high voltage gel electrophoresis power supply (considering the voltage it might even be used for capillary electrophoresis as 3.5kV is too high for most gels).

Yes, as I mentioned in the intro it is primarily intended for two-dimensional gel electrophoresis. This uses 2 phases, one using isoelectric focusing across a pH gradient to separate the proteins by their isoelectric point, followed by a second phase at 90 degrees to the first, which sorts by molecular weight.

As a consequence, the power supply can be programmed to run up to nine separate phases with different voltage/current/power profiles.

Nice looking board. You don't happen to have a schematic?

Alas, no. I would be very happy if anyone knows where I might find one.

You should be able to improvise a shrouded connector using some PVC tubing of appropriate size, bits of wire, gold-plated pins from D25 connectors, and silicone glue?

Maybe. The 2mm socket is drilled into a protruding brass post which is buried over 20mm deep in the outer socket:



Making a reliable and safe connector will be a challenge...

[PedroDaGr8]

NIce, this is a high voltage gel electrophoresis power supply (considering the voltage it might even be used for capillary electrophoresis as 3.5kV is too high for most gels).

Yes, as I mentioned in the intro it is primarily intended for two-dimensional gel electrophoresis. This uses 2 phases, one using isoelectric focusing across a pH gradient to separate the proteins by their isoelectric point, followed by a second phase at 90 degrees to the first, which sorts by molecular weight.

As a consequence, the power supply can be programmed to run up to nine separate phases with different voltage/current/power profiles.

I completely missed that part  Yeah, one of my co-workers has been doing a large number of IEF gels to resolve some antibody stability issues though our gelsonly require around 600V (then again we aren't doing 2D only 1D).

[robert555]

Made in Sweden, yey!
Nice teardown, i like high voltage stuff!

[samofab]

If you plan to modify the connectors on the front, I recommend replacing them with MHV connector (looks like BNC, but it's good up to 5kV & 3A).

[Monkeh]

I was watching that very auction. Looks like a really nice piece of kit.

[LaurenceW]

Hello Rolycat,

I have just scored one of these power supplies on Fleabay. I am looking to use it as a general purpose HT voltage supply. I can see that I am going to have to <ahem> modify one of the safety features - namely its ability to detect ground currents and shut down. Did you ever get hold of a schematic for this or any similar designed units?

[tom66]

How does it sense output voltage and load current?

[rolycat]

Hello Rolycat,

I have just scored one of these power supplies on Fleabay. I am looking to use it as a general purpose HT voltage supply. I can see that I am going to have to <ahem> modify one of the safety features - namely its ability to detect ground currents and shut down. Did you ever get hold of a schematic for this or any similar designed units?

Afraid not - and it was permanently shut down for a few months because the IEC inlet/filter exploded and chucked its guts all over the PCB:



Of course, the unit was switched off at the time, so when I went into my lab to be greeted with a nasty stench it took a while to figure out what had caused it. You may want to keep yours unplugged or switched off at the wall when not in use.

I have recently installed a replacement inlet/filter, and it's running again. Very handy bit of kit when you need some serious volts, but as you say the circuit is very safety-conscious.

[tautech]

That's never a pleasant sight. 
Being a switchmode supply, you would be wise to check the E-caps for signs of degradation.

Or maybe it was just a case of the mains input filter doing its job? 

[ve7xen]

I believe Schaffner inlet filters from the 90s have a history of doing this, it plagues test equipment too. If you replace it, don't use NOS, is the general advice.

Thanks for the interesting teardown. Surprising that the board doesn't like *all that* different from a low voltage one, was expecting more obvious attention to isolation (though I'm sure it's well designed it just doesn't show).

Dave did a teardown of another electrophoresis supply a while ago, if you haven't seen it:

[rolycat]

I believe Schaffner inlet filters from the 90s have a history of doing this, it plagues test equipment too. If you replace it, don't use NOS, is the general advice.

Yes, I contacted Schaffner and they recommend the current model FN9226-3-02 as a replacement. It's missing the plastic flanges around the screwholes, but should fit OK. It was pricey though, so in the event I used another brand of filter which happened to fit pretty well.

Dave did a teardown of another electrophoresis supply a while ago, if you haven't seen it:

I did watch that, thanks. An interesting teardown as always, but I wasn't very impressed with the EC250-90 - the general design and regulation seemed more primitive than the Pharmacia models I've seen.

[HighVoltage]

Interesting to see those blue 47nF capacitors in the voltage multiplier section. ( I think they are also made in Sweden but I forgot the name)
And then see the German made WIMA at the output stage.
I remember the days, when we opened anything of quality and it was full with red and yellow WIMA capacitors.
These days, you really have to look for them.

Also the high voltage diodes look like they are of high quality, may be Vishay or so.

It would be really nice to look at a schematics for this instrument.
May be the layout is so nice, because it was for medical applications and money did not matter too much.
Any Idea how much this unit was, when it was brand new?
Thanks for these nice tear down pictures, I really enjoyed looking at them.

[rolycat]

How does it sense output voltage and load current?

Good question. The only tap I can see from the output stage is two high voltage 10M resistors in series lurking under the output terminals. They connect to the positive output at one end and two of the non-inverting inputs of a TL074 quad op-amp at the other.

[rolycat]

Interesting to see those blue 47nF capacitors in the voltage multiplier section. ( I think they are also made in Sweden but I forgot the name)

Rifa:

Since swallowed by the Kemet Corporation. The large blue 470n X2 capacitors and the white 2n2 Y2 caps in the mains input stage were also made by Rifa.

The transformers are also Swedish - the control section supply transformer was made by Transformator-Teknik AB of Åmål, Sweden.
(Incidentally the town is famous; there's an eponymous film with a very controversial title.)

It would be really nice to look at a schematics for this instrument.

May be the layout is so nice, because it was for medical applications and money did not matter too much.
Any Idea how much this unit was, when it was brand new?

It's still a current model, cosmetically tweaked as the EPS 3501 XL. These are quoted by GE Healthcare, (who bought Amersham Lifesciences, who bought Pharmacia), at $4,971.

Thanks for these nice tear down pictures, I really enjoyed looking at them.

My pleasure.

[HighVoltage]

Yes, RIFA, that was the name...  ... we used them in the 1980th a lot in projects in Sweden.

I was so much intrigued by your teardown, I found a EPS 3501 XL in like new condition and just bought it. It should be here in a week or so. Then I will open it up and see, if there are any visible differences. Thanks for your inspiration.

[Lodoiska]

Hi!
I know this is an old thread, but just in case some of you are still here... Has anyone tried this power supply with non-sheated 2mm plugs? I also got one, but as it has been specified, the connectors for this are really expensive, when you can find them at all. So I was wondering if someone had tested it successfully with normal 2mm plugs, without bypassing the built-in securities?

Thank you!
Lodo

[Yansi]

Interesting to see those blue 47nF capacitors in the voltage multiplier section. ( I think they are also made in Sweden but I forgot the name)
And then see the German made WIMA at the output stage.
I remember the days, when we opened anything of quality and it was full with red and yellow WIMA capacitors.
These days, you really have to look for them.

These days you get a lot of red low spec caps from Wurth instead 

[HighVoltage]

Hi!
I know this is an old thread, but just in case some of you are still here... Has anyone tried this power supply with non-sheated 2mm plugs? I also got one, but as it has been specified, the connectors for this are really expensive, when you can find them at all. So I was wondering if someone had tested it successfully with normal 2mm plugs, without bypassing the built-in securities?

Thank you!
Lodo

Hello Lodoiska and welcome to the forum.

I have made my own connectors with gold plated MultiContact 2mm banana plugs for the EPS 3501 XL.
It works really well, is safe to use and no security issues at all.

[Lodoiska]

Hi!
Thank you and than you!
You have no idea how much your original post has helped me; I was going mad looking for info on this power supply's connectors. Not even in the manual do they specify what is required!! You were the only one to specify it. And I am lucky you still are a member

So, if I understand well, a (quality) non-sheath 2mm banana plug will work? Because a 2mm male to 4mm female can be found easily, and the electrophoresis cables available in my lab are with the new 4mm sheath standard. That would be so much more simpler and economic than finding the right "science" adapter...

(yup, I am that weird, I am going to use this for what it was originally meant... ;P )

Thank you so much,
Lodo

[HighVoltage]

I am traveling right now til the weekend.
Then I can upload some pictures if you want.

No, do not use 2 to 4 mm adapter, that is not safe !!!

I used gold plated 2 mm straight banana plugs and made myself some
holders / spacers out of teflon (PTFE)

On one side of the holder the 2mm banana plug comes out
On the other side a good quality high voltage cable comes out
I have no idea how the original cable and plug looks like but the one I built is perfect for my needs
and 100% safe!