51X PSU Cartridge

Hi There,

I wanted to have some toughts on something i'm thinking to build for msyelf, i've already done some stuff and thinking regarding its build, meaning, worked on PCB's and as you can see some
3D Modelling just to get an idea of how all would fit and assemble together.
But some toughts advice, learning etc... is always welcome.

I wanted to have some sort of 51X lunchbox, an all in one solution, and tought this might make it happen, with 2 modules more than the Api one actually,
And if really want to go authentic, add a handle on the side haha.....
So basically it's a PSU Cartridge, that would take 3 module space, and so leaving 8 modules to be feeded.
Chunger had done something like that just for powering up a couple of modules if you remember?
Anyway there are a lot of things to take into account for building this, and i'm waiting on some informations to see if it would be doable on the way i tought about it.

But there are a couple of factors that i maybe omitted, and maybe a better way of doing all this? so that's why i'm asking for feedbacks and tought, pros and cons etc....

One of the main concerns and limitation i found is the Power transformer, it has to be a low profile one, the webshop here in France that makes custom Toroidals have Low Profile option,
and the max VA that "could" fit, because there is just maybe a mm tolerance to get the thing in (120mm open window on rack) well that would be their 120VA one. giving about lets say 1.4A fo the +/-24 and 16V rails on paper... and so it's dimensions are 119mm Diameter and 34mm high on paper also, I'm actually checking with them if they can do and garranty tight tolerances because real world could be way different.

Second Concern would be the weight of this transformer, on paper it's 1.5Kg huh.... and that would mean doing a tight and sturdy mechanical assembly...
On the PSU, the only PCB that has the cardedge is the Vreg module, i tought that having a sturdy mechanical fit between modules and the fpd attachement, would suffice in terms
of attachment? Maybe i'm tottaly wrong?

As for the PCB and the circuit, i sticked to the one that Silent Art had done for the circuit, but with a little less Voltage on the Capacitors side, since as you can on the sketchup drawing,
My disposition allows to have only max 35mm diameter and 40mm high capacitor, of course parralel some caps could do, maybe...

Options on the PSU would be Led and Fuse in front, Led beeing on the fused line.
I added A Neutrik Connector on front as well, for if wanting to use this module as an external unit, or it can even be a bench PSU just for feeding stuff, or maintenance stuff...
would need some simple DIY metal case, with a heatsink on one side or so, to help dissipation if going external and if i feel like taking the heat on a full 11 Space rack for random modules? Could be risky tough....?
And trimmers hole on front, to be able to fine tune the voltages.

As for the dissipation of the Vregs, i made a PCB for beeing able to home etch on double sided board, and this one has square holes to make the regulator pass under the PCB and to be able to connect directly on L Bracket, wich would have a 3mm aluminium plate on it to make a bigger and fatter heatsink, and since all would be tightened together with the front 3 Space FPD,
that would increase dissipation, now how much, only experimenting will tell...

The cabling would be a little tricky, but with a little discipline it should do, i made all connections on Molex, and some to solder directly...
But it will end up clean...

Of course inserting the PSU, would have to be done with the rack on the floor and facing up, for beeing able to insert easily and tightn everything before
putting the rack flat.


So any ideas toughts, critics are welcome. Maybe i'm over or not thinking of it enough?


T.

Tony,

Not to discourage but we looked into this last year and decided not to take it further. Volker did a sketch for a linear version and I even did some preliminary work on a switching (with a switching designer friend of mine) module.

I don't think anybody would like to see an IEC connection throught the front. Putting it to the back requiers a new design.

But the most important point is that you will not be able to accommodate sufficient heatsink in that space.

sahib said:

Tony,

Not to discourage but we looked into this last year and decided not to take it further. Volker did a sketch for a linear version and I even did some preliminary work on a switching (with a switching designer friend of mine) module.

I don't think anybody would like to see an IEC connection throught the front. Putting it to the back requiers a new design.

But the most important point is that you will not be able to accommodate sufficient heatsink in that space.

Click to expand...

Hi Sahib, yes Volker told me about it.

Well IEC on front i don't mind, it's really for my use, not something i'd like to propose, as said it's for personal use.

As for Heatsink well yes could be tricky, + the fact that i need to make sure the power transformer could pass...

Maybe would need to scratch my head a little more for Dissipations etc... But you really think that for, lets say randomed 8 modules it would be
getting dangerously hot?
EDIT: it surely will  :-\

Zayance 
make the front all heatsink
move the fuses inside
the power plug makes a switch
heatsink becomes handle

Alternatively, perhaps you could put the heat sink inside, but replace the circular handles with large holes, that would allow ventilation of the heat sink.  One on the bottom, one on the top, convective airflow through vanes of a heat sink.  The vanes can offer protection from fingers intruding into the inside as well.

If you recess the heat sink, you can make the holes into handles as well.

However, I am of the opinion that you don't need to use front panel space for power supply, it has a lot of engineering challenges.  Might be better to re-engineer the back of the rack, and add a power supply there.

Hi guys, thanks for the toughts and feedbacks.

JamesW said:

Zayance 
make the front all heatsink
move the fuses inside
the power plug makes a switch
heatsink becomes handle

Click to expand...

Yes i tought of going like this as well, fitting a big heatsink on front, like TO3 stuff,
would be taking a lot of the front space tough, but yes an option i'll try scratching my head around.

As for the power plug making he switch, not sure if that's a very elegant idea, maybe better still having this one
cutting phase and neutral... EDIT: But maybe the only way if need that space, hmmm.

Heatsink becomes handle yes

As for the dissipation i'll do some search to have a better idea of the dissipation required for those LM350's,
and will see if there is a better option for power transformer also...

bruce0 said:

Alternatively, perhaps you could put the heat sink inside, but replace the circular handles with large holes, that would allow ventilation of the heat sink.  One on the bottom, one on the top, convective airflow through vanes of a heat sink.  The vanes can offer protection from fingers intruding into the inside as well.

If you recess the heat sink, you can make the holes into handles as well.

However, I am of the opinion that you don't need to use front panel space for power supply, it has a lot of engineering challenges.  Might be better to re-engineer the back of the rack, and add a power supply there.

Click to expand...

Yes maybe Heatsink inside, taking one module....

If not using the front, then the back PSU would have to be same size anyway, not more, and would need to use your SubD's for connecting...
same engineering challenges maybe?


Anyway, still some homework to do...

Any ideas toughts are welcome again.

Thanks a lot.

What if only transformer, rectifiers and the big caps on your module, maybe with a common 48V for your phantom rail, but feed your own backplane with your raw DC rails and do the voltage regulation per pair of moduleslots to get generated heat shared by some voltage regulators. Instead of LM350 could then be 317/337.

Harpo said:

What if only transformer, rectifiers and the big caps on your module, maybe with a common 48V for your phantom rail, but feed your own backplane with your raw DC rails and do the voltage regulation per pair of moduleslots to get generated heat shared by some voltage regulators. Instead of LM350 could then be 317/337.

Click to expand...

hmmm, yes ala rackit, but then means one custom backplane to be ordered, since i don't have 3.2mm epxy to home etch it, and would be messy
if done so i guess....
So manufacturing one could be an option, a little costy for one, but an option true...

Allright following the suggestion of jamesW and some previous toughts, i've redone a Sketch, to have a better view of this option.

So all fuses inside as well as the mains one.
Trimmers would be on the sides of the PCB inside, Bourns Z type ones...
Vregs would be hardwired going from PCB Molex to the front by an open window, or
actually no, i can redraw the PCB to have those Vregs on edge of the PCB so no hardwiring.

EDIT: AND so could also have a rectagular Aluminium panel, something like 20mm thick and 90mm long from Vregs on PCB
to the 4mm Thick fpd, and the Big Heatsink on front, dunno if sandwiching would be very efficient, but since it's aluminium,
and adding some thermal paste between all this and you get a nice triple whopper with cheese of Dissipation...
Well just a tad, since thermal paste is mainly for getting the flattest surface possible....

I Have a Heatsink in stock taken from dump, that is similar to this sketched one, a little taller
for TO3 pakage, and from similar designs, could have about 0.6°C/W, wich could be ok, maybe a little better
since i was planning on using 4mm Aluminium Panel as FPD, so that would add to the overall...

The IEC would be one like this, this one is kind of expensive, will look around better, but just to give an idea.
Ths one would need to open a square hole on the Heatsink and would need to have a squared hole of 1.5 or 2mm (not hole but i don't know what's the name in English) on front of the 4mm thick fpd, to be able to be inserted in place, yes since max Panel Thickness is 2.5mm for them.. I can have access to milling machine so..... A little complications but doable...
http://fr.farnell.com/jsp/search/productdetail.jsp?sku=1176805

There could also be LED's that would be hardwired from Vreg PCB to the second module maybe, and would need to drill holes
on the Heatsink to have a better view of them, again doable...

The Overall weight is increased of course, getting it to about more than 2Kg (with Power transfo) of weigth attached to the case with 6x 4/40 screws with 2mm thick panel hole....
Not sure about that as well :/

AND still need to make sure that the 120VA "Low profile" rated transformer could get in there, if not, all this has to be tought again...
I'm having a hard time believing that those Power transformer manufacturers can garranty tight tolerances? I'm not too much aware about that, but maybe possible? Any of you guys could confirm or enlight me a litte more on that?


What do you think?

I still like the separate power supply... but... Here are some other ideas.

If you intend to run the module on it's side (ala-lunchbox), your heat sink is oriented properly, but if not, it would be better to orient the fins vertically.  There is a convective flow that can develop between the fins that will help keep cool air against the sink (Newton - "the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings")

If you will run it both ways, angled fins would look rather stylish.

If you want a larger sink, you can have longer fins in your design (I found when I did mine on the front that the only constrain was to fit it behind the front panel of an SKB case.)

Another option would be, since you will be using this nice thick steel case, is to use the space below the XLRs in the back, run the Voltage Regulators on wires (the way the existing GDIY PSU does) to the back area (they will slide nicely under the backplane which floats) and bolt through that panel to a long narrow finned heat sink. ( or heck... the case itself might be enough, it is a massive steel black body).

If you use fins, recommend you round the top of them so as to save your knuckles when plugging in XLRS.

I built my supply before sahib had his ready so I used 2"X 2" x 1/8" about 9" long aluminum angle and have had no heat issues with it in a non vented case. You should be able to get the same area with your heatsink and less current demand.

You may need the support of all the slots on the back plan.

Thanks for the ideas Bruce0, will see what i go for, but yes it will be ala Lunchbox, and well will see what are out there in terms of Heatsink designs, but since i have one in stock, that's less on the total bill.
But yes i'd like  too keep it as a Module, could be handy.

But on some other thinking, i don't know why i stuck my head on using definit space from the Brackets arrrhhh, well because i could get a 150VA power transformer with less diameter, but of course more height, but then no more mm tolerance, the Transformer will pass, but will only need to have the Vreg module a little less high, and use SMD caps maybe, and so a better and beefier power transformer would be used, wich is always better...
On the other hand, having the fuses hidden inside that tight space now, is a little annoying, i tought of putting some sort of window on back of it's bracket and holders under PCB so to have a better access and view of them, hmmm dunno, i think all the Fuse holders will be to high, we don't want them to be on the exterior of the bracket.
EDIT: Could use SMD Fuses, small and would fit under PCB, allowing to have a window, and so an easy access...

The Rectifying module and Caps, would have the 48V regulator and its cap on it, so to be able to free space on front of the Vreg module, for having a tightening screw for the TO3 Heatsink on Panel... right on the center of it etc...

Will not be possible to have Vreg directly on board but will have to hardwire and use Molex, so they will be fitted and plugged in before screwing heatsink on fpd etc...
Still thinking about all this, since it has to be easy to assemble as well as dissmantle as always
But i think it should be good to go, as JamesW's experience, and an interesting module to DIY.

You may need the support of all the slots on the back plan.

Click to expand...

yes, well, dunno, could maybe even do with 6x 4/40 screws holding all this and only one module fitted on socket,
and all modules tightened together of course...

Any other ideas are welcome, again and again  , thanks a lot for the participation.

If you want a larger sink, you can have longer fins in your design (I found when I did mine on the front that the only constrain was to fit it behind the front panel of an SKB case.)

Click to expand...

Actually Speaking of this, my heatsink fins might be too long if want to go in a rack case also......37mm long

Not sure what the spec allowed current on the 24 volt rails but do you need max current per module on both sets of rails? - probably not!
I`m sure ive read that the psu will deliver enough for a rack of 17V and a rack of 24 volt modules!
Total the max current draw for the modules you expect to load in the 8 slots - if you swap a 17V module for a 24V youre just moving the heat from one reg to the other.
Use low dropout regs and lower winding voltages if you have a custom mains transformer - this should reduce the heatsink requirements.

If its a portable/tabletop solution - you can get a padded case that you just lift the unit out of. This will give you more cooling options.

mikeyB said:

Not sure what the spec allowed current on the 24 volt rails but do you need max current per module on both sets of rails? - probably not!
I`m sure ive read that the psu will deliver enough for a rack of 17V and a rack of 24 volt modules!
Total the max current draw for the modules you expect to load in the 8 slots - if you swap a 17V module for a 24V youre just moving the heat from one reg to the other.
Use low dropout regs and lower winding voltages if you have a custom mains transformer - this should reduce the heatsink requirements.

If its a portable/tabletop solution - you can get a padded case that you just lift the unit out of. This will give you more cooling options.

Click to expand...

Waiting for the transformer as we speak to be able to assemble and test it out.
A challenging build for sure, i actually use some SMD parts for saving space as well as giving more acces on fuses for ex.
Yes im pretty confident all will be ok in terms of current draw/cooling now, and i'm sure the module would power a full rack as well. Will see when this one is finished.
The idea was to make it modular/ Portable etc... so yes it would be some sort of table top solution (with a padded case if want to) as well as fitted in rack for live or location recording stuff.. (depends on the depth of the rack doors tough, but i'm ok) just an all in one solution, that would still be able to power a full rack, and also could serve as a bench PSU since it will be pretty small at the end, so pretty handy i think.

Finally received the Power Transformer  .

Let's move forward...

Little update:

Metal work with the PCB's seem to be within specs. Will show some more details later on, still a lot to do...
Stuffing the boards, checking them, Wiring all this, and see if all is good, cross fingers.
Tricky for sure   .

Looking good, and nice logo too!!


The Gimmer

Good stuff Tony. Following with interest.

yep very interesting !!!