GroupdDIY 511 Racks: round 5.5 available

[sahib]

Jan,

You are correct in pointing out. I also had that in mind and I should have mentioned. These are really what I had lying about at the workshop and with the inital testing the dissipation was pretty good. The L section is 25 x 25 x 5mm. However, I'll take you up on this and order T section for the actual production. Not greatly more expensive.

The heatsinks were left over from good old days when you wanted samples they would send you boxes of them. However, in the right quantity they are not all that expensive as I am not going to use black anodised.

On my initial testing with approximately half the size of one of the chunks, a single regulator with 16V running at 1.45A settled around 45 degrees C.  I did the testing with my simpler temperature sensor but I have just ordered a new probe and I'll do a really stiff point testing. However,  the heatsink was not coupled to the case during testing. With the aid of the case I expect the temperature to remain the same on the L section.  If that happens then the T section is going to be icing on the cake.

 

[Denyle Guitars]

Got me thinking about DIY'ing some heat pipes.  ;D

 

[sahib]

This weekend has not been as productive as I hoped it to be. Unfortunately I had to fix few things at home and I am just rushing out to collect my son. I am finished for today.

However, a little raking around the workshop producted two bits of T section aluminium profiles that were left over from the rack ears for the first batch of 511. So JDB put it into my head and I'll replace the L sections tomorrow.

In the mantime here are more pictures. The bridge rectifier I had did not have the same footprint as on the pcb but a little bending of the legs solved it. Also the way Mr Murphy is  it turned out I was short of ceramic caps and omitted them on the rectifiers. Not critical. Instead of 240R I had 121R and connected them in series vertically. Also scraping the bottom of my junk box produced two different types of trimmers. As you can see the transformer is raised off the bottom plate for better ventilation. It would have been obviously better heat dissipation if it was mounted to the base directly but the base does not have indentation for the mounting screw and the head of it would stick out interfering with the equipment below on the rack. But in terms of insulation/safety measure this is a better practice. Also there is no need for it to dissipate into the case as its temperature rating is way over what it is going to run into.

 

[[silent:arts]]

wow Cemal

I would have never expected me producing so much heat
however, looks like you will be able to power up 3 "normal loaded" racks with that cooling [not recommended].
8) 8) 8) work!

 

[sahib]

We like it hot don't we?  ;D

 

[tallpine]

hello,
this is my first post. i joined to find out more information on this 51x rack you have been building.
i did not read through the entirety of this massive thread you got here, but i skimmed the latest pages, and i have to say kudos on all your hard work. i am new to the whole 500 series style DIY and found about it through an engineer buddy of mine who recommended i check out classic API kits and what not, and hence found this message board after some research.

i am very interested in getting on the list for 51x rack unit with PSU. is it fully assembled, or is it still in the kit stages where i would need to put the whole thing together, or components etc?
either way, i can build it out hopefully, but if it comes assembled and ready to "plug and play" i would be interested in that too.
sorry if i am coming off as a newbie, but i am eager to get my hands on these as soon as potentially possible.

please let me know if there's an email address or means of contact that i could send any other correspondence to. thank you for your time

peterbartsocas(at)gmail(dot)com

 

[sahib]

Welcome to the forum.

511 comes as a kit but very easy to build.

Power supply will also come as a kit.

Stay tuned and follow this thread.

 

[sahib]

Update on psu test. Almost 2 hours  into the test the temperatures settled.



Each of 16V rails is loaded with 10R 100W resistor.

Each of 24V rails is loaded with 15R 100W resistor.

Current drawn from each rail 1.6A.

The wattage of the resistors is red herring. I have used larger ones because they run cooler as they have larger metal body.


Ambient temperature is 19 degrees C.


16 V Rails

Regulator tabs between 64.5C and 54.5C
T bracket  43.7C
Heatsink 40.3C


24 V Rails

Regulator tabs between 87.1C and 90.5C
T bracket  52.5C
Heatsink 46.2C


Bridge Rectifiers 72.3C-79.1C

Transformer 52.7C

PCB around the rectifiers 51.3C

Board generally 34.5C -45.3C

Capacitors 34.5C - 38.6C


Case temperature under 30C

 

[zayance]

 

[jsteiger]

+100 Cemal! 

nice work! 

 

[[silent:arts]]

great test Cemal.

will call and blame Mr. Mueller tomorrow, since he said the transformer will be 50C + ambient under full load.
it should be 69C - 51.3C is far too cold ;D ;D ;D

I think your cooling is adequate, and the cooling of the bridge rectifiers seems necessary.

 

[sahib]

Yes, anything made in Germany can't be trusted. It never lets you down. ;D

The outcome of the test makes the point that the size of the heatsink does not become a factor after a while. You have to cool the regulator at tab. As JDB pointed out previously expecting to dissipate very high power from TO220 package has to have some reality check. 24V rails hit 90 degrees. By the way, the temperature difference between the two regulators is due to the imbalance of the resistive load. They are well mounted with plenty of heat transfer compound.

We obviously never specified to run a full 11 module from 16V or 24V only. It is 5 or 6 module on either side and the result above shows that the psu will handle it well and run much cooler.

However, me being mechanically minded, I have already thought of an aluminium clamp that will go over the regulator by being in contact with the body from the top and dissipating additional heat into the T bracket. I am sure this will reduce the temperature at tab by about 20C and will be a great help to 24V side. It looks like an additional expense but not anymore expensive than the pass transistor and the additional mechanical work it brings.

 

[Brolik]

Awesome work man, you guys are ridiculous.

Are you intending to integrate the aluminum clamp set up into the first batch case design and kit, or are you comfortable with the current dissipation?

No reason really, just incredibly interested and excited to get this whole thing together.  ;D

 

[sahib]

Although current set up will work well with the reduced load (by almost half), I will incorporate the new clamp design. In fact I missed to mention that the clamp will also have fins.

 

[[silent:arts]]

But you know the LM350 specs are up to 125C
and there is no chance to reach the full load in one rack with todays modules

however, if you can improve - than improve

 

[sahib]

True. This is already pushing it to max. I am not sure what the exact standard is on 500 series modules but running 6 modules based on 150mA each, we are way comfortable.  In terms of  additional work on the T bracket it is only two more tapping operation, so not a big deal and we might as well do it. The bracket could be additional and if one thinks he may need to go beyond then it is available.

Anyhow, now we can get on with the final cost. I'll speak to you and Jeff on e-mail.

 

[jdbakker]

24 V Rails

Regulator tabs between 87.1C and 90.5C
T bracket  52.5C
Heatsink 46.2C

OK, that suggests that the thermal interface between the T-bracket and the heat sink isn't the weakest link. Good.

[Mr. Grumpy sez and now close the case and mount it in a typical rack surrounded by other powered equipment and see if the 24V reg doesn't go into thermal shutdown. Smart money says it will]

However, me being mechanically minded, I have already thought of an aluminium clamp that will go over the regulator by being in contact with the body from the top and dissipating additional heat into the T bracket. I am sure this will reduce the temperature at tab by about 20C and will be a great help to 24V side.

Perhaps. The thermal resistance through the plastic body itself is high enough that the dissipative properties of such a clamp will not matter much. On the other hand, it is fairly well documented that pressure (below the point of cracking the case, obviously) does increase thermal conductance between regulator tab and heat sink (or, in this case, the T-bracket).

But you know the LM350 specs are up to 125C

I did see the smiley; however that's junction temperature, not case temperature. Sahib didn't show where/how he measured the tab temperature: on the exposed top of the tab or with a bead thermocouple through a hole in the T-bracket just below the regulator die. The latter is the 'real' case temperature; it's not uncommon to have a temperature gradient of up to 10 degrees between the two. The junction is hotter still.

We obviously never specified to run a full 11 module from 16V or 24V only. It is 5 or 6 module on either side and the result above shows that the psu will handle it well and run much cooler.

and there is no chance to reach the full load in one rack with todays modules

To borrow a line: past results offer no guarantee wrt future performance. At the very least it would be nice to document this somewhere, if only to make troubleshooting easier for unsuspecting techs a few years down the line.

JDB.
[and now Mr Grumpy had better be off to bed if he's planning to get rid of that nasty flu anytime soon]

 

[sahib]

I wish Mr Grumpy to get better soon. A nasty flue can be very annoying.

I measured the tab temperature just on the edge carefully without short circuiting the tab to mounting screw.

You are correct on the temeperature resistance of the plastic case. However, my simple logic tells me that if it has a much reduced temperature than what's below, then there will be some heat transfer through it. Having said that by reading my previous post, I might have been far too optimistic with the amount of reduction. But I will give it a go with the additional clamp arrangement and measure the tab temperature to see how much difference it makes, if it does any.

In terms of closing the lid of the case I actually did it and the ventilation apertures are sufficiently large. However, you are quite right that once it goes inside a rack with other equipment around it the story will be different. But that is if we draw 1.6A from each regulator. With half that it won't be a problem.  But and again a big but, we can always reach out for a fan cooling. I have means to greatly reduce the vibration created by such device.

 

[Spiritworks]

Please forgive my confusion on this power supply issue: Am I wrong to believe that the designed power supply will be sufficient for all eleven modules, if used at the same time? Mr Sahib mentions only six modules in a previous post. How do we balance the modules between the 16 volt and 24 volt rails? What if someone has modules that operate on only one of these voltages?

 

[[silent:arts]]

don't get confused. this discussion is about the maximum possibilities, and as far for today they can't be reached with todays modules.
Mr Grumpy & Mr Sahib have a hobby: reach it to the maximum, make it bullet proof for the next 100 years
some kind of sport.

while this is not bad, compare it with the reality
which module takes to full advantage of drawing the full specs at all 4 voltage rails at the same time?
I'm not aware of even one, and you would need to install 11 of those modules in the same rack to reach Mr Sahibs heat

in a "normal" installation, with eleven different modules, the PSU won't even get warm (as mentioned by some users)
most people won't use the 24V rails anyway. the specs are fine, at the real maximum it might get hot, that is normal.
we could design a new PSU which doesn't get hot, but if it will double / triple the price ...
let them do their sports, it will improve the result for the worst case, don't panic