DIY Modular Synth Power Supply (sorta)

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jakobprogsch
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Post by jakobprogsch » Sat Apr 13, 2019 11:30 am

The documentation of these (I have a BEL HCC-15-3) mention "forced air cooling in restricted environments/for full load operation at 50°C".

I'm not sure what exactly that means? Is "restricted environment" a well defined technical term? What exactly does the temperature refer to?

For now I assume that temperature refers to the environment (air) temperature? I'm currently trying to figure out if my setup is fine temperature wise by incrementally adding more modules. Without any forced cooling the PSU frame around the transistors reaches 50°C with slightly over 700mA of modules installed.

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Post by jakobprogsch » Sat Apr 13, 2019 5:26 pm

I installed some more modules. I'm now at 1250 mA (+12V) and 1150 mA (-12V) and closed up all the open spaces with cardboard. After two hours this was the result:
Image

The transistors on the left appear to have lower temperature than the case but that is just a property of how their surface reflects in the FIR spectral range. They are at least as hot as the case.

The big CapXon HT caps (these if I identified them correctly) are at 50-55°C and the two really hot spots are a pair of big resistor and the rectifier diodes at 70-80°C it seems. At least the way I read the data sheets that all seems to be comfortably within their operating range?

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Post by jakobprogsch » Mon Apr 15, 2019 12:30 am

Continuing the monologue. I added more modules and also routed some holes into the back of my case where the PSU PCB sits since that was a fairly low hanging fruit. This made all the "non heating" components like capacitors about 5°C cooler but the diodes and resistors are essentially unaffected.

Image

In the heat image you can nicely see the hot air exiting at the top.

I'm now close to the final intended load (1750mA +12V) and the case around the transistors (2N3055) reaches about 70°C the big resistors whose purpose I don't know are getting close to 100°C and the rectifier diodes (1N5401) are still at 80°C. I just don't know if that is ok or not? The data sheets lists an operating temperature of 50°C before derating. But that refers to the ambient temperature is my understanding? which inside the case is still only about 30°C.

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Post by moogah » Mon Apr 15, 2019 9:00 pm

Been doing some research on building my own monster size eurorack case, wondering if anyone knows a good reason for the Bel Labs 10A supply costs almost 70$ more than the SL/Condor one at mouser.

https://www.mouser.com/ProductDetail/Co ... qAEALw_wcB

https://www.mouser.com/ProductDetail/Be ... Ba5PO6A%3D

Self edit: looks like I see an array of smaller lytic caps on the SL version. Wondering what the other differences might be.

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Post by jakobprogsch » Wed Apr 17, 2019 8:53 am

I'm pretty close to just writing this off as an educational experience and go with some other PSU (Doepfer? Erika?). Adding a 92mm computer fan helps a lot with temperatures (~20°C lower). But then I have a fan that makes noise and should probably be on its own power supply?

And independent of that on rare occasions it seems the positive rail doesn't come on? Usually after being turned off for a while. Maybe some overcurrent protection is kicking in when all the caps in the system draw current at once? But that is with the psu only about 50% loaded?

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Post by moogah » Thu Apr 18, 2019 1:36 am

jakobprogsch wrote:I'm pretty close to just writing this off as an educational experience and go with some other PSU (Doepfer? Erika?). Adding a 92mm computer fan helps a lot with temperatures (~20°C lower). But then I have a fan that makes noise and should probably be on its own power supply?

And independent of that on rare occasions it seems the positive rail doesn't come on? Usually after being turned off for a while. Maybe some overcurrent protection is kicking in when all the caps in the system draw current at once? But that is with the psu only about 50% loaded?
Don't take this as knowledgeable advice: the number of caps drawing current won't provide a current draw spike that resembles the "normal" current draw. Is the PSU module a nice new one? Quite possible it just can't stabilize anymore with even 50% of its "normal" capacity plugged. Easy troubleshooting method right there IMO.

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Post by jakobprogsch » Thu Apr 18, 2019 4:42 am

moogah wrote:
jakobprogsch wrote:...
Don't take this as knowledgeable advice: the number of caps drawing current won't provide a current draw spike that resembles the "normal" current draw. Is the PSU module a nice new one? Quite possible it just can't stabilize anymore with even 50% of its "normal" capacity plugged. Easy troubleshooting method right there IMO.
It is a new one. I'm not sure I got what the easy troubleshooting method is? The issue is difficult to reproduce. I saw it three times in total so far.
On the oscilloscope I see that the positive rail always comes on slightly later by a few milliseconds.

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Post by Rex Coil 7 » Fri Apr 19, 2019 7:02 am

jakobprogsch wrote:I'm pretty close to just writing this off as an educational experience and go with some other PSU (Doepfer? Erika?). Adding a 92mm computer fan helps a lot with temperatures (~20°C lower). But then I have a fan that makes noise and should probably be on its own power supply?

And independent of that on rare occasions it seems the positive rail doesn't come on? Usually after being turned off for a while. Maybe some overcurrent protection is kicking in when all the caps in the system draw current at once? But that is with the psu only about 50% loaded?
FANS (if needed): Use a much larger fan turning at less RPM than 92mm. If possible, use a 200mm fan (preferably a "Noctua" .. which is the brand name). A larger fan turning at less RPM is a lot less noisy and still provides plenty of CFM (cubic feet per minute).

PSU: Most power supplies are NOT rated at 100% duty cycle. That is to say, if the specs rate the PSU at (let's say) 10 amps, it most likely cannot deliver that much power for ten minutes without AT LEAST a 10 minute cooling period.

I know of precisely one manufacturer of modular synthesizer power supplies that actually rates their PSU systems at 100% duty cycle (the specs provided dictate the power supply running at full load at what is known as "continuous duty cycle" ... meaning whatever the specs are is what the power supply can produce for ten minutes out of ten minutes ... no cooling period or no "reduction" of output to protect the PSU required) ...

LINK = http://hinton-instruments.co.uk/paprod/ ... lpower.htm

You'd also be better off using two (or even three) smaller power supplies that total the current requirements you need rather than one big power supply.

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Post by jakobprogsch » Fri Apr 19, 2019 11:33 am

Rex Coil 7 wrote:FANS (if needed): Use a much larger fan turning at less RPM than 92mm. If possible, use a 200mm fan (preferably a "Noctua" .. which is the brand name). A larger fan turning at less RPM is a lot less noisy and still provides plenty of CFM (cubic feet per minute).
Yep, the 92mm fan was just what fit in the existing case design that didn't originally include a fan. 92mm is the largest standard size that I can squeeze "into" the psu itself to directly blow at the pcb. It's more of a temporary fix/experiment to see how big a difference that makes.
PSU: Most power supplies are NOT rated at 100% duty cycle. That is to say, if the specs rate the PSU at (let's say) 10 amps, it most likely cannot deliver that much power for ten minutes without AT LEAST a 10 minute cooling period.
I'm not close to maxing out the amperage though. The PSU specs rate it at 3A per rail (3.4A and derate 10% for 50Hz operation in my case). All of the above thermal experiments are with loads in the 1.2-1.8A range. With my current module mix It would seem I'd max out at 2-2.2A if the case was completely filled.
You'd also be better off using two (or even three) smaller power supplies that total the current requirements you need rather than one big power supply.
Yep, that's what I'd go with on a do over for sure. It would require me to redo the case though (or at least the back of it).

Picture for reference. The Wiring on the inlet has in the meantime been fixed and covered. Also there is a earth connection between the earth bar on the left and the 0V bar in the middle that is covered up by the middle mounting rail in this picture.
Image

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Post by Staticcharge » Tue Jul 30, 2019 8:24 am

Is it me or has anyone else notice the Pittsburgh modular ep-360 case is using a pair of meanwell rs-120-12 psus in series plus a lil 5v psu. Is it recommended to use two 12v psus in series.

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Post by Staticcharge » Wed Aug 21, 2019 5:40 am


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Re:

Post by Cat-A-Tonic » Fri Jan 31, 2020 9:15 am

jakobprogsch wrote:
Fri Apr 19, 2019 11:33 am
Rex Coil 7 wrote:FANS (if needed): Use a much larger fan turning at less RPM than 92mm. If possible, use a 200mm fan (preferably a "Noctua" .. which is the brand name). A larger fan turning at less RPM is a lot less noisy and still provides plenty of CFM (cubic feet per minute).
Yep, the 92mm fan was just what fit in the existing case design that didn't originally include a fan. 92mm is the largest standard size that I can squeeze "into" the psu itself to directly blow at the pcb. It's more of a temporary fix/experiment to see how big a difference that makes.
PSU: Most power supplies are NOT rated at 100% duty cycle. That is to say, if the specs rate the PSU at (let's say) 10 amps, it most likely cannot deliver that much power for ten minutes without AT LEAST a 10 minute cooling period.
I'm not close to maxing out the amperage though. The PSU specs rate it at 3A per rail (3.4A and derate 10% for 50Hz operation in my case). All of the above thermal experiments are with loads in the 1.2-1.8A range. With my current module mix It would seem I'd max out at 2-2.2A if the case was completely filled.
You'd also be better off using two (or even three) smaller power supplies that total the current requirements you need rather than one big power supply.
Yep, that's what I'd go with on a do over for sure. It would require me to redo the case though (or at least the back of it).

Picture for reference. The Wiring on the inlet has in the meantime been fixed and covered. Also there is a earth connection between the earth bar on the left and the 0V bar in the middle that is covered up by the middle mounting rail in this picture.
Image
Is combining PCB distribution and Busbars like this a good halfmeasure?

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Re: Re:

Post by Graham Hinton » Fri Jan 31, 2020 10:18 am

Cat-A-Tonic wrote:
Fri Jan 31, 2020 9:15 am
Is combining PCB distribution and Busbars like this a good halfmeasure?
Half measure is a bit optimistic, it's more like a tenth measure.

All this example achieves is a good low resistance between the 0V of each busboard. The weak points are still the busboards and the wires to the PSU.
The latter should be much heavier gauge and connected to the centre of the busbars. Measure the voltage drop and ensure that it is below 10mV. Alternatively, connect the PSU sense wiring to the busbars and then the voltage drop doesn't matter because it is inside a feedback loop.

If you are going to use busbars the real question is why reduce their effectiveness by using pcbs and then ribbon cable when you can connect directly to the modules in one go?

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Re: Re:

Post by Cat-A-Tonic » Sat Feb 01, 2020 7:39 am

Graham Hinton wrote:
Fri Jan 31, 2020 10:18 am
Cat-A-Tonic wrote:
Fri Jan 31, 2020 9:15 am
Is combining PCB distribution and Busbars like this a good halfmeasure?
Half measure is a bit optimistic, it's more like a tenth measure.

All this example achieves is a good low resistance between the 0V of each busboard. The weak points are still the busboards and the wires to the PSU.
The latter should be much heavier gauge and connected to the centre of the busbars. Measure the voltage drop and ensure that it is below 10mV. Alternatively, connect the PSU sense wiring to the busbars and then the voltage drop doesn't matter because it is inside a feedback loop.

If you are going to use busbars the real question is why reduce their effectiveness by using pcbs and then ribbon cable when you can connect directly to the modules in one go?
Thank you for the replies.

I'm in the process of rebuilding/modifying the first Frac cabinet that I built (5 3u Blacet racks and a 1u for utilities).
I got a 3.4A PowerOne PSU to replace the 2 Blacet PSUs that were in this cabinet before.
I was planning on using the 4 Blacet busboards with enough headers for these 5 racks of modules.
I figured I could get away with using a screw terminal block as a common point between the busboards.
Then I remembered having some spare aluminum rails and considered using those instead of the terminal block...

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Re: DIY Modular Synth Power Supply (sorta)

Post by StillNotWorking » Sat Feb 01, 2020 9:52 am

Using this online calculator it becomes clear what Hinton is advocating. Although the comfort of using standard power supply cabling inside my eurorack won my decision making I still like to better understanding by example.

A typical 28AWG ribbon cable has an area of 0.072 mm² according to 3M datasheet. Multiply with 2 approximate something between 25 and 26AWG see table far down on the calc page.

Calculating with 26AWG a 10 mV drop approximate 47 cm long ribbon cable with a typical 80mA load.
To keep within 10mV drop a 150mA load can have a 25 cm long ribbon cable.

While these number show pr. module I'm believe Hinton ment to look for 10mV total drop measured at the busboard end with all modules connected.
looking for service manual for the Clavia ddrum AT or ddrum III

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Graham Hinton
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Re: DIY Modular Synth Power Supply (sorta)

Post by Graham Hinton » Sat Feb 01, 2020 10:11 am

StillNotWorking wrote:
Sat Feb 01, 2020 9:52 am
While these number show pr. module I'm believe Hinton ment to look for 10mV total drop measured at the busboard end with all modules connected.
Yes. My 10mV rule is a quick and easy way of checking the resistance of the main supply cables where currents are typically above 1A.

Basically with all power distribution you can never get the resistance low enough and you can't get zero, but you should try to get it all as low as practical and you should think of the whole system as a network of very low value resistances and examine the effects of those resistances on the rest of the system.

You can get away with ribbon cable on low current modules because the power rails usually have a much larger resistances in series and it only effects that one module. Dual modules are another matter. Again with low current modules there are six wires in parallel for the 0V, but with high current modules taking more on the +ve than the negative, there are plenty of digital modules with flashy displays that take over 200mA on the +ve and a few tens of mA on the -ve, the current difference flows in the 0V which lifts the 0V on the module pcb by that voltage drop. Patch two of those modules together and you have a 0V on each end of the patch cable that are jumping up and down creating screen currents.

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Re: DIY Modular Synth Power Supply (sorta)

Post by StillNotWorking » Sat Feb 01, 2020 12:34 pm

Graham Hinton wrote:
Sat Feb 01, 2020 10:11 am
there are plenty of digital modules with flashy displays that take over 200mA on the +ve and a few tens of mA on the -ve, the current difference flows in the 0V which lifts the 0V on the module pcb by that voltage drop. Patch two of those modules together and you have a 0V on each end of the patch cable that are jumping up and down creating screen currents.
Thanks Hinton! That sentence make much of what I've read from you fall into a place where there now are some more but still minor understanding of this topic.
looking for service manual for the Clavia ddrum AT or ddrum III

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Re: DIY Modular Synth Power Supply (sorta)

Post by Cat-A-Tonic » Fri Mar 20, 2020 7:05 am

Frac cabinet with combination busbar and pcb distribution.

Image

3A @ 15V
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