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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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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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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Re: DIY Modular Synth Power Supply (sorta)

Post by Grayns » Wed Apr 01, 2020 7:17 am

Hi chaps, I'm planning on sorting out my power setup soon and was hoping to run the plan past some more knowledgable people to see what everyone thinks? (is this the right place to post this?)

I currently have a bunch of MFOS 'wallwart supply' boards and seperate AC wallwarts powering everything, and am looking to upgrade. The proposed plan is:

- construct an external case holding a relatively large centre tap transformer and bridge rectifier to output +/- 12VAC RMs unregulated. Use wicked wide traces and heavy copper and bus bars on PCB to go full belt and braces on current carrying...This way all the mains voltage is contained in one unit so I've just one box to worry about making super duper safe.

- use individual power supply boards inside each synth case with liner regulators & capacitors going to bus boards (one for each row of modules). I would like to continue using these boards (with very minor modification - see schematic) as I've got a bunch of them and they have some lovely 3.6C/W heat sinks on that work a treat...

The questions/ concerns I have:

The grounding - obviously working with mains I want to get this right for safety. Am I correct in thinking I should ground the earth coming from the mains plug to to chassis of the transformer box, and not connect centre tap on secondary to chassis as it may not be at the same potential as this?
And then connect centre tap to chassis in the synth cases?

Multiple linear regulators - I have read that using multiple linear regulators in parellel requires extra circuitry to balance the load sharing, but am thinking this is only if the outputs are directly connected... In my proposed plan with each set of regulators going to an individual row of modules am I right in thinking the loads will be shared correctly?

Voltage difference of regulator outputs - with each power supply board having tolerances is there going to be issues with output voltages varying very slightly between boards? I don't see how this would be any different to my current setup but thought I'd check.

Anything else I have missed?

Here's the parts that i'm thinking of using:
Transformer - https://www.rapidonline.com/vigortronix ... 2v-88-0030
Rectifier - https://www.rapidonline.com/dc-componen ... 0v-47-1012

Ive attached a digram of the plan along with schematics, many thanks, and apologies for the long post!
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Re: DIY Modular Synth Power Supply (sorta)

Post by Graham Hinton » Wed Apr 01, 2020 5:58 pm

Grayns wrote:
Wed Apr 01, 2020 7:17 am
The proposed plan is:
... full of mistakes. Was it meant to be an April Fool's joke?

It would take at least an hour to address all the issues and I'm afraid I don't have time at the moment. I may come back to it.

The short answer is don't start buying parts and building this. You need to do some proper calculations and read up on transformer basics, you clearly don't understand the voltage and current relationships between AC and DC so that would be a good place to start.

And you don't ground the Earth, the Earth grounds the chassis and the 0Vs.

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Re: DIY Modular Synth Power Supply (sorta)

Post by Grayns » Wed Apr 01, 2020 6:27 pm

...well that shot me down hahaha. Don't worry wasn't going to buy parts. Had posted here to try to learn, if you do find the time I'd rip your arm off for advice etc :)

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Re: DIY Modular Synth Power Supply (sorta)

Post by Graham Hinton » Fri Apr 03, 2020 11:49 am

A distributed scheme like this is going to have problems with a common reference. You are connecting each part together with wires called "Gnd" that are carrying largish currents and there will be differential voltage drops all over the place. You can have multiple voltage regulators, but not like this.

Let's look at the transformer first. One big common one is not a good idea, all your eggs are in one basket, but this analysis will apply to any size.
The rating of 250VA is derived from the product of maximum AC voltage and the maximum AC current. Why is this called VA and not Watts? Because the two are not necessarily in phase and you only get 250W when they are, otherwise it will always be less. The secondaries are 12Vac 10Aac, but you have assumed that means 10A is available and also incorrectly put a 10A fuse on the primary. The latter will not blow until you draw 2.5kW and the toroid will have melted like a PSU2. The mains current will be the load current divided by the turns ratio which is 230:24.

You won't get anything like 10A from the secondaries. If you could use the full cycle the average DC current should be the AC current divided by sqrt(2) or 1.414, but you can't even get the full cycle. The diode bridge only conducts when the diodes are forward biased so that is when the secondary voltage is higher than the voltage on the reservoir capacitor plus the diode drop. Current is dumped into the capacitor approaching the peak of the rectified sinewave and drawn out constantly by the regulators so the voltage there looks like a distorted sawtooth and you have to keep the lowest point above the regulator dropout voltage, in this case 15Vdc.

The transformer is specced as 230Vac primary, but nowhere has 230Vac mains. It will be 240Vac in the UK and 220Vac in Europe and calling it 230Vac +/-10% is just an EU bureaucratic fudge. It means that you have to design the run on 230V -10% and cope with the waste heat of 230V + 10%. You used to be able to get transformers with a 0-220-240 tapped primary which was far more sensible.

So there are a whole list of factors that conspire to give you less voltage and current than you thought you were going to get.
Grayns wrote:This way all the mains voltage is contained in one unit so I've just one box to worry about making super duper safe.
Putting the mains in one box won't achieve safety, especially with your fuse. The mains is separated from the low voltage circuitry only by the thin insulation on the transformer windings. If anything happens to that, e.g. by overheating, your whole system become live. Safety is only achieved by making sure that the whole system fails safe in the event of any fault in any part. One of the modes of PSU failure is rectifier or reservoir capacitors going short circuit, how do you contain that?

tbc

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Re: DIY Modular Synth Power Supply (sorta)

Post by Grayns » Fri Apr 03, 2020 2:14 pm

Graham Hinton wrote:
Fri Apr 03, 2020 11:49 am
Safety is only achieved by making sure that the whole system fails safe in the event of any fault in any part.
I'm going to leve this to the professionals. i tried. A LOT more research needed methinks. Thanks for taking the time Graham, It's appreciated. I shall keep researching and studying, and one day will be confident in my abilities and have another go, but not now hahaha.

In the meantime, I think I'm going to go with one of the meanwell supplies - there's plenty of documentation on which ones to use etc, and that seems more my speed.

Thanks again mate!

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