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Wiring a +12v PSU to get -12v
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Wiring a +12v PSU to get -12v
oinkbanana
Looking to build a monster case I was recommended a pair of HE12-10.2-AG PSU, that each put out +12v

Seeing how I need +12v and -12v, how do I go about wiring one of them for the -12v? Anyone got a schematic on how to wire up both supplies to a standard busboard?


I know you can normally just invert the ground and the +12v to get -12v, BUT seeing how the two PSU will be sharing a ground, I have doubts this will work since one +12 would be connected to the ground of the other PSU. this seems like a recipe for disaster.
pugix
Wow, 10.2 amps. Huge size, too. You'll need 10 bus boards with 20 connectors each in that case to make it worthwhile. There is no special advantage in having all your modules powered by a single supply.

No reason you couldn't use two of these for +/-12. For the negative one, the positive output terminal would go to common (don't call this ground) and the negative would be -12V. Wiring from the supplies to the bus boards would need to be done properly, with heavy gauge wire. I can't tell you how to do that, but others in DIY could. You should be connecting both power supply cases to earth ground. This is not connected to any output terminal of the supply.

In short, you are looking at a serious DIY project, involving AC mains wiring. It's dangerous! If you are trying to save money, this is not the way.

Paul Schreiber, Synthesis Technology, is about to come out with high quality Eurorack power supplies and bus boards. He calls them Lil' Stinker and Big Stinker. You would not have to wire AC mains, because these work from standard wall warts.
oinkbanana
1512hp total... it's not going to little. (I'm currently at 924hp, so I'm being realistic about upcoming expansion plans)

the plan isn't so much to "save money" but to build an efficient dense setup (with internal bridges) instead of stacking smaller cases..
What kind of PSU setups do others go with for Mega cases like this?



the PSU alternative i had considered was getting a half dozen doepfer PSU3... but that'll probably be more messy
I don't want to do wallwarts.
Rex Coil 7
oinkbanana wrote:
1512hp total... the plan isn't so much to "save money" but to build an efficient dense setup (with internal bridges) instead of stacking smaller cases..
All well and good. This is a studio synth, yea? I'm presuming so since I don't know too many people that would want to use such a large single piece of gear in live gigs (hard to lift).

With it being one single large power system, if your one single large power supply has troubles then the entire system is down.

oinkbanana wrote:

What kind of PSU setups do others go with for Mega cases like this?
Multiple power supplies, flexible links, and bus bars.





These are a few of my own in various stages of completion.












If you do nothing else, be absolutely certain to design your cabinet(s) around the power system ... NOT designing the power system around the cabinets. So take care to design the power system first, make it double the capacity of your calculated need, then design the cabinet and all other things around the power system.

** Power system first (2x your calculated needs).
** All other things second.

The power system should take design priority over all other things.

* Use linear power supplies.
* Use REAL power cables for your modules (the phrase "ribbon cable" should not be anywhere on your system's features list). Hand-make your power cables if necessary. It is not difficult to do.
* Use bus bar distribution systems. These are readily available through the commercial market, or you may construct your own ... do not underestimate the labor involved.
Rex Coil 7
pugix wrote:
.... For the negative one, the positive output terminal would go to common (don't call this ground) and the negative would be -12V. Wiring from the supplies to the bus boards would need to be done properly, with heavy gauge wire. I can't tell you how to do that, but others in DIY could. You should be connecting both power supply cases to earth ground. This is not connected to any output terminal of the supply....
The "ground" on the secondary output of the transformers is properly defined with the phrase "Zero Volt". As was mentioned above by member *pugix don't call it the "ground", it's called Zero Volt (0v).

If it's on the primary side of the transformer it's then called "ground" ("Earth") ... but if it's on the same side of the transformer as the positive and negative outputs (aka the secondary side) then it's not called "ground" it's known as "0v".

Ground is ground, zero volt is zero volt. Do not confuse the two. They are very different things. Unfortunately you're going to run across any number of folks who will not know that difference as you move along through your project. As long as YOU have it straight in your head, it's all good.

I'm subbing to this one, I always tend to learn a few things in technical threads .. so I'm curious about what will be said this time 'round.
tema
By the way, apart from these are easier to find, is there any advantage of using separate power supplies for plus and minus 12v over dual out +-12v ones?
oinkbanana
tema wrote:
By the way, apart from these are easier to find, is there any advantage of using separate power supplies for plus and minus 12v over dual out +-12v ones?


If you can suggest a PSU that outputs +-12v with more than 10amps, I'm all ears!
Rex Coil 7
oinkbanana wrote:
tema wrote:
By the way, apart from these are easier to find, is there any advantage of using separate power supplies for plus and minus 12v over dual out +-12v ones?


If you can suggest a PSU that outputs +-12v with more than 10amps, I'm all ears!
A few welding machines come to mind ....
Rex Coil 7
How were you planning to split the zero volt rail? Both the negative and the positive power supplies (in your dual PSU design) would have their own zero volt rails ... how would you go about doing that?

(I think there's more than ~one~ reason why this isn't done already.)

the Zero-Volt rails/busbars/links would have to be very heavy with as close to a zero-ohm resistance as absolutely possible. Then they'd need to be tied to one-another. But I don't know if that could be made to practically work. Key word there is "practically".

Why don't you go with two HDD15-5-AG PSUs? They're even $15 per unit less costly. You're still using "only" two power supplies and still getting 10 amps per rail. The difference being that the way you're proposing splits the negative and positive power systems, the manner I suggest is simply splitting the loads ... y'know, like normally done.

Either way you're still using two power supplies. Just a note here, no matter which way you go be sure to design in a really REALLY solid zero volt return rail.

LINK = https://www.mouser.com/productdetail/bel-power-solutions/hdd15-5-ag?qs =sGAEpiMZZMtl%252b%2Ft8G5TWgGQYpyG3MfPySfLzk2gi2wU%3D

thumbs up
oinkbanana
Rex Coil 7 wrote:

... NOT designing the power system around the cabinets. So take care to design the power system first, make it double the capacity of your calculated

that is golden advice. and the only thing I've ordered to date are rails, but the depth will depend on the Power.

busbars... tempting. keeps the resistance down, that's for sure.


Rex Coil 7 wrote:
How were you planning to split the zero volt rail? Both the negative and the positive power supplies (in your dual PSU design) would have their own zero volt rails ... how would you go about doing that?

honestly, I don't know. that's the nature of my original question.

Rex Coil 7 wrote:

Why don't you go with two HDD15-5-AG PSUs?
Either way you're still using two power supplies.

That looks like it'll actually be simpler and solves the issue of using different +12 and -12 PSUs.


Rex Coil 7 wrote:



what are the PSU you're using in this pic?


looks to be the same size as what I'm aiming for and you've got 4 PSU going.
If I had to guess:
top two only have 3 bus bars (+12v, -12v, ground) HDD15-5-AG?
and the bottom two has 4 bus bars (+5v, +12v, -12v, ground) HDCC150W-A+G?

Is it better to go with a PSU that has the 3rd output, or just getting a 5V adapter? I currently only have 2 modules with 5v, and no plans for more.
Graham Hinton
1) Don't use 10A power supplies, especially a cheap open frame OEM type.

If you have a 10A load that is 240W and a linear PSU will dissipate the same so the whole system is a 500W heater. You have to get that heat out of the case and if you don't want to use noisy fans the PSUs need to be mounted on large metal panels to act as radiators. You should not just mount those OEM PSUs inside a wooden box.

At full load the rectangular transformers will buzz like hell. The 2A ones are bad enough and can be heard across a room.

You need five times thicker cabling for a 10A PSU than a 2A one and a 2A one needs a lot to minimise the voltage drops.

2) Grounding. The overall grounding scheme for a multiple PSU system is shown here:



0V is not "Ground", but it is grounded and the route is important. The diagram shows wires as resistors, because their relative values are important and so are the currents going through them.

The mains Earth has multiple functions. It's primary one is for safety, it is also used as a voltage reference. Most of the time there will be very small currents in the Earth wiring, but under a fault condition it may have to conduct 25A before a fuse or trip blows. That path should not be via pcbs and thin wires.

PSUs do not normally have their DC outputs referred to Earth, they are "floating" like a battery. It is better to wire each output terminal to the distribution 0V separately and to ground the 0V directly to mains Earth. This is shown as Rwire in the diagram. Note that the PSU supply cables are carrying high currents so for every milliohm and amp there will be a millivolt drop.

There should be no current flowing in Rwire, but there will be when you start connecting modules to other gear with unbalanced cables. If there are no other connections there will be a common path via the mains distribution Earth wires, but each PSU will be separated by approximately 0.3 Ohms. Bonding Chassis terminals together will make a lower resistance path, but the best method to is explicitly connect the 0V distributions together with an even lower resistance. All paths exist in parallel, but most of the signal return currents will be in the lowest resistance path.

I recommend Dinse connectors and at least 16mm2 cable, 25mm2 externally, for connecting 0V between cases.

MrsWedge
If you are using 2 12v supplies to make +/-12v DO NOT connect the zero reference to earth ground. The earth ground, if used at all, should be connected to the chassis to reduce EMI, not to the zero reference. It is not necessary to use the earth ground - how many electronic devices do you have that have 3 prong mains plugs?

Reading through this thread and there seems to be some confusion about what the amperage rating of a constant voltage power supply means. If you connect a circuit that draws say 100mA to a 2A supply, it will still draw the same amount when connected to a 10A supply. The larger supply simply gives you more headroom.
pugix
MrsWedge wrote:
If you are using 2 12v supplies to make +/-12v DO NOT connect the zero reference to earth ground. The earth ground, if used at all, should be connected to the chassis to reduce EMI, not to the zero reference. It is not necessary to use the earth ground - how many electronic devices do you have that have 3 prong mains plugs?


Many external mixers have 3-prong mains plugs and their chassis is earth grounded, including every 1/4 inch jack sleeve on the mixer. If you omit the Rwire between 0 volts and earth ground on your supply chassis and then run an output cable from the modular to the external mixer, the cable shield becomes Rwire. How do you get around this in a system like the one under discussion here?
Graham Hinton
MrsWedge wrote:
If you are using 2 12v supplies to make +/-12v DO NOT connect the zero reference to earth ground. The earth ground, if used at all, should be connected to the chassis to reduce EMI, not to the zero reference. It is not necessary to use the earth ground - how many electronic devices do you have that have 3 prong mains plugs?


You obviously do not know what you are talking about and should not be posting advice like this.
MrsWedge
Dunno, but I would guess that's one of the reasons that balanced lines are used to transmit signals in PA systems. The ground is used for shielding.
MrsWedge
Graham Hinton wrote:
MrsWedge wrote:
If you are using 2 12v supplies to make +/-12v DO NOT connect the zero reference to earth ground. The earth ground, if used at all, should be connected to the chassis to reduce EMI, not to the zero reference. It is not necessary to use the earth ground - how many electronic devices do you have that have 3 prong mains plugs?


You obviously do not know what you are talking about and should not be posting advice like this.


There is always that possibility. However, I have a BS in physics and a MS in instrumentation engineering, so there is a possibility that I do know what I'm writing about.
skyshaver
MrsWedge wrote:
Graham Hinton wrote:
MrsWedge wrote:
If you are using 2 12v supplies to make +/-12v DO NOT connect the zero reference to earth ground. The earth ground, if used at all, should be connected to the chassis to reduce EMI, not to the zero reference. It is not necessary to use the earth ground - how many electronic devices do you have that have 3 prong mains plugs?


You obviously do not know what you are talking about and should not be posting advice like this.


There is always that possibility. However, I have a BS in physics and a MS in instrumentation engineering, so there is a possibility that I do know what I'm writing about.


How many years practical experience do you have designing and building power supplies for modular synthesizers and other electronic musical instruments and devices?
JohnLRice
Another reason, IMHO, not to use a single massive power system for a massive modular is the potential problems that a single point of failure brings.

If your power supply dies then your entire system is down, unless you carry a spare at all times. This would be critical in a live situation and possibly critical in a studio situation if you are working on a deadline of have paying customers trying to work.

And worst case scenario the power supply dies catastrophically and permanently takes all the modules it can with it! BOOM! zombie

With multiple power supplies the potential for downtime and destruction is reduced.
Graham Hinton
MrsWedge wrote:
However, I have a BS in physics and a MS in instrumentation engineering, so there is a possibility that I do know what I'm writing about.


There might be a possibility that you will understand why you are wrong then.

In mains powered audio equipment the Signal Common 0V and Chassis should both be connected to the mains Earth at the point of entry and then kept separate. Connector screens should be connected to chassis for EMI requirements and safety considerations. Safety and EMC are legal requirements, but they differ in various world regions. AES recommendations are not a legal requirement. A lot of modular synthesizers are built to evade the costs of testing and certification for these requirements and most of the designs predate EMC so drawing conclusions from what you see will not tell you the correct way that it should be done. AES recommendations are ignored.

The various laws of man covering electrical safety and EMC only apply to products as sold rather than the system they end up in as used. The laws of physics don't make that distinction. In fact it would be very difficult to market a complete modular system under current legislations because certification would have to be obtained for every permutation and combination. By selling separate modules and external PSUs certification is not needed for analogue modules and digital modules are sold illegally because no-one has complained to authorities--yet...

This situation results in lots of problems experienced by end users who are forced in to the role of systems integrator whether they have the skills or not. Grounding is often incorrect. What can be got away with for single consumer products does not apply to large interconnected systems where the user can directly touch the electrically active parts.

Telling people to not connect the 0V to Earth is either ignorant or irresponsible. EMI is a complex subject and not as simple as just connecting to Earth. Most modular synthesizers do not have any screening or EMI considerations. They should, but they don't. That's the situation on the ground, it's a minefield and you have just stepped in to it without any experience of mines.
Rex Coil 7
DISCLAIMER: I am not employed, compensated, or paid in any way by Hinton Instruments or Graham Hinton. I'm not even on their customer roster.

I just know ~good~ when I see it.

EDIT: I was drafting this while the (above post) was posted, so I don't mean to sound as though I am simply aping what Graham said just above. He simply types a LOT faster than I do! lol

oinkbanana wrote:
.... what are the PSU you're using in this pic?
This picture (above) is of one of Graham Hinton's systems. That system has both 12v and 15v systems on board since it houses 12v and 15v modules. All of the power supplies are Hinton Instruments PSUs which use toroidal transformers (the round type of transformers that don't ~^>buzz<^~ under heavy loads .. rectangular or "squarish" transformers are easy to make poorly and are often kinda crappy, which means they have a tendency to "bzzz" or humm under heavy loads ... the round "Toroidal" transformers are generally made better just by design if nothing else).

The large "H" shape made of aluminum in the center of the cabinet is the zero-volt tie that connects all of the zero-volt rails of all of the power supplies together (no matter they be 12v or 15v). I did not build this system, it is a Graham Hinton construct (just to be perfectly clear).

My own bus bar power distribution system (pictured a few posts up) is a "hacksaw and hammer" version of what is available from Hinton Instruments.

oinkbanana wrote:
Rex Coil 7 wrote:
Why don't you go with two HDD15-5-AG PSUs? Either way you're still using two power supplies.

That looks like it'll actually be simpler and solves the issue of using different +12 and -12 PSUs.
Yes, it will be a lot simpler. Especially since those types of power supplies (ones with positive and negative) have shit-tons of supportive information within Muffwigglers in regards to "how to" connect and hook-up. You could say that using power supplies of that type have a "convention" that has been developed over the years within the modular synth community. You will find far more support on how to connect two (or more) of these .. ~ahem~ .. "conventional" type power systems together for large systems than you will find regarding the use of a negative PSU and a positive PSU. That translates to more minds on-board if you do end up having troubles down the line. I can point to a hundred users here in Miffwugglers that use pos/neg power systems ... I can point to no-one that uses a positive psu and a negative psu.

oinkbanana wrote:
[in the picture of that large system] it looks to be the same size as what I'm aiming for and you've got 4 PSU going.
If I had to guess:
top two only have 3 bus bars (+12v, -12v, ground) HDD15-5-AG?
and the bottom two has 4 bus bars (+5v, +12v, -12v, ground) HDCC150W-A+G?

Is it better to go with a PSU that has the 3rd output, or just getting a 5V adapter? I currently only have 2 modules with 5v, and no plans for more.
HAAHAA! ~Plans~ .... yea well, all of us "plan" a lot of stuff, but few of us ever find ourselves sticking to such things. As I've always suggested (and will continue to suggest), calculate your (~ahem~) "planned" total load .. then double it .. and use those figures to make your decisions for you from there on out. Over-engineer this stuff, even the 5 volt stuff. It costs a lot less to do it right the first time, than it does to do it over.

As for the power supplies in the image of the large system .... they're not "Power One" (or "Bel Power" .. or any of the round transformer style) PSUs, those are all 100% Hinton Instruments systems .... all the way from the Mains input plugs to the module power cable connections .. and every-single-thing in between. At the end of the day they end up costing only fractionally more than stuffs of far lesser fortitude.

Myself? I am currently using linear power supplies (grounded ... thank you very much), bus bars, hand made power cables. Happy.

MrsWedge wrote:
If you are using 2 12v supplies to make +/-12v DO NOT connect the zero reference to earth ground. The earth ground, if used at all, should be connected to the chassis to reduce EMI, not to the zero reference. It is not necessary to use the earth ground - how many electronic devices do you have that have 3 prong mains plugs?
Woa! Hold on there, big shooter. This is a very poor set of suggestions. Do not do this. And, addressing the last question there, I have zero electronic devices that have no third prong, at least none made after 1990 or so (at least 30 years+ old stuffs).
MrsWedge wrote:
Graham Hinton wrote:
MrsWedge wrote:
If you are using 2 12v supplies to make +/-12v DO NOT connect the zero reference to earth ground. The earth ground, if used at all, should be connected to the chassis to reduce EMI, not to the zero reference. It is not necessary to use the earth ground - how many electronic devices do you have that have 3 prong mains plugs?

You obviously do not know what you are talking about and should not be posting advice like this.

There is always that possibility. However, I have a BS in physics and a MS in instrumentation engineering, so there is a possibility that I do know what I'm writing about.

Your formal education is irrelevant. What you suggest is dangerous, poor practice, and lacks recognition that any advice (good or bad) is too easily taken to task by those that do not know any better .... said another way, it's highly irresponsible of someone of your education level to say such things. Really now, at your level of training you should know better.

No. Just ... no.

cool
wackelpeter
Rex Coil 7 wrote:
[ This is a studio synth, yea? I'm presuming so since I don't know too many people that would want to use such a large single piece of gear in live gigs (hard to lift).


Even if this would be a Studio synth i would also face the cahnce that once you might be moving... who should transport such a monster synth?

And yes, the Argument with a failed PSU and the whole System down is a great one too.

I would stick to something that is easier to move and could be operated independently.
NV
oinkbanana wrote:

Is it better to go with a PSU that has the 3rd output, or just getting a 5V adapter? I currently only have 2 modules with 5v, and no plans for more.


Eurorack modules that use 3.3V or 5V are common and becoming even more so, but 99% of them regulate this from the +12V rail and very few allow jumpers for using an external 5V supply. That's why you see so many modules with something like 160 mA on +12V and 20 mA on -12V. It's not ideal but it's how the market has evolved, and some of the cases you find that offer 5V on the busboards are just regulating it from +12V as well. Designing a new eurorack module that specifically requires external 5V at this point is basically just scaring away customers.

Because of this buying multiple triple output supplies will be unnecessary expense, weight, and general hassle to accommodate the very few modules that need it. 5V adapters work and just one will probably cover all your needs if you can bunch your 5V modules onto the same busboard, although they also regulate from +12V. If you want to avoid this you could pick up a single small 5V linear supply and wire it to just one section of boards/bars/whatever, then have that section be where you put all your modules that require external 5V. In general it's better to avoid a heavily lopsided current draw from a dual PSU, but it's also not really something that can be avoided in eurorack presently other than trying to balance out current draw per PSU with module placement.
Graham Hinton
Rex Coil 7 wrote:
This picture (above) is of one of Graham Hinton's systems. That system has both 12v and 15v systems on board since it houses 12v and 15v modules.


Actually there is no +/-15V as it is a Eurorack system, but there is +5V on the lower half.

Quote:

I can point to a hundred users here in Miffwugglers that use pos/neg power systems ... I can point to no-one that uses a positive psu and a negative psu.


There is a disadvantage to PSUs that have a single COM output. This will have a single cable that carries the difference between the +ve current(s) and the -ve current. With the distribution 0V connected to Earth/Ground as a reference that means that the COM point is moving dynamically by the voltage drop in this cable and both +ve and -ve supplies are referenced to that. That means that each power rail modulates the other.

By wiring the returns separately to the distribution, as in my diagram above, this does not happen. Each regulator is separately referenced to 0V and the voltage drop in the return is the same as the one in the supply side which may be minimised with heavy cables. If they are wired like this it doesn't matter if they are the same physical PSU or not.

My new generation of PSUs don't have negative regulators, just as many positive regulators as necessary wired appropriately. As a lot of systems are +12V heavy I can put in more regulators on the +12V rails and split the distribution.
oinkbanana
This thread has been full of good advice.
I'm not gonna go with the original plan of a +12v supply and a separate -12v supply.


Graham Hinton wrote:


This diagram is perfect. Thanks so very much Graham
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