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DIY power supply (take 2) - Bel Power - Will this kill me?
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Author DIY power supply (take 2) - Bel Power - Will this kill me?
donturner
After spending many hours attempting to build a power supply out of a Meanwell RT65b (https://www.muffwiggler.com/forum/viewtopic.php?p=3079816) I ditched it and bought a linear PSU. It's a Bel Power HCC15-3-AG with 2 outputs: 12V @ 3.4A and -12V @ 3.4A. It seems very similar to the Condor and Power One supplies which I've seen in other DIY builds.

Here's the mains wiring from the back:



And from the front with the busboard wires attached and perspex cover attached (I know it's pretty ghetto).





Ripple measurements with the scope, measured on busboard +12V:



Some questions:

- Is it going to kill me, anyone else or burn the house down?
- Related to the above: those 2N3055 transistors casings at the front are at -12V and 25V respectively on the outside. I accidentally touched one with a spanner which was also connected to earth and blew the 1A fuse in the IEC inlet. Should I insulate them somehow?
- It hums (and I'm pretty noise sensitive so it's quite annoying) - is there anything I can do to reduce this? I've tried mounting the PSU on a rubber mat to damp the vibration, it worked a bit but still audible (wish I'd gone for a toroidal transformer tbh).
Gandalf
I would have pushed the power unit as close to the mains input to (a) shorten the leads, (b) maximize internal space in the rack for modules, (c) maximise distance from power unit to as main modules as possible.
technically, hot-melt glue is not an acceptable mechanism for insulating mains. Look at the later Doepfer PSU2 installations. ALL the mains connections where kept close together and hidden under an earthed metal cover. You should have something similar, earthed metal cover ALL the mains wiring and terminations INCLUDING the top of the power unit to prevent access to those mains terminals. Just because you have an insulated sleeve over the solder/tabs, woudl you feel comfortable being able to touch any of this while it is powered up? I WOULDN'T.
Move it all together and put a metal housing over it. Then you can feel a LOT more comfortable.
I would also prefer to see the main connection on the heatsink as the common point for the EARTH wires rather than junction block.
sduck
Is there a fuse in there somewhere? There should be. Otherwise, yes, it could kill you.
jamos
I had the same problem of noise from a similar power supply, and replaced it with a toroidal core Ssupply that's reduced that problem. Look at some of Graham Hinton's posts on power supplies, he will explain why that noise is pretty much inherent in those rectangular transformer supplies.
donturner
Quote:
I would have pushed the power unit as close to the mains input


Yes, I tried that, but then I couldn't get my hand/glue gun in easily. Also, the transformer is *heavy*, it made more sense to me in the end to have it more centrally located because it makes the overall case more stable.

Quote:
woudl you feel comfortable being able to touch any of this while it is powered up?


I mean, there's a *lot* of hot glue on there, at least 2mm, I didn't want any chance of getting electrocuted. I'm fairly confident that touching it wouldn't electrocute me.

Quote:
I would also prefer to see the main connection on the heatsink as the common point for the EARTH wires rather than junction block.


Right. Not doubting you but interested to know why that's better than the WAGO junction block (which also provides GND to the busboard)?

Quote:
Is there a fuse in there somewhere?


Yes, there's a 1A fast-blow glass fuse in the IEC inlet.

Quote:
replaced it with a toroidal core Ssupply


I think I'm going to have to do that. I'm sat next to it and the hum is driving me crazy!
oldenjon
Move your PSU outside the case?
keninverse
oldenjon wrote:
Move your PSU outside the case?
This is what I do with all my linears. I have two 3u cases for my euro and some hammond ventilated boxes for my 4u. Power inlet is a 4 or 6pin XLR and cable is multicore west penn 18awg. I use 3u subracks though so each subrack has its own power inlet.
donturner
How would moving the psu outside fix the hum?
Gandalf
donturner wrote:
Quote:
I would have pushed the power unit as close to the mains input


Yes, I tried that, but then I couldn't get my hand/glue gun in easily. Also, the transformer is *heavy*, it made more sense to me in the end to have it more centrally located because it makes the overall case more stable.

Quote:
woudl you feel comfortable being able to touch any of this while it is powered up?


I mean, there's a *lot* of hot glue on there, at least 2mm, I didn't want any chance of getting electrocuted. I'm fairly confident that touching it wouldn't electrocute me.

Quote:
I would also prefer to see the main connection on the heatsink as the common point for the EARTH wires rather than junction block.


Right. Not doubting you but interested to know why that's better than the WAGO junction block (which also provides GND to the busboard)?

Quote:
Is there a fuse in there somewhere?


Yes, there's a 1A fast-blow glass fuse in the IEC inlet.

Quote:
replaced it with a toroidal core Ssupply


I think I'm going to have to do that. I'm sat next to it and the hum is driving me crazy!

You typically need at least 3mm AIR-GAP. Hot melt glue does not pass the insulation test so 2mm is probably not even close.
What about the mains wires (blue and brown) do you really want to be able to touch them?
The more connection points you have in the earth chain the weaker it is. You should take all earth connections to the one large bolt and have each one spaced using a star-washer and finish with a double nut to lock it together.
There are plenty of discussions on these forums about the fact that the SIGNAL 0V (the one on your busboard and modules) should NOT be connected to EARTH. EARTH is a safety connection to prevent you from being electrocuted, it is not a 0V reference. You are committing the common sin of confusing EARTH, GROUND, COMMON and 0V which are DIFFERENT things and ideally need to be treated in their own way.

You can miswire this as much as you want, if only you get killed then 'who cares' hihi , but you injure or kill anyone else then that is a DIFFERENT story and I wouldn't want to be involved in those legal discussions.
Signs REGULARLY say, ONLY to be done a LICENSED ELECTRICIAN. This is for a VERY GOOD REASON!
donturner
I take your point about insulation - I'll replace the inlet for a more suitable one, get one of those insulation boots and box in the mains wires.

Quote:
There are plenty of discussions on these forums about the fact that the SIGNAL 0V (the one on your busboard and modules) should NOT be connected to EARTH. EARTH is a safety connection to prevent you from being electrocuted, it is not a 0V reference.


From my previous build thread, here's what Graham Hinton said: "By making the busboard 0V referenced to Earth the COM will be floating with respect to the 0V, but that's OK and preferable to having your entire 0V common floating wrt to the COM terminal."

Here's my busboard terminal blocks:



The bottom one is connected to the PSU -12V, COM and +12V outputs. The top one has GND connected to EARTH to provide a 0V reference as per the guidance from Graham.

If my busboard is not connected to EARTH to provide a 0V reference then where should I derive my 0V reference from? It can't come from the PSU because of the differing loads between the positive and negative outputs.
Graham Hinton
Gandalf wrote:
There are plenty of discussions on these forums about the fact that the SIGNAL 0V (the one on your busboard and modules) should NOT be connected to EARTH.


Where?
If so they are wrong.

Try reading AES48 which is the recommended practise for audio equipment.

Quote:

EARTH is a safety connection to prevent you from being electrocuted, it is not a 0V reference.


It is BOTH and a drain for induced charges. The mains Earth has to function for all three purposes and that means it has to be wired in a very specific order. This is where a lot of people go wrong.

The mains Earth has to be the 0V reference because it is the only one you have. If you attempt to make a separate so-called "Clean Earth" that is extremely dangerous as you may be introducing potential differences of over 50kV into your equipment when there is a close lightning strike.

Quote:

You are committing the common sin of confusing EARTH, GROUND, COMMON and 0V which are DIFFERENT things and ideally need to be treated in their own way.


You are committing the common sin of posting misinformation and creating more confusion.

There are only three different types of ground with internationally standardised symbols. Earth and Ground are alternative words for Mains Earth. (Signal) Common and 0V are the same thing.



They have to be connected together at the mains inlet of any equipment and kept separate thereafter. Note how many schematics use the wrong symbols for Signal Common which causes confusion like yours.
khakifridge
donturner wrote:



I'd arrange for the earth wire coming from the IEC receptacle to be longer than the live and neutral wires. That way, if (when) the receptacle is ripped from the case, the earth wire is the last thing to be disconnected.
LED-man
I’m wondering very often why people without skills touch Main Power.
Here in Germany it’s not allowed.
And no insurance will pay your burned house if you ignore it.
Furthermore many forum doesn’t allow support for main power handling in balance with regional laws, because users can point the fault on the forum responsible person in case someone give wrong infos or missed safety warnings.
Local electricians are not expensive and can make some tests for the client.
(Isolation tests etc.)
Kampfzwerg
I share LED mans opinion.

Hot snotting mains wires is just not an option. Never!

If I can give you some advice: get a residual-current circuit breaker!

'cuda
jakobprogsch
Independent of the safety/hum aspects I'd also carefully watch temperatures. My experience was that these get uncomfortably hot even with ventilation slits at the top and bottom of the case and directly behind the PSU. When nearing 2A total draw I'd see 100°C+ on various components (rectifier diodes, that one large resistor) as well as the big exposed pass transistors. And that was without covering the open side with an acrylic cover. I had mounted the psu upside down though to prevent stuff falling into it.

I posted some of those issues here: https://www.muffwiggler.com/forum/viewtopic.php?p=3042996#3042996

Edit:
Quote:

I’m wondering very often why people without skills touch Main Power.
Here in Germany it’s not allowed.

So, you have an electrician come over to hang your lamps?

Edit2: very off topic I guess but I was curious because of the above and apparently in Germany you indeed aren't technically allowed to hang your own lamps but here in Switzerland that is specifically excluded. Meaning you are allowed, provided a residual current breaker is installed. Interesting. Also at least the Swiss regulations I found specifically talk about electrical installations (outlets, fuseboxes, solar installations etc.) but not devices you connect to it. So I guess I have some more searching to do to see what the rules there are.
LED-man
Jakob, Please check the DIN VDE.
3500 standardize
https://www.kopp.eu/de/blog/entry/uebersicht-der-wichtigsten-vde-norme n-fuer-die-elektroinstallation
cornutt
jakobprogsch wrote:

Edit2: very off topic I guess but I was curious because of the above and apparently in Germany you indeed aren't technically allowed to hang your own lamps but here in Switzerland that is specifically excluded. Meaning you are allowed, provided a residual current breaker is installed. Interesting. Also at least the Swiss regulations I found specifically talk about electrical installations (outlets, fuseboxes, solar installations etc.) but not devices you connect to it. So I guess I have some more searching to do to see what the rules there are.


Note that a lot of this differs in different parts of the world. In much of the USA you can do pretty much any wiring in your own home, if you live in a single-family house. Larger jobs will usually require permits and inspections. I did much of the wiring in my house, and yes, it was inspected. Smaller jobs and repairs can be done without a permit. Our ordinary residential wall-outlet power is only 120V so it's somewhat less dangerous.

We call an RCD a "ground fault interrupter", or GFI. Most GFIs here are in the form of receptacles that have the GFI function built into them, although you can get GFI breakers.
Mungo
LED-man wrote:
I’m wondering very often why people without skills touch Main Power.
Here in Germany it’s not allowed.
And no insurance will pay your burned house if you ignore it.
Furthermore many forum doesn’t allow support for main power handling in balance with regional laws, because users can point the fault on the forum responsible person in case someone give wrong infos or missed safety warnings.
Local electricians are not expensive and can make some tests for the client.
(Isolation tests etc.)
It is an important point, the testing of an mains wired product/appliance once it is finished and before it is used is an important step to check the safety. Many electricians would be unfamiliar with the wiring configuration so its useful to share the information freely so that suitably skilled people can assemble it correctly.

There are many great options for eurorack power that don't have any mains wiring and eliminate those risks, most people should be guided to those. But there is a group of loud users on this site who argue anything other than linear mains earthed supplies are to be avoided for noise/safety/performance/cost matters, when the truth is other options are all about the same if you select appropriate options.
Mungo
cornutt wrote:
Note that a lot of this differs in different parts of the world. In much of the USA you can do pretty much any wiring in your own home, if you live in a single-family house. Larger jobs will usually require permits and inspections. I did much of the wiring in my house, and yes, it was inspected. Smaller jobs and repairs can be done without a permit. Our ordinary residential wall-outlet power is only 120V so it's somewhat less dangerous.
Distribution (fixed in place) wiring rules are still very specific to each country, but the regulations for products are becoming more and more common across the world. Multi national companies already design products that meet all the different regulations in the countries they sell into. But accessing the regulations usually costs money, so DIY builders can't even see the rules unless they first pay hundreds of dollars for each standard document.
donturner
Quote:
But there is a group of loud users on this site who argue anything other than linear mains earthed supplies are to be avoided for noise/safety/performance/cost matters, when the truth is other options are all about the same if you select appropriate options.


Out of interest what power supply would you buy/build if you needed 2A on the +12V rail and had a budget of $150?
Rex Coil 7
donturner wrote:
Related to the above: those 2N3055 transistors casings at the front are at -12V and 25V respectively on the outside. I accidentally touched one with a spanner which was also connected to earth and blew the 1A fuse in the IEC inlet. Should I insulate them somehow?
Holy shit ... ~yes~ ... you should "insulate them somehow" by never .. EVER .. having your hands or tools inside of that thing when it is plugged in to the wall socket or whatever you're plugging that hot mess into.

First rule ... do not stick your hands or tools into the synth unless you can see the mains power plug is unplugged from the wall socket with your own eyes.

"Yes" ... it will kill you. "It" being your practices. Substitute "it" with "you". So yes, YOU will kill you if you continue to use unsafe working practices.

d'oh!
Rex Coil 7
donturner wrote:


Quote:
woudl you feel comfortable being able to touch any of this while it is powered up?


I mean, there's a *lot* of hot glue on there, at least 2mm, I didn't want any chance of getting electrocuted. I'm fairly confident that touching it wouldn't electrocute me.
So you're going to bet your life on "fairly"? Are you also "fairly" certain that stepping in front of a bus won't kill you?

You need to listen to the wiser minds in this thread, they are here to help you. As for me, I'm out. There are already people far wiser than myself offering very solid help.

pbear :(
Graham Hinton
donturner wrote:
those 2N3055 transistors casings at the front are at -12V and 25V respectively on the outside. I accidentally touched one with a spanner which was also connected to earth and blew the 1A fuse in the IEC inlet. Should I insulate them somehow?


Search for "TO-3 transistor cover".
JohnLRice
donturner wrote:
Quote:
But there is a group of loud users on this site who argue anything other than linear mains earthed supplies are to be avoided for noise/safety/performance/cost matters, when the truth is other options are all about the same if you select appropriate options.


Out of interest what power supply would you buy/build if you needed 2A on the +12V rail and had a budget of $150?
While I know it's not a response you want to hear, I'd say that your budget shouldn't dictate what power supply you can get, but the requirements of the collection of modules you want to use should dictate what power system you should get. If you can't afford to get what you need in a reasonable amount of time, consider selling one or more modules to generate the funds needed to purchase the power supply components you should have down the road when you've managed to re-buy the modules you sold. cool
Mungo
JohnLRice wrote:
donturner wrote:
Quote:
But there is a group of loud users on this site who argue anything other than linear mains earthed supplies are to be avoided for noise/safety/performance/cost matters, when the truth is other options are all about the same if you select appropriate options.


Out of interest what power supply would you buy/build if you needed 2A on the +12V rail and had a budget of $150?
While I know it's not a response you want to hear, I'd say that your budget shouldn't dictate what power supply you can get, but the requirements of the collection of modules you want to use should dictate what power system you should get. If you can't afford to get what you need in a reasonable amount of time, consider selling one or more modules to generate the funds needed to purchase the power supply components you should have down the road when you've managed to re-buy the modules you sold. cool
To be fair most power supplies can just be added to in larger cases, start with one and then as you need more power add another later as needed to power extra bus boards. But some planning ahead can be cheaper in the long run if you invest more at the start.

donturner wrote:
Out of interest what power supply would you buy/build if you needed 2A on the +12V rail and had a budget of $150?
You are already on the "second" attempt having discarded the power supply you first chose. The price of the power system is more than just the open frame power supply, but regardless if your key parameter is 2A on +12V....

Tiptop Audio uZEUS with the Boost Adaptor

Under your budget, either new or second hand, and keeps all the mains power safely away from the case.
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