I don't agree about the supplies being 2 or more quadrant devices though. These power supplies will not be anything more than single quadrant outputs, ie they supply a positive voltage and a positive current, ie they will not sink current (unless they have a cro bar circuit and the voltage is high enough to trip that).

I was talking about the general case and I thought I had mentioned that this was assuming that the supplies can sink current -- I meant to, but obviously forgot, so thanks for bring it up.

 

Each cable has the addition of a random resistance which is the contact resistance of the connector.
That connector looks like a Microfit 3.0, but I can't quite scale it from the picture. I used a connector that looked like that once, and it melted at way below its rated current.
Most connector manufacturers advise against using two poles in parallel for a high current connection, unless rated well below double the rating of a single pin, because of the tendency not to share current due to contact resistances.
Also, most multipole connectors have a lower current rating when all poles are carrying current.

 

View attachment 318519I think it's pretty obvious from this image that there are no protection circuits for each output. If there were, they would be visible on this picture. All I can see is a very large track commoning all the outputs.
There may be fuses on the other side of the board, but if there were, why didn't they work?

I said it takes the path of lowest resistance. If that low resistance is a short circuit, you have all the current down one cable, and 135A down 2.5mm^2 cable equals a fire, as you found out.
Think of your house consumer unit, with a 100A mains supply on 16mm^2 or 25mm^2 cable. Would you wire the sockets on 2.5mm^2 cable without a separate fuse for each circuit?

Oh the misconceptions about fuses. Fuses do not protect cabling from overloads, they offer protection only in cases of hard faults with huge fault currents. And there are no fuses in the picture because there are no fuses and there are no fuses because they would have been the first source of fire.
A fuse operating at its rated current will take up to 30 days to blow, if it blows at all. Double the rated current and that comes down to 30 minutes. It gets down to ms only at 4 to 10 times the current rating and in the mean time it melts everything in sight.
fuses are not for overloads. PSU current limiting does that. Fuses are for hard faults with high fault currents.

 

I was talking about the general case and I thought I had mentioned that this was assuming that the supplies can sink current -- I meant to, but obviously forgot, so thanks for bring it up.

NP.

 

Yes, but I don't see any indication that these supplies have ballast resistors. If the crypto boxes the TS is using were intended to be powered by multiple supplies (which I rather doubt), then MAYBE they incorporate ballast resistors. But at these currents, they will have to be pretty small and if they aren't well matched, that will cause its own problems.

Did you notice the small signal cable with many wires in it? The supplies may be designed to share using the magic share terminal. This is a common enough trick for better supplies. They all output a voltage proportional to their output current. They output this voltage through a resistance and they are all connected together. Now each power supply can determine if it is carrying more or less than its share of the load by looking at the voltage across the resistance. If a power supply is trying to output a higher than the average voltage then it is carrying more load than the others. A lower voltage, less of the load than the others.
If they are using an output resistance in the actual high current outputs then they could use remote sensing for the output voltage to maintain good regulation and use an artificial resistance (force the control loop to droop the output voltage in response to load current) to achieve output resistance load sharing without the actual resistor and the actual heat it would produce.
These are just two options. The popular two options, but the first one is most likely for a low output voltage like these supplies have.

 

Yes, but I don't see any indication that these supplies have ballast resistors. If the crypto boxes the TS is using were intended to be powered by multiple supplies (which I rather doubt), then MAYBE they incorporate ballast resistors. But at these currents, they will have to be pretty small and if they aren't well matched, that will cause its own problems.

Output resistance for these power supplies could only really be used for sharing the current between the output wires and connector pins. The resistors you are looking for are the wires and connector pins. I am not convinced that the pcb design is sufficiently well matched between the outputs to ensure the sharing remains uniform though. I would have expected to see short (roughly equal length) traces from each connector pin to a bus bar bolted to the pcb. I think that is what it would take but again, that will not help two power supplies to share, just the wires from a single power supply.

 

This is where you're completely wrong, if you read my convo above with Ian0 thats exactly what he is saying, and in multiple posts.
Which Ive been disputing all along because it sounds incorrect.



And I appreciate the help, however when something doesn't sound right it makes sense to challenge it.

Going back to the point in question, Your post made sense to me as you described the wires in a "bundle", an accurate representation, the power is obviously intended, and does, flow through the bundled wires out through the numerous molex connectors (despite Ian0s opposing view)

Also, There are numerous things that can go wrong in such PSU to cause a fire, the most obvious is the wire ratings and ampage, but I posted here to see other suggestions.(maybe faulty ac/dc conversion, poor soldering, etc)

I will reach out to the manufacturer now, good idea.
And also will open one up and get some inside photos to see if load balancing exists.

Your problem is not the power supplies per se. The burns are all at the far end of the output wires. So unless the supplies are not sharing via the magic sharing terminal, if there is one, the problem is more likely to be your connections / motherboard. And there is plenty there to be suspicious of.

 

Because they have no concept of safety and compliance with regulations.

Sorry Ian0, but I think it is you that is incorrectly assigning regulatory requirements where there are none, and assuming safety concerns where there are none. I mean, which standard do you think they are in breach of?

 

Re 25mm^2
Would the PSU not be distributing the power over the smaller sections of wire.

re load, The 8 PSU were powering 4 crypto rigs, 2 per rig.
4 double sockets, every 2 sockets had 4mm^2 twin earth

Yes, the smaller wires will share and probably quite well. Not sure what you mean by 'twin earth' but you are correct about the sharing amongst the smaller wires.

 

No. The power is going to head towards the lowest load resistance.

Ohms Law, that all I'm sayin'.

 

No. The power is going to head towards the lowest load resistance.

Yes, not no. Yes. Ohms Law Ian0.

 

Oh the misconceptions about fuses. Fuses do not protect cabling from overloads, they offer protection only in cases of hard faults with huge fault currents. And there are no fuses in the picture because there are no fuses and there are no fuses because they would have been the first source of fire.
A fuse operating at its rated current will take up to 30 days to blow, if it blows at all. Double the rated current and that comes down to 30 minutes. It gets down to ms only at 4 to 10 times the current rating and in the mean time it melts everything in sight.
fuses are not for overloads. PSU current limiting does that. Fuses are for hard faults with high fault currents.

A fuse is intended to operate indefinitely at its rated current. That’s why it‘s called its rated current.
Fuses are also designed to operate without catching fire. A protection device which catches fire whilst doing its job would be a very silly protection device.
And fuses do protect cabling from overload. That’s why we use them in our houses. That’s why we calculate the cable size so that the cable can operate at an elevated temperature for long enough for the protection device to operate.
True, they are the last line of protection after everything else has failed, but other protection systems do fail.

 

Its the Third Kirchoff Law: if the wire exerts the smoke, the amperage in this wire is too large.
And Fourth Kirchoff Law: If wire cach the fire, it amperage is far too much for this wire.
And Fifth Kichoff Law: If wire explodes, it amperage was even more larger than in case of 4.th Law.

 

Did you notice the small signal cable with many wires in it? The supplies may be designed to share using the magic share terminal. This is a common enough trick for better supplies. They all output a voltage proportional to their output current. They output this voltage through a resistance and they are all connected together. Now each power supply can determine if it is carrying more or less than its share of the load by looking at the voltage across the resistance. If a power supply is trying to output a higher than the average voltage then it is carrying more load than the others. A lower voltage, less of the load than the others.
If they are using an output resistance in the actual high current outputs then they could use remote sensing for the output voltage to maintain good regulation and use an artificial resistance (force the control loop to droop the output voltage in response to load current) to achieve output resistance load sharing without the actual resistor and the actual heat it would produce.
These are just two options. The popular two options, but the first one is most likely for a low output voltage like these supplies have.

While that can load balance amongst the various wires coming out of each PSU, how does it balance the current output by two (or more) different PSUs that are powering the same device? How does one PSU know what its share of the current is since it has no idea what the other PSU is outputting? How can it compare it's output to the average output when it can't know what the output of the other PSU is? There would need to be some kind of connection between the two supplies at other than the point of power entry to the device in order for them to do the necessary sensing and/or exchange of information.

 

A fuse is intended to operate indefinitely at its rated current. That’s why it‘s called its rated current.
Fuses are also designed to operate without catching fire. A protection device which catches fire whilst doing its job would be a very silly protection device.
And fuses do protect cabling from overload. That’s why we use them in our houses. That’s why we calculate the cable size so that the cable can operate at an elevated temperature for long enough for the protection device to operate.
True, they are the last line of protection after everything else has failed, but other protection systems do fail.

Have a look at:
https://library.e.abb.com/public/114371fcc8e0456096db42d614bead67/2CDC400002D0201_view.pdf
if you don't believe me.
For normal 5x20mm fuses (fast acting, Schurter fuses https://www.schurter.com/en/datasheet/typ_SP_5x20.pdf) they will take over 30mins to blow with a 1.5x to 2x rated current flowing and at 1.5x a 1A fast blow will be dissipating 2.5W, a 10A fuse will be dissipating 3W, a 12,5A fuse dissipates 6.9W at 1.5x and a 16A fuse dissipates 7.4W and still they will take 30 minutes or more to blow.
At rated current, the 1A fuse dissipates 1W and the 10A fuse, 2W. These are significant in continuous operation. If you don't see an issue with a fuse losing that much power for 30 minutes when it is enclosed in a fuse holder and/or in close proximity to other components then I don't know what to say. It seems to me that fuses are best when the fault currents are big and flowing. Creeping up on an overload current will melt everything else first.
These Ian0, are the facts despite whatever you believe. The facts are only "silly" if you misunderstand the purpose. You are correct though, fuses in electrical installations are there to protect the installation (mostly the wiring), not the appliances.

 

While that can load balance amongst the various wires coming out of each PSU, how does it balance the current output by two (or more) different PSUs that are powering the same device? How does one PSU know what its share of the current is since it has no idea what the other PSU is outputting? How can it compare it's output to the average output when it can't know what the output of the other PSU is? There would need to be some kind of connection between the two supplies at other than the point of power entry to the device in order for them to do the necessary sensing and/or exchange of information.

And in your pics I thought the white ribbon cable was part of the power supply connection. It is not so my assumptions and description were all wrong and pointless. I did find the power supply elsewhere and noticed that there are 5 molex connectors on wires from the psu and one more daisy chained from each of those. So the sharing will still happen but not all connectors will be sharing equally. The first 5 will be taking a bit more than the others I think. I can't say if the difference would be big or small. I suspect it would not be huge but also not nothing.

 

Have a look at:
https://library.e.abb.com/public/114371fcc8e0456096db42d614bead67/2CDC400002D0201_view.pdf
if you don't believe me.
For normal 5x20mm fuses (fast acting, Schurter fuses https://www.schurter.com/en/datasheet/typ_SP_5x20.pdf) they will take over 30mins to blow with a 1.5x to 2x rated current flowing and at 1.5x a 1A fast blow will be dissipating 2.5W, a 10A fuse will be dissipating 3W, a 12,5A fuse dissipates 6.9W at 1.5x and a 16A fuse dissipates 7.4W and still they will take 30 minutes or more to blow. If you don't see an issue with a fuse losing that much power for 30 minutes when it is enclosed in a fuse holder and/or in close proximity to other components then I don't know what to say. It seems to me that fuses are best when the fault currents are big and flowing. Creeping up on an overload current will melt everything else first.
These Ian0, are the facts despite whatever you believe. The facts are only "silly" if you misunderstand the purpose.

You are implying that a fuse under overload conditions is designed to start a fire. What nonsense.
I am more than familiar with the fusing characteristic and MCB tripping characteristics from the IEE wiring regulations.

 

Sorry Ian0, but I think it is you that is incorrectly assigning regulatory requirements where there are none, and assuming safety concerns where there are none. I mean, which standard do you think they are in breach of?

EN 60950-1

 

Have a look at:
https://library.e.abb.com/public/114371fcc8e0456096db42d614bead67/2CDC400002D0201_view.pdf
if you don't believe me.
For normal 5x20mm fuses (fast acting, Schurter fuses https://www.schurter.com/en/datasheet/typ_SP_5x20.pdf) they will take over 30mins to blow with a 1.5x to 2x rated current flowing and at 1.5x a 1A fast blow will be dissipating 2.5W, a 10A fuse will be dissipating 3W, a 12,5A fuse dissipates 6.9W at 1.5x and a 16A fuse dissipates 7.4W and still they will take 30 minutes or more to blow.
At rated current, the 1A fuse dissipates 1W and the 10A fuse, 2W. These are significant in continuous operation. If you don't see an issue with a fuse losing that much power for 30 minutes when it is enclosed in a fuse holder and/or in close proximity to other components then I don't know what to say. It seems to me that fuses are best when the fault currents are big and flowing. Creeping up on an overload current will melt everything else first.
These Ian0, are the facts despite whatever you believe. The facts are only "silly" if you misunderstand the purpose. You are correct though, fuses in electrical installations are there to protect the installation (mostly the wiring), not the appliances.

Dude, you're making Rogue Engineers look bad.