MUFF WIGGLER Forum Index
 FAQ & Terms of UseFAQ & Terms Of Use   Wiggler RadioMW Radio   Muff Wiggler TwitterTwitter   Support the site @ PatreonPatreon 
 SearchSearch   RegisterSign up   Log inLog in 
WIGGLING 'LITE' IN GUEST MODE

Overloading power suply, what actually happens ?
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Author Overloading power suply, what actually happens ?
GodMadeUsFonky
what actually can happen when you overload your power suply ? what kinda damage can happen.

and also what kind of tolerance do you use when it comes to planning modules 80%, 90%, 100% of what your power suply can handle ??
L-1
Usually one of power regulators became too hot and this supply (+ or -) turned off.
Just me
As mine approached overload, rhe quantizer quit and the oscillators wouldn't track. Never pushed it harder.
Graham Hinton
GodMadeUsFonky wrote:
what actually can happen when you overload your power suply ? what kinda damage can happen.


If you mean linear PSUs, as you draw more current than can be delivered the regulators will drop out of regulation and this will start with small dips in the power rail at twice mains frequency and with more current become larger dips and then a lower wavering voltage.

Different parts of the circuit will get hotter than they are intended to and what happens next depends on what protection has been built in. Regulator ICs will shut down when they get too hot internally or if a high current is detected. There should be fuses to protect the transformer, but if not the laquer on the windings will start to melt (it has a distinctive smell) and then you could get a short and a blown transformer.

Quote:

and also what kind of tolerance do you use when it comes to planning modules 80%, 90%, 100% of what your power suply can handle ??


That depends on the PSU and the modules, some modules may have a wide dynamic power range. Most PSUs are optimistically rated, but most module current draws are worst case so it sort of partially cancels out. The only way to be sure is to measure it.
GodMadeUsFonky
Allright thanks.

I'm using a doepfer 9u low cost case with the standard power suply that comes with that. But I'm starting to push the maximum, so I was figuring out what power solution to add to it. And how much I should leave as a tolerance. Also dealing with a couple of modules with unknown current draw.

I'll just make sure it's enough in any case, but I didn't know what could happen when drawing too much.
pugix
If the power supply is a good one, when a little overloaded it will do less of a job of voltage regulation, and when overloaded a lot (like a short) it will just shut down the power output. A little overload can almost be worse than a lot, because you may not notice that your modules aren't working quite right. VCO may be a bit unstable, or there is low level 60hz hum in your audio. I try to keep my supplies loaded to no more than 80% of rating, but since they are Power-One, they do a pretty good job even when loaded higher. If you have room for a bigger supply, it's better to err on the side of too big than too little.
A Dingleberry Monstrosity
I thought my maths was broken a while back, but it turned out to be my power supply in some way. I thought it had enough amperage, but I guess it didn't.

What would happen is that everything would function normally, but after a minute or my maths would basically freeze up. Installed a beefier supply and the problem went away completely seriously, i just don't get it
filmersam
Sorry if this is a stupid question, it probably has an obvious answer- Why do limitations exist with power supplies? I mean, why not make a power supply that would be hard to overload?
daverj
filmersam wrote:
Sorry if this is a stupid question, it probably has an obvious answer- Why do limitations exist with power supplies? I mean, why not make a power supply that would be hard to overload?


Every power supply puts out a certain maximum amount of power. The more power it supplies, the larger it is, the heavier it is, and the more expensive it is. People typically don't want to spend a lot extra for power they aren't going to use.
giorgio
hertz donut sounds wacky when it doesn't have enough power
JohnLRice
Additionally, and I don't have time to look it up and verify but, I'm pretty sure i read that for at least linear supplies the efficiency starts to drop off the closer you get to the maximum rated output.
John Nonjohn
I had a situation where a single power supply was having trouble powering on all the modules I had linked up to it. I was driving around 18-20 modules, both MOTM and Blacet, off the MOTM 900 Power Supply. Sometimes, the PSU adequately powered all the modules, and sometimes only some of the modules would power on and behave correctly. I ended up buying another power supply and better distributing the load out to the two power supplies. That solved the issue. So, there were no blown modules or busted parts on any of the modules, even as they were being slighly underpowered. Today, my modular has 6 power supplies (1x Blacet PSU and 5x MOTM PSU's) driving around 80 modules. It works for me!
JohnLRice
There's another thing that happens with some power supplies when being run close to their rating. When you first power on your system, the total in-rush of current can be so high it can cause the power supply to think it's overloading and shut down to protect itself. Usually only a problem when running near its rated limit (how near I don't know) Some folks, like CatGirlSynth and Oakley maybe hmmm..... make a little delayed powerup board that powers up your system in halves or thirds to prevent the in-rush lockup.
Graham Hinton
filmersam wrote:
Sorry if this is a stupid question, it probably has an obvious answer- Why do limitations exist with power supplies? I mean, why not make a power supply that would be hard to overload?


The larger a PSU is the harder it is to distinguish small faults. A module failure that draws, say, 2A would not trip a 10A PSU, but could fry the module. Distribution of high currents also ups the ante on all the cabling to overcome voltage drops.

The most scary part is having a modular system costing thousands connected to one PSU that could take it all out under fault conditions. It is better to have several smaller PSUs with some redundancy and a spare.

Large PSUs require a lot of respect and additional devices to protect you from them, even when turned off. If you have ever seen a spanner dropped across a car battery you will know what large currents are capable of. Or what a UPS can do to someone wearing a ring on their finger... Allowing users to freely connect up modules to a high current PSU is not a good idea.


JohnLRice wrote:
There's another thing that happens with some power supplies when being run close to their rating. When you first power on your system, the total in-rush of current can be so high it can cause the power supply to think it's overloading and shut down to protect itself.


Inrush currents are normally caused by a cold transformer trying to charge the main reservoir capacitors. The module capacitors are not often a problem unless they are particularly large. We use NTC inrush limiters on the mains side.
soundwave106
In a way, part of me still think that doesn't answer the question in some ways though. You think the cost difference between a 1A linear power supply and a 2A linear power supply would not be significant (it certainly doesn't seem so when I look up supplies on Digikey), but it would certainly lead to less problems with power hungry modules (or overload due to lots of modules, since 2HP and 4HP modules now exist). Better to have more *capacity* than less, especially since I don't put 100% faith in a modules' listed power ratings (only if a modular manufacturer provided peak and average values, or guaranteed the value they provided was peak / max, would I feel confident).

OTOH, Graham's point about protection is a really good one, the only overload protection in a modular system right now is at the power supply (maybe some modules have protection too but not all). Bus boards and individual connections typically aren't protected in any way. In that sense, it might be best to solve power capacity problems with redundancy.
davebr
JohnLRice wrote:
There's another thing that happens with some power supplies when being run close to their rating. When you first power on your system, the total in-rush of current can be so high it can cause the power supply to think it's overloading and shut down to protect itself. Usually only a problem when running near its rated limit (how near I don't know) Some folks, like CatGirlSynth and Oakley maybe hmmm..... make a little delayed powerup board that powers up your system in halves or thirds to prevent the in-rush lockup.
I had this situation and I have a power supply in every cabinet. It seemed to occur mostly with the +/-15V @0.8A PowerOne supply. I designed my own power-on delay since it was before either of the mentioned ones existed. I agree with the philosophy that you want a power supply sized about right for the load, not too large, and not too small. At a minimum, you need to derate to 80% so my 0.8A is a 0.64A supply.

I have a power supply in each cabinet and a spread sheet that calculates the power supply load. In general, they are all at 50% to 60% with one at 72% of the full load current, so more like 63% to 75% and one at 90% of the derated spec.

Dave
cretaceousear
Is it good practice when setting up a system to check with an ammeter what the current draw really is?
No one ever seems to mention doing that here.
(Providing of course one has a meter capable of taking the expected 1-2 amp current.)
Graham Hinton
cretaceousear wrote:
Is it good practice when setting up a system to check with an ammeter what the current draw really is?
No one ever seems to mention doing that here.
(Providing of course one has a meter capable of taking the expected 1-2 amp current.)


The problem is that multimeters have what is called a "burden voltage" which is the voltage drop across it and it may be several volts on a cheap meter. This means that the modules will have a low voltage when the meter is inserted inline and will not be drawing the same current.

You could measure the voltage across a very small resistor, like 0.1Ω or 0.01Ω, but you really don't want even that resistance permanently in the distribution as it causes module interaction. It could be switched in and out with a bypass switch.

There are better ways to detect the current draw now and our next generation of PSUs (available in about a month from now) feature LED indication of 50%, 80%, 90% and 100% of rated current draw on each rail. That's all you really need to know, if it goes into the red you need another PSU.
daverj
If you do use the amp meter part of a multi-meter, it helps if you understand what the burden voltage spec is for each range of your meter. That makes it easier to decide if you want to actually do it or not. It also lets you understand how far off the reading probably is.

For example, the specs on my meter say that in the 500ma scale the burden voltage is 3.3mv/ma. That means that if I am measuring 100ma with it the meter drops 330mv. So if I'm looking at current from +12v, only 11.67v is getting to the circuit. So the current used when a full 12v is sent, without the meter in the way, is going to be higher than what I am reading. Probably about 3% higher in this case, so it still gives you a pretty good idea of the current flow. (if it reads 100ma, then without the meter it probably uses 103ma)

On the other hand, the 5A (5000ma) scale on this meter has a burden voltage of 45mv/A. That means at that same 100ma load the meter is only dropping 4.5mv. So 11.995v is getting to the circuit and the current draw at 12v is going to be virtually identical. (about 0.04% higher than shown)

With this particular meter, even at 1000ma the voltage drop is small enough that the reading would be within about 4ma of the true amount of current being used by the system. But as Graham says, you wouldn't want to leave it attached permanently. But it isn't unreasonable to measure the current draw at some point that way.

But your meter might have radically different burden voltages, so might have different results. The advantage of using a known resistor size, as Graham describes, is that you define your own burden voltage by the value resistor you select. In my case, at the 5A scale, my meter has an equivalent resistor inside of 0.045 ohms. But in the 500ma scale it has the equivalent of 3.3 ohms. So if I use my own 0.1 ohm resistor and read it as a voltage instead of current, at 100ma I am only off by less than 0.1% (assuming the resistor is accurate).
mousegarden
I also have a Doepfer LC9, with very few modules in it right now, but I've spec'd it out with a variety of things over then last few months, all sorts of combinations, and the most I've got up to on the + rail is about 1000ma. I'm certainly not going to worry about overheads at that figure, it's easy to get paranoid about this, my take on this is that we have 1250ma, so use it, just don't take the piss is my advice......

Guinness ftw!

MouseGarden
Nantonos
1000mA continuous seems like a lot for a module which is optimistically rated for a peak of 1250mA, with undersized filter capacitors which are probably not rated for more than a few thousand hours at 105C, sandwiched between an overheating toroid and sizzling, undersized heatsinks.

The concept of dropping out of regulations was explained in the thread. It's not as simple as 0 to 1249 no worries, 1251 stops working.

I'm currently drawing around 550mA on +12V from a Clicks n' Clocks (Doepfer PSU2 clone), and if it gets up to 800 will be looking to get a new case/psu/bus system.
Riggar
Just to throw something into the mix ... how important are 'high quality' power supplies in our modular world? I thinking audio here (quality-wise) - and for those who've grown up with Hi Fi over the years, we've seen over and over again just how important the PSUs are in the audio chain.
Graham Hinton
Here's a way to measure the current draw using a 4 pole 3 way rotary switch plumbed in between the PSU and the distribution system:



In the centre position 2 both resistors are bypassed, in position 1 the meter reads the voltage across the 0.01Ω resistor in the positive rail and position 3 the one in the negative rail. Read the voltage in mV, multiply by 100 and call it Amps. No damage will occur if the meter is disconnected. The wiring and contacts should be low resistance so it does not add significantly to the 0.01Ω.

Nantonos wrote:
It's not as simple as 0 to 1249 no worries, 1251 stops working.


Both linear and switched PSUs work by charging and discharging a reservoir capacitor. When you attempt to draw more current than can be put into the capacitor it does not degrade gracefully, you don't get just a few mV less on the rail.

In the case of a linear PSU the regulator input is a triangle/sawtooth waveform with a dc offset. The more current that is drawn the steeper the downward slope and the offset falls. When the lower tip of the sawtooth drops below the voltage necessary to keep the regulator working those tips will appear as drops in the dc rail voltage. That's why everything starts buzzing at 100Hz or 120Hz.

A switchmode PSU will depend on the exact design, but it will be equally undesirable.

This is why you need to know the peak to peak ripple & noise voltage at full load as part of the specification.



Riggar wrote:
how important are 'high quality' power supplies in our modular world? I thinking audio here (quality-wise) - and for those who've grown up with Hi Fi over the years, we've seen over and over again just how important the PSUs are in the audio chain.


HiFi amplifier PSUs are often not regulated and the voltage can dip on transients, they would be a lot more expensive if regulated PSUs were used. Although I have seen some audiophiles using cupboards full of HP industrial kiloWatt power supplies, most of the market wouldn't bear the cost even at the expensive end.

High quality is non-optional and the measure of quality is whether a PSU delivers the rated voltage and current and what the worst case ripple is.
MUFF WIGGLER Forum Index -> Modular Synth General Discussion  
Page 1 of 1
Powered by phpBB © phpBB Group