Power Supplies

?

PC power supplies

you are right lucifer

The main problem with using a large number of capacitors in series is that they have a tendency to explode after a short period of time. I found this out in electronics after trying to connect 4 high uF capacitors in series. Ten minutes later there was a loud explosion, and part of the tabletop was on the floor....

Did I say series?

Dc power supply

Thanks

Well its a little costly But what about this for a power supply

Last one I was using, I took all the red wires and all the black wires on the mobo connector and joined them together for each electrode respectively. Better than just using just one wire at 30A!

Tim

Eh...I have no idea what I am talking about...In Craig's link:

I assumed the double circles in pin 11 meant 2 wires, and was confused when mine had only a single wire...oops

[Edited on 12-7-2005 by rogue chemist]

Pinlayouts and schems for connectors

ATX power supply pinlayout and schems

Oh dear...

A 'switching' supply is one that uses internal switching to regulate the output. It does not mean the output is a square wave! The output is flat DC.

Switching supply topologies are used because they are (or can be ) more efficient than linear supplies. So they don't get so hot.

Quote:

Originally posted by Twospoons Switching supply topologies are used because they are (or can be ) more efficient than linear supplies. So they don't get so hot.

They are also much lighter, smaller, and cheaper once it's been designed and a few ten thousand units have been produced.

Tim

Done building the powersupply.

Quote:

Originally posted by 12AX7 Quote: Originally posted by Twospoons Switching supply topologies are used because they are (or can be ) more efficient than linear supplies. So they don't get so hot. They are also much lighter, smaller, and cheaper once it's been designed and a few ten thousand units have been produced. Tim

MIG welder maybe, but stick or TIG has a constant-current output so the voltage varies from say 70V open (zero amperes) to 20V arc (at say 100A). One solution may be to max out the current control, which would work reasonably on my stick welder, which uses a variable magnetic shunt and tops out at 225A. Using it at something less, say 50-100A should have acceptable regulation.

Reducing the primary voltage would be an ideal solution, but then you need a massive buck transformer or variac. Droooool, 240V variac.

Tim

Power supply and electronics in general

Leave the other wires alone, +5 and +12 are the only ones with enough snuff behind them to be of use. -5 and -12 are almost always rated under an ampere, so unless you have an experiment you *know* will be safe and use less than rated current, leave 'em alone.

If in doubt, you can open the case (mind the high voltage parts, they might carry a charge) and trace what wires go where. Usually, the red wires meet in a tight grove for +5V (something printed on the circuit board, or nearby such as a capacitor, should say something in that range), and likewise for the yellow +12V lines and a whole mess of black ground leads. Those are the most powerful so need the most wires.

Newer supplies may have a few 3.3V lines BTW. I forget what color that is.

Tim

So red and black, then.

I have an older supply, the better part of a decade probably. None of that ATX junk.

One more little thing. When I got the unit, there was no power button to turn it on, just a bunch of wires where a switch once was. To get the thing working, I connected the wires labled 'L' with each other where the switch would have been, likewise with the 'N'. Sound good?

Careful with that. It'll probably work, but I'd check the circuit board or wiring to make sure you aren't either swapping wires (not too big a problem, but could cause trouble to a grounded power cord), or worse, shorting both sides!

Tim

Can two PC powersupplies be hooked up in parallel to get around 40A output on the 5V line? Or would bad things happen? And is there a limit for how many could be put into parallel?(I just got access to a large number of old computer parts ). I imagine at some point they would have to be plugged into separate wall outlets though...

[Edited on 23-1-2006 by rogue chemist]

Why is it important that they both come on at the same time? Could current flowing into the PSU through the output cause 'bad things'(I seem to be overusing that phrase recently) The supplies will be on the main lines so the breaker for that room will be the regulator I guess(beats fuses, I went through way too many with my furnace). I have noticed with computer PSUs that inside they do have a fuse, although the filament looks pretty beefy, I think that only prevents major shorts as the PSU turns off when more amps are pulled from a line than what the line is rated for.

As I am using this for electrolysis I will not be doing this but for my own curiosity, can the PSUs outputs be hooked up in series(to get a higher voltage) or would that cause a short? I am wary of connecting outputs in series after an incident I had when I was little in which I thought if I conected the 'positive' and 'negative' parts of 2 separate wall outlets I could get 240V(I wanted to zap a pickle it higher voltage)...need less to say the wire I used(it was stranded Cu-wire exploded in a nice shower of sparks at the end when I stuck it in the socket...

Hmm...seeing as this is turning into some sort of super power supply I might as well add in an option to impress some AC on the DC, for those sensitive electrochemical oxidations

EDIT: Thanks Bio2, but I am afraid my source is pretty much the odds and ends, so matching brands, let alone models is not likely. I also understood very little of the terms in your post so I should likely do some electronics reading before I do this...
But a quick stupid question...what does a rectifier of the type found in the supply look like? I did a google image search and I do not see many similarities between the guts of my supply and the image result pictures.

[Edited on 24-1-2006 by rogue chemist]

Putting voltage sources in parallel is not a really wise thing to do. If the power supplies have a small difference in voltage (e.g 4.8 volts and the other one 5.0 volts), then a current flows, which can become really high (the resistance probably only is in the order of 0.05 Ohm or even less).

Another effect is that when one of the supplies powers on, and the other doesn't, then huge currents may flow into the not-yet powered device. It depends on the electronics what happens precisely, but I bet that these things usually are not fun .

Making a series connection of power supplies is safe, provided that the power outputs are "floating", relative to earth. IIRC, a PC power supply indeed has floating output, its GND (0 Volt) is not connected to earth.

I made myself a fool-proof powersupply from a PC power supply. I use the concept of current control for electrolysis experiments. That gives much more consitent results (I tried with electrolysis of NaBr, making KBrO3, by precipitating the resulting bromate with KCl). In order to keep things chaep, I use fixed resistor networks, but it works like a charm. I also put all resistors in small glass vials, reducing the chance of accidental short circuits. A complete description is on my website:

http://woelen.scheikunde.net/science/chem/misc/psu.html

It is easy to build. Only the 12V output is needed, because I use current control. The PSU allows at least 10 A of current, but the resistor network limits the available current. Of course, with other resistors, you can obtain higher currents.

Anyway, at my situation, not the PSU or resistors are limiting the current, but my anodes. If I use more than 1 A of current, then my anodes pulverize very fast.

Current limiting resistors on the output terminals

Partly for the "I have a 50A power supply" bragging rights, and partly because in my antimony separation from solder experiments I have pulled more amps than the supply could handle on the 12V line(although I have changed designs since then). I guess its mainly a 'I have the resources so why not' type thing. And I perhaps wanted to draw an arc to make a bit of carbide, but after reading the above posts the number of supplies in series and parallel needed for that would be downright mad! So I do not think I will be doing that right away...

Tumadre, you mentioned the diodes but did not say where they should go, but I am guessing in series with the output?.

So after reading the above I will start with only 2 in parallel, use resistors of the appropriate value to bring all outputs to the same voltage, the diodes once I find out where they go, and put a switch on one of the output lines of one PSU so I have the option to only have one supply worth of current. Sounds good? I will vary the amps with number of cells, resistors, electrode distance and such.

Luckily I have already built one powersupply from a single computer power supply in the past, so I am not completly clueless here. It has served me well in the past.

Now any problems with impressing some AC in parallel on the DC output of a single power supply? Of course at the same voltage. And Does "impress" really mean to just have AC and DC going through the same wires at the same time?



[Edited on 25-1-2006 by rogue chemist]

So I was at the place I get the PSU's, and I ended up with a 350W one, 35A on the +5V line. Looks like I may not have to risk the capacitors blasting through my hand. I think I'll just stick with a single PSU as I think 35A will work for most things. I really can't imagine ever needing more. I did learn some cool stuff from the replies above.

[Edited on 26-1-2006 by rogue chemist]

Power "good" sensor and load

Thanks Lambda

That link is actually quite similar to the page I followed when making my first power supply from a computer power supply: http://web2.murraystate.edu/andy.batts/ps/powersupply.htm
The only difference between the two pages seems to be the currents involved, and as such, the use of a power resistor instead of a sandbar type resistor. My current power supply has just a sandbar resistor pulling an amp, and it gets hot despite being next to fan. For a future power supply I will be sure to use a power resistor as those seem to be better intended for high current uses.

A question for the circuit gurus , please take a look
at the attached file and tell me if the modernized
and hexfet adapted " emitter follower " I have
drawn in the schematic will work as I am thinking it will .

On rare occasion I have been reading and have
encountered the term " electronic rheostat " used
in various ways for no specific circuit which of course
is never illustrated either . But what I have supposed
is that such a device would work similarly as do the
resistance wire rheostats , limiting current by their
IR heat loss , and voltage drop across the semiconductor
when it is operating in the active region .

Anyway , there are uses for these simpler circuits where the noisy waveforms and ripple generated by PWM and other switching type power supplies is unacceptable .

I have been thinking about possible ways of speed / power controlling permanent split capacitor asynchronous AC motors
such as 1/10 horsepower and less , using off the shelf standard motors , and not the more expensive inverter duty
motors as are required for PWM variable frequency drives .
The simple circuit I have been contemplating could work
well open loop and it could also very easily have the feedback loop closed with some modification and added components . Anyway it looks to me like the basic circuit should work , but I haven't tried it yet .

Take a look and tell me what you think .

I don't see how that would happen since the source has to follow the gate , the same as does the emitter have to follow the base in an NPN emitter follower . The source will
be at the same voltage as the gate which is Vref.
The idea is that a greatly current amplified Vref. appear on
the right hand side of the AC load , with the rest of the voltage above Vref . being dropped across the mosfet being
forced to act as a power resistor .

Hmmmm , please analyze and elaborate .

Please talk me through it by the half cycle ,
because I don't see it looking straight at it

Edit : see attachment for the mosfet modus operandi

[Edited on 2-2-2006 by Rosco Bodine]

Attachment: mosfet used as source follower.pdf (93kB)
This file has been downloaded 1084 times

For a few hours I have been studying the proposed circuit
and I still don't see the problem . However should you prove to be correct because of something I'm not seeing in terms of direct or parasitic paths , I have been thinking about how to remedy the problem of the barbecued mosfet so that volunteer mosfet number two has a happier time of it .
What I am thinking is to self-bias the mosfet from a local
supply derived from its own DC rails across the power bridge rectifier , using an optocoupler to control the gate , and using
Vref. to drive the transmitter side of the optocoupler . The ultimate voltage would probably be 6 volts less across the AC load , but the mosfet would be bulletproofed . I am thinking a 400 volt rated mosfet minimum , 500 volts even better , for the same reason as the 370 volt capacitor rating if you have a PSC motor as the load , the peak to peak doubling of voltage that can happen because of the capacitor .

Edit : I have been retracing the paths using different colored highlighters for the two halves of the cycle , and now I see the problem . It wouldn't hurt the mosfet , but neither would the circuit provide fullwave regulation . When the bottom AC rail is negative going the mosfet can't function as a source follower but would be in saturation at any of the higher Vref. settings . The result would a baseline shift for the AC through the load with regulation only upwards from 50% and an asymmetrical output to the load . So ....back to the drawing board

I can do better and I will sketch this hopefully better idea
and post it here .

The alternative idea which probably has a better chance of working , involves a ganged pot directly between the AC rails with each separate Vref. from the wipers driving the gates of two separate N channel mosfets each having their drain connected to the respective AC rail and the source of each mosfet connected to opposite ends of the AC load . The mosfets operate sequentially as source followers during the half cycles when their drain is positive , with the return diode in the non-conducting mosfet completing the path through the load to the rail which is negative on that half cycle . The ganged pots are connected between the AC rails in the way that the wiper of each moves towards rail voltage of the respective mosfet whose gate is supplied increasing Vref. as the pot is turned clockwise . This should provide a balanced circuit with a symmetrical AC output and no baseline shift and using fewer parts than the other idea , as well as dividing the heat dissipation between two mosfets when the voltage is set for lower levels . I have never seen this circuit I have in mind , but it seems so simple
it would have to work .....I hope



[Edited on 3-2-2006 by Rosco Bodine]

See my edit above , I found the problem and
thought of a better circuit at about the same time

Here's the simpler circuit that I am thinking
would be sure to work . Any criticisms or
comments or suggestions are welcome .


With regards to the breakdown voltage ,
I thought it was customary practice that
the manufacturers put zener protection
on the gates . I have seen the zener on
manufacturers data sheets , and sometimes
the return diode is a zener too , something
would have to be a higher rated zener than
the max allowable drain to source voltage .

One thing which would probably not hurt is
to parallel an external return diode across the
mosfet to split the heat dissipation from the
internal diode which occurs on each half cycle .
Yeah running any semiconductors in that
active region where they are in fact semiconducting
and acting as resistors is going to produce a whole
lot of heat , so big old heatsinks would be a good idea ,
even a fan cooled CPU heatsink would probably
be a good solution for this circuit when operating
at medium output voltages where the mosfets are
dumping as much heat as the motor .

[Edited on 3-2-2006 by Rosco Bodine]

@densest

Look at the attached file showing the evolution of the
circuit design which I have been contemplating , and
consider why certain advantages are provided over
a variac , such as being able to set a minimum voltage
where the adjustment begins to effect adding power to the motor . The use of control circuitry also provides locations
where logic input is possible to be applied to make the circuit behave differently in response to sensed conditions .

For example when the circuit is first powered up , the existing
voltage setting could optionally be over-ridden by external signal specifying some selected number of complete cycles of full voltage to the motor to provide extra starting torque ,
and when the counted number of full voltage cycles has
completed , the circuit resumes operation at its setpoint voltage just after the motor breakaway into rotation .

What I am looking at is simple ways of improving the performance particularly of off the shelf 1/10 hp and less permanent split capacitor AC motors , using something
better for the task than triac based sine wave choppers .
The trapezoidal waveform from the circuit I have attached
is more nearly zero crossing with its waveform being continuous to less than 2 volts of zero on each half cycle
before dropout . This should be a very quiet circuit in
terms of any unwanted harmonic effects or spikes .

IGBT's could be used as easily as MOSFET's .

Edit : I may have the left side of the range adjustment pot
drawn wrong , and moving the wrong direction .
I just drew this and am looking at it . I think
its coil probably needs to be above ......yeah I'll have to redraw it and repost the corrected schematic . I have made
some changes and really should redraw the entire schematic
in a better layout . Long day .

I'm too tired to redraw the whole thing so forgive the smudges from my erasures and corrections . Here's the
corrected schematic for where I am now .

[Edited on 4-2-2006 by Rosco Bodine]

Zero crossing firing and cycle skipping

Lambda ,

Be careful with cycle skipping or people
will say the real truth is that you are
performing burst modulation

Page 10 on the attached file may interest you .

[Edited on 4-2-2006 by Rosco Bodine]

Attachment: Triac Inductive Load Control Circuits.pdf (92kB)
This file has been downloaded 920 times

The latest corrected revision of the mosfet circuit I am
considering is first attached at the end of my fourth
post above counting this post as one . Please take a
look . I think this particular circuit will work fine and
can be matched to the characteristic of a particular motor
in a particular application by using different value
power resistors for the fixed idle current value to the
motor , to supply just sufficient power that the motor
will barely turn , windmilling under light load . The value for these fixed resistors will have to be selected by first doing a rheostat test with the motor and 4 diodes ( two in series forward biased paralleled with two more in series reverse biased ) and measuring the resistance value needed for setting the idle current . These power resistors will divert much of the heat dissipation from the mosfets when the adjustable voltage is at minimum , reducing the heatsinking requirement . The redundant return diode I have added externally across the mosfet drain to source will also halve the return diode dissipation which would otherwise be there in the mosfet . The added zeners are likely to be 15 volt and are redundant gate protection . Candidate mosfets are Hitachi 2SK1837 , overkill for sure , but the overkill translates to ruggedness at little extra cost above using a minimal device for the mission critical component and having a failure
later from too little transient immunity .

I think I will reattach the schematic file here since I am further describing the circuit here in more detail and it
may be lost in the posts above departure to other related
circuits .

There is an idea which I have wondered if it has ever been
explored by the industry regarding the possible use of
many CdS photoresistor elements paralleled as regions
to form a " power photoresistor based optocoupler " ,
a " power vactrol " if you are familiar with the signal level
vactrol optocoupler by Perkin Elmer . Such devices are
high voltage AC photoresistors which might be arrayed
in sufficient number in parallel , deposited directly on a
heatsinkable substrate and driven by high output LEDS ,
to form a high current capable full wave line voltage AC controller , driven by TTL voltage levels , and passing
the AC power with the waveform completely unchanged
except in terms of controlling its voltage . Has anyone
heard of such a device ?

Anyway the revised mosfet circuit from the earlier discussion
is reattached here . I will likely prototype and test this
particular revision attached below since it seems workable in visualization of how it should work . Now if only Murphy's Law will not discover what I may have missed , it should be all right

I am going out on a limb here , but there is always the possibility when anyone is drawing a schematic for a
dedicated circuit for a niche application , that what they
design is entirely novel , since if they could find the circuit
already published in an application note as a commonly known circuit , then there would be no need to invent it
themselves in the first place . So it is just possible that
what I have done is propose an entirely new circuit in
one of those necessity is the mother of invention scenarios ,
and the fact it is a simple circuit in no way rules that out .
So if anybody should run across this circuit already published somewhere , please let me know since it also likely that often these sort of things turn out to be that in the lands where no wheel was to be found , it was reinvented by one genius after another who are all cousins of mine

[Edited on 4-2-2006 by Rosco Bodine]

Exactly where do you expect blown junctions and why ?
And who cares about dumping heat and " wasted power " from smoothly controlling a sub-fractional horsepower motor
when you don't get something for nothing in this case ,
and the wasted heat amounts to about what is dumped
from your computers CPU heatsink right now .....that's
wasted power too , but very necessary to get done
what business is at hand . All in all the waste is less than
what is dumped by the average desk lamp , and that waste
goes away completely as the voltage setting is raised to
maximum . The heat dumping only occurs at the lower
voltage settings .


When it comes to the matter of active closed loop speed regulation , there is a method which is fairly simple to implement to provide for fine control of the speed when
there is not a great variation of the load , perhaps in the range of plus or minus 10% . The method involves eddy
current braking being applied as a parasitic load to a motor
to increase its slip and reduce its stable rpms at a given voltage . If you have two iron core inductors with their
airgaps widened sufficiently that the opposite edges of an aluminum disk on the motor shaft is travelling through the airgaps during rotation , the magnetic field through the gap induces eddy currents in the disc and produces a torque loading on the motor which varies quadratically with rpms or with the strength of the field which may be varied by the current through the electromagnets . There is some inherent
speed regulation present with this sort of parasitic load ,
and the effect can be increased by active control of the current through the electromagnets , which can decrease or
increase the torque load on the motor which varies its
slip speed and rpms accordingly , even if the voltage to the motor is held constant . This is similar to the scenario where
a car with an automatic transmission is stopped on a steep uphill grade and a little throttle is applied sufficient for the car
to roll uphill , but a little pressure on the brake pedal holds
the vehicle in position ......yes power is being " wasted " but
for very good reasons which the situation requires , a balancing of forces which allows the vehicle to only roll forward when the traffic light changes and pressure on the brake is released , with no chance of rolling backwards and
smashing the grille of the police car stopped behind

Now that's regulation !

[Edited on 4-2-2006 by Rosco Bodine]

Bah... Dig out a switchmode power supply chip, a pair of MOSFETs, rig a ferrite transformer (all of ten minutes winding one) with DC restorer for gate drive, rectify the line voltage then chop it, add a filter and you've got a PWM class D amplifier, 95% efficient or better, and if you generate your own drive signal you can get any frequency, amplitude or waveform you want.

For something this small, pffbt... but anything over a half horsepower, this is how it's done.

Tim

For those really critical range hood ventilator fan
speed settings when only the best will do ......

make this little gem the powerhandler and the manufacturer
will throw in the dedicated workstation with user friendly
interface for free

http://www.ballantinelabs.com/bli1620a.htm

Then again , when it's a five dollar motor ......
there just has to be an easier way

Actually my first thought on this project was to open up
an inexpensive uninterruptable power supply and
see if it would be possible to easily adjust the voltage
output from the inverter .

The output would already be well filtered sinewave
so it would simply be a matter of being able to adjust the output voltage . The input side is already there for keeping the battery charged , but of course the battery isn't needed for the use to which the UPS power stage would be adapted .

[Edited on 5-2-2006 by Rosco Bodine]