Benchtop PS build woes. - Page 1
Forum section: electronics / beginners

author: TheSniper
author_rank: Contributor
timestamp: May 30, 2013, 12:36:04 pm
content: All / Dave,Im endeavoring to build a replacement bench top PS.Primary reason: my old one while it works. Lacks much current and I figure its a great project to get my head in the game too.what I have:I have several DC PS laying around. their old server switched PS tune d in to about 12 V. (Inside Pots will allow for adjustment up to about 15V safely) and go up to about 60 amps or so as needed.Im totally happy with that range. I would like to add some features to these units. likeVoltage and current control. as well as a few analog or digital read outs.I was going to use a bank of 2n3055 controlled by a 2n2222 or similar then controlled by a LM723 but Im pretty sure it wont give me the precision control voltage or current individually I want directly.I stumbled onto your 2 part Lab power supply posts (great job ). while they were very nicely done they dont exactly lend their selfs to the range Im looking for. say 0 to 15V and 0 to 60 amps. or on the low side say 2-3 volts would be okay too.I have read lots of posts regarding Benchtop PS's but most are say 0-12 or 3-24 with currents around 1 to 2.FwiW, I was going to start with a MOT (wound myself), Bridge rect and a bank of Caps as the primary supply, (then the above)But then I said Heck I have a stack of Hi current PS... why not use them and add the Control circuits.any chance you could lead me in the right direction for a base?Im on Info overload in regards to what base path to stay on.TIASam

author: Paul Price
author_rank: Super Contributor
timestamp: May 30, 2013, 11:18:50 pm
content: Just between me and the god of lightning next door, whadja goin' 2 do with 60-amps?

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: May 31, 2013, 07:06:09 am
content: Frankenstein

author: TheSniper
author_rank: Contributor
timestamp: May 31, 2013, 04:38:43 pm
content: Well on the big end of the PS I was hoping to fill the need for another project Im working on Anodizing.to do any anodizing one requires a PS. and depending on the size or (qty x size) of your parts basically resultsin the need for a hefty constant current PS. if you were doing the same parts over and over again you could build asingle stand alone one voltage,current PS. But Im always in need of different size parts. This means Variable.And while Im not doing any Anodizing. I could enjoy this PS as a reg PS for other projects.-Sam

author: Paul Price
author_rank: Super Contributor
timestamp: May 31, 2013, 04:58:08 pm
content: If you go the linear way, you could even use it for a desk or a bed(add a mattress), it will keep you warm while things bubble and anodize themselves silly nearby.I would go with a single MCU acting as a power supply SMPS control circuit, controlling several discrete power MOSFETs acting as constant current regulator by setting output compliant voltage to force the required current. Several MOSFETs that could be switched in sequence and in and out to meet the current current requirements and to keep the individual size of the switching inductors and schottky diodes small and cheap and easy enough to buy or salvage. I have done this successfully before but I miss the bed upon the linear scheme. Works only in fixed, not-so-quick-varying-load situations like with an anodizer.

author: c4757p
author_rank: Super Contributor
timestamp: May 31, 2013, 05:00:54 pm
content: Quote from: TheSniper on May 31, 2013, 04:38:43 pmYou'll find it much easier not to combine the "holy shit that's a lot of current" supply with the general purpose supply.

author: TheSniper
author_rank: Contributor
timestamp: May 31, 2013, 05:25:43 pm
content: Quote from: c4757p link=topic=17369.msg240031#msg240031 date=137[quote author=Paul Price on May 31, 2013, 04:58:08 pmPerhaps I should clarify. say Im going to do a job that requires 12 @24amps. I would like to be able to get close to that setting. Done, next job 15 v @30 amps. done.... etc..Im not an expert but Im sure that the goal is to have the PS be able to lock down on a fixed Current situation. But from job to job be able to vary the Lock down current.Sam

author: TheSniper
author_rank: Contributor
timestamp: May 31, 2013, 05:38:09 pm
content: Quote from: c4757p on May 31, 2013, 05:00:54 pmCP4757, Yes, I would agree But I dont intend on building a dedicated PS for each job I embark on too. So, to some degree it needs to be variable.say like this unit.http://www.caswellplating.com/electroplating-anodizing/power-supplies/rectifier-50-amp.htmlAlso I found this unit another user made.https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxiZXR0aW5hbmV1bXJ5cnxneDo1ZWMyNWUzNTliYWYyMDRlThoughts?.

author: TheSniper
author_rank: Contributor
timestamp: May 31, 2013, 06:01:57 pm
content: Quote from: carbon dude oxide on May 31, 2013, 07:06:09 amFrankenstein would be easy if I were smarter.Most of my projects end up being mostly aluminum, Which end up getting polished or painting or worse yet nothing.So for me the anodizing is a totally new project. Ive been reading up following for several months now and am trying to gather upa reasonable arsenal of tools to throw at it.Some of my projects can be seen here.http://thesn1per.blogspot.com/if you look at most of them their aluminum based. and being able to anodize some of them would just be too too cool.SamFrankenstein will have to wait!

author: Paul Price
author_rank: Super Contributor
timestamp: May 31, 2013, 06:34:44 pm
content: And you could also use a 60-amp version to instantly vaporize any other projects you are working on.

author: Christopher
author_rank: Frequent Contributor
timestamp: May 31, 2013, 06:40:09 pm
content: Build it and try it out! Only way to learn!Pd=(Vin-Vout)*I Therefore lower voltages will make it really hot.Not on a 40A load at first though.. don't want to blow up your house! Then we have the chicken-egg situation of how to try this with you having no CC supply in the order of 100A.

author: c4757p
author_rank: Super Contributor
timestamp: May 31, 2013, 06:44:22 pm
content: Quote from: Paul Price on May 31, 2013, 06:34:44 pmIf you insist on using a 60A power supply for general purpose use, I'd suggest a switch that limits the maximum output to 3A or so, and a nice, large and bright LED that blinds you when it's set to 60A.My opinion is that power supplies should be either "always dangerous" or "never dangerous". If it can hit 100V, it shouldn't go below 50V, and if it can hit 60A, it shouldn't go below 3A.

author: LaurenceW
author_rank: Frequent Contributor
timestamp: June 01, 2013, 10:44:44 pm
content: Yeah, C4757p, an LED strapped across a 24V 40A power supply oughta be bright enough!For a short while, anyway... BLINDING FLASH=High Current Power Supply ON!Sam, this is an interesting project, but i am inclided to agree with others about the dangers of trying to build a one-size-fits-all solution. A supply capable of delivereing tens of amps won't be easily and safely controllable down at hundreds of milliamps, I'd suggestDo you need control of the current, voltage, or both? If you are talking about significant power, here, can you not get away with a Swithed Mode power supply? But an SMPS is not the best place to start a complex high power project, if you don't have previous experience, I'd respectfully suggest. I might look for a prebuilt controller, and then build a case, metering, sockets, etc., to suit my project.And be careful! Just because it's 12/24V, doesn't mean it's "safe", if there are tens of amps behind it. I once saw a telecoms engineer weld himslef to a piece of equipment with exposed 48V power supply bus bars, with his metal watch strap... which he shouldn't have been wearing, of course.

author: Paul Price
author_rank: Super Contributor
timestamp: June 02, 2013, 05:40:10 am
content: You are a little vague about the Server Switch Mode Power Supplies you have as a core for your 60-amp power supply.Are you sure they each can output 60-amps? At what max voltage?I must know what you are starting out with to go further.

author: metalphreak
author_rank: Frequent Contributor
timestamp: June 02, 2013, 08:18:37 am
content: They would be 12V and there are quite a few server power supplies that go beyond 1000W (that's 80A right there).

author: Strada916
author_rank: Frequent Contributor
timestamp: June 02, 2013, 11:07:29 am
content: Easiest way to control all that current is to use an electronic dummy load. You would contect it in series to the load in question. The 1 amp one Dave built would do your low power grear. I have not tried this yet but it's one of my ideas to try out. Otherwise buy yourself a kit psu. Such aswww.altronics.com.au/index.asp?area=item&id=K3218

author: TheSniper
author_rank: Contributor
timestamp: June 03, 2013, 06:47:49 pm
content: All,It seems I have underestimated how easily I could build a power source for my anodizing project.also its a shame I have 4 to 6 Server class PS lying around that seem to have the voltage/current ranges built in.I was thinking it would only be a matter of building a secondary voltage/current control circuit.Not that I need another project, perhaps I should just source a pre built unit. I will ask one more question thoughI see a Power device commonly in the plating business called a "power/current rectifier" here is one example of such a beast.http://www.caswellplating.com/electroplating-anodizing/power-supplies/cc-cv-rectifier-0-30v-30-amp.htmlAgain thanks for all the input.

author: Paul Price
author_rank: Super Contributor
timestamp: June 03, 2013, 08:14:37 pm
content: I can see the practical way of using several small switchers(12 modules min., but not more than 21 total, andeach only 1 1/2 by 3-in module in size or even smaller)each to deliver approx 3 to 5 amps to the load. Cost would be low if you can find the magnetic cores for the switchers cheap enough. The IC's are cheap enough to accomplish this).I can see the cost per each 3-amp or 5-amp module below $5 to $10 US if you buy the diodes, capacitors, reg IC chips and inductors in lots of 10 or more or have a source for surplus toroidial cores such as from discarded power supplies form computer PC's.It wcould be not so hard to switch in or out each module with a MCU controlling the operation.As current requirements increase, you can manually enable(for safety) or MCU automatically enable more switchers to each contribute their fair share to the output load demand.This means you could build something like this into a box much smaller at a cost much cheaper than that big DC Rectifier boat anchor power supply. Even though it just many hundred US bucks for a pre-built "DC Rectifier" unit, it would cost equally as much to ship it anywhere as it probably weighs 60 kilos.It is simply a matter of redundancy and setting voltage and sensing current for each supply, something a small MCU can do easily enough.Even if 21 modules were necessary to accomplish this task, you could switch them in and out in banks of 3 or more to accomplish this task to step through load requirements 9amps at a time to accomplish the job at hand.You could adj. the current limit in this way with just a few tiny switches and two pots to set voltage and max current.And all this with not so much money spent, not too much trouble to build and not so much power wasted trying to accomplish this with a linear mode solution you must buy. It could fit all into a much lighter, smaller box. Probably the finished unit would not weigh more than 20-30 lbs, depending of the weight of the Server Power Supply unit contributing to this total.A great advantage of this approach is that you would have a modular construction that you could easily replace any defective module quickly if you have any repair to be made and this monster could be so safe to use with just one 3-amp module for any small power application you need a supply for.I can easily visualize all 12 modules ( just 1 1/2-in tall) each standing vertically next to each other on a breadboard or on a printed circuit.What's more this project can be built in steps, perhaps adding just a fraction of the modules to the project each week, while having a working power supply with only the first module installed.The whole thing could fit comfortably into a small desktop low-profile sit-down computer case recycled from the bit bin.Be sure to add at least one 3-in mini-PC power supply fan to cool the approx 20 to 30 watts max of wasted heat generated at full 60 amps power output.

author: TheSniper
author_rank: Contributor
timestamp: June 03, 2013, 08:50:41 pm
content: Paul,Thanks for the post/Suggestion.So what I hear you saying is I would/could use 1 or more of my Server PS and then modularly turn off or on each Module or bank of modulesto sneak up my current requirements? how would I control the over all voltage? or would this be something at the modul level?I suppose a modular schematic would be a great help. and then for each add'l amp or bank of amps I would just add the necessary amount ofmodules.Using this idea would the final voltage be controlled at the end of the line or in succession with the modules? I understand the Current grows with each module turned on.Sam

author: Paul Price
author_rank: Super Contributor
timestamp: June 03, 2013, 09:03:10 pm
content: The deal is you can't get more voltage out than the SERVER PS can put into this arrangement, but the approx. 0-12V out can be perfect PS for low voltage hi-current anodizing work you want to do.Attached: A schematic tested of one raw SMPS power suipply module. Only the feedback pin circuit needs to be cut and connected to a comparator (described below) and the IC's enable pin must be tied to a output pin on the MCU controlling this game. R2, the ouput adj. control is removed and replaced by a connection to a comparator output(see below for details).The voltage in would not be the 55V in nor 59V out in the attached using the IC shown 2576HV model, just use the LM2576-adj cheaper IC and you feed into all the modules the lower output of the Server Switcher PS maxed out to it's highest voltage (>13V?? tweaked by you.)You feed each modules power supply output voltage to all + comparator inputs(though a 1k resistor for protection) . Use one LM393 comparator output to each feedback pin on each switcher IC on each module. Tie the comparator output to a 10K pull up to +5V and connect the comparator output to the feedback pin on each IC on each power supply module. The control voltage is the same for all modules and fed from a single op-amp with a gain of 2.5 to set the desired voltage output voltage at the comparator - input pin. You get two comparators per LM393 and 4 for each LM339 LM2903. It is simply a matter of enabling the shutdown pin for each IC on each module and using a common control voltage up from 1.2 volts for each module or ganged team of modules to switch modules that are all commonly connected to the output. With a simple -2V regulated power on the control op-amp neg. supply pin you can control all outputs down to 0-volts with a high degree of regulation.If you use wire small enough (20 AVG) from each output to the monster 60-amp banana posts at the output, each output module will automatically balance its load against all others (keep all output leads short and the same length from each module to sense resistor and then to flat wide copper to connect to the big banana + term. output to accomplish this.)The MCU programming is not very complicated to accomplish this. A 40pin MCU uses its output pins to enable all the modules becauseeach switcher IC has a MCU logic level enable pinA single pot connected to an A2D input on the MCU can be used to enable each module as required according to current setting by the pot and another pot is used to set the desired output voltage. As an alternative, if you have a PWM output pin left over, you can easily set the output voltage with PWM and a simple RC integrator into the +input of the x2.5 buffer amplifier feeding the comparators controlling output voltage of all modules connected together. In this way you can convert a current-limited power supply to a precision constant-current high-compliance power supply or switch automatically between modes according to load changes. A second A2D input scaled with a voltage divider would give the MCU feedback of the output voltage and a third with a current reading fed back from the current measurement amp would be needed to accomplish constant current/constant voltage operation.Each module would be switched in or out of the power loop by the MCU controlling the inhibit pin of the IC.You can buy LED/CMOS 3 or 4 1/2 digit display for lest than $5US on Ebay to hook up to the MCU or just direct to the main output with an op-amp(for current) to monitor output voltage(directly with a scaling resistor). It is easy enough to add just .a .01 ohm current sensing resistor to each modules negative return, take that signal to a cheap(Av=150 gain) set op-amp and get the current output for each module, or each gang of modules, to get a signal to be fed for the MCU to sum up all the currents and display the correct result,It is much less wiring and op-amps and circuitry though, to use just one .001 ohm shunt and one op-amp to do the current sense of monitoring the voltage across a single sense resistor connected to the output + or ground return to get a current reading. The .01 multi-resistor sensor method on each module gives you a highly more complicated, but diagnostic view of each switcher's operation.You can just use one large .001 ohm sense resistor (or one made easily from 10 .01 ohm SMD resistors in parallel) that is connected to the + or -ground output of all the modules connected together to a flat fat piece of copper and with a single simple op-amp to magnify this reading and using a 3-position rotary switch to select the op-amp gain, you can select to see full scale reading of 1-amp/10amp/100amps.One or two 40-pin DIP MCU packaged chips, so easy to work with, like the PIC 16F887 that has 12 A2D input configurable pins for the measuring jobs would do all the jobs cheaply for both control and monitoring of the modules.

author: TheSniper
author_rank: Contributor
timestamp: June 07, 2013, 12:30:38 am
content: All,For your approvalOr higher resolution image can be found here.http://thesn1per.blogspot.com/2013/06/ps-schematic.htmlI did have a few questions:1:The Gnd tie points. When and where do I isolate the Incoming PS from all the other?So basically 2 sets of Ground points..(right?)2:How do I decide on the Cap sizes? or is it a trial and error thing.3:How do I size the Inductor? and type correctly.4:What would be the best scheme for fusing properly.5:the MCU controls the current... Hos does the voltage(adjustment) come into play?6: On the LM2878chips the C Boost (pin 3)does notget used?7: Do/will I need to ground the heat sinks for the LM2878 chips?8: is it safe to source the 5V+ from the Main Power supply (pre regulators?) or should I incorporate a stand alone Regulatorfor this purpose?9: on the Comparators. Does it matter if I use 2,4 or any combination of them?I hope everything else is correct.I left off things like the1:MAIN PS on off switch.2:any power leds' etc...3 etc... To be determined.

author: Paul Price
author_rank: Super Contributor
timestamp: June 07, 2013, 03:05:53 am
content: Download a free schematic drawing software tool that doesn't print out results on a black background. Hard to read and terribly expensive to print on any printer.I urge you to carefully read aka study the excellent design info on the LM2678 data sheet before asking questions.The best questions become best answered when the answer is already almost known.A well-understood question is often gifted a clear answer.

author: TheSniper
author_rank: Contributor
timestamp: June 07, 2013, 03:11:02 am
content: Will Setup for White background.... and post new pics.

author: TheSniper
author_rank: Contributor
timestamp: June 07, 2013, 03:33:30 am
content: Okay, Hopefully its looking better now.? Uploaded hi res white background images to site.here...http://thesn1per.blogspot.com/2013/06/ps-schematic.html

author: ftransform
author_rank: Frequent Contributor
timestamp: June 07, 2013, 02:13:29 pm
content: Quote from: LaurenceW on June 01, 2013, 10:44:44 pmwhat happened to him? Did he lose his hand? Or did it just weld him down and blow the fuses?

author: TheSniper
author_rank: Contributor
timestamp: June 07, 2013, 03:59:14 pm
content: Quote from: LaurenceW on June 01, 2013, 10:44:44 pmLW,Although it would be a plus. the on the lower end of the scale. if it stopped at 1.0 or heck even up to 4.5 at it lowest setting I could live with that.Voltage and current need to both be adjustable.I hear you on the safety factor. and appreciate the reminder , BUT. theirs more everyday things that'll probably get me first.!Sam