My Adventure:  To design and build a linear 13.8Vdc / 80Amps (seeking advice)  - Page 1
Forum section: electronics / projects

author: FJHookah
author_rank: Contributor
timestamp: May 08, 2016, 05:33:52 pm
content: Hello,I'm seeking your advice and expertise for a new project that I've recently started. My objective is to design and build a very high quality, very safe, very stable 13.8v Linear DC Power Supply that can sustain up to 80 Amps at a 50% to 75% duty cycle. At this stage, I've pieced together a design based on old schematics found while cruising the web that makes use of the LM723 voltage regulator. I've upgraded various components in support of the high current requirement of this power supply. For example, I'll be using a single 2N5686G to drive 10 output stage 2N5686G Series Pass Transistors. Each output transistor is capable of 50 Amps and a breakdown voltage of 80Vdc. Yes, this is perhaps a bit overkill, but it also means that driving the power supply at the full spec of 80 Amps is only pushing the 2N5686 output transistors at approximately 16% of their maximum which hopefully means it will be fairly easy to keep them properly cooled without the need for 75db of Fan noise. The output current will be load-balanced using 0.047 Ohm 12.5W resistors (chassis mounted w/heat sink casings) to ensure each transistor is equally sharing the load. My hope is that by doing it this way, it will help improve the long-term reliability of the power supply.Let me share a little about the build objectives and key power supply features:The primary use is for my HAM Radio hobby. Granted, I do not need an 80 AMP 13.8V supply for my hobby, as I'm typically only needing up to 50 AMPS, but I wanted to challenge myself and learn at the same time. To be honest, there is a little bit of a cool-factor in building such a beast of a linear supply the right way, including applicable safety features. I currently use an Astron VS-70M that struggles to drive a VHF amplifier that I use quite often. The Astron supply is supposedly capable of 56 AMPS full duty-cycle, but trust me, it would require liquid nitrogen to keep it cool at that output level. I want to build a power supply that wouldn't even break a sweat at 60 AMPS full duty-cycle.Design criteria - 13.8V, 80 AMPS at up to 75% duty-cycle, soft starting, over voltage protection, current limiting, short circuit protection, remote voltage sensing and automatic passive and active cooling fan control (with removable and cleanable dust fan filters).The power supply needs to look as GREAT as it performs. I'm strongly considering using a Chassis sold by diyAUDIO that has large external fin heat sinks which both sides of the chassis completely. It is in a 4U size chassis and 400mm deep. It's a large chassis, yes, but the size is required for the Transformer, filter caps, etc. The company will also perform ALL of the CNC machining if I submit a CAD file to them. This means that it will be professionally built and drilled / CNC'd, with black anodizing making it the best looking DC supply in Texas! (smiling).I'm not as concerned with the cost to build this power supply as I am building it correctly, to spec, with rock-solid protection features as noted above. For example, the chassis alone will be approximately $550, the Transformer was $225 shipped, the pass transistors were $154, the balancing resistors were $65, the filtering caps were $206, and the bridge was $68. This will end up costing approximately $1400, which is completely ok with me.Here is a listing of critical components with their specs that I've selected and sourced already:AC power entry: TE Connectivity filtered module (with built-in rocker switch)AC power entry fuse: 13 AMP push-button breaker (metal casing)Transformer: Antek 1500VA 17V (they are building this one for me, as it is not a common size)Bridge Rectifier: IXYS 160 AMP, 1200 V. Max surge = 2800 Amps, Vf = 1.43, power dissipation = 300W at 25C, screw mountingFilter Caps: Vishay 0.082F / 50V (quantity 2) for a total of 0.164F filteringPass Transistors: 2N5686G (quantity 11, with one used as the Driver). 50 AMP / 80VCurrent-balancing resistors: Vishay 12.5W 1% - 0.047 OhmsQuestions and some of my current challenges that I'm struggling with:Aftter the bridge rectifier, there is a momentary switch that will be placed on the front panel of the chassis. The idea is that the switch will open the gates, so to speak, for the inrush of current caused by having such a large transformer and huge filtering caps. I need a way to adequately 'slow-start' this beast. What are your thoughts?I've considered going with a parallel bridged rectification design instead of using just one bridge, but am I right in thinking that there would not be much benefit from going with a parallel bridge setup? Should I stick with just the one 160 AMP bridge or consider two in parallel?I've ordered the Transformer with 17 VAC on the secondaries, assuming that the post-rectification process will yield me approximately 24 to 26 'no-load' raw DC volts. With what I've read and researched thus far, the heavy loaded DC volts will sag to approximately 16 to 17 due to normal transformer load sag expectations. Is my assumption accurate; what are your thoughts?I'm attaching rev1 schematics with hopes that this project may peak some interest such that you feel encouraged to offer advice, share your technical expertise, and perhaps even follow me along this exciting journey. There's no doubt I have a lot to learn, and I'm open to your harsh critique, although if you throw a little humor in once in a while that would be great too!Thanks!Steve

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 08, 2016, 05:47:56 pm
content: Why not a dual mode linear/switcher where the switching part is only active in transmit mode?

author: nctnico
author_rank: Super Contributor
timestamp: May 08, 2016, 06:07:23 pm
content: I agree. I'd get a 12V switching PSU from Ebay, turn up the output voltage a little, add some post filtering using common mode chokes and extra capacitors and be done with it.

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 08, 2016, 06:59:15 pm
content: Quote from: FJHookah on May 08, 2016, 05:33:52 pmJust a minor point, but the specs of the transistors is not going to change what you are going to dissipate ((rectified voltage-13.8V)* Amps), so the cooling job will stay the same.I think you want S2 parallel to R1, not in series.Also, what is the SCR going to blow when it triggers except R3?Are you measuring the current for one transistor and hoping that it will be the same for the other 9?

author: Towger
author_rank: Super Contributor
timestamp: May 08, 2016, 07:06:50 pm
content: When money is no object. Where is the fun of hacking a old rack/blade server PSU up to 13.8 when you can build a 4U beauty which hardly makes a sound.

author: German_EE
author_rank: Super Contributor
timestamp: May 08, 2016, 07:18:56 pm
content: OK, some construction notes from someone who really has been there and done that, although mine is 120A and a two man lift.1) A separate transformer and rectifier driving the 723 is a good idea because it keeps it more stable and keeps load fluctuations out of the regulator circuit.2) Decouple everything, especially around the 723 and the bases of the power transistors. Ferrite beads on every base connection is a good idea as well.3) Slow start circuit, run a 50 ohm resistor in series with your mains supply and put a pair of relay contacts across it. Drive the relay coil with the voltage across your main bridge rectifier. This will give a soft start circuit that remains in circuit for a fraction of a second until the contacts close but those contacts and that resistor need to be BIG.4) If you can lift it on your own it isn't big enough.5) Dump that 10 ohm resistor after the bridge rectifier, at 80A it will (in theory) drop 800V and generate 64KW of heatGood Luck!!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 08, 2016, 07:48:24 pm
content: If cost is no object, I suggest hiring a Consultant (nudge, nudge..) to fully review the design and ensure it's right the first time...Tim

author: John Heath
author_rank: Frequent Contributor
timestamp: May 08, 2016, 08:50:06 pm
content: I had a thought. An off the self lead acid car battery will act as both voltage regulator and filter condensers. All that is left is an off the self battery charger capable of a 40 to 50 amp charge. With the main job taken care of superficial window dressing should never be underestimated. First appearance is everything. I would suggest a flat black front face , it screams testosterone , with 200 AMPs in bold white print. Follow this with a PIC to display any irrelevant variable that comes to mind to dazzle and amaze the technical staff. Internal temp , outside temp , heat sink to ambient air difference temp , fan air differential pressure with estimated hours to air filter change. There is no such thing as too much information , more much like money is always better. I am being humorous about this but there is a grain of truth here. Sound engineering is not always enough. I little superficial razzle and dazzle can go a long way to sell a project.

author: Seekonk
author_rank: Super Contributor
timestamp: May 08, 2016, 09:32:03 pm
content: There are nice power supplies out there like Xantrex XTR7.5-80 and other series cheap on ebay, <$100 shipped. Just place one of these in series with an unregulatd 7-9V transformer/capacitor supply. Voltage sense on the outside of the circuit, manual shows how.I have an old 7.5V 150A linear supply I'd love to get rid of. Looks like an easy conversion to full wave bridge the transformer, new caps and just some minor circuit changes. Thought of doing it years ago but it is just so damn heavy.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: May 08, 2016, 10:33:35 pm
content: I bet you can design something really nice if you put the thought into it.Since you are going all out have you thought about water cooling? It sounds like you have a fairly serious installation and you can redirect the heat somewhere else this way. And have a more unique piece of equipment. Granted, then you need to deal with pump electronics etc, but keeping a comfortable work environment will be worth it potentially.I would add a inrush limiting circuit. For this class of supply I would do a 555 timer + relay to short out a current inrush resistor once the capacitor banks are saturated.You might also want to put in a current limiting circuit on the output that also shorts out, so the load that you connect to it will also not experience a surge. I believe capacitors are just as stressed discharging at charging. If you connect a low impedance load do it, do you want 80 amps to shoot right out of your supply ? This you could do with a "full current" interlock, i.e. monitor your meters and disengage the current limiting, you could do this in steps.You could also make a fast acting anti short circuit, which would short the supply internally if a fast current transient is detected.I would also put panel meters on the current and voltage, possibly dial indicators to keep it simple and low noise.I would also put in thermal protection, i.e. a thermal disconnect if the heat sink over heats. I don't see an output fuse.you probobly also want a mains supply indicator (neon/LED).make sure your fuses are easy to accessalso, how are you routing the current? bus bars?also, i would add a big ass disconnect switch (read about EMO switches)

author: FJHookah
author_rank: Contributor
timestamp: May 08, 2016, 10:37:51 pm
content: Op here....I just now read through the responses thus far. Thank you for the thoughtful comments and suggestions. I knew posting this thread would prove valuable for the project. To the whiteboard I go, thanks guys!Steve

author: sarepairman2
author_rank: Frequent Contributor
timestamp: May 08, 2016, 10:43:25 pm
content: also with this bad boy you probobly want to add a remote disconnect option.I.E. the ability to design equipment that you hook up to it to tell it to shut down with a simple fault signal. i would do an optically isolated TTL or whatever interface.It does not need to be complicated, it would just help de-enegerize things to limit the scale of electrical fires that might come about with high power RF shit, so you don't need to design your other equipment with heavy duty relays and stuff. even if you do, you can have super visor circuits and redundancy (which you should have messing around with 80 amps!)also think about how to route ground in your rack.if you want to be fancy, you could add a fiber optic disconnect bus, so that on your other equipment faults can be indicated by simple LED's which would shine into your power supply, terminating the output.This is what you should probobly do if its a RF noise heavy environment, rather then TTL on the remote disconnectthen other things could just have fault LED's routed to fiber optics. simple to design, reliable circuits.

author: AF6LJ
author_rank: Unknown
timestamp: May 08, 2016, 10:51:26 pm
content: Keep us posted on your project.Most everyone has already mentioned what I had in mind.The only other thing I would do is put a 100 amp fuse between the last filter cap and the pass transistors. If something goes wrong at these current levels it can get down right destructive. You have enough voltage overhead that you can afford to loose a couple hundred millivolts in a fuse / fuse holder. Better safe than sorry....

author: Jebnor
author_rank: Regular Contributor
timestamp: May 08, 2016, 11:05:35 pm
content: With regards to your soft start option, take a look at Daves teardown of theIt shows one soft start option in there.

author: xrunner
author_rank: Super Contributor
timestamp: May 08, 2016, 11:11:26 pm
content: Quote from: FJHookah on May 08, 2016, 10:37:51 pmSee, I told you you'd get some good suggestions!(Steve is a ham that lives in my area and frequents a local repeater - I suggested that he post his design here for the EEVBloggers to review

author: FJHookah
author_rank: Contributor
timestamp: May 08, 2016, 11:46:08 pm
content: Quote from: PA0PBZ on May 08, 2016, 06:59:15 pmR1, perhaps not working as I'm thinking it should in series, is supposed to help slow the inrush of current when S2 is actuated. Thoughts? Another gentleman responded with a suggestion to bump up that resistor to 50 Ohms, but it would need to be fairly large in order to tame the inrush apparently. I think I'll make that edit in the schematic now and see what we think.Regarding the SCR; that's one of my design roadblocks.... I'm not quite sure how I want to effectively shutdown the PS once D5 conducts and fires the thyristor SCR1, but as it stands if the load voltage hits 15 volts (creating an over voltage scenario), the SCR short circuits C1 through R3. That's all fine and dandy right, but what I have to add to the circuit is a method to prevent C1 from recharging on the next subsequent rectifier cycle, which would then effectively shut down the PS as desired. I've seen a relay used in a schematic like this one; I'll edit the schematic to get your thoughts on its practicality and function. I'd appreciate your feedback again if you don't mind.Regarding current measurement; when the current across R21 reaches 8 amps (which is an indicator that the power supply is generating close to 80 amps total), the voltage from R11 and R12 is approximately .9 which is tapped from R11 to bias a transistor in the LM723 regulator chip, thereby making use of its current limiting function. But yes, you're absolutely right to notice that I'm only taking measure from one of the 10 pass transistors. I'm not sure how to design the circuit to take individual measurements from all 10 and run that through a comparator of sorts which might then assume the duty of feeding the LM723 .9 volts to turn on its current limiting function? I'm wide open to suggestions on improving the functionality of current limiting for this design. Thoughts?

author: FJHookah
author_rank: Contributor
timestamp: May 08, 2016, 11:54:02 pm
content: Quote from: sarepairman2 on May 08, 2016, 10:33:35 pmOutstanding suggestions; you've just given me another few days worth of work and I love it, haha.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: May 09, 2016, 12:09:56 am
content: yea finish a design then give yourself some time off to do something else for a while so you can think clearly about it again, your starting a complicated project, this class of design you could easily have an employer pay for your work if they had the need.my other suggestion is to put significant thought into the wiring of the thing, i.e. figure out what kind of crimps/connectors you are going to use, figure out how to route wiring, wire gauges, etc.no one thinks of this, but the "interconnects" design is actually a skill in itself... the design only begins on the circuit board.. then you have complicated systems engineering.i suggest looking at WAGO/weildmuller for connectors.and i suggest learning about DIN RAIL mounting, and spending some time looking at how to do cables right (i.e. strain reliefs, zip ties, shrink tubing, cable covers..i suggest big ring lugs on high current carrying wires... then you can use big ass bolts as connectors.think about how to guard things against short circuits (i.e. covers, enclosures, fully shrowded connectors).you will also have to use proper torque if you do this...this project may cost you alot more then you think if you want to do the systems engineering professionally... crimp tools for instance... maybe brazing bus bars even.. torque wrench or possibly turns measurement on ring lugs.. proper grounding..be sure to properly ground your chassis..putting together what i like to call an experiment and designing a piece of lab equipment are two completely different things.Once you have some know how you can make your experiments nicer, but making a nice piece of servicable test equipment is an art in itself, even if you have to do zero PCB level work.programmers got it easy, man.scenario: you need to do work trouble shooting it. how do you prevent it from blowing up if you accidentally drop a screw?you might also want to include some test points in shielded locations that you can safely measure something for trouble shooting.i have seen long time engineers argue for a LONG time about things that a hobbyist would just consider non issue.all this may seem like over kill, but if you ever want to actually design an industrial product this is what you should do. of course, there is no harm in making a piece of shit that is convenient, I do it all the time, but i would not necessarily leave it unattended or rest easy around it.also, do not design for compactness in mind. Compact things go through many many revisions etc. if you make it compact you will just be cursing yourself later when you find something that you want to change (and you will).

author: sarepairman2
author_rank: Frequent Contributor
timestamp: May 09, 2016, 12:24:45 am
content: However, on the plus side, you are the financier for your project. This is a HUGE plus.If you are willing to spend money then it is much easier to get a solution, plus you have much less frustration to deal with. In a company your beautiful design will be gutted by bean counters and you will get frustrated when you design to this level, then something is denied, making half of your "robust decisions" irrelevant due to the decreased reliability/performance/etc as a consequence of the "financial adjustment"and you can't get into a philosophical design argument with other engineers (like i often do)... so long you don't let the eevblog forum get into your head...its just a hobby manalso since its an RF supply, you might just wanna put a actual POWER meter, like watt meter on the thing, so you can calculate efficientcies or some shit easily

author: FJHookah
author_rank: Contributor
timestamp: May 09, 2016, 12:34:40 am
content: Quote from: sarepairman2 on May 09, 2016, 12:24:45 amWell stated. If only I had a neighbor like yourself willing to drop by and sit at my workbench with me daily until I crack this nut

author: FJHookah
author_rank: Contributor
timestamp: May 09, 2016, 12:36:53 am
content: Quote from: Jebnor on May 08, 2016, 11:05:35 pmThanks for posting the video... I like the extensive input filtering and will incorporate some of that straight away. Also, ah ha! They use a big resistor in parallel with a relay to control in-rush. I'm updating the schematic now.

author: mariush
author_rank: Super Contributor
timestamp: May 09, 2016, 01:48:13 am
content: Here's a suggestion ...Have a look at LT4320 - ideal bridge controller chip:http://www.linear.com/product/LT4320. You pair it with 4 high quality mosfets and it should be doable to have a bridge rectifier of up to 30-40 Amps. I'm not sure you'd find mosfets good enough to build a 80 amp rectifier with it.The benefits would be1. minimal heat generated ... you have maybe a couple of watts lost on each mosfet (you need 4) so let's say 10w in total for something like 30-40 amps of current , compared to 2-2.5v times current for the classic bridge rectifier2. less capacitance required - since there's a much smaller voltage drop on the mosfets you'd need much less capacitance to keep the voltage above some threshold required to regulate the power supply to 13.8vIt was already tested with up to around 30A :https://www.eevblog.com/forum/beginners/a-niche-chip-for-mains-powered-ac-gt-dc-'linear'-based-psu/You could for example give up on your custom transformer and just buy a couple of these :http://www.antekinc.com/an-8412-800va-12v-transformer/and use one such IC + mosfets for two windings of each transformer (out of 4) , so in total you'd have 4 bridge rectifiers. You'd have a DC output with a peak of about 17v at the end of each rectifier, so you just need to add capacitance to stay above around 15v to then regulate down to 13.8v

author: AF6LJ
author_rank: Unknown
timestamp: May 09, 2016, 02:06:15 am
content: Quote from: FJHookah on May 09, 2016, 12:36:53 amThat is the Go-To method for inrush current limiting when large currents are involved. Suggestion on the resistor (since you are running this on 110V I assume you will only need one)I used thesewww.ohmite.com/cat/res_200.pdfIn an inrush current limiter in my legal limit HF amplifier.They work great, very overload tolerant, and a heat sink is not required.They do have to be elevated above the board a bit, if you are using a PC board for your inrush limiter.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: May 09, 2016, 02:35:06 am
content: another idea for you:in case you want to use that high power for other voltages or w/e, it might make sense to make two enclosures on a rack, one for the unrectified DC and one as the step down power supply.that way you could do things like try to experiment with designing a step up supply, or have different voltages, or whatever.design would also be a bit less stressful this way, since you could have the arguably simpler rack done, with AC MAINS considerations in mind, then design the other rack with DC practice in mind.just have some bus bars go up to the smaller form factor regulator...the filter and transformer are really the mass bulk of the design.additionally not having these elements in the same chassis would allow easier airflow/thermodynamic design of the regulator section.If you want it very sleek you could probably make the regulator section slim, then have a single squirrel cage/enclosed style fan blowing over separately ducted transistor row(s) (arrange them like a army parade maybe?) .. put nice filters on the fan too.this would allow you to optimize airflow as you don't have to deal with big capacitors and shit getting in the wayyou don't have to build an iphoneI find it very soothing psychologically to divide up a project into different usable components. I hate the idea of having some kind of monsterous workload before I can get something remotely usable... since if you build the unregulated DC box you could hook up something simpler/etc to it. beastly inductive heater... spot welder.. electrolysis... furnace.. etc. unregulated supplies have tons of uses because you don't need to worry about doing anything more then blowing a fuse.. and if they go its a quick fix. You don't need to worry if a inductive kick weaked all your regulator transistors or such . doing any kind of electrical energy experiments with a regulated power supply makes me nervous.

author: FJHookah
author_rank: Contributor
timestamp: May 09, 2016, 03:19:24 am
content: Found a solution for the inrush resistor sitting in a parts bin here at the shack...

author: sarepairman2
author_rank: Frequent Contributor
timestamp: May 09, 2016, 05:12:24 am
content: i have used those before. a russian trick is to solder it upsidedown on support wires so if it overheats it will fall and break the circuit.

author: Circlotron
author_rank: Super Contributor
timestamp: May 09, 2016, 07:53:49 am
content: The capacitor input filter will present a power factor of about 0.6 to your 1700VA transformer so that means you will only be able to draw about 1020 watts continuous from the transformer. Have you considered using a choke input filter? At these power levels it makes a lot of sense. Spreads the conduction of the bridge rectifier diodes over a much greater portion of the AC waveform, as well as making ripple filtering easier. Near sinewave ripple so what is left is also less audible.Also, there are a lot of ultracapacitor banks you can get nowadays that are meant to go across a car battery, or in some cases even replace the car battery. I have on on my car in fact. 60 odd Farads across the output would do wonders for transient current capacity.http://www.ebay.com.au/itm/Ultracapacitor-Module-Battery-Eliminator-Car-Audio-Starting-Remote-Power-Solar-/111699706891?hash=item1a01d2440b&pt=LH_DefaultDomain_0&nma=true&si=4Q7ZGG%252BUylk78QbwZxamhv5NHik%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

author: AF6LJ
author_rank: Unknown
timestamp: May 09, 2016, 12:41:00 pm
content: Quote from: FJHookah on May 09, 2016, 03:19:24 amHere are the ones I used...I didn't design the board W7RY did. His circuit is self powered and works well. He supplies the board and the BOM you have some latitude in the parts you use. I didn't want to use the sandbar resistors in the BOM so I picked up the Ohmite 200 series resistors.

author: FJHookah
author_rank: Contributor
timestamp: May 10, 2016, 09:58:37 pm
content: Updated Design with new Schematics....Hi gang, Op here. So after receiving a load of excellent recomendations, I've updated the design and schematics with the following:Decoupled the Pass TransistorsReworked the schematic drawing in a different program (easier to use - DigiKey's Schemit)Added extensive input common-mode filtering prior to the power transformerAdded MOVs for input line protection from surgesAdded a 100 Amp output Fuse for peace of mind and additional safetyAdded a 100 Amp current shunt and a nice LCD backlit Meter (will need to add beads for RFI protection to the new meter)And finally, added a larger current in-rush resistor and a 5-pole Relay (the Relay performs double duty; 1) RL1b shorts out the inrush resistor shortly after the Momentary 'On/Off' button is turned On. 2) It opens the circuit in theory when RL1b is activated when SCR1 fires due to over-voltage issue, rendering the PS offline and bleeds the huge filter caps.I would like your thoughts on the design at this point; is the math good enough to proceed to building prototype PCB and supply in a wooden chassis?My biggest design challenge, one that's kicking my hiney at the moment, is whether the RL1a/b design will function as designed by providing in-rush shorting of R3 before R3 melts, as well as shutting off the power supply at the relay when SCR1 fires. I'm lost on how to design this part. Thanks!And finally, if I were to hire a professional to perform a deep-dive on this design to ensure it's accurate and safe prior to building a prototype PCB and building the supply for initial theory validation and safety checks, how much money would you estimate that service could be?

author: Circlotron
author_rank: Super Contributor
timestamp: May 10, 2016, 11:49:33 pm
content: The bases of all the series pass transistors are driven through capacitors.Not good.

author: AF6LJ
author_rank: Unknown
timestamp: May 10, 2016, 11:54:30 pm
content: Just a couple of notes.1. Your inrush limiter is much easier to impliment on the primary. You won't need a 100Amp relay.Something nice and pedestrian like a relay with 25A contacts (make and break current rating) and a coil that is say 12 or so volts you can use with a dropping resistor just after the bridge rectifier.2. When I suggested the 100A fuse I meant it to go after the filter cap and before the pass transistors...That is a much better place.3. sense your supply is linear all that input filtering is way overkillYou don't have to worry about RF coming down the AC line and getting past your power transformer and causing problems. There is so much winding to core capacitance in a 60HZ power transformer any RF will get sucked to the core and to groundYou could leave C1 and the MOVs that should be well enough filtering.....

author: FJHookah
author_rank: Contributor
timestamp: May 11, 2016, 03:08:43 am
content: Thanks for the helpful comments. This project is a bit over my head, but that's how we challenge ourselves. The AC Entry receptacle that I purchased from Mouser includes the common-mode filtering you see in the schematic, so I can't remove that unless I decide to use a non-filtered receptacle. I've made the edits to the series pass transistor bases, and moved the 100A fuse. I'll do some more research on how to incorporate the inrush relay. I like the idea of dealing that with in the AC entry stage; many viable relay options for that solution. I still haven't been able to wrap my head around the work-flow electrically for that piece of this puzzle.It's times like this that I really wish there were a few mentors locally, that I could convince hanging out in my lab for a couple of days to check my math would be a rewarding and fun experience, haha.Thanks again... I appreciate all the feedback I can get.Since the edits I've just made are minor, I won't republish a schematic revision just yet.

author: AF6LJ
author_rank: Unknown
timestamp: May 11, 2016, 03:14:34 pm
content: Quote from: FJHookah on May 11, 2016, 03:08:43 amI didn't know about the mains entry connector, that's cool.Moving the fuse means that not only is the regulator and the load protected from overload but the small voltage drop the fuse will introduce into the circuit is ahead of the regulator and won't t regulation.There are a couple of ways to operate the inrush current limiting.Having the relay contacts on the primary side with your limiting resistor is the preferred way.How you energize the relay coil can be done with an RC network, and rectified mains to provide voltage like the one I used in my amplifier, or you can drive the relay coil off the unregulated DC, using the inrush resistor on the primary side and the slowly building DC voltage across your caps to pull in the relay contacts after a second or two.QuoteTake it a step at a time.Build up the regulator, incorporate one transistor, use another DC supply to feed it, and put a small load on it. Then add the rest of the pass transistors and put it under the same small load. (a half dozen amps or so) and make sure they are sharing the load.When you get your big transformer, caps, and diodes you will be ready to go knowing your regulator is functioning properly.

author: oldway
author_rank: Super Contributor
timestamp: May 11, 2016, 04:29:12 pm
content: For transformer and rectification, I should use a triac preregulator to reduce power dissipation in series power transistors.

author: mariush
author_rank: Super Contributor
timestamp: May 11, 2016, 04:46:31 pm
content: Another thought...LM1084 (or LT1084) ... linear regulators capable of 5A max with 1.3v max drop ... there was also LT1083 with 7.5A max but it's discontinued nowadaysTake 5 of these, slap them on a nice heatsink. use a 0.01 ohm resistor between the outputs of each one and the final output to share the output between all regulators and connect the feedback/adjust pins of all to a couple of resistors to configure the output to 13.8v - if the outputs are on a large copper/some other metal rail .. you can take the feedback directly from the output jack.You now have a "module" that's capable out outputting a maximum of 25A, as long as the input voltage is minimum 13.8v + 1.3v let's say 15.5v minimum ...You can now make 4 identical "modules" and you can drive each module at 20A, and still have a reserve to go up to 100A .. each ldo will see maximum 4A on it and minimum about 8w dissipated on each to-220 device. The 0.01 resistor of each LDO will dissipate a watt or so.You can add fuses to disconnect a module if some ldo blows up / shorts and you won't lose the whole power supply, you'll only lose 20-25 amps.I'm not sure how well this kind of design will scale up to so many ldo regulators, not sure about the balancing, how well 20 of them will balance the current between them. There's going to be some imbalance as they heat up, the voltage out of them will slightly vary but that's taken care by the resistors on each regulator output ...Anyway, it's about $2.5 per LDO so about a $50 investment for all and maybe a couple of dollars for the small resistors... and you can start with one module and test the 20-25A output with some 12v car lightbulbs / halogen lights.

author: FJHookah
author_rank: Contributor
timestamp: May 11, 2016, 06:05:34 pm
content: great ideas; keep'em coming. Also, if there's a math guru out there that has the time, take a look at my schematics to see if there are any obvious gotcha's. I plan to validate the regulation circuit tomorrow as time permits.Oh, thought that I might have hit a system design roadblock this morning. I ordered the pass transistors (2N5686G) and associated sockets last week. They arrived yesterday so last night I did a quick test-fit; NO-GO. It turns out that the 2N5686G, due to its higher current capability than the rest of the 2N line, has larger diameter emitter and base Pins. Unfortunately the data sheets do not always differentiate between the two Pin sizes. The majority of sockets available for the TO-3 package are made for the smaller Pin sized transistors (2N5302G for example). I called Keystone and TE Connectivity (the two largest makers of the TO-3 sockets), TE makes them, whoohoo! They are 10-times more expensive than Keystones, but hey I'm not complaining.

author: AF6LJ
author_rank: Unknown
timestamp: May 11, 2016, 06:47:56 pm
content: I am not big on sockets, over time you can have high resistance connections and that can cause problems down the road. you might look into using Molex pins if you are sure you want to have solderless connections.

author: donmr
author_rank: Regular Contributor
timestamp: May 11, 2016, 07:10:52 pm
content: It looks like you have shorted out the common mode chokes on the input. They won't do much that way.

author: FJHookah
author_rank: Contributor
timestamp: May 11, 2016, 08:12:08 pm
content: Quote from: donmr on May 11, 2016, 07:10:52 pmAre you referring to the ground icon just below the Mains entry AC Signal icon perhaps? The wiring of the choke is all inside the power entry module, so I did my best to draw it schematically. I can see how the ground icon at the entry would make it look confusing. If you're referring to something else, please explain, thanks.

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 11, 2016, 08:23:20 pm
content: Quote from: FJHookah on May 11, 2016, 08:12:08 pm

author: poorchava
author_rank: Super Contributor
timestamp: May 11, 2016, 08:29:43 pm
content: Have I missed the post where somebody points out that linear PSU of that power is just a stupid idea unless you're looking to build a heater?

author: AF6LJ
author_rank: Unknown
timestamp: May 11, 2016, 08:56:31 pm
content: Quote from: poorchava on May 11, 2016, 08:29:43 pmThey are more forgiving and in the long run, more reliable.Besides here in the US we have electricity to burn.

author: AF6LJ
author_rank: Unknown
timestamp: May 11, 2016, 08:58:16 pm
content: Oh and I almost forgot.You don't have to spend half your life trying to keep the damned thing from generating broadband noise, we amateur radio operators have enough of that to deal with.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 11, 2016, 09:55:51 pm
content: The low power factor will not allow so much power at the DC side. 80 at 13.5 V are nearly 1100 W. With some loss for the diodes you are at 1200 W minimum - no loss for the regulation included. With just a rectifier and filter cap this would be something like 1800-2000 VA for the transformer and already to much for a 13 A mains fuse. So no way around some power factor correction.In a linear supply this would be a big choke. At this high power it may not be that bad, as chokes like transformers get better when getting larger - but expect the choke to be nearly as large and heavy as the transformer. At least it could also save on the filter caps.The regulator should get it's own supply to minimize the dropout, so less power is wasted and less heat generated.

author: FJHookah
author_rank: Contributor
timestamp: May 11, 2016, 10:26:58 pm
content: Quote from: PA0PBZ on May 11, 2016, 08:23:20 pmGot it, thanks

author: FJHookah
author_rank: Contributor
timestamp: May 11, 2016, 10:49:29 pm
content: Quote from: poorchava on May 11, 2016, 08:29:43 pmAlthough sarcasm is seen as good humor, given in the appropriate context, did you have anything useful to add to the discussion? If you're bored and would like to make me smarter; would you be so kind to provide an example basic schematic of how I could implement a timing circuit with the associated components required to manage the horde of inrush current I'm assuming the combination of the 1500VA transformer and the 164kµF filter caps will draw at Power-On? That would be most appreciated and useful. Based on some great feedback I've received thus far, I'd also like to add a separate transformer supply for the regulator. If you could draw that out in a simplistic fashion, I would be most appreciative. Perhaps you have a few favorite links on the web that you might offer, where I could learn how to do this myself. Otherwise, we'll simply clap, smile, and put quarters in your hat each time you grace the thread with your comedic outbursts.

author: FJHookah
author_rank: Contributor
timestamp: May 11, 2016, 10:55:00 pm
content: Quote from: Kleinstein on May 11, 2016, 09:55:51 pmHmmm, I did not account for that much loss. I'll start reading up on that straight away, thank you. Although I must say, if the only corrective action is to add a 32lb choke, this design will quickly find itself in trash can.

author: AF6LJ
author_rank: Unknown
timestamp: May 11, 2016, 10:55:30 pm
content: Quote from: Kleinstein on May 11, 2016, 09:55:51 pmThis is a good point and companies like Astron who have been making power supplies for two way, and amateur radio for decades do this on their higher power supplies.

author: AF6LJ
author_rank: Unknown
timestamp: May 11, 2016, 10:56:43 pm
content: Quote from: FJHookah on May 11, 2016, 10:55:00 pmYour design will work fine, it isn't that different from an Astron RS-75.