ac 2 dc conversion - Page 1
Forum section: electronics / beginners

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 09, 2021, 04:48:56 pm
content: I'm thinking about using my wall power.But I need dc not ac, because my machine is dc.Do you need a 2000 watt diode - for 240v/10a? How big are these things?Then I could put a diode bridge, instead of just rectification, and then theres a way to get rid of the bounce, and get it more level to dc, and I cant remember how you do this, but I think a charge pump does it? - and its a small conversion from a dc bridge.Anyone can help me here? thanks for any reply.

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 09, 2021, 05:05:30 pm
content: https://au.banggood.com/20pcs-10A-1000V-Plastic-Axial-Rectified-Rectifier-Rectifying-Diode-p-1464096.html?utm_source=googleshopping&utm_medium=cpc_organic&gmcCountry=AU&utm_content=minha&utm_campaign=minha-au-en-pc&currency=AUD&cur_warehouse=CN&createTmp=1&utm_source=googleshopping&utm_medium=cpc_bgcs&utm_content=tanya&utm_campaign=tanya-ssc-aug-all-1129&ad_id=400330096020&gclid=Cj0KCQjw-4SLBhCVARIsACrhWLUOKvOh4BFAov9hJq27DHxqVtZq5pTQSvzEOII1ZThUolKSiMSPNhQaAjvIEALw_wcBcan you use these? its rated to 10 amps and way over rated at 1000 volts.Its really cheap too. how come resistors cost so much! resistors are more expensive by a mile, when it comes to hiwatt, your better off with 28 guage nichrome and force yourself to work with low resistances.

author: rstofer
author_rank: Super Contributor
timestamp: October 09, 2021, 05:28:51 pm
content: I would probably use a full wave bridge rectifier rated at least 1000V 30A. Maybe like this:https://www.digikey.com/en/products/detail/vishay-general-semiconductor-diodes-division/PB3010-E3-45/4875119Maybe I would go for overkill: 1000V 50Ahttps://www.digikey.com/en/products/detail/nte-electronics-inc/NTE53020/11649474You need to look at the datasheet and figure out whether you need a headsink. The device immediately above is easy to bolt to a heat sink surface.As long as I am only buying one or two, delivery is far more important than price.

author: tunk
author_rank: Super Contributor
timestamp: October 09, 2021, 05:30:34 pm
content: QuoteIn a low voltage DC power supply you usually use capacitors.I think a rule of thumb is to use ~2000uF/A, and that this will giveyou around 4Vpp ripple. I don't know how realistic this is, since youwould need some huge 400V capacitors. And remember that thiswill give you ~340Vdc.

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 09, 2021, 05:47:07 pm
content: rstofer - are u making a power supply?Im not sure about the thermals of this at all, I best be careful, like your saying.For the smoothing cap->if you use R*C, it looks like 16 farads for 60hz at a millohm resistance if you dont want to clip the cap. (apart from only needing 10% of the 10 amps. because of the sine wave going in)Thats a bit shocking, that's in the realm of super capacitors not electrolytics!its a little unorthodox, but if you've got 2.7 volt ~3 farad super caps, you could put 88 in series and get to 240volt, and they are about $1 each, and they go onto a little 8x10 board.Strange, I didnt think that would even need to be done, but that calculation for the smoothing cap is way overblown more than I expected.https://www.amazon.com/MCIGICM-Capacitor-capacitance-tachograph-Electromechanical/dp/B07BLQGRQY/ref=sr_1_4?dchild=1&keywords=super+capacitor&qid=1633801155&sr=8-4

author: Monkeh
author_rank: Super Contributor
timestamp: October 09, 2021, 05:53:10 pm
content: What exactly are you trying to do, and why are you thinking of messing around with 240V AC?

author: mariush
author_rank: Super Contributor
timestamp: October 09, 2021, 05:54:04 pm
content: First of all, what DC voltage do you machines actually use? I doubt they're running on 200-300v DC.AC voltage can be rectified using a bridge rectifier, which can be either 4 separate diodes or 4 diodes in a package. You can also parallel multiple bridge rectifiers to reduce the current going through each one.Your 230v AC will be converted to DC with peak voltages up to sqrt(2) x Vac - 2 voltage drop of diode inside bridge rectifier = 1.414 x 230v - 2 x ~ 1v = ~ 320vThen, you need to smooth out the DC voltage using capacitors or inductors. Like someone above says, you'll need around 2-3000uF per A of current, so that's quite a lot of capacitors.You can approximate with formula C = current / [ 2 x ac frequency x [ v peak dc voltage - minimum voltage desired) ]So for example for 10A and minimum 300v DC, you have C = 10 / 2x50x(325-300) = 10/2500 = 0.004 Farads or 4000uFIf you want at least 315v, you're going up to C = 10/2x50x10 = 0.01F or 10,000 uF and for 5v ripple, you have C = 10/500 = 0.02 or 20000 uF (2000 uF per A like the above person says)Also keep in mind that the bridge rectifiers will have losses, you lose 2 x voltage drop on diode inside x current ... so for 10A of current, the bridge rectifier will produce around 20 watts of heat which have to be dissipated ... either using a big heatsink or a fan.

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 09, 2021, 06:04:32 pm
content: Thats a cool idea for splitting the load onto lots of diode bridges in parallel. Thanks for the tip, I might be doing just that!Yes that smoothing capacitance is rather large indeed. I wonder if you put enough caps there it actually ends up going totally level.Monkeh - why do I need all the power? ... its a secret...<EDIT> you probably wouldnt want to be touching the ends of the smooth cap array, thats for sure... Dead. </edit>

author: Kleinstein
author_rank: Super Contributor
timestamp: October 09, 2021, 07:23:43 pm
content: With some 2000 W there are limits on the power factor an harmonics. So just a simple rectifier and filter cap, as with low power (e.g. 10 W) applications is likely not working well. Without PFC the 2000 W power from a simple rectifier could blow a 16 A fuse, at least getting close, so it may trip or at least run quite hot.

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 09, 2021, 07:32:37 pm
content: Yep, I reckon tripping the houses safety is very likely, maybe I'll divide the voltage a little as well.

author: Zero999
author_rank: Super Contributor
timestamp: October 09, 2021, 07:41:36 pm
content: What device do you need to power? Beware that the rectified voltage could exceed the device's rating.No, the diode doesn't need to be 2000W, because it only dissipates a small amount of power, which goes to the load.You need a bridge rectifier, rated to more than 10A and a decent heat sink.

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 09, 2021, 07:58:18 pm
content: Quote from: Zero999 on October 09, 2021, 07:41:36 pmsupercap charger, my own circuit. Its basicly just a step down transformer, but it works with dc so I need to rectify it at least.Im going for 1000 amps. Its a bit like a jump starter for a car.

author: rstofer
author_rank: Super Contributor
timestamp: October 09, 2021, 08:26:05 pm
content: Quote from: Capernicus on October 09, 2021, 06:04:32 pmTo get a perfectly flat output, the capacitor voltage would always equal the rectifier peak voltage. Therefore, the diodes would never conduct! And it gets worse!There is another problem: conduction angle. The diode only conducts when the capacitor voltage is less than the rectifier output. But this means that all of the power must be conducted through the bridge when that voltage relationship exists. If the capacitor voltage doesn't sag very much, the diode isn't on for very long and it has to conduct all of the required power in that short period of time.Look at the second hump in the bottom graph. That 1-cos area is the only time the rectifier conducts. It's nowhere near a significant part of the period and this means there needs to be a lot of power conducted during that brief period. The first hump is starting from 0V across the cap - initial startup... You're looking at the area between the label and the next voltage peak. Pretty short period!https://electronics.stackexchange.com/questions/433165/whats-the-conduction-angle-for-a-full-wave-rectifier-with-filter-capacitor

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 09, 2021, 08:38:11 pm
content: Quote from: rstofer on October 09, 2021, 08:26:05 pmso you think that the cap actually spits back into the diode bridge? It might do, I'll have a think about it.But theres other designs for full wave rectification, you might not be using a diode bridge, theres a version that only has 2 diodes, maybe that might work better? But still it has the same issue that you need more capacitance for a flatter response the same. And I guess it could still have the same back discharge problem.Maybe a voltage follower could fix it, then u add a little load before the smoothing capacitor.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 09, 2021, 09:28:40 pm
content: The 2 diode rectifier usually needs 2 phases, like a center tapped transformer.There are ways to smoothen the current and improve the power factor. There are special switched mode circuits to regulate the current to a more sine like waveform (active PFC) and in the old days large inductors can be used to smoothen the current. Inductors get better when larger so for higher power they can become attractive again. Still expect the choke to be about as heavy as the transformer.As a beginner one should not work with high power electricty. Even if the voltage there are dangers possible at high power, e.g. from stored energy in inductors, that may in case of a failure provide a deadly shock.

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 09, 2021, 09:48:53 pm
content: I just had a bummer, I thought I could use a ground someway to get a rectify without diodes, but turned out it didn't work.I'm a little experienced with shocks, Ive made a marx generator before, and I know not to go around with a voltmetre without being careful about touching both sides of a string of capacitors, but maybe I shouldn't do this unless I really need to. But I think I do.I don't know what 5 farads feels like at 240 volt tho yet, that sounds a little scary. High voltage super capacitor chains have got to be deadly.I wonder if you can time an oscillator up to 60hz and then you can switch your way through the ac->dc process, that might help.

author: rstofer
author_rank: Super Contributor
timestamp: October 09, 2021, 09:55:55 pm
content: Quote from: Capernicus on October 09, 2021, 08:38:11 pmOF course not! It simply means the diode isn't conducting and therefore is not supply power. Any power required by the system when the diode is turned off must be provided by the capacitor. What it comes down to is the diode current is much higher than you might expect because it has to provide the load power and recharge the capacitor simultaneously.QuoteYes, there is a 2 diode full rectifier design but it requires a center tapped transformer.https://electronicsdesk.com/difference-between-half-wave-and-full-wave-rectifier.htmlRemember, it's not back discharge, it is simply no power provided through the diodes until the capacitor voltage falls far enough to allow the diode to conduct. Since this occurs near the peak of the sine wave, as soon as the voltage begins to drop and the capacitor voltage hasn't sagged very much, the diodes are no longer conducting.

author: Monkeh
author_rank: Super Contributor
timestamp: October 09, 2021, 10:11:35 pm
content: Quote from: Capernicus on October 09, 2021, 09:48:53 pm?!QuoteIt feels like dead.

author: gcewing
author_rank: Regular Contributor
timestamp: October 10, 2021, 10:18:07 am
content: Quote from: Capernicus on October 09, 2021, 09:48:53 pmThe fact that you use the word "yet" in that sentence is concerning. YOU DO NOT EVER WANT TO FIND THIS OUT, it will probably be the last thing you learn.

author: gcewing
author_rank: Regular Contributor
timestamp: October 10, 2021, 10:34:09 am
content: Quote from: Capernicus on October 09, 2021, 07:58:18 pmThis is confusing. Transformers work with AC, not DC. Is it some kind of switching converter?Please stop trying to be secretive and tell us exactly what you have in mind. What you've suggested so far sounds very dangerous and not very effective. If we know what you want to achieve, we will be better able to help you achieve it safely.

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 10, 2021, 11:45:06 am
content: So I'm going for a record time for charging a super capacitor.Capacitors take dc to charge, not ac, so I guess I could have transformed it and then did the diode bridge ac->dc conversion after the transformer in high amp mode, but since I am using capacitors to do the transforming in the form of a "Reverse Marx Generator" I actually do the ac->dc conversion first, and then I boost amps reduct volts after.It actually could be highly dangerous, so I'm planning on treating it all like a potential open razor on the desk, and going do a few catholic cross signs every now and again I bet.Its very important for me to finish this thing, Because ur not taking advantage of your *portable* super caps unless your cutting down that charge time, then they can compete with LIPO's, because LIPO's have to be stuck on the charger for hours, and caps could be a matter of seconds, if I am guessing right about stuff i've heard, thought of, etc.Everyone is basicly shitting on super caps all over the internet, saying they are no good for drones, over LIPOs, but they arent even fully utilizing their potential. When I see people mixing super caps with batteries, I really think they just ruining it completely, the batteries just slow them down.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: October 10, 2021, 12:41:28 pm
content: hmm, I don't know, but if I don't fully misunderstand your project, you're heading right for a top listing on the Darwin Awardat least follow the basic rule of any valve circuit work: always keep one hand in the pocket; but no idea if this will be sufficient

author: xrunner
author_rank: Super Contributor
timestamp: October 10, 2021, 12:52:27 pm
content: Quote from: Capernicus on October 10, 2021, 11:45:06 amStarting to sound like an old redneck joke here in the states -"Hey - hold my beer and watch this!"

author: tooki
author_rank: Super Contributor
timestamp: October 10, 2021, 01:18:41 pm
content: Quote from: Capernicus on October 10, 2021, 11:45:06 amOh boy…Quote from: Capernicus on October 10, 2021, 11:45:06 amCouldbe?!?Quote from: Capernicus on October 10, 2021, 11:45:06 ama) this isn’t the kind of thing where “guessing” is even remotely wise, andb) your guessing and thinking is wrongRemember that no matter how smart you are, unless you are Stephen Hawking, there’s always someone out there smarter than you. The consequence of this is that practically no ideas are actually new. Whatever you think of, someone else has thought of first. That doesn’t necessarily mean it’s a bad idea, of course. But whenever you have an idea about what sounds like a good approach for something, asking “why should I do this?” isn’t actually particularly helpful. What you need to ask is “whyhasn’tanyone else done this already?” There are many possible reasons, ranging from “it violates the laws of physics”, to “it’s theoretically possible, but the technology doesn’t exist yet”, to “it has, in fact, been done before” (and it either failed in the market, or it succeeded and you simply aren’t aware of commercial implementations), to “we used to do it but now have something better”, to “it makes no financial sense”, to “it’s unsafe or illegal”.Or, as is likely the case here, your assumptions are incorrect and there weren’t actually any compelling reasons to do it.LiPo vs supercap shouldn’t even really be a question, because they’re not substitutes for each other. Sure, there is some overlap in energy storage applications. But these are so far apart that it’s kinda like comparing sugar vs vinegar: sure, they’re both food ingredients, they each have their place in the kitchen, and there is a tiny bit of overlap in applications (they can both be used to preserve food), but beyond that it’s senseless to compare them.Quote from: Capernicus on October 10, 2021, 11:45:06 amSo, applying the question of whydon’twe do something: Whydon’twe use supercaps instead of lipo batteries? First big clue: compare the energy density (specific energy). Second clue: what do you typically need more of, peak power (instantaneous power) or runtime?And think about your assumptions, and then go out and verify whether they’re even correct. For example, is charging speedactuallythe limiting factor in typical lipo applications?

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 10, 2021, 01:44:28 pm
content: You said it yourself "peak power".... peak power may not be important during discharge, but it may be very important during charge.I hear on the internet you charge LIPOS on their peak discharge. If you did that for a capacitor its actually infinity.And the 2000 watts is no biggy, this could easily be just the same as any other thing u pop in the wall, But i'm going to utilize the whole lot of it at once and make a "battery charger" that full charges 3000farad supercapacitors in 10 seconds.Much nicer. Just imagine all the $$$... all for me... all for me...The other thing is it probably doubles as a car jump starter, if you can get a cable to inside your house.

author: mariush
author_rank: Super Contributor
timestamp: October 10, 2021, 03:25:21 pm
content: There's big differences between super capacitors and batteries.For example, capacitors can discharge down to 0v while batteries will discharge down to around 2.8v and then you have to stop discharging them or you're gonna damage them.Lithium batteries are also around 4.2v when fully charged, then quickly go down to around 3.7v where they sit around as they discharge and towards their end of charge they go down to around 3v.So if you put 4 lithium batteries in series, you know you're gonna have 4x4.2v ... 4 x 3v = 16.8v ... 12v while with super capacitors you're gonna have 4 x ~2.7..2.85v = 11.4v down to 0v.You can probably try having 100 super capacitors in series to get the voltage of 285v, but you'll just blow up your fuse... like any capacitor when discharged the capacitor will "suck in" a lot of current, so you need to limit charging and that will cause an increase in charge time.Here's a typical 3000F capacitor, check datasheet...https://www.eaton.com/content/dam/eaton/products/electronic-components/resources/data-sheet/eaton-xl60-supercapacitors-cylindrical-cells-data-sheet.pdf0.23 ohm esr ... it's gonna have hell of a inrush current.Keep in mind that unlike batteries these super capacitors are also only rated as cycles of discharge from full voltage to HALF voltage, not fully discharged... and keep in mind charging fast would cause the capacitors to heat up but you have to keep them below around 65c, probably even less..Last but not least ... consider the total capacity ... a 3000F 2.7v has about 3Wh of charge in it... a laptop battery can have nearly 100 Wh ... and you can have multiple batteries totaling 100Wh charged in parallel in less than 1h.

author: tooki
author_rank: Super Contributor
timestamp: October 10, 2021, 03:56:17 pm
content: Quote from: Capernicus on October 10, 2021, 01:44:28 pmIt arguably mattersmoreduring discharge than during charge. But again, sugar vs vinegar: you can’t compare things that serve fundamentally different purposes.Quote from: Capernicus on October 10, 2021, 01:44:28 pmThe maximum charge rate of a lipo battery depends on the specific battery. Some allow for very high currents, others do not, and the maximum charge and discharge rates can be the same or different. Gotta look at the datasheet for a particular cell.Capacitor maximum charge current istheoreticallyinfinite, but it’s not infinitein practicebecause a capacitor (like all electronic components) also has parasitic resistance and inductance that WILL limit the current. And depending on the capacitor, it could actually self-destruct. Just because a capacitor can theoretically charge at, say, 100,000 amps doesn’t mean its leads and plates wouldn’t vaporize if you actually tried to do it.Quote from: Capernicus on October 10, 2021, 01:44:28 pmThe amount of power available at your mains outlet is not infinite. That’s why, for example, charging a Tesla at home is very, very slow if you don’t have a special high-power EV charging system installed.Not that any of this matters. The energy density of supercaps is so much lower than lipo that they’re simply not going to displace them. It’d take a quantum leap in energy density for them to become competitive.Quote from: Capernicus on October 10, 2021, 01:44:28 pmTrust me, I’m not even the slightest bit concerned about you out-earning me with this, since there’s literallyzerochance your idea will work.Quote from: Capernicus on October 10, 2021, 01:44:28 pmThey already make portable car jump starters, as well as ones that plug in. Nothing new there.

author: cemelec
author_rank: Contributor
timestamp: October 10, 2021, 03:57:11 pm
content: A capacitor energy storage is 0.5 x C x V^2Your 5F capacitor at 240V (if such a thing exists outside of a defence lab) stores144 kilojoules. At peak 240 x sqrt 2 (340V) it is289 kilojoules.A rifle bullet leaves the muzzle with typically about7.5 - 10 kilojoules.1gramof TNT can release4 kilojoules.A capacitor can deliver its energy in microseconds.I think your project might qualify for a Darwin award, and I would sincerely ask you to pursue some other ideas.

author: Monkeh
author_rank: Super Contributor
timestamp: October 10, 2021, 04:09:26 pm
content: Quote from: cemelec on October 10, 2021, 03:57:11 pmOff the top of my head I can only think of a couple of a couple of cartridges used in elephant guns in that range.. most cartridges used today are in the 1.5-3.5kJ range, with a few magnums pushing 5kJ. Carry on..

author: cemelec
author_rank: Contributor
timestamp: October 10, 2021, 04:44:00 pm
content: Quote15 gram bullet at 1000m/s = 7500 Joules. Very high end rifle bulletYou are right, maybe 2kJ more typical for say a Lee Enfield or somethingMakes his project even more dire than I thought.

author: Monkeh
author_rank: Super Contributor
timestamp: October 10, 2021, 05:22:59 pm
content: Quote from: cemelec on October 10, 2021, 04:44:00 pm3-3.5kJ for .303, they're a little light. 8mm Mauser, .30-06, both edge about 4kJ. .308 sort of sits in the middle of those.Yes, he's (trying to..) play with energy levels he doesn't quite grasp. Perhaps if we express this in terms of say a small car doing 40mph? About that sort of ballpark..

author: Capernicus
author_rank: Frequent Contributor
timestamp: October 10, 2021, 05:46:41 pm
content: I wonder what charging a capacitor with a plugginable portable car jump starter would be like? maybe it does charge the cap in 10 secs! =)(I just looked and they have dismal 12-16 amp performance, what im doing is 88x the power of that.)About killing yourself with super caps, I think it only becomes a problem with too many in series, otherwise ur ok.