toroidal core for high current
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From: tm on 19 Jul 2010 20:36 "legg" <legg(a)nospam.magma.ca> wrote in message news:tlr9465o3s45emvvlhh77j85ahnhgocngh(a)4ax.com... > On Mon, 19 Jul 2010 10:21:52 -0700 (PDT), Jenkins > <phreon111(a)gmail.com> wrote: > >>On Jul 19, 8:34 am, "Tim Williams" <tmoran...(a)charter.net> wrote: >>> "Jenkins" <phreon...(a)gmail.com> wrote in >>> messagenews:45a92d0d-d2a1-451f-93f3-62c9bee710c9(a)q22g2000yqm.googlegroups.com... >>> > How physically large does a toroidal core need to be to handle a 100A >>> > smps buck or flyback configuration? > <snip> >>> >>> > Volts In 250 V >>> > Volts Out 25 V >>> > Vripple 0.25 V >>> > Load Current 100 A >>> > Freq. 50000 KHz >>> >>> 50MHz? > <snip> >> >>That should be 50khz and not 50Mhz. L = 450uH... still seems >>relatively small. > > It is four orders of magnitude greater than your previous effort, and > your main source of error, here. > > 1% ripple in a single stage filter may be impractical. > A 25V filter inductor will exhibit signifigant core loss and a 100A > winding on same will not be simple to achieve. > > If the solution is as 'small' as you think, you'll be a lucky guy. > Legg is right. Take a look at 100 amp DC "inverter" welding power unit. In fact, that might be a good source of parts. You would need to convert it from constant current to constant voltage. The Miller units have good technical support and documentation. Tm --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: Jenkins on 19 Jul 2010 22:23 On Jul 19, 3:23 pm, Tim Wescott <t...(a)seemywebsite.com> wrote: > On 07/19/2010 12:01 PM, Jenkins wrote: > > > > > On Jul 19, 1:12 pm, Tim Wescott<t...(a)seemywebsite.com> wrote: > >> On 07/19/2010 10:22 AM, Jenkins wrote: > > >>> Guys, it should be obvious it was 50khz and not 50Mhz, I made a > >>> mistake when I was entering the data to paste it in. > > >>> Volts In 250 V > >>> Volts Out 25 V > >>> Load Current 100 A > >>> Freq. 50 KHz > >>> Vripple 0.25 V > >>> Duty Cycle 10 % > >>> Ipp Inductor 1 A > >>> Ipk Inductor 100.5 A > >>> Irms 99.500418759588 A > >>> L 450 uH > >>> C 800 uF > > >> And look! The inductor value has changed! > > > duh! Did I say they wouldn't? Just curious... have you ever made a > > mistake in your life? I made a mistake entering the data... get over > > it. It's not the end of the world. > > I wasn't criticizing; forgive me if it came across that way. > > And I do make mistakes -- sometimes I think I've screwed up when I > haven't :-). hehe, ok. np. > > >> Regardless, going from 250V to 25V means that the output stage will only > >> be on for 10% of the time, which is putting severe demands on an already > >> heavily used inductor. Why don't you want to use a transformer? > > > I thought the whole point of smps was reduce the transformer size? > > When I and others say "why don't you use a transformer", we mean "why > don't you use a switching regulator topology with a transformer". If > you use a transformer with a turns ratio sufficiently less than 10:1 to > insure 5V out when the input is at it's lowest ebb then you will > minimize the amount of energy that must be stored in the magnetics, and > hence their size. > Ok, I don't have a huge problem with it but it seems that it may add significantly to the cost. I'd prefer the isolation provided by a transformer but I'd also like to reduce costs. A simple buck converter topology would work fine except I may have issues with discontinuous mode which I would like to get around. In fact I need a somewhat variable supply of ~1A to ~100A. I'm not sure I could implement an efficient topology such as Full- Bridge Push Pull converter at those currents and voltages. The main issue I'm having is determining the transformer and inductors to use. The site you gave me shows some cores that should work but I'm not sure how well as they still seem awful small. I would expect a transformer to be at least the size of my fist and not one of those ones one typically sees in PC SMPS's. Of course I may be wrong if the size is somewhat proportional to the switching frequency. Just a thought but I wonder if I could parallel several smaller buck converters, with or without isolation such as the flyback or fullwave, which would allow me to switch them in as I need more current. I could have one 50W, 25W, 10W and 1W. This would require current sensing but shouldn't be an issue as it doesn't have to be accurate. I guess the problem here would be current sharing? Thanks
From: Tim Williams on 19 Jul 2010 22:32 "Jenkins" <phreon111(a)gmail.com> wrote in message news:3e5cb4e2-a242-461e-8bbc-7fd0fe300363(a)w12g2000yqj.googlegroups.com... > Just a thought but I wonder if I could parallel several smaller buck > converters, with or without isolation such as the flyback or fullwave, > which would allow me to switch them in as I need more current. You can. In fact, this is what most multiphase controllers do automatically, with the bonus of phase shift between outputs, which reduces average current ripple. If you're making one from scratch, remember to throttle them in parallel, so none are hogging current. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Jenkins on 19 Jul 2010 22:33 On Jul 19, 7:50 pm, legg <l...(a)nospam.magma.ca> wrote: > On Mon, 19 Jul 2010 10:21:52 -0700 (PDT), Jenkins > > > > > > <phreon...(a)gmail.com> wrote: > >On Jul 19, 8:34 am, "Tim Williams" <tmoran...(a)charter.net> wrote: > >> "Jenkins" <phreon...(a)gmail.com> wrote in messagenews:45a92d0d-d2a1-451f-93f3-62c9bee710c9(a)q22g2000yqm.googlegroups.com... > >> > How physically large does a toroidal core need to be to handle a 100A > >> > smps buck or flyback configuration? > <snip> > > >> > Volts In 250 V > >> > Volts Out 25 V > >> > Vripple 0.25 V > >> > Load Current 100 A > >> > Freq. 50000 KHz > > >> 50MHz? > <snip> > > >That should be 50khz and not 50Mhz. L = 450uH... still seems > >relatively small. > > It is four orders of magnitude greater than your previous effort, and > your main source of error, here. > > 1% ripple in a single stage filter may be impractical. > A 25V filter inductor will exhibit signifigant core loss and a 100A > winding on same will not be simple to achieve. > > If the solution is as 'small' as you think, you'll be a lucky guy. > > RL It's not small as I 'think'. That was the whole point. I did the wrong calculation and it came out extremely small. Even with the fixed calculation it still seems relatively small. I was figuring it would be several hundred mH's and probably twice the size of my fist.
From: Jenkins on 19 Jul 2010 22:35
On Jul 19, 7:36 pm, "tm" <no...(a)msc.com> wrote: > "legg" <l...(a)nospam.magma.ca> wrote in message > > news:tlr9465o3s45emvvlhh77j85ahnhgocngh(a)4ax.com... > > > > > On Mon, 19 Jul 2010 10:21:52 -0700 (PDT), Jenkins > > <phreon...(a)gmail.com> wrote: > > >>On Jul 19, 8:34 am, "Tim Williams" <tmoran...(a)charter.net> wrote: > >>> "Jenkins" <phreon...(a)gmail.com> wrote in > >>> messagenews:45a92d0d-d2a1-451f-93f3-62c9bee710c9(a)q22g2000yqm.googlegroups.com... > >>> > How physically large does a toroidal core need to be to handle a 100A > >>> > smps buck or flyback configuration? > > <snip> > > >>> > Volts In 250 V > >>> > Volts Out 25 V > >>> > Vripple 0.25 V > >>> > Load Current 100 A > >>> > Freq. 50000 KHz > > >>> 50MHz? > > <snip> > > >>That should be 50khz and not 50Mhz. L = 450uH... still seems > >>relatively small. > > > It is four orders of magnitude greater than your previous effort, and > > your main source of error, here. > > > 1% ripple in a single stage filter may be impractical. > > A 25V filter inductor will exhibit signifigant core loss and a 100A > > winding on same will not be simple to achieve. > > > If the solution is as 'small' as you think, you'll be a lucky guy. > > Legg is right. Take a look at 100 amp DC "inverter" welding power > unit. In fact, that might be a good source of parts. You would need to > convert it from constant current to constant voltage. The Miller units > have good technical support and documentation. > > Tm > Ok, I'll try to look at some of those circuits and see how different they are and maybe try to peek inside my welding machine and see what in there. Thanks |