In this application I do not see the need for such an extremely high power supply capacitance. Especially so given that in common commercial high current power supplies they only have a hundred to a few hundred uf per running amp at most on a 60 HZ iron core transformer based power supply.
In my books for a ~150 amp 22 VDC power supply 30 - 50,000 uf of lower ESR electrolytics backed by a few hundred uF of poly capacitors or even old metal can PFC capacitors to compensate for the HF load aspects would be a great plenty.
Hi SB,Wouldn't metal film caps like a MKP type of something similar to them be more appropriate for this application?
Hell, those Polyprop caps are good prices SB- nice find.Hi spec, this is where I bought mine, price has gone up a small amount since buying but still pretty reasonable.
https://www.surplussales.com/Capacitors/Polypropylene/Box-Caps/MKP-MKT.html
They have a pretty good array of others too. https://www.surplussales.com/index/Polypropylene-Polyester-Box-Type-Capacitors.html
Such low value capacitors would result in the plus and minus 22V lines being, to a first approximation, 120Hz rectified sine waves, rather than DC with a 1V ripple at 120Hz, as I had intended.
Hell, those Polyprop caps are good prices SB- nice find.Shame I don't live in the States.
spec
I am thinking 40,000. uf on the +22 vdc side and 40,000.uf on the -22 vdc side. 30,000. uf on each 15 vdc.
As TCM says, the three 12V power supplies (reduced by me from 15V) do not use much current: 100mA would do, in theory, but I would advise at least one amp for the two supplies for the output transistors and at least 5A (as a contingency for future experiments), for the power supply supplying the driver chip isolated electronics. It is also advisable to have all three supplies regulated. Three terminal regulators would be fine for the two 1A supplies but a separate mains powered power supply would be advisable for the 5A supply (dirt cheap on ebay).30,000. uf on each 15 vdc. I need to read the data sheet again I think I need 6 amps on 1 of the 15 vdc power supplies i can wind 3 coils in parallel to get 6 amps with #24 wire that is 36 turns on the secondary with 240 vac on the primary. Somewhere I read 4 to 6 amps?
May I suggest you try using two MOTs and connect the primaries in series. Then have an identical secondary winding on both transformers, which are connected to the rectifiers as shown by the sketch of post #65.I have several MOT transformers I can use but the primary coil is usually 100 turns on all of those that is 1/2 was is needed for 100% duty cycle. I have some good transformers I can destroy for the EI core then rewind it with the correct primary for 100% duty cycle this EI core is larger for correct primary winding for 100% duty cycle but not sure I really need 100%. I have a 2500 watt EI core I saved from a cooked transformer it will need to be wired 240 vac on the primary. I still have not decided which EI core to use yet. I have a coil winder for my lathe I can wind this transformer in 30 minutes. I use to have a good supply of enamel coated copper wire #16 to #30 sold it all but 3 rolls of #24 each roll is 100 lbs each. #24 will be good for the two 10.5 vac windings that will give me 14.8 vdc my notes says, add 2% for loss. I can use 75 amp wire to get 15.5 vac = 21.9 vdc. I can change any winding by 1/2 or 1 turn or any multiple of that to get any voltage I need.
I have just looked at the ripple current with 40,00uF reservoir capacitors. With a 60Hz transformer, a full wave rectifier, and 100A current drain, a 40,000uF reservoir capacitor would result in a ripple voltage of around 22V. So a 40,000uF reservoir capacitor would do no smoothing at all, to speak of. The other problem is that such a huge ripple voltage would result in a correspondingly huge ripple current which no capacitor could stand.I am thinking 40,000. uf on the +22 vdc side
As TCM says, the three 12V power supplies (reduced by me from 15V) do not use much current: 100mA would do, in theory, but I would advise at least one amp for the two supplies for the output transistors and at least 5A (as a contingency for future experiments), for the power supply supplying the driver chip isolated electronics. It is also advisable to have all three supplies regulated. Three terminal regulators would be fine for the two 1A supplies but a separate mains powered power supply would be advisable for the 5A supply (dirt cheap on ebay).
Afraid I led you astray with the high current requirements for the three 12V (15V) supplies- over caution.
May I suggest you try using two MOTs and connect the primaries in series. Then have an identical secondary winding on both transformers, which are connected to the rectifiers as shown by the sketch of post #65.
2 MOTs is series r like 2 light bulbs n series. If you put a 100w bulb is series with 75w bulb and run them on 240 vac the 60w bulb burns out. With transformers the load on the secondary determines the load on the primary so both loads need to be identically matched.
very wise- I like it. Gently gently is the way forward.I will probably start out with 1 MOT on 120 vac to build and test the circuit keep the power low until I know it works like it should.
.I have no scope but my VOM works to read the DC ripples. On DC it reads DC volts. On AC it reads the AC ripples. If there is no DC ripple there is no reading on AC. The smaller the DC ripple the smaller the AC reading.
I mentioned using batteries earlier on. Four batteries would give +-24V nominal. Another approach would be to use switch mode power supplies, but that would be expensive, unless you used SMPs pulled from scrap equipmentIf line ripple is that much of an issue just use two multi tens of AH 12 volt deep cycle batteries in series for the capacitor bank.
It is a concern in that full ripple reduces heating effect to 0.707, as stated a few times before.Personally I don't see DC ripple being much of a realistic concern here.
I fully agree and with a 100A that would workout to 1F, which would be excellent, but a touch expensiveEspecially considering that in typical non SMPS systems 1000 uF per running amp is considered a great plenty.
That would be even better and gives 2F and 3F for 100A drain.Even high power audio amplifiers don't go much over 2000 - 3000 uF per amp on a 50 - 60 Hz power system.
That is a sweeping statement TCM and cuts across the very principle of arriving at an optimized design for a particular set of circumstances.I think you guys are playing to heavy on ideal power supply theory and not practical reality here given the application.
Of course using a high and non isolated supply would be good from the efficiency point of view, but again as stated before it would be unsafe, but also I think you would have practical difficulties building a coil to match a high voltage, but I have not looked into this in detail.Personally I think that if you want to run in the multi KW power levels you need to step up to running off normal line voltage and be done with it.
Hmm I am not sure about that.Trying to do so at low voltages just adds too many other component sizing and cost related problems.
Not sure of your objective here. I have already stated what capacitors would be needed for a 2.5V ripple current at 100A drain.Otherwise for the values of capacitance you think need you either have to step up to using car audio power capacitors (multi Farad with low ESR) stacked in pairs or step up to super caps with multi hundred F ratings and put a bunch of them together.
But then if you do that you drive your diode bridge peak amp levels into the kilo ampere ranges provided your rewound MOT windings own resistance plus core saturation limits doesn't choke everything off anyway.
I do not see any problems with the bootstrap circuits. Garry has got a handle on that and posted a perfectly reasonable approach and TCM and I have discussed this area with him. This is a normal design process.With the problems so far I can't wait for the ones coming with the bootstrap circuits for the ucc21520 when it comes to them.
It is a concern in that full ripple reduces heating effect to 0.707, as stated a few times before.
Of course using a high and non isolated supply would be good from the efficiency point of view, but again as stated before it would be unsafe, but also I think you would have practical difficulties building a coil to match a high voltage, but I have not looked into this in detail.
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