Switchmode at mains frequency, my HP 6433B power supply - Page 1
Forum section: electronics / projects

author: oz2cpu
author_rank: Frequent Contributor
timestamp: December 12, 2023, 11:36:09 am
content: SWITCHMODE most people thinks it is a thing that opperates at kHz frequency,correctly normally it is to make inductive parts and transformers smaller and the capacitor values smaller too..How ever here is another Hewlett Packard powersupply made with switchmode technology,but opperating at MAINS frequency, see all details in my latest video :https://youtu.be/u-XKrOtuTX4interesting side effects of using mains frequency : large transformer = heawy unit, high peak current, slow regulation responsebut still very high efficiency

author: CaptDon
author_rank: Super Contributor
timestamp: December 12, 2023, 02:54:47 pm
content: Yes indeed, look at the Sorenson / Raytheon 80-33 (80 volts max, 33 amps max) units made by the 10's of thousands. Takes a gorilla to lift it!! It is mains switched and therefore requires a HUGE filter capacitor bank to reduce ripple. The supply has horrible transient response, However with the huge filter bank those supplies can support hundreds of amps of inrush current to the unit under test!!! We tested and designed 74 volt input fuel transfer pumps for locomotives and those old Sorensons were the treat!!! They laughed at transients!! The high frequency SMPS's that were bought to replace the Sorensons were crap!!! They couldn't handle any transient above the maxed out current limiter which responded instantly so we had to add an insanely huge filter bank to ride through the transients. One of our rigs was basically the two locomotive batteries (32vdc each) with the very expensive yet basically useless for our purpose high frequency SMPS acting as nothing more than the battery charger / sustainer. GE was hell bent on throwing away the old Sorensons and I was hell bent on fishing them out of the dumpster and repairing the control board and putting them right back into service!!

author: macboy
author_rank: Super Contributor
timestamp: December 12, 2023, 04:21:11 pm
content: Thanks for that, I have never seen that HP design before. I did know of their use of phase control of the AC for linear regulators. I did own an old HP 6282A 0-10 V @ 10 A. This was a linear regulator, but the raw DC for the series linear regulator was pre-regulated by phase control of the (secondary) AC from the main transformer. A pair of SCRs replaced the high side diodes in the bridge rectifier. These were fired at an appropriate point in the AC cycle to keep the voltage across the main filter cap just high enough that the series regulator transistors had only 3 V across them at all times.

author: SeanB
author_rank: Super Contributor
timestamp: December 12, 2023, 05:01:03 pm
content: That phase control, though with only a single SCR, and a half wave rectified mains input, was used by the millions in the most popular original Phillips TV chassis designs, and also carried on into the 1990's in a good number of sets, though with now having a bridge rectifier before it to stop the main issue of a half wave rectifier, DC current flow in the mains.Phillips G11, which did, because they were all wired with a UK plug from the factory, so thus all had exactly the same DC current flow, cause quite a few older distribution transformers in residential areas to catch fire, because of the hundreds of TV sets all contributing to DC current saturating the transformer core, and the losses in the core rising to massive levels, till the oil expulsion from heat either blew all the oil out, and the transformer burnt out, or it blew the distribution fuses. Average power use of 300W, which was done with an 11A current pulse on roughly every second mains cycle, and which also caused UK grid massive harmonic problems.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: December 12, 2023, 05:08:35 pm
content: thanks CaptDonI actually own a Sorensen DCS80-37 3kWI think it is one of the most powerfull units in my collection at the moment,my model is a classic switchmode, no preregulation, I even made a little video about ithttps://youtu.be/P1hLVcWFBq0

author: armandine2
author_rank: Frequent Contributor
timestamp: December 12, 2023, 06:59:46 pm
content: ... you haven't got one of these as well have you?https://www.elektormagazine.com/magazine/elektor-199010/32232

author: coromonadalix
author_rank: Super Contributor
timestamp: December 12, 2023, 07:04:26 pm
content: bookshttps://archive.org/download/Elektor_Archive_1990-2011

author: CaptDon
author_rank: Super Contributor
timestamp: December 13, 2023, 12:38:52 am
content: The ones I worked on were mains Triac switched on the 60Hz input and the transformer took up about 60% of the total volume of the supply. Monsterously heavy and required two people to rack it or un-rack it. Two huge filter capacitors took up another 30% of the internal volume with the remaining 10% dedicated to the control board and control pots etc. We had some of the Sorensons similar to yours and they were dedicated to the testing of steady loads like the CIO panels (Locomotive Common Input / Output) housing up to 25 I/O cards plus CPU. The beast Sorensons were used for motor / pump testing. We had 2 rack space 1KW and 2KW supplies (80-13A) and 3 rack space 3KW supplies all were Sorenson / Raytheon.The only repairs I ever made was cleaning the edge connector of the control board and replacing capacitors on the control board when the output voltage wouldn't go above about 2 volts. These were common easily fixed problems but GE always through them in the dumpsters and I always watched for them so I could salvage and repair them.

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 13, 2023, 03:26:21 am
content: Some companies, notably Semikron, manufactured “inverter grade” SCRs, but even those could only switch at a couple of kilohertz at most, well within the most annoying audible range.Transformer and inductors had to be potted in heavy tar or epoxy to mitigate, but never completely eliminate, the whining.

author: twospoons
author_rank: Frequent Contributor
timestamp: December 13, 2023, 04:24:48 am
content: I have the big brother to the one in the OP. It does up to 50V / 50A (yes thats 2.5kW!). Uses a thyristor pre-regulator, with a linear post regulator. Weighs about 45kg, mostly from the massive iron transformer in the middle.

author: MathWizard
author_rank: Super Contributor
timestamp: December 15, 2023, 10:41:02 pm
content: Quote from: macboy on December 12, 2023, 04:21:11 pmSo how noisy would you say that 6282 was compared to some other design without Triac's ? I've only worked with triac circuits and parts a few times, but they can have pretty funky waveforms.I have some salvaged stereo transformers that have just a little too much voltage for a lot of chips, and I had to drop a 10-20V once across resistor's. I should try redone some of that with BJT's. But I wondered back then about Triac's too. IDK if it's doable or practical, or expensive, but I'd still consider it for some project's