<![CDATA[when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking]]>when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking

]]>https://board.circlewithadot.net/topic/98ef9f6e-3c5a-4743-99ae-5384d96d7115/when-i-say-that-the-imsai-8080-psu-has-soda-can-sized-caps-i-m-not-jokingRSS for NodeThu, 30 Apr 2026 22:34:06 GMTTue, 21 Apr 2026 22:48:03 GMT60<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 18:52:14 GMT]]>@lynn As a schoolboy I worked with a cast-off LACE MK II analogue computer.

Which was valve based, and had big power supplies with very large capacitors.

My little brother discovered that if you took a spare one of these, and clamped its terminals in a stand nicked from the chemistry lab, and then put 6.3v AC at many, many amps across the terminals from one of the computer's massive valve heater transformers, the capacitor can would shoot right across the school playground.

]]>https://board.circlewithadot.net/post/https://c.im/users/TimWardCam/statuses/116449865523791695https://board.circlewithadot.net/post/https://c.im/users/TimWardCam/statuses/116449865523791695Wed, 22 Apr 2026 18:52:14 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 16:52:41 GMT]]>@brouhaha @fae yeah I donโ€™t wanna modify the front panel of my IMSAI but I did consider putting something like that inside somewhere ๐Ÿ™‚

If I ever go for a more homebrew S100 system something like that would be cool on the front panel for sure

]]>https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116449395462548706https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116449395462548706Wed, 22 Apr 2026 16:52:41 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 14:17:26 GMT]]>@brouhaha @lynn OMG I had never heard that https://www.youtube.com/watch?v=bMS6G83NqFQ

]]>https://board.circlewithadot.net/post/https://mastodon.social/users/rrmutt/statuses/116448784993070061https://board.circlewithadot.net/post/https://mastodon.social/users/rrmutt/statuses/116448784993070061Wed, 22 Apr 2026 14:17:26 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 12:35:58 GMT]]>@brouhaha @fae @lynn

The designer of the Rational R1000 told how his engineering-ring once shorted pins on this backplane.

Link Preview Image
Fil:R1000 s100 Backplane 2.jpg - DDHFwiki

favicon

(datamuseum.dk)

Those grey metal blocks at the bottom is where you bolt on the AWG 3/0 cables to the power-supplies, each of which is rated for 200A.

]]>https://board.circlewithadot.net/post/https://expressional.social/users/phloggen/statuses/116448385959377914https://board.circlewithadot.net/post/https://expressional.social/users/phloggen/statuses/116448385959377914Wed, 22 Apr 2026 12:35:58 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 12:29:53 GMT]]>@lynn @fae
One of my friends put ammeters on the front panel of his homebrew system, since he often reconfigured it, and wanted to keep track of how much current margin he had.

]]>https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116448362048622752https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116448362048622752Wed, 22 Apr 2026 12:29:53 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 12:28:35 GMT]]>@lynn @fae
Even so...
Most cards other than 8080 CPU cards had their main power draw on the +5V rail. Notable exceptions were dynamic RAM cards using 4K or 16K DRAMs, which drew a lot of current from the +16V (+13.5V IMSAI) rail.
I could see having a 22-slot backplane full of fancy cards that each drew perhaps 3A of +8V. AFAIK, no stock S-100 chassis had a power supply that could handle that, nor could any stock backplane, and you'd need extra cooling fans blowing over the cards.

]]>https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116448356959232722https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116448356959232722Wed, 22 Apr 2026 12:28:35 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 12:14:28 GMT]]>@brouhaha @fae I mean, who knows. With a large enough backplane, and cards... The Matrox ALT-256 claims you can add up to 24 of them to get 24-bit color ๐Ÿ™‚

]]>https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448301430066682https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448301430066682Wed, 22 Apr 2026 12:14:28 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 12:13:16 GMT]]>@fae @lynn
I think they were suggesting that the chassis full of cards consumed 1400A from one or more of the DC supply rails. An obvious exaggeration.

]]>https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116448296717632430https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116448296717632430Wed, 22 Apr 2026 12:13:16 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 11:56:11 GMT]]>@fae @brouhaha the 1400 amps was most likely an exaggeration, going by the IMSAI's original PSU manual, though maybe with the IEEE-696 spec they went a little crazier, i'd have to look that up ๐Ÿ™‚

]]>https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448229572559986https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448229572559986Wed, 22 Apr 2026 11:56:11 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 11:54:14 GMT]]>@brouhaha @fae fairly confident that one of the I/O ports was wired up for a parallel keyboard due to the character terminal card installed, but this thing came with neither the keyboard or disk drive, and I have since tried to re-wire the I/O card (I might still have pics of the original config somewhere, but like... good luck finding the right keyboard. i'll just talk to it over serial, somewhere down the line, probably)

]]>https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448221909615823https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448221909615823Wed, 22 Apr 2026 11:54:14 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 11:53:06 GMT]]>@brouhaha @lynn ah yea, and i was assuming the 1400A was the caps discharging?

]]>https://board.circlewithadot.net/post/https://pony.social/users/fae/statuses/116448217454930539https://board.circlewithadot.net/post/https://pony.social/users/fae/statuses/116448217454930539Wed, 22 Apr 2026 11:53:06 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 11:52:11 GMT]]>@brouhaha @fae I'm confident this was a single user system though -- there's an original CPU-A (i8080), a few RAM boards i think adding up to ~64k, ROM board, cassette interface, disk interface, serial/parallel I/O, and a character terminal ๐Ÿ™‚

]]>https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448213853366909https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448213853366909Wed, 22 Apr 2026 11:52:11 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 11:50:01 GMT]]>@brouhaha pretty sure this is all factory. It's also the PSU-C, Rev 1, the very first one they did.

I think a few months in they changed a bunch of the design, including replacing the transformer to one that can be wired for many different input voltages, though the caps were all wired from the top, exposed, so a little more dangerous ๐Ÿ™‚

]]>https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448205293448168https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448205293448168Wed, 22 Apr 2026 11:50:01 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 11:47:35 GMT]]>@brouhaha @fae 11 cards including the front panel ๐Ÿ™‚ I donโ€™t know if Iโ€™ll keep this config though.

Also keep in mind this is with all slots filled โ€” while itโ€™s a 22 slot backplane technically, only every other position of the board is populated with a slot

]]>https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448195727349637https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448195727349637Wed, 22 Apr 2026 11:47:35 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 11:44:46 GMT]]>@brouhaha @fae by the time that song came out, large configs were the norm ๐Ÿ™‚ but even before that, they turned out to be pretty decent multi user systems if you stuffed them full of cards

]]>https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448184636689703https://board.circlewithadot.net/post/https://woof.tech/users/lynn/statuses/116448184636689703Wed, 22 Apr 2026 11:44:46 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 11:33:57 GMT]]>@lynn
Color me unimpressed with IMSAI's use of 15VDC rated capacitors (assuming those are factory spec) on a supply rail they rate for nominal 13.5VDC. I never before noticed that IMSAI did that.
Aluminum electrolytics don't need DC bias derating like ceramics, but they should still be specified with some headroom. 15V is only 11% over nominal, and line voltage can easily be vary over time by more than ยฑ11%.
๐Ÿ˜ž

]]>https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116448142098781462https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116448142098781462Wed, 22 Apr 2026 11:33:57 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 11:02:28 GMT]]>@fae @lynn
But if you are wearing a metal watch, ring, etc, and get one of the supply rails shorted through it to ground or another supply rail, the supply will give all of the amps it can (usually much beyond its rated output, at least for seconds) through that metal. It can't electrocute you, but the metal can heat up enough to cause a serious burn. With a ring, potentially serious enough to lose the finger.
Lesson: remove watch and hand jewelry while working inside computers. Even PCs.
4/

]]>https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116448018356929944https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116448018356929944Wed, 22 Apr 2026 11:02:28 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 10:59:50 GMT]]>@fae @lynn
While almost everyone is aware of the dangers of AC line voltage, it is uncommon for people to be aware of the potential danger of low voltages. Skin contact with the +/-16V DC in an S-100 system is incredibly unlikely to cause any harm. You can grab the +16 with one hand, and -16 with the other, and your skin has high enough resistance that nothing happens.
3/

]]>https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116448007963546994https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116448007963546994Wed, 22 Apr 2026 10:59:50 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 10:56:29 GMT]]>@fae @lynn
The most common configuration IMSAI 8080 provided 22 slots and a beefy power supply, which resulted in MITS and other S-100 vendors having to offer similar configurations.
If you really did fill up a 22-slot backplane (e.g., with CPU, a few I/O cards, and sixteen 4K RAM.cards), you really needed a lot of amps. I'm sure that large S-100 system configurations were the inspiration for the song.
2/

]]>https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116447994837820465https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116447994837820465Wed, 22 Apr 2026 10:56:29 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 10:53:07 GMT]]>@fae @lynn
The S-100 bus power supplies were nominally +8V, +16V, and -16V, filtered but unregulated. Each card was expected to have linear voltage regulators from +8V to +5V, and, if needed, ยฑ16V to ยฑ12V.
The more cards in your system, the more amps of each supply you needed, though the "1400 amps" in the song is gross exaggeration.
Early Altair 8800 systems, and some others, had small backplanes with few slots, and were provided with wimpy power supplies.
1/

]]>https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116447981585206174https://board.circlewithadot.net/post/https://mastodon.social/users/brouhaha/statuses/116447981585206174Wed, 22 Apr 2026 10:53:07 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 10:30:02 GMT]]>@brouhaha @lynn i always wondered what that line was referring to... but last time i went digging i never found an answer... i guess now i know ๐Ÿ˜„

]]>https://board.circlewithadot.net/post/https://pony.social/users/fae/statuses/116447890812335279https://board.circlewithadot.net/post/https://pony.social/users/fae/statuses/116447890812335279Wed, 22 Apr 2026 10:30:02 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 09:41:07 GMT]]>@lynn @halcy I once disassembled an unsalvageable Thing that I donโ€™t even remember the purpose of and it had like ten 500 ฮผF / 250 V capacitors the size of a small boulder (think 500 ml cycling water bottle) each

โ€ฆthat were still rather charged.

]]>https://board.circlewithadot.net/post/https://tearoom.tearmoon.com/users/mia/statuses/01KPT914Y1DP9QA2T4VZZ45929https://board.circlewithadot.net/post/https://tearoom.tearmoon.com/users/mia/statuses/01KPT914Y1DP9QA2T4VZZ45929Wed, 22 Apr 2026 09:41:07 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 06:49:20 GMT]]>@lynn I want to sip the power juice

]]>https://board.circlewithadot.net/post/https://mastodon.gamedev.place/users/Ronflaix/statuses/116447022944475152https://board.circlewithadot.net/post/https://mastodon.gamedev.place/users/Ronflaix/statuses/116447022944475152Wed, 22 Apr 2026 06:49:20 GMT<![CDATA[Reply to when I say that the IMSAI 8080 PSU has "soda can sized caps", I'm not joking on Wed, 22 Apr 2026 06:45:33 GMT]]>@lynn feels like these could double as a smoke machine in a jiffy

]]>https://board.circlewithadot.net/post/https://icosahedron.website/users/halcy/statuses/116447008083248391https://board.circlewithadot.net/post/https://icosahedron.website/users/halcy/statuses/116447008083248391Wed, 22 Apr 2026 06:45:33 GMT