Power Supply

[fixit9660]

I'm researching building an SC503/Z180-based system and I'm wondering about power.

Whilst I feel the 600Watt ATX PSU I've got lurking spare may be a little over-zealous, I don't want to run out of juice with a small PSU in a short while, especially as power limitations can cause some really odd performance issues.

I also don't want to discover later that I'm missing one or more useful voltage supplies, like 21.5 volts for burning EEPROMS, or similar.

In this respect, the ATX PSU (over)supplying Amps in every category, and +3.3v, +5v, +12v, -12v supplies, seems to have its attractions.

Does anyone know what their particular "brew" is using in terms of volts and amps please?

I realise this is bit "how long is a piece of string", but I'd like to get some idea of what voltages and power to provide.

[Alan Cox]

On Tue, 21 Mar 2023 at 14:38, fixit9660 <fixi...@gmail.com> wrote:
>
> I'm researching building an SC503/Z180-based system and I'm wondering about power.
> Whilst I feel the 600Watt ATX PSU I've got lurking spare may be a little over-zealous, I don't want to run out of juice with a small PSU in a short while, especially as power limitations can cause some really odd performance issues.

Unless you specifically need other voltages or start hanging floppy
disks and physical spinning rust off it then most people seem to be
using the standard USB 500mA wall warts and similar. It doesn't need a
lot of power. It's all CMOS and the memory is generally a single 512
or 128Kbyte SRAM not banks of 4116.

If you do need disks and all the rest of it then a small ATX PSU (with
some appropriate size fuses) does make a decent power option.

[David Richards (djrm)]

I find most boards will run off either 5v or 12v, and for this I usually use one of the following:

 * 5V USB directly from PC

 * 5v USB from powered hub

 * 5v/12v from external disk power socket on PC

 * +12 -12 5V from small proprietary scrapped PC
I se Alan has raised the point about using a fuse - good advise, A big PC supply could do a lot of damage.

I was caught out trying to program some 21 volt eproms recently but a coin cell in the Vpp lead came to the rescue!

[Dave White]

I've just bought a bunch of these - great for reusing old PC power supplies and gives me all the voltages I need. You can change the fuses for smaller values if you want to reduce the risk of damage to your systems.

24 Pin Desktop ATX Power Adapter Board Computer ATX Power Supply Breakout Transfer Board Outlet Wiring Adapter Extension Module| | - AliExpress

Four of them, with cases and shipping came to under $15.

[fixit9660]

I just realised I never thanked you for the all for the help. Apologies, and thank you!!! (It only took me just over a year :-(  ) I finally ordered an SC591, an am hacking a smaller ATX PSU for now. Thanks again.

[horus falcon]

How Do, All?

I'm late to this discussion, so sorry if not well informed on all aspects.  That said:

There are power supply units made by Meanwell which are compact, efficient, and provide good  amounts of capacity inexpensively.  These can be found in various places... the usual suspects:  AliExpress, Ebay, Mouser, Jameco, Digi-Key, etc., and Meanwell has a distributor locator at:  https://www.meanwell.com/distributors.aspx if you need to find someone in your locale.

Is that "SC591" an ADSP-SC591 DC/DC Converter?  If so, and you intend to program the DSP on board, you'll want to look at:  https://www.analog.com/media/en/technical-documentation/application-notes/ee442v01.pdf

Later On,
David

--
You received this message because you are subscribed to the Google Groups "retro-comp" group.
To unsubscribe from this group and stop receiving emails from it, send an email to retro-comp+...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/retro-comp/15f5769d-14e3-4dca-8ce6-3b6a82ab4c61n%40googlegroups.com.

[horus falcon]

Hi, Andrew,

Oh, that would be another board by Steven Cousins?  Off I go to Tindie, then!  Thanks.

Later On,
David

On 4/1/24 09:14, fixit9660 wrote:

Hello David.

The SC591 I bought is the Z180 CPU-based package, of Backplane, CPU, and Power input monitor. You can see it here: https://smallcomputercentral.com/modular-z50bus-system-sc500-series/ and here 

https://www.tindie.com/products/tindiescx/sc591-z180-romwbw-cpm-computer-kit-for-z50bus/

I might end up buying discreet PSU's like you mention because the ATX is overly large in size and power, but it's what I've got at the moment, so is free, and designed for powering a computer.

Cheers,

Andrew.

To view this discussion on the web visit https://groups.google.com/d/msgid/retro-comp/ab600480-dd3f-4eb8-a1e0-717c4639dc76n%40googlegroups.com.

[horus falcon]

Mornin', Andrew,

I see this is rather more complex than the SC126 that I have, and uses an input source of between 8 and 15 vdc. Consider using a small sealed lead-acid or LiPo battery, maybe?  I run my SC126 from any of three 10,000 maH phone bank batteries, which makes it easily portable, but it only requires 5 vdc.  It also eliminated any and all ripple, so it runs cool and without any untoward effects.

In any case, and with any power supply you might choose, this ought to be a fun project.  There's a BASIC-80 (aka MBASIC) manual in ROMWBW's contrib section that's my doing, and some how-to's on establishing serial comms and other stuff, too.  Enjoy building this project!

Later On,
David

On 4/1/24 09:14, fixit9660 wrote:

Hello David.

The SC591 I bought is the Z180 CPU-based package, of Backplane, CPU, and Power input monitor. You can see it here: https://smallcomputercentral.com/modular-z50bus-system-sc500-series/ and here 

https://www.tindie.com/products/tindiescx/sc591-z180-romwbw-cpm-computer-kit-for-z50bus/

I might end up buying discreet PSU's like you mention because the ATX is overly large in size and power, but it's what I've got at the moment, so is free, and designed for powering a computer.

Cheers,

Andrew.

On Monday 1 April 2024 at 11:21:15 UTC+1 David Reese wrote:

To view this discussion on the web visit https://groups.google.com/d/msgid/retro-comp/ab600480-dd3f-4eb8-a1e0-717c4639dc76n%40googlegroups.com.

[fixit9660]

Hi David.

I did consider employing some batteries, but only because they make excellent ripple and other noise absorbers. I hadn't thought of running the whole thing off one. Food for thought.

Thanks for the BASIC-80 note. Downloaded and considering printing/binding it. PDF's are "ok" for the odd reference but I find there's nothing better than the printed page for several reasons; you don't have to boot it up to read it, and you can put notes in the margins, amongst others.

Amongst your Contrib notes I saw the Propeller keyboard docs; My aim is to eventually have a stand-alone system, with keyboard, and display of some sophistication, so that was intersting too.

So much that I used to have and need to replace. <sigh>

[horus falcon]

The notes on Propeller were contributed by someone else, but, yeah, that whole section is packed with good stuff.

Later On,
David

To view this discussion on the web visit https://groups.google.com/d/msgid/retro-comp/885f23d8-2d54-44b1-8ddd-6b50cf56c4ben%40googlegroups.com.

[Harry Speer]

20:36, 8:36 PM, Tuesday, June 9th, 2026

Re: Using an ATX Power Supply to Power-Up your Backplane(s) ??

Resurrecting an old thread from about 2 years ago,   1. Have any of you used an ATX power supply to power-up your RCBus or RC2014 Backplane ??   2. How well, or how badly, did it go ??   I am figuring to put my RCBus computer inside of an old ATX PC Case.   Another reason to use the ATX is to power real floppy drives  with floppy diskettes, and possibly also an IDE/PATA Hard Drive. 

So Please,  if you have used an ATX  P/S  for your Backplane, Did it Work ??

Harry

[Dave White]

As I mentioned a few posts up, I'd just bought some adapters from AliExpress. Since then, I've used them on a couple of projects and had no problems with them.

[Alan Cox]

Other than blowing up a very cheap grade ATX PSU due to a bug in my prototype fine. Gives you a good 5v and 3v3, power good for a clean reset. Make sure it's got fast acting polyfuses or similar for the current range you actually need as the max current on ATX is large.

Alan

To view this discussion visit https://groups.google.com/d/msgid/retro-comp/c576f39f-1971-4be1-a645-517d3b2fc466n%40googlegroups.com.

[Harry Speer]

After Due Consideration, I am choosing a set of 3 Mean Well Single Output Power Supplies instead.

For the +5 V DC, I already have one of the Tiny Mean-Well Model # RS-15-5 PS  -   +5V @ 3 Amps,  15 Watts.

I also already have one of the slightly bigger Mean Well for +12V DC  -  a Model # RS-25-12   -  +12V,  @ 2.1  Amps,  and 25 Watts.   I had bought these back when I was focused on S-100. 

So then I checked the Mean Well datasheet PDF's and chose a  Mean-Well # RS-15-12,  for the  -12V DC @ 1.3 Amps, 15.6 Watts  -  as this was the lowest amount of current I could get for a Mean-Well RS series at 12 Volts DC Single Output.   

To make it acts as a  -12V power supply,  Just swap the Plus and Minus,  basically  wire  the +12 V DC  "backwards".  And Since this is Only for the RS-232 drivers, the MC1488 driver chips,  I feel quite certain that 1.3 Amps will be more than enough.  This one is only $8.60 USD with Tax and possible tariffs.  Mouser.Com.   

As for the ATX supply,  I may use that in future for Drives and for ATX chassis cooling fans.   I think one small 80mm fan will be plenty and the case already has that opening just next to the ATX Power Supply. 

I would just keep it at low RPM or But a High Quality 80mm like a Noctua.  Overkill, I know, but they are pretty darned quiet and I like that a LOT.   I have been Very Pleased with each of the Noctua Fans I have bought, even with the extra cost above most other brands.  Noctua is really a good example of  "You Get what you pay for".  Exceptionally high-quality.  I'm beginning to get used to the "muddy brown" color. 

 

These little single output Mean-Well Power Supplies are pretty well built but I think I may want a set of 3  small fuses and any other protection between the power supplies and the actual Backplanes.  I have  already "test fitted"  the two RCBus Backplanes Side By Side.  Using Steve Cousins SC709 Backplanes Here:     

https://smallcomputercentral.com/rcbus/sc700-series/sc709-rcbus-backplane/ 

 --  and they fit side by side and take up about the same space as an ITX motherboard.  And I have one of Steve's  Dual-Backplane prototype cards.   SC736  -  Steve calls it a  "RCBus Prototyping Module".    A photo of one of these fitted to the 2 backplanes is here: 

  

 https://smallcomputercentral.com/wp-content/uploads/2026/01/sc736-in-use-a-w600.jpg  

The reason I am using 2 backplanes is analogous to the VME Dual-Backplanes - J1 and J2 - to be able to handle the 32-bits of Address Bus and 32-bits of Data Bus for the Future 68020 CPU and the 68030 CPU. 

I am starting off with a set of Mark Durham's  68000 on the RCBus  cards.  See Marks GitHub pages here:  

https://github.com/MarkD833/RCBUS-68xxx

Mark was very generous to ship me a set of his blank boards some months ago.  But not yet built. 

I have been delayed building them because of my eye-sight problems.  I recently had an appointment with my eye doctor and she prescribed a set of "soldering glasses" for use with an additional  "desk mounted magnifier with light" - as I need the soldering surface to be magnified in addition to the glasses.  

I'm hoping that getting these working all together will allow me to see the board, with parts, and the soldering iron and the solder, all In-Focus so that I can begin the soldering work.  I did not anticipate that these would be needed. An unpleasant surprise that has delayed my work quite a bit.  

And I also saw some "soldering glasses" on Facebook but those would NOT be prescription.  I am very "antsy" to get things moving ahead here. 

My thanks again for all of your suggestions and input !!  All of them have been very helpful, especially about the amount of current that an ATX can output. I will use extra caution to limit how much current can feed my backplanes, in addition to the voltage regulation. Very Many Thanks !!  Very Helpful !!

Harry