8v switching power supply

[Al Kossow]

I don't know if anyone has come across this model of 12v supply before, but it is adjustable from 0 to 12v
and it works fine as an 8v supply for S-100 systems as an alternative for the monster linear non-regulated
supplies normally in the system

MZMW MS-600-12

『USA』12V 50A 600W DC Switching Power Supply Adapter PSU for LED Light/3D Printer | eBay

+V: DC power output “+”. Load stability:±0.5%. -V: DC power output “-“. Output Frequency:85%. Output Current:50A. Output Power:600W. Connection instruction. High efficiency and low operation temperature.

www.ebay.com

 

[gslick]

MZMW, because MW was already taken.

A Mean-Well RSP-320-7.5 is $53.20 at DigiKey. It is rated at 40A at 7.5V, with an adjustment range of 6V - 9V.
215*115*30mm vs. 215*115*50mm of the MZMW MS-600-12.
Working temperature of -30 ℃ ~ +70 ℃ vs -10 ℃ ～ +50 ℃ of the MZMW MS-600-12

I wonder how the construction quality of the two brands compare. Looks like the adjustment range of Mean-Well 12V supplies doesn't go down as far as 8V, and they have fewer models with 7.5V outputs than 5V and 12V output models. Their 7.5V models with higher power ratings than the RSP-320-7.5 are a lot more expensive.

 

[cjs]

I wonder how the construction quality of the two brands compare.

Mean Well has an excellent reputation from all I have heard. My own experience is that my $40 Mean Well 4-rail PSU doesn't have a minimum power draw to maintain accurate voltage regulation, whereas a outwardly similar $20 unit requires you to, put a certain amount of load on the +5V (and I think +12V?) rails or the voltage will swing out of spec. (This was noted in the spec sheet, though.)

 

[norwestrzh]

I'm using a Mean Well S-150-9 on a 5v only backplane (no +/-12 required). It is easily adjustable to +8v and works very well. Specs. say it is capable of 16.7 A output. Way more than what I require.

Roger

 

[johnx993]

I used the MeanWell equivalent to replace the linear PS in my Altair 8800a.
It's been working without fault since 2019. Very pleased with it.

 

[Hugo Holden]

I think there is nothing at all wrong with the original Analog power supplies with the iron core transformers. They are big, heavy and expensive and from an earlier World of power supply design, but it is those things that make them more interesting and fun for vintage computing. Plus they have a couple of advantages, there is no switching noise and generally they don't fail in a way that threatens downstream parts. But, of course, you have to be enthusiastic enough to source the big iron cored transformers, or have a transformer company wind them for you, and to buy the required very high uF value capacitors (values like 50,000 uF typical) and use industrial style bridge rectifiers bolted to your chassis. But when you have done that, it is all very "steam punk" and much more satisfying and authentic than any off the shelf modern SMPS to power an S-100 computer, that will put interference all over your MW AM radio band. Maybe I'm one of the few who has some romantic attachment to the vintage technology, but this is the "vintage" computer forum right ? Do you really want to fit a Tesla Electronic motor drive system into your model T Ford and program it to "insane" mode ?

 

[Al Kossow]

I think there is nothing at all wrong with the original Analog power supplies with the iron core transformers.

There is if you no longer can lift it youself and you want to do something with the chassis.

 

[cjs]

There is if you no longer can lift it youself and you want to do something with the chassis.

Vintage computing is not for the weak! :-)

 

[peter@vcf]

A big advantage of using switch mode power supplies is that there is minimal 50/60 Hz ripple at the output. This means you can run the 8V rail at say 7V which significantly reduces temperature of the onboard regulators.

 

[Hugo Holden]

A big advantage of using switch mode power supplies is that there is minimal 50/60 Hz ripple at the output. This means you can run the 8V rail at say 7V which significantly reduces temperature of the onboard regulators.

That is true.

In many cases, in certain applications, where noise was an issue, oscilloscopes for example, the power supply design M/O was to have switching regulators initially. This got the output voltage stable, even with line fluctuations, so that this voltage could be fed into final analog regulators, with minimal heat dissipation in those regualtors.

In most cases, the DC supply in vintage S-100 computers had to be kept in the 8.5 to 11V range, prior to the 5V regulators on the boards, because they require a minimum of 7.5V input and line voltage fluctuations had to be allowed for.

But it is very hard to resist the alure of large iron cored transformers, big rectifiers and gigantic electrolytic capacitors, oh how they turn my head.

To run my SOL-20 at the lowest possible line voltage and not have it bothered by line voltage fluctuations, I designed this machine:

https://www.worldphaco.com/uploads/THE_CONSTANT_VOLTAGE_MACHINE.pdf