External PSU for Falcon

[jwd]

My falcon had its internal PSU blow a few years after i bought it new in the 90s, as i had loads of ATX PSUs lying about i didn't bother to fix it so binned it and used a newish ATX from the time, falcon seemed to behave better (less crashes) and ran cooler so the idea of an external brick suited me.

Fast forward to today and my falcon needs some love, firstly a new PSU, logic would suggest a brand new ATX as a replacement for my old ATX, simple plug and play for me. I mentioned my setup to @Badwolf at the recent show in Hythe and he did mention that new ATX style PSUs require a minimum load and regulate the voltages on the 3.3V line, so not such an easy replacement then. Looking at some specs of newish ATX they do require minimum loads some on 12V (more than falcon uses) and 3.3v which it obviously doesn't. I even have some older ATX (seasonic mini) but alas requires a higher 12v minimum load than the falcon uses. The answer would be to place a dummy load on the outputs but this is a bit messy for my liking so if anyone knows of a modern ATX that doesn't require minimal loads for regulation please let me know (i doubt there is tbh), alternatively the other option I was looking at is :

https://www.ami64.com/product-page/retr ... -eu-au-usa

Seems ok, obviously need a different connector end which isn't a problem but more to the point its built with retro care in mind.

Does anyone have any reservations on the above for a Falcon?

[Badwolf]

Seems ok, obviously need a different connector end which isn't a problem but more to the point its built with retro care in mind.
Does anyone have any reservations on the above for a Falcon?

Can't remember what the 5V line current requirement is for the Falcon. Is 4A sufficient? Feels like it should be, but not sure what the offical requirements are.

I can't see anything else obviously wrong. 12V is massively overpowered for what's needed, but no obvious harm unless you short it.

I'd tend to agree with your reasoning that something built ground-up to keep old hardware working seems like a better match than a modern off-the-shelf ATX.

Cheers,

BW

[mrbombermillzy]

Maybe an SFX form factor PSU?

I had this exact problem when trying to get something that would accept a low load, when putting an Amiga 500 board into a Checkmate 1500+ case.

It may have more of a chance of fitting into the F030 case too if you are lucky/creative.

I can try to get info on a low load model for you.

EDIT: Here's one that will work with the F030, although it's not the thinnest: https://www.checkmate1500plus.com/Products.aspx?id=379

[Badwolf]

EDIT: Here's one that will work with the F030, although it's not the thinnest: https://www.checkmate1500plus.com/Products.aspx?id=379

17 Amps! Put a fuse on the output of that bad boy.

BW

[exxos]

A low power ATX such as the mini ones which can be around 125w-250w would be better. Still a massive overkill for like 20watts the falcon may use.

[frank.lukas]

Why not repair the original Falcon power supply? It's a good power supply.

[exxos]

Why not repair the original Falcon power supply? It's a good power supply.

He said he binned it.

[jwd]

Thanks for all the comments, didn't know about SFX PSU tbh, having a dive into them but seem most require minimum drivers as per their big brothers.

@mrbombermillzy had a look at that (SFX-200W), looks good but can't find minimum load specs for it, found a checkmate pdf that actually talks about it (see quote below) so strange the SFX PSU they sell wouldn't have the specs listed fully

Below from - https://checkmate1500plus.com/generalfi ... l-V2.0.pdf

Some notes on power supplies
Compared to a typical PC, Amigas use very little power. An unexpanded
Amiga 1200 uses less than 10W for example, and with an ‘030 CPU and
hard drive added to the system the power consumption is still most likely
less than 15W. PC power supplies tend to be marketed on their maximum
power output capacity, as this is critical for today’s power-hungry CPUs
and GPUs. However, their design typically also has a minimum power
draw requirement, which is a minimum amount of current that is needed
to flow in order to properly regulate their output. Many power supplies
will shut down if they try to start without the minimum required load
(in this case, the PSU will run for a second or two before shutting itself
down), but some – especially cheaper models – will allow their output to
vary and drift, potentially damaging the Amiga.
Minimum load conditions aren’t often published in the specifications of a
PSU, but they can sometimes be found in the technical data sheet if one
is provided. As a rule of thumb, the minimum load requirement is lower
for power supplies with a lower maximum output – 100W is likely to be
more than enough for any Amiga setup. Good quality PSUs will also tend
to have a lower minimum load requirement than poor quality units. A
PSU should be selected that has a minimum load requirement which can
be met by the Amiga and its peripherals.
In addition, the PSU picture is further complicated by the fact that
PSUs generally have a main output rail, to which all the other rails are
secondary, and which is the rail for which the minimum load is most
important. This used to be the 5V rail, which was the most heavily used
Section 26
98 | User manual version 2.0
Rail 15 Ohm 10 Ohm 5 Ohm 2 Ohm
3.3V 0.22A / 0.73W 0.33A / 1.1W 0.66A / 2.2W 1.65A / 5.4W
5V 0.33A / 1.67W 0.5A / 2.5W 1A / 5W 2.5A / 12.5W
12V 0.8A / 9.6W 1.2A / 14W 2.4A / 28.8W 6A / 72W
rail in the past, and is the most heavily used rail in the Amiga. But in
more recent times, PSUs instead have used the 3.3V rail as their main
output, which the Amiga doesn’t use and therefore doesn’t provide
any load at all to meet the minimum loading requirements. Even more
recently, to cope with the huge concentrations of power required in
CPUs and GPUs, the 12V rail has become the main output, with PCs then
converting this supply to lower voltages locally for whatever parts need
it. The Amiga uses small amounts of 12V power, which in combination
with extra peripherals like mechanical hard drives and fans may or may
not meet the supply’s minimum load requirements. Using the 12V rail as
the main power source for the computer has meant that the 5V rail has
been relegated to much lesser duties, and as a result its capacity has
been reduced in modern supplies. There should still be plenty available
for Amiga use, but it’s something to bear in mind – any PSU that offers
less than 4 or 5A on the 5V rail might cause problems on a heavily
expanded setup

Can't actually find written Falcon load specs but can find the spec of the Falcon PSU form the service manual :

2022-11-09_16h00_23.png (112.74 KiB) Viewed 1682 times

7 amps (+5v) seems excessive for a base Falcon, no spinner in mine so that will reduce load too, suppose should really measure mine under load and see.

Leaning towards the "RetroPower PSU Amiga OLED Digital International" but again will need to ask them about minimum load characteristics and whether no load on the -12v line will have any effect

or am i being too paranoid here ?

[exxos]

IIRC the falcon pulled 2 amps on the 5v rail. Maybe 100mA on the 12v. Did document it somewhere by think those are about correct.

[Badwolf]

...or am i being too paranoid here ?

Yeah, reckon you are. I doubt the 12 and -12 rails will have any bearing on a PSU built to drive an Amiga. I doubt they'll even actually measure 12V.

It's pretty much just floppy (12V) which is bugger all and RS232 (-12) which is the square root of the former.

It claims 4A and...

IIRC the falcon pulled 2 amps on the 5v rail. Maybe 100mA on the 12v. Did document it somewhere by think those are about correct.

...that should be just dandy, I reckon.

BW