Ampere overhead for CPC464

Started by Zuki, 07:46, 12 January 22

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Zuki

I am bringing my old CPC464 back to life. My old CTM640 is long dead, but with a salvaged cathode-ray TV and an external power supply the dear old CPC sprung back to life (after cleaning the on-off switch).
Now the cheap external powersupply has died, and this time I want to buy something better.

I know, that the the CPC464 should be feeded 5V at 2A.

Now my (electro-noob) question: Can I risk frying anything if I get something with a +2 ampere output? (I know, that a higher Ampere output makes me able to drive more expansions directly on the bus, but is there anything I should be aware of?)
I am considering this guy: https://minielektro.dk/stromforsyning-sps-25w-5v-5a.html?gclid=Cj0KCQiA8vSOBhCkARIsAGdp6RSVHzy94dOWrtLSy0pu6gGHNWmv9ksKAwfSnBLRg4Uc0eg9jpRl4RQaAtfnEALw_wcB

The plug should be connected with "live" on the internal pin - that I can do - but, again is there anything else I should be cautious of? Would it be better to get the version with 3 Ampere output?

Hope you can help. After being mothbagged for +30 years, the thing is now up and running again. Would be so sad to fry it because of some stupid mistake ;)

Best,
Zuki

pelrun

The current rating of a PSU isn't how much current is forced into the circuit - it's how much current can be *drawn* by a device before the PSU can't maintain it's voltage any more and it sags. So no, it doesn't normally matter what the current rating is as long as it's higher than what the device needs.
The only risk of a very high current rating is if the device is faulty and has a short - the short will then pull as much current as it can and can potentially burn; in that case you *want* the PSU to run out of steam before things get worse. So it's better not to have a 20A rated PSU when 3A is sufficient.

Zuki

Thank you for your kind answer.

Can I ask, what you would suggest - the 3A or the 5A version? I intend to run a couple of extensions; A M4 board (that wifi gotta use some power), a RAM/ROM expansion etc.
I think 3A should be more than enough for this, but as I take it, there would be no harm in going for the 5A?


best,
Z

pelrun

If 3A causes problems then 5A won't be any better, you would probably need to find a 5.1-5.3v supply instead.

GUNHED

Take a 5A, most of the time the actually just bring up 3A... or drop voltage with more than 2A or so.
Here quality is needed, better take an old PC PSU instead of switching PSU (bad!).
http://futureos.de --> Get the revolutionary FutureOS (Update: 2022.03.09)
http://futureos.cpc-live.com/files/LambdaSpeak_RSX_by_TFM.zip --> Get the RSX-ROM for LambdaSpeak :-) (Updated: 2021.12.26)

pelrun

A PC PSU *is* a switching PSU.  ??? 99% of supplies on the market are switching. You're definitely not going to get a 2A+ non-switching supply unless it's a lab PSU that weighs several kilograms from the big transformer that needs to be in it.
So I really don't see the point of that advice. I've used all sorts of switching supplies right down to a dodgy hacked together low-frequency board with no issues that weren't ultimately something else.

Zuki

Thanks for the advices.
I am unfamiliar with the concept of "linear" vs "swithced" PSU's


I think the one I've bought must be swithched, as it is quite small. https://minielektro.dk/stromforsyning-sps-25w-5v-5a.html?gclid=Cj0KCQiA8vSOBhCkARIsAGdp6RSVHzy94dOWrtLSy0pu6gGHNWmv9ksKAwfSnBLRg4Uc0eg9jpRl4RQaAtfnEALw_wcB

I see, that some posters dislike swithced PSU's. - I'd like to know why? Is there a risk of damaging the CPC, or is it some question of stability issue?

Thanks in advance

GUNHED

Quote from: pelrun on 05:54, 13 January 22
A PC PSU *is* a switching PSU.
Only the modern ones, not the ones you get for cheap.


About switching psu's: You don't have to believe me, just ask an hardware expert like @Bryce . Maybe he can comment on that and bring us on 'up today'.
http://futureos.de --> Get the revolutionary FutureOS (Update: 2022.03.09)
http://futureos.cpc-live.com/files/LambdaSpeak_RSX_by_TFM.zip --> Get the RSX-ROM for LambdaSpeak :-) (Updated: 2021.12.26)

pelrun

#8
YES EVEN THE ONES YOU GET FOR CHEAP.  :picard2: :doh: Especially so, as the kilograms of raw iron in a real linear psu make those the expensive ones.

Bryce is not the only person here with valid hardware expertise.

Bryce

Quote from: GUNHED on 21:40, 13 January 22
Only the modern ones, not the ones you get for cheap.


About switching psu's: You don't have to believe me, just ask an hardware expert like @Bryce . Maybe he can comment on that and bring us on 'up today'.

All PC PSU's are switching PSU's, right back to the days of the 8086, whether cheap or expensive. I have never seen a linear PC PSU.

Bryce.

Zuki

Well it certainly is working now.


Thanks for all your kind advice!  :)


Best,
Zuki

GUNHED

Quote from: Bryce on 09:51, 14 January 22
All PC PSU's are switching PSU's, right back to the days of the 8086, whether cheap or expensive. I have never seen a linear PC PSU.

Bryce.
If you ever come to Munich, then step by. My Desktop CPC has a PSU with copper coil. Yes, it makes some head, and it heavy like a stone, but I never ever had power problems.  :)
Next time I need to open it I will take some pictures, but you won't see much because the PSU is located at the bottom.


It's fun system though, it has:
- 6128 mainboard
- 3" drive (no belt, direct motor)
- 5,25" drive (HD drive actually, but used in MFM mode)
- Real-Time-Clock
- 224 KB EPROM space
- 576 KB RAM (all together)
- HD20 hard disc with four partitions of 5 MB
- Two joystick ports
- One Mouse port
- Floppy ABBA switch (and side switch), true Ready signal of course
- DOS and OS switch
- Reset button
- 50 / 60 Hz switch
- Video out for CPC and VGA monitors
- Video out for Television and Video Recorders
- Built in speaker (not much better though)
- and.... a real PSU  ;)
http://futureos.de --> Get the revolutionary FutureOS (Update: 2022.03.09)
http://futureos.cpc-live.com/files/LambdaSpeak_RSX_by_TFM.zip --> Get the RSX-ROM for LambdaSpeak :-) (Updated: 2021.12.26)

SRS

ok, this is now quite off topic, but: having copper coils is not a sign of a linear PSU. Switching PSU do have copper coils, to, but smaller ones as they work with higher frequencies. what is nearl all the "trick" why it makes them cheaper. less iron, less copper, less space ...

'ave a look here: SMP Wikipedia

Bryce

Quote from: GUNHED on 17:26, 14 January 22
Quote from: Bryce on 09:51, 14 January 22All PC PSU's are switching PSU's, right back to the days of the 8086, whether cheap or expensive. I have never seen a linear PC PSU.

Bryce.
If you ever come to Munich, then step by. My Desktop CPC has a PSU with copper coil. Yes, it makes some head, and it heavy like a stone, but I never ever had power problems.  :)
Next time I need to open it I will take some pictures, but you won't see much because the PSU is located at the bottom.


It's fun system though, it has:
- 6128 mainboard
- 3" drive (no belt, direct motor)
- 5,25" drive (HD drive actually, but used in MFM mode)
- Real-Time-Clock
- 224 KB EPROM space
- 576 KB RAM (all together)
- HD20 hard disc with four partitions of 5 MB
- Two joystick ports
- One Mouse port
- Floppy ABBA switch (and side switch), true Ready signal of course
- DOS and OS switch
- Reset button
- 50 / 60 Hz switch
- Video out for CPC and VGA monitors
- Video out for Television and Video Recorders
- Built in speaker (not much better though)
- and.... a real PSU  ;)
I'd be more interested in knowing the make and model so that I could investigate its specs.

Bryce.

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