Power supply

[villain]

I really need to replace my CTM and therefore want to connect a TV with scart to my 6128. What I'm still looking for is a "power supply". Any recommendations for my purposes? I'm in Germany with no skills in electronics. :-)

[Bryce]

You actually need two power supplies, unless you go looking for a single supply that can give you both 5V and 12V.

I'm currently working on a small project that will conver the 6128 to a single 5V supply, but it's still in the prototype phase.

Bryce.

[villain]

Jep, but in any case I have no ideas which power supplies I could buy. :-) I was hoping there might exist something I could order anywhere... Universalnetzteil oder sowas.

Do you know when your little project will be finished? Maybe I could be patient for a little while.

[Bryce]

I'll be building and testing 4 prototypes within the next two weeks. If they work as expected and you can wait that long you can be an official tester.

Bryce.

[villain]

That would be a honour to me. :-) Two weeks are nothing in CPC's world.

[1024MAK]

The only currently available commercial product that I know of and can find is this on eBay


Mark

[SRS]

I'm in Germany with no skills in electronics.

Which part of germany is that with no electronic skills ? kaiser-wilhelm-land ?

I have two powersupplys, one "multipurpose" 5V and one 12V (from an old medion flatbed scanner which are very cheap at the bay) where I added a cpc compatible plug for about 45cent. Okay, you need some multimeter, soldering or screwdriving skills (Lüsterklemme und Schrumpfschlauch) for it ... but its quite easy to do.

[villain]

Which part of germany is that with no electronic skills ? kaiser-wilhelm-land ?

I have two powersupplys, one "multipurpose" 5V and one 12V (from an old medion flatbed scanner which are very cheap at the bay) where I added a cpc compatible plug for about 45cent. Okay, you need some multimeter, soldering or screwdriving skills (Lüsterklemme und Schrumpfschlauch) for it ... but its quite easy to do.

Tsts... "We" lost Kaiser-Wilhelms-Land already in 1919. :-) I'm quite close to the roots of Gottlieb Daimler, Carl Benz and Ferdinand Porsche but only from a geographic point of view.  (Mir sind dia wo's ganze Land am Läba halted  ).

Thanks to you and @1024MAK for your advices. If necessary I will think about them, but first of all I will wait for Bryce's results.

[SRS]

Bryces idea sounds interesting, indeed.

[1024MAK]

One method that can be used, is to buy a single output power supply unit (PSU), typically a modern switch mode type (SMPSU). Then use a DC-DC converter to supply one power feed to the CPC6128.

Either use a 5V PSU, and a boost type DC-DC converter to get the +12V supply. Or use a 12V PSU and use a buck (step-down) DC-DC converter to get the +5V supply. In both cases, the PSU must be rated for the maximum combined currents AND output powers on both the +5V and +12V supplies.

I have used a variation of this technique on another retro computer, where replacement PSUs (with multiple outputs) is hard to get.

Mark

[Lazy Dude]

One quick (ish) solution is to buy a small pc power supply second hand €20 on ebay, post 2000 dell optiplex ones are my fave.
You will need to sort out the dc connectors though, but as a reliable psu goes it's just the job.
Don't be tempted by cheap chinese stuff you see!

[Bryce]

One method that can be used, is to buy a single output power supply unit (PSU), typically a modern switch mode type (SMPSU). Then use a DC-DC converter to supply one power feed to the CPC6128.

Either use a 5V PSU, and a boost type DC-DC converter to get the +12V supply. Or use a 12V PSU and use a buck (step-down) DC-DC converter to get the +5V supply. In both cases, the PSU must be rated for the maximum combined currents AND output powers on both the +5V and +12V supplies.

I have used a variation of this technique on another retro computer, where replacement PSUs (with multiple outputs) is hard to get.

Mark

That's pretty much what my device is going to do. I'll be using a step up DC/DC converter to bring the 5V up to 12V. It's easier than doing a step down because the 12V rail uses a lot less current and it's also not variable, ie: The 5V rails load changes as you add expansions, whereas the 12V is pre-defined to the current that the drive requires.

However, there's a mistake in your calculation above: The 5V PSU needs to supply more current than just the sum of the 5V and 12V rails, because if for example the 12V rail needs 1A (which it doesn't but it makes the calculation easier) and the DC/DC converter is 96% efficient, then pulling 12V 1A from a 5V source would require almost 2.5A from the 5V supply.

In reality the 12V rail actually only pulls about 150mA, but this will require an extra 375mA from the 5V PSU.

Bryce.

[1024MAK]

However, there's a mistake in your calculation above: The 5V PSU needs to supply more current than just the sum of the 5V and 12V rails, because if for example the 12V rail needs 1A (which it doesn't but it makes the calculation easier) and the DC/DC converter is 96% efficient, then pulling 12V 1A from a 5V source would require almost 2.5A from the 5V supply.

Yes, absolutely, you can't get something for nothing! Which is why I said "AND output powers on both the +5V and +12V supplies". I wanted to keep it short without going into the full details. But you have now explained it nicely.

I agree, for most machines, using a 5V main supply and a boost type DC-DC converter to get the +12V supply is the best arrangement.

I look forward to seeing your developments

Mark 

[villain]

I'll be building and testing 4 prototypes within the next two weeks. If they work as expected and you can wait that long you can be an official tester.

Bryce.

Any news?

[Bryce]

Yes, I've made the PCBs and now just need to find time to solder them up. Many repairs and general life have been slowing things down though.

Bryce.

[Bignumbas]

I like these as replacement powers supplies.
You can get them to match whatever voltages/amps/polarities you require.
They will run any of the old computers and you only have to add cables to screw connectors, no soldering.
You can find component boxes to fit them in if you want.
The one below will run an AMIGA 500 and a lot of other things.


https://www.aliexpress.com/item/New-product-hot-selling-50w-triple-output-net-50b-enclosed-switching-power-supply-CE-approved-5V/32607221364.html


and this one for a TI99/4A, it connects directly to the mainboard


https://www.aliexpress.com/item/low-cost-new-series-50w-triple-output-net-50a-enclosed-switching-power-supply-dc-5V-12V/32607262497.html?spm=2114.13010608.0.0.OXoxN1

[TotO]

Prefert the +5V/+12V/-5V version, if a day you expect to use it with some JAMMA PCB too. 

[1024MAK]

I like these as replacement powers supplies.
You can get them to match whatever voltages/amps/polarities you require.
They will run any of the old computers and you only have to add cables to screw connectors, no soldering.
You can find component boxes to fit them in if you want.
The one below will run an AMIGA 500 and a lot of other things.

https://www.aliexpress.com/item/New-product-hot-selling-50w-triple-output-net-50b-enclosed-switching-power-supply-CE-approved-5V/32607221364.html

and this one for a TI99/4A, it connects directly to the mainboard

https://www.aliexpress.com/item/low-cost-new-series-50w-triple-output-net-50a-enclosed-switching-power-supply-dc-5V-12V/32607262497.html?spm=2114.13010608.0.0.OXoxN1

As with all things in life, just be aware that most cheap items are produced to a price point. It's hard to properly assess the quality and safety of power supplies like this without buying samples and extensive testing and taking some apart to see the construction. Although these do give plenty of details, and the specs given at first glance aren't terrible.

When thinking about what you want to power your retro computer, first off, you want a power supply that does meet appropriate safety standards so that it can never give anyone an electric shock. Second, you want a power supply that has a well regulated output that is noise and glitch free, and which can properly handle changes in LOAD and line voltage. Third, you want it to have proper mains side filtering, and output filtering so that it does not act as a radio noise transmitter. Some poorly designed switch mode power supply units, when connected to the mains, can radiate significant RF noise for more than 500 yards...

So, to sum up, will a cheap PSU be safe for you, your computer and for others using the radio spectrum near you?

Mark

[Bignumbas]

Switch mode power power supplies are a nasty piece of kit to start with.


Yes, mains supply AC is dangerous. These PSU's are meant to be enclosed away from being touched, they have live exposed AC terminals.
I have been in IT for over 30 years and I still see cheap PSU's made to a price point in Cheap PC's AND brand name PC's that scare me that you buy from mainstream shops.
Luckily when switchmode PSU's die they usually go open circuit and stop unlike transformers.


These PSU's have an RF standard they meet: EMC standards Meet FCC PART 15 J Conduction class B
[/size]FCC Part 15 rules cover both unintentional radiators (devices such as computers and TV receivers, all of which may generate radio signals as part of their operation, but aren't intended to transmit them); and intentional radiators (such as garage door openers, cordless telephones, wireless microphones, etc., which depend on deliberate radio signals to perform their jobs).


I have seen lots of online instructions for converting PC PSU's to be 12v/5v power supplies which include adding internal power resistors.
I had one supplied with an Amiga 500 I bought that had the resistor zip-tied to the air hole grill on the inside. A nice plastic zip tie that melts.


Finally, pretty much everything you buy now is cheap stuff made in asia, some good some bad so its buyer beware!
They sell fans here in Australia in supermarkets that cost $15 (9 pound) they last about a year in most cases. Fireproof - highly unlikely, but they are doubled insulated with a lot of burnable plastic.    But, they are cheap. Just like those cheap phone chargers that catch fire, or iphones and Samsung mobiles.......maybe we should get samsungs  standards checked out

[pelrun]

Switch mode power power supplies are a nasty piece of kit to start with.

There's nothing wrong with a PSU being switch-mode. There's a problem with cheap crap, but cheap crap is a problem regardless of the product.

[rcmolina]

May help ...


http://www.nightfallcrew.com/16/10/2014/amstrad-cpc-6128664-power-supply-cisco-34-0874-01/