CA-PSU and Ground wire

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Don't Panic. Please wash hands.
  • Hello Jens,


    I am looking at your CA-PSU and wonder why have you decided to exclude connection to regular ground(earth) ? I am not an expert, just old fashion guy, that is more use to having computer connected to house earth wire.


    Also I have original Amiga 1200 PSU and got weird reading on Ground and Shield. I expected only one of them to have zero resistance between earth wire and them. I would expect zero resistance between shield and earth wire on 240V side ? Both show zero resistance to earth wire. Is this normal or is CAP out of order ?

    Amiga boots and works on this original PSU.

    Thanks and BR, Luka

  • I am looking at your CA-PSU and wonder why have you decided to exclude connection to regular ground(earth) ? I am not an expert, just old fashion guy, that is more use to having computer connected to house earth wire.

    Shield is not excluded. It is connected with a high-voltage capacitor to GND. Reason is that the input filter of the A1200 is a current-compensated coil. If you'd make a direct connection between GND and shield, then part of the current would flow past the filter, taking the whole coil into magnetic saturation. In that state, it would not filter at all, and fail CE testing. Hence, shield is only connected to GND with a capacitor, and that even needs to be a high-voltage unit, as it may need to take quite high spikes during contact-discharge testing (on my prototype, a 50V cap actually blew, and luckily, that already happened in pre-compliance testing - lessen learned, not too expensive :-)).


    I'm aware that other PSU tinkerers just connect shield and GND, which is plain wrong. We do actual engineering, we give a warranty, and you have someone to turn to if something doesn't work. And you've surely read about the liability insurance - the unit passed quite some testing to get that. Find that with any other vendor.

  • Hello Jens,


    That is the weird part. I have original Commodore Amiga 1200 PSU and when I check connections I see no resistance between Earth wire (on 240V connector) and GND and Shield wires (On Amiga connector side), like they are all connected. Is this normal on original commodore?

    I checked friend's PSU from Amiga shop (A-Power I think) and weird also. GND wire (Amiga connector side) is directly connected(no resistance) to Earth wire (240 V connector), while Shield has resistance between Shield wire (Amiga connector side) and Earth wire (240 V connector). I expected other way around., that shield is for Earth wiring to "House Earth".

    And your PSU has no connection to real Earth wire (on 240V connector). Was that intentional, since latest computers all are connected to earth home wiring ?

  • That is the weird part. I have original Commodore Amiga 1200 PSU and when I check connections I see no resistance between Earth wire (on 240V connector) and GND and Shield wires (On Amiga connector side), like they are all connected. Is this normal on original commodore?

    If you can rely on the Earth wire to be connected properly in a house, you can certainly do that - it will ease CE testing a lot. However, if there's a competitor who says that it must also measore OK in an environment without earth connection, Commodore would have been out of luck, as shield always carries high-frequency noise that must be carefully taken into account.


    I checked friend's PSU from Amiga shop (A-Power I think) and weird also. GND wire (Amiga connector side) is directly connected(no resistance) to Earth wire (240 V connector), while Shield has resistance between Shield wire (Amiga connector side) and Earth wire (240 V connector). I expected other way around., that shield is for Earth wiring to "House Earth".

    I also measured the A-Power PSU in the past, and found the same. I already explained the reasons for not connecting Shield to GND yesterday - so the A-Power PSU is OK on that part. However, it's not OK to use an open-frame chassis for a distant power sink, as the power supply is not designed for that. Claiming that this thing is "for Amiga" is plain false advertising, as you can easily measure that the thing violates three out of three key specifications from Commodore.


    And your PSU has no connection to real Earth wire (on 240V connector). Was that intentional, since latest computers all are connected to earth home wiring ?

    Sure, that's intentional. The PSU has X- and Y- capacitors on the primary side, so high-frequency content can be deflected into the grid, and ultimately to earth (as every house has earth and zero connected at some point). This indeed increases the conducted emissions part, but we're well under the limit line after I added a few inductors on the DC-DC converter.


    So what you do in your considerations is to separate the electric and the magnetic part of the EMI, and take care of each problem by itself, which ultimately solves the whole problem (after all, that's what engineering is about!). As a result, we've passed CE without an earth wire connection and are therefore compliant with all kinds of weird house installations.


    I would have loved to skip that part of the development, but if you have an insurance watching you, and you intend to go international, you can't rely on an earth wire to be present in all cases. Yes, you have it in most European countries, but it's rare in the US, for example.

  • I must say that I am impressed by your activity on forum, to answer on our questions.

    I ordered CA-PSU today due to 4 reasons:

    - Overall knowledge, passion to build a PSU even better then commodore one and standing by it

    - Support and responsiveness

    - To support overall Amiga scene of which you are an important part of

    - To motivate you to finally release 68060 accelerator, my dream CPU I never owned:P


    The reason I started this thread was due to being surprised PSU is so vital also on Amiga and having some boot problems on rebuilding them after 9 years of no Amiga usage. I have made "an Amiga" PSU years ago from PC 486 AT PSU and actually never had any problems or chrashes even with Apollo 1240. I know I connected Amiga GND to PC PSU GNG(Black wires) and Amiga Shield to PC PSU case (which is grounded by earth wire). So I was surprised amiga shop PSU has Amiga GND connected to Earth wire(at least I could not detect and resistance).

    Do not use this old PC AT PSU anymore but original one or borrowed amiga shop one.

  • I have made "an Amiga" PSU years ago from PC 486 AT PSU and actually never had any problems or chrashes

    That's because AT PSUs mostly have the 5V rail as their main regulation rail. This has changed with ATX, where 12V is the main regulation rail, and precision on the 5V rail is much lower. In other words: You got away with it, because the PSU technology of the time was better-suited for the Amiga.

  • The last reply was more than 365 days ago, this thread is most likely obsolete. It is recommended to create a new thread instead.