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Question about using ATX PSU for DC Power

tech3475

Hi, my apologies if this is the wrong place to ask but it seemed like it made the most sense.

 

In a few months I'm going to be putting my Amiga 1200 into a new case and power it using an ATX PSU, one thing I'd also like to do as part of this project is to internalize the scan doubler I use at the same time and power it using the ATX PSU.

 

The Scan Doubler in question is a GBS-8220, according to the manual (link: https://www.mikesarcade.com/estore/datasheets/GBS-8200-booklet.pdf), it can take 5V 2A but the issue I have is how to power it safely.

 

The original idea was just to solder it to a molex connector on the 5V rail and power it directly, but I'm concerned over whether this is safe without some kind of protection in place (I've seen resistors used for example or a fuse for similar purposes).

 

The other idea is to get some kind of circuit regulator and possibly use the 12V rail, stepping down to 5V.

 

Any advice is appreciated.

 

Thank you.

  • Looking at the board photo on the data sheet you linked to, it sure seems like there's an inline PTC fuse on the board right before what looks to me like an input reservoir cap. I assume both the barrel jack and the two-pin right angle header have a common hot lead; if so you have input protection as long as the ripple on the 5V rail of the ATX supply is less that 1Vpp (it probably is.)

  • in reply to rusgray

    Thanks, makes things allot easier for me.

     

    I’ll double check the connection with a continuity tester to be sure, but I’d be surprised if it isn’t common.

  • in reply to rusgray

    Not sure if I can see a PTC fuse. I Googled for some clearer photos and found this one:

    image

    [Source: http://www.retro-commodore.eu/wp-content/uploads/2014/03/BGS-8200.jpg ]

     

    Rod

  • in reply to 14rhb

    You're correct; the part that I thought might be a fuse has the reference designator 'D2' in that clearer photo, making it a diode.

  • in reply to rusgray

    I just realised that’s the wrong variant.

     

    Here’s a link to the original listing I bought:

    Alftek GBS-8220 CGA/EGA/YUV/RGBS to VGA HD Video Converter Board https://www.amazon.co.uk/dp/B07CNM8KH1

     

    Looks like there’s still only a diode and a voltage regulator, though.

     

    So should I still do something or will a direct connection be ok?

  • in reply to tech3475

    Given the amount of current an ATX PSU can deliver on the +5v rail I would add a series fuse between it and this board - 2A would be a good start.

     

    Rod

  • in reply to 14rhb

    To confirm what I'm reading, so it's safe/suitable to use e.g. a 240v 2A fast blow fuse in this case?

     

    Looking around, I am seeing converters intended for cars which can go from 12V to 5V 3A with (supposedly at least) overload protection, seeing as how I may need to buy fuses and maybe a holder, are these a reasonable alternative or potentially dangerous?

  • in reply to tech3475

    Hi Chris,

     

    From that spec sheet you provided it shows the Scan Doubler requires 5v @2A my suggestion was that you fuse this board to prevent any excessive current flowing into it should a fault arise. If you are running your Amiga as well off the ATX PSU I would include another fuse in that feed (again to prevent a fault on that board drawing too much current). I don't know what current an Amiga can draw so cannot advise on that.

     

    Regarding your 12v=>5v @3A converter, I see no reason why that could not be used to power the Scan Doubler but you would likely overload it powering both the Scan Doubler and your Amiga at the same time.

    Those sort of convertors are also often cheaply made and sometimes over rated vs. what they can actually achieve in continuous use and with sub-optimal cooling.

     

    Stepping back a bit, I'm assuming you are looking at the ATX PSU because you have one spare and cannot/don't want to buy anything else? ATX PSU can do a lot of damage if you get a short and of course they are noisy. You can buy some small switch mode encapsulated units for a similar price to the 12v=>5v units e.g. https://cpc.farnell.com/ideal-power/25hk-ay-050a300-dh/desktop-psu-5vdc-3a-c8-vi/dp/PW04182?st=5v%203a%20power%20supplie…

    image

    The one above is 5v @3A for <£10 (UK prices)

     

    To confirm what I'm reading, so it's safe/suitable to use e.g. a 240v 2A fast blow fuse in this case?

    This is my worry, if you are asking this, then without any disrespect to you, is it something you really want to be doing. If I were doing this I would measure the current, be prepared to adjust the fuse value or replace if I got the value wrong and give the unit a soak test of running it for a few hours checking for excessive heat/smell etc. Lastly "safe/suitable" prompts the question "Where are you using it?" - I would be happy doing this for my own use but would be far more cautious if it were a demo at school or in a shop. Hope that helps.

     

    Rod

  • I should give more details.

     

    The Amiga mobo is going to be put in a new case and powered by the PSU using the standard motherboard connector via an adapter I’m buying.

     

    The Scan Doubler I plan on powering through the molex connector you’d typically use for disk drives using a spare molex plug I have. So in the case of say that adapter I mentioned earlier, it would be used only for the Scan Doubler and nothing else.

     

    I already have an external DC adapter for the scan doubler but I’m trying to internalise it if possible.

  • in reply to tech3475

    powered by the PSU

    Is this the ATX PSU you are looking at using?

     

    I think some pictures of what you have would help the E14 community to make better suggestions.

     

    ps: glad to see the Amiga is still being used. In my opinion the Amiga and Atari 1040ST were great computers that brought low-cost processing up to another level; appealing to both professional and gaming users.

     

    Rod