English Amiga Board - View Single Post - Choosing a new ATX power supply for an expanded Amiga 4000

Daedalus · 20 September 2019, 13:27

I don't know I'm afraid, but both adaptors are pretty simple. The most important thing is that you get a PSU that's stable at low loads. Unfortunately, most modern PSUs are made for PCs that primarily use 12V, and as such will require a minimum load on the 12V rail to keep it regulating. The Amiga primarily uses the 5V rail with very little 12V usage of around 0.1A or less (~1W). This is compounded by manufacturers rarely publishing the minimum load requirements for PSUs, instead concentrating on the maximum, which is more relevant for PCs. Your best bet of finding a suitable supply is to buy a quality branded one with a *lower* rating - no point in buying a 750W unit when your Amiga possibly only uses around 50W.

A dummy load can be applied to the 12V rail which might help some PSUs work better with low loads. A large wattage resistor using the chassis as a heatsink for example will increase the load on the 12V rail and might improve behaviour of marginal supplies.

I recently built a custom adaptor that allows software power off as well as the use of momentary switches, but still doesn't negate the need of a carefully selected PSU. I used a Corsair SF450 SFX PSU for that build and it works fine, so that's an option for your setup too.

20 September 2019, 13:27	#28
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,346	I don't know I'm afraid, but both adaptors are pretty simple. The most important thing is that you get a PSU that's stable at low loads. Unfortunately, most modern PSUs are made for PCs that primarily use 12V, and as such will require a minimum load on the 12V rail to keep it regulating. The Amiga primarily uses the 5V rail with very little 12V usage of around 0.1A or less (~1W). This is compounded by manufacturers rarely publishing the minimum load requirements for PSUs, instead concentrating on the maximum, which is more relevant for PCs. Your best bet of finding a suitable supply is to buy a quality branded one with a lower rating - no point in buying a 750W unit when your Amiga possibly only uses around 50W. A dummy load can be applied to the 12V rail which might help some PSUs work better with low loads. A large wattage resistor using the chassis as a heatsink for example will increase the load on the 12V rail and might improve behaviour of marginal supplies. I recently built a custom adaptor that allows software power off as well as the use of momentary switches, but still doesn't negate the need of a carefully selected PSU. I used a Corsair SF450 SFX PSU for that build and it works fine, so that's an option for your setup too.