exxos's Atari, Amiga & retro forum

I bought a meanwell RT-50B to replace the innards of a dead Commodore PSU so I can power my CD32 without having to use a 110>220V power converter.


It all went relatively well, it's very simple and easy to set up. I drilled a hole on the side of the Commodore case and fastened the meanwell with a screw.

Unfortunately I am not impressed with this PSU. At full load it only delivers 4.65V to the Amiga motherboard (with the potentiometer cranked up to the max) which is a little low and causes instability with the TF330 connected. The original PSU delivers 4.75V under load and there are no stability issues.

My quest to find a replacement PSU for the CD32 continues...

I did a Meanwell mod on my a1200 which is quite heavily loaded with mods/accels etc, I think I used the rt-65b and this seems to output 5v stable, no crashes or problems.

Do you have 110V supply there?
I have made a few of these and have used them for a while now and they are pretty rock solid. I'm using them in the UK so 240V and get a solid 4.9V/12.2V under load from them consistently (not cranked up). Maybe there's an issue with lower voltages on the 110V range?

PaulJ_2.0 wrote: ↑Thu Jun 10, 2021 9:57 pm Do you have 110V supply there?
I have made a few of these and have used them for a while now and they are pretty rock solid. I'm using them in the UK so 240V and get a solid 4.9V/12.2V under load from them consistently (not cranked up). Maybe there's an issue with lower voltages on the 110V range?

Yes, we use 110V... I was thinking of the same thing. I should check if it behaves differently when plugged into a 220V converter. But the whole point of this was to get a PSU I can use without converters.

alenppc wrote: ↑Thu Jun 10, 2021 10:00 pm Yes, we use 110V... I was thinking of the same thing. I should check if it behaves differently when plugged into a 220V converter. But the whole point of this was to get a PSU I can use without converters.

Even at 220 you may experience the same results. 240V is still 10% (almost) higher than 220V, that probably equates to your 10% loss on voltage on the 12V and 5V conversions. That being just 0.5V on the 5V rail means a lot though.

where are you measuring 5V at? The motherboard? Have you compared with the output post on the PSU? Those taped joins look a little sketchy - tried a thicker wire and cleaned contacts where the PSU cable connects to the board?

Yes, I measured this at the motherboard. I checked the PSU output terminals and there is no voltage drop there, just at the motherboard.

I reused the original Commodore cable since... a wire is a wire. I soldered a small extension to reach around the other end, and heatshrink-wrapped it, that's all.

Even if I measure the voltage at the other end of the cable (connector, unplugged), I get 5.77V, it's just at the motherboard that it drops a lot.

EDIT: fun fact, the commodore PSU measures 5.10V at the connector but it doesn't drop nearly as much at the motherboard as the meanwell.

alenppc wrote: ↑Fri Jun 11, 2021 2:29 am I measure the voltage at the other end of the cable (connector, unplugged), I get 5.77V, it's just at the motherboard that it drops a lot.

Unplugged as in unloaded? What do you see at the PSU if you load it with only a dummy load? Your connections seem suspect.

I've used a couple of Meanwell RD-50s in retro projects and they've been solid and reliable, somewhere near the middle of the adjustment range.

Hi.

You reminded me that I did the same. Although I read you have to put some power resistors across one of the terminals to simulate a load that a PC would be using. Then the 5v did not drop so much.

I found it gave my CD32 picture interference on an LCD display. I have changed my setup now, but did not like the idea of hot resistors inside the PSU box.
Anyway, I recapped my standard Amiga PSU and have a CD32 lead and normal Amiga power lead coming out (I only power 1 item at a time). That seems to work fine.

I have also used this power supply, but in Australia we have 240v mains.

I was able to turn the 5v line up and have it stable at 5.1 with no problems at all.
I also found this PSU gave interference on the video signal, wavy lines, quite noticeable.

I took it back to the shop because of the video interference.