Meanwell Power Supply

[CubeTheory]

Hi.

I know this has been covered here a fair bit, but I wanted to show you mine, which I finished tonight and get some feedback on my findings.

I was given a faulty A500/600 PSU by my friend and when i turned it on it was oscillating really loudly and producing little to no output. I know that in the past this particular PSU had failed and been repaired, so I wasnt interested in trying to save it.

I'd been reading this thread and Ian Steadmans PSU guide and saw mention of the RPT-60B, so I decided this would be a good candidate for putting in this box.

I have it installed, sitting on stand-offs, and on a brass plate, which ties the 2 earth points together nicely, and the shield and shield ground pin is main earth referenced. This is one curiosity as my big heavy old Type 1 A500 Linear supply doesn't have continuity between these 2 pins, but the shield is mains earth referenced.

The other pins connect into the PSU, to the +5, +12, -12, and COM. I didn't fit an inline fuse because one of the few good things about living in the UK is the superior fused plugs we have. Plus the PSU has 2 (albeit soldered) fuses on board (T2.5A, 250v).

I noticed some concern about the RT-50B needing loading with power resistors to make it stable, and I haven't done that in the case of the RPT-60B, as I'm seeing a constant +5.02v, +11.75v & -11.81v without load.

So far I've only tested it with the Amiga 500 once, and all seemed fine. Is there anything I should change or be concerned about?

I haven't probed it with the scope while under load yet, either.



EDIT: Looks as though the Shield pin isnt connected at all on my Type 1 A500 Linear supply

[aeberbach]

RPT-60B is what I have used in multiple supplies, internal in the A1200 and to replace the old C= model inside the brick for the other machines. What you've done looks very neat - even used proper plugs! I just used the pins without housings, heat shrinking each one and plugging each wire individually.

I have never used load resistors. There has always been plenty of load from the Amiga to get it started - perhaps not much of a concern when powering electronics from the 80s more so today's micro-current parts.

[Daedalus]

Originally Posted by CubeTheory

I have it installed, sitting on stand-offs, and on a brass plate, which ties the 2 earth points together nicely, and the shield and shield ground pin is main earth referenced. This is one curiosity as my big heavy old Type 1 A500 Linear supply doesn't have continuity between these 2 pins, but the shield is mains earth referenced.

Nice job. Commodore's PSUs seem inconsistent in this regard - some connect the earth through to ground, others don't. But the Meanwell units are designed for earth connection so that's fine.

The other pins connect into the PSU, to the +5, +12, -12, and COM. I didn't fit an inline fuse because one of the few good things about living in the UK is the superior fused plugs we have. Plus the PSU has 2 (albeit soldered) fuses on board (T2.5A, 250v).

Yeah, it is nice having a fused appliance plug, but it would be poor practice to rely exclusively on that when you're powering equipment that can't handle the current further downstream. In this case, the on-board fuses are ideal for the extra protection you need.

I noticed some concern about the RT-50B needing loading with power resistors to make it stable, and I haven't done that in the case of the RPT-60B, as I'm seeing a constant +5.02v, +11.75v & -11.81v without load.

So far I've only tested it with the Amiga 500 once, and all seemed fine. Is there anything I should change or be concerned about?

The regulation on that and similar models of Meanwell is based on the 5V rail, so once that reaches the minimum load, all the rails should be in spec. The other rails having a minimum load may simply be to do with power ratings of individual parts - not having the load there might drive some parts beyond their specification. It's hard to know what the long-term results of this might be, bug I've been running similar setups (not necessarily for Amigas) for many years with no ill effects.

[Hewitson]

That's an extremely professional job. Seriously, probably the nicest modded PSU that's ever been posted on here.

I personally would have avoided using the large brass plate, though.

[CubeTheory]

Originally Posted by aeberbach

RPT-60B is what I have used in multiple supplies, internal in the A1200 and to replace the old C= model inside the brick for the other machines. What you've done looks very neat - even used proper plugs! I just used the pins without housings, heat shrinking each one and plugging each wire individually.

I have never used load resistors. There has always been plenty of load from the Amiga to get it started - perhaps not much of a concern when powering electronics from the 80s more so today's micro-current parts.

Thanks. Using the connectors was a no-brainer for me as Digit-Key had them in stock when i ordered the PSU and they were really cheap. I also like the fact i can disassemble it quickly and easily if i need to swap out the PSU for any reason.

My first test on the Amiga caused no issues, booted of my external Gotek ok, and the internal Floppy. haven't tried daisy-chaining my other external drive. I'll do that next.

[CubeTheory]

Originally Posted by Daedalus

Nice job. Commodore's PSUs seem inconsistent in this regard - some connect the earth through to ground, others don't. But the Meanwell units are designed for earth connection so that's fine.

Thanks for clarifying. I've not modded the connector and cable in anyway, so it was interesting to discover that they were wired up differently.

Originally Posted by Daedalus

Yeah, it is nice having a fused appliance plug, but it would be poor practice to rely exclusively on that when you're powering equipment that can't handle the current further downstream. In this case, the on-board fuses are ideal for the extra protection you need.


The regulation on that and similar models of Meanwell is based on the 5V rail, so once that reaches the minimum load, all the rails should be in spec. The other rails having a minimum load may simply be to do with power ratings of individual parts - not having the load there might drive some parts beyond their specification. It's hard to know what the long-term results of this might be, bug I've been running similar setups (not necessarily for Amigas) for many years with no ill effects.

Yeah, it wasn't immediately clear to me from the data sheet that loading up the 5v rail would bring the others in spec, but reading that the RT-50B would require this on the 12v rail concerned me a little. so thanks again for that.

[CubeTheory]

Originally Posted by Hewitson

That's an extremely professional job. Seriously, probably the nicest modded PSU that's ever been posted on here.

I personally would have avoided using the large brass plate, though.

Really appreciate the feedback, i like it when things are neat and tidy, and i can disassemble quickly to swap parts out if necessary. Worth the little extra effort.

Why would you have avoided the plate? there was a number of reasons for it, I had the brass available, its a good conductor and acting as a ground plane, to link the 2 ground points together. Also it should provide a limited amount of additional shielding due to it being grounded.

Once it's all closed up, its pretty safe.

[Hewitson]

Originally Posted by CubeTheory

Really appreciate the feedback, i like it when things are neat and tidy, and i can disassemble quickly to swap parts out if necessary. Worth the little extra effort.

Agreed.

Originally Posted by CubeTheory

Why would you have avoided the plate? there was a number of reasons for it, I had the brass available, its a good conductor and acting as a ground plane, to link the 2 ground points together. Also it should provide a limited amount of additional shielding due to it being grounded.

I would have avoided the plate because it's unnecessary. A simple wire would have sucfficed, although I don't believe the FG is intended to be connected to ground.

[Daedalus]

Originally Posted by CubeTheory

Yeah, it wasn't immediately clear to me from the data sheet that loading up the 5v rail would bring the others in spec, but reading that the RT-50B would require this on the 12v rail concerned me a little. so thanks again for that.

If you look at the block diagrams in the datasheets it will usually show you which rails are used for the feedback circuit, and therefore which ones are depending on the correct load for regulation and which are simply slaved of another rail. It might still be a good idea to load the 12V rail as required, but it won't affect the regulation.

Originally Posted by Hewitson

I would have avoided the plate because it's unnecessary. A simple wire would have sucfficed, although I don't believe the FG is intended to be connected to ground.

I use a plate in most of the conversions I do, but more for mechanical reasons. A plate lets you mount the module securely while still using the original PSU case screw pillars. These modules connect earth to ground internally (and usually have a significant conductor area dedicated to it), so it is intended, and doesn't need a wire (or plate) for electrical purposes.

[Hewitson]

Originally Posted by Daedalus

II use a plate in most of the conversions I do, but more for mechanical reasons. A plate lets you mount the module securely while still using the original PSU case screw pillars.

True, but I'd just drill a few new holes in the bottom of the case.

Originally Posted by Daedalus

These modules connect earth to ground internally (and usually have a significant conductor area dedicated to it), so it is intended, and doesn't need a wire (or plate) for electrical purposes.

Sorry, I should have specified externally. I realise there's an internal connection inside many of these units (but certainly not all).

[CubeTheory]

Originally Posted by Daedalus

I use a plate in most of the conversions I do, but more for mechanical reasons. A plate lets you mount the module securely while still using the original PSU case screw pillars. These modules connect earth to ground internally (and usually have a significant conductor area dedicated to it), so it is intended, and doesn't need a wire (or plate) for electrical purposes.

I should have mentioned it was also for securing the PSU

The PSU is grounded through the mount point M1 and the data sheet states that M1 is a safety ground and M2 should also be connected for better EMC performance. so, you're correct, its not actually required but no harm in doing so.

[CubeTheory]

Originally Posted by Daedalus

If you look at the block diagrams in the datasheets it will usually show you which rails are used for the feedback circuit, and therefore which ones are depending on the correct load for regulation and which are simply slaved of another rail. It might still be a good idea to load the 12V rail as required, but it won't affect the regulation.

Of course. The detection circuit is off +v1 which is 5v

[Digital Man]

Nice! I've actually been contemplating this myself and looking at those exact models.

I did have a question about A500 power supplies. Can/do they cause damage to the A500? Mine appears to be working fine, but I have had weird issues lately with some addon equipment. Just wondering if I am risking permanent damage like with an old C64 power supply.

[nogginthenog]

There are at least 2 different types of A500 power supply. Linear (super heavy) and switch mode.
I don't think there is much risk. The capacitors could fail but shouldn't do any damage.

Not sure which type provides the higher current.

The C64 power supply was dodgy. I built my own with a 5v module & a 9V transformer.

[Daedalus]

There's always a risk of a PSU failing and destroying whatever it powers, even with new PSUs. But the risk is pretty low from Amiga PSUs - they tend to fail by having poor load regulation (resulting in lower output voltage and high ripple & noise, manifesting as instability of the computer, especially with additional hardware) due to worn out capacitors, or simply failing to produce any output at all due to some other failure. To output a voltage higher than spec under load is pretty rare. The C64 PSUs are a different story of course, and are quite prone to failure with a high output. But they're a very different design.

[Methanoid]

Anyone used DavePoo's open PCB design with their Meanwell conversions? He lists a couple of compatible PSUs and others as "maybe" compatible.

321503-02 is mine.. That is a "maybe" model

EDIT: And mine looks totally different to the same model number in DavePoo's video

My PSU is 312503 (with 2 stamped on the casing afterward) and its TOTALLY different.. all the screwholes are in the corners. Loads of space. How are people stopping the Meanwell flapping around inside? Hotglue?? :-)

Images of my PSU innard https://ibb.co/KmCd5Px & https://ibb.co/dD8Tvmh if U wanna see what I mean

[Methanoid]

Any advice on putting Meanwell inside this

https://ibb.co/xs06fD5

Hotglue it in place? Dont want to drill holes in bottom if I can avoid...

Is it just a case of attaching wires at either end or more needed?

RT-50B 50W is £20 inc (well £19.20 and random object to get to the £20 free postage!)

[wiz12]

Originally Posted by Methanoid

Any advice on putting Meanwell inside this

https://ibb.co/xs06fD5

Hotglue it in place? Dont want to drill holes in bottom if I can avoid...

Is it just a case of attaching wires at either end or more needed?

RT-50B 50W is £20 inc (well £19.20 and random object to get to the £20 free postage!)

Something like this might be what you're looking for.

https://www.thingiverse.com/thing:2696615

[Methanoid]

Thanks. I know the designer on Discord so will ask him some questions :-)

[Mathesar]

Actually, the "linear" heavy A500 supply also contains a switching regulator for the 5V power.
However, it also contains a crowbar circuit in case something goes wrong limiting the voltage to the Amiga.