H5 with external PSU. Power requirement

[ijor]

I need to use an external PSU for my H5 motherboard. Of course it is possible to just use a standard ST PSU with some kind of cable extension. But, honestly, I don't feel very comfortable with that kind of setup. If going with an external PSU, it will probably be much safer to use something fully enclosed.

My first thought was to use a Molex PSU. I have a couple already. And it shouldn't be too difficult to adapt the connector. But I'm not sure these PSU are regulated good enough. And more important, I don't know if they deliver enough power. Do we have an estimate of the typical power requirement for an H5 without a real floppy?

I know it is possible to build all sort of solutions. But I need something more or less ready to plug-in with a simple cable adaptation.

Edit: Forgot to mention that (I think) I don't need 12V. Which is only required for some Scart monitors and very old floppy drives?

[exxos]

@sporniket Has successfully used USB power supplies. The problem is some of them are not regulated very well. Pretty much anything which is preferably regulated at 5VDC will work. I don't think it needs to be more than about 2 amps. So go with 3amps to be safe I guess.

12V is only connected to the RGB port on the H5. I did not even bother to wire the 12V to the floppy connector as it wouldn't make much sense to use such a old drive on a H5 anyway.

Maybe something along these lines with a DC jack..
www.amazon.co.uk/Adapter-Universal-Tran ... B09PD3XM1G

[frank.lukas]

... what is a Molex PSU? You mean a pico psu with an external 12V power supply? 80 watts is the smallest and there are ATX adapter cables to build a connection cable to the Atari mainboard.

[sporniket]

@sporniket Has successfully used USB power supplies.

Yes, on my STe, documented there : viewtopic.php?f=9&t=5939

Pretty much anything which is preferably regulated at 5VDC will work. I don't think it needs to be more than about 2 amps. So go with 3amps to be safe I guess.

I did my test with a floppy emulator (goex), I don't know how much need a real floppy drive when the motor is on.

[ijor]

... what is a Molex PSU?

I probably should have said an AC/DC converter with Molex connector. This:
https://www.coolerguys.com/products/100 ... ex-adapter

The beauty of this kind of PSU is that it does have 12V and that it doesn't even need a custom cable, just a use a standard Molex to floppy power cable that I already have.

But again, I'm not sure how well regulated this is. It is certainly regulated to some degree, since they were commonly used for external drives. The ones I have are 2 AMP, which I guess it is borderline. Probably ok with a Gotek?

[exxos]

Probably will be fine anyway being a switchmode.

I measured my H5. "Idle" and with floppy being accessed.

IMG_1040.JPG

IMG_1041.JPG

[ijor]

Probably will be fine anyway being a switchmode.
I measured my H5. "Idle" and with floppy being accessed.

That's great. Thanks a lot Exxos.

I understand I can plug the Molex to Berg cable directly, right? I have this:

https://www.adafruit.com/product/425

The 4-pin Berg connector is female, so I cannot connect it to the floppy cable. But it fits in the normal 6 pin PSU connector. Just connect in the middle seems fine? That way I get red to red (5v), two black to black (ground), and yellow to blue (12V). Sorry for the silly question, but I'm a bit scared to inject 12V in the 5V rail by mistake.

[ijor]

Replying to myself ..

The 4-pin Berg connector is female, so I cannot connect it to the floppy cable. But it fits in the normal 6 pin PSU connector. Just connect in the middle seems fine? That way I get red to red (5v), two black to black (ground), and yellow to blue (12V). Sorry for the silly question, but I'm a bit scared to inject 12V in the 5V rail by mistake.

Ah, no. PIn 5 of the ST connector is yet another ground. I need to cut the 12V cable, or not connect the connector directly and just use a couple of male to female jumper cables.

Edit: I thought I could connect the Molex to Berg cable directly to one of the AUX power connectors on the H5. But they are not populated in my motherboard.

[exxos]

The 4-pin Berg connector is female, so I cannot connect it to the floppy cable. But it fits in the normal 6 pin PSU connector. Just connect in the middle seems fine? That way I get red to red (5v), two black to black (ground), and yellow to blue (12V). Sorry for the silly question, but I'm a bit scared to inject 12V in the 5V rail by mistake.

Ah, no. PIn 5 of the ST connector is yet another ground. I need to cut the 12V cable, or not connect the connector directly and just use a couple of male to female jumper cables.

You slightly lost me.

On the ST there are multiple PSU points.

The normal one is 5-5-0-0-0-12

and the 4 port power is the same as the floppy cable 5-0-0-12

Capture.PNG

So your molex connector should match the 5-0-0-12 pinout I would presume ?

[ijor]

You slightly lost me.

Yeah, I was thinking in loud voice, and actually without much thinking. Sorry about that.

So your molex connector should match the 5-0-0-12 pinout I would presume ?

Yes.

On the ST there are multiple PSU points.
The normal one is 5-5-0-0-0-12
and the 4 port power is the same as the floppy cable 5-0-0-12

But only the "normal" 6-pin connector is populated in my H5 board. Otherwise I could connect it directly to one of the 4-pin AUX ports. No big deal. I'll use a couple of jumper cables for 5V and GND.