Questions about MeanWell RT65-B

[fpmpaolo]

Hello people.
I'm about to make a PSU for my A600 and I need a little help.
My machine has a Vampire, a 32Gb SD card, 1MB ChipRAM and an original Chinon drive.

I tried to read TONS of guides but the more I read, the more I get confused.

01. How much voltage on the 5V rail?
Some say it must be plain 5V despite of modern accelerator boards and setup. Should I do so?

02. Where do I test the 5V?
Some say to test on the MeanWell, some say it's better to test and have 5V on the FDD connector.

03. Do the +12 and -12 need dummy load?
Purists say yes. Some say it works without.

I have a Voltmeter + Amperometer as on the image.
When I give plain 5V on the Vampirized 600, it gives me 20A.
If I use only 1.3 or 3.1 KS it gives me 17A.

Are they right?

 

[btp]

Mr. Ian Stedman, a very knowledgeable guy when it comes to Amiga and PSUs, measured the consumption of a fully loaded and with an 060 accelerator equipped A1200 at less than 16W.

Amiga power supply guide – Ian Stedman’s Website

So, you can understand that your MeanWell PSU capable of delivering 65W won't have any problem supplying with power you Amiga 600 (even with the vampire accelerator)!

If I remember correctly the RT-65B has a potentiometer to adjust the 5V rail voltage so that you can compensate for any losses due to cable and connector and make sure your equipment receives a voltage as close to the 5V it needs. To measure properly the voltages that the machine is receiving you need to take measurements inside the Amiga. The floppy drive power connector is a convenient place to measure (be careful not to short the voltages rails with ground)

 

[8 Bit Dreams]

Have built about 15 PSU supplies based on MeanWell RT65-B, and I can surely say: these are way better than some other brand new PSU supplies You can find on the other bay. The best thing (but also a probem) is that You can adjust power rails on them.

Unfortunately there is only one adjustment knob, so turning up +5V rail will also push +12V rail up. So be prepared to get +14V - 16V when You get Your sweet spot for +5V...

Now because of that You need to install some kind of additional DC-DC converter. I've took these:

And set them to 12V. That's it, now 12V rail looks perfect no matter what is happening on 5V rail.

As about Your questions:

01. How much voltage on the 5V rail?
Some say it must be plain 5V despite of modern accelerator boards and setup. Should I do so?

you will get best performance in the range of +4.95 - 5.05V
+4.89 and lower may cause potential problems (especially, when system gets warm)

02. Where do I test the 5V?
Some say to test on the MeanWell, some say it's better to test and have 5V on the FDD connector.

Please do measurement on the CPU or Kickstart socket - that's the correct way to do it. Only that way You can see how much the Chips are getting.

03. Do the +12 and -12 need dummy load?
Purists say yes. Some say it works without.

Not really needed, but You can add nice led illuminated cooler or LED keyboard, Your system will be thankful for that

I have a Voltmeter + Amperometer as on the image.
When I give plain 5V on the Vampirized 600, it gives me 20A.
If I use only 1.3 or 3.1 KS it gives me 17A.

This is incorrect, seems amp meter was connected wrongly and measurements are done incorrectly...
Best regards,

8 Bit Dreams

 

[roy_bates]

thats some weird and strange meter you have there that reads volts in place of amps,and besides all that strangeness ness,the meanwell only puts out 8 amps max on the 5 volt rail
not sure how you/the meter managed that,or even the meanwell supply

 

[8 Bit Dreams]

It was connected incorrectly

 

[fpmpaolo]

Thanks for all your replies. There's been a misunderstanding about my voltimeter.
The picture from the first post comes from Ali-Express, it's not on my PSU. This is where I bought my Volt-meter.


@8 Bit Dreams what is that little board? Could you please link me one on Amazon, I can0t find it on Ali Express. How do you use that?
Where do I have to measure on the KS?

@btp I know Steadman's guides. I cannot understand WHERE I need to have 5V.

I mean. If I want plain 5V on the floppy connector, I need to turn potentiometer on my RT65B up to 5.10.
If I want plain 5V on the PSU, I need to turn the knob up or down until 5V

 

[Bandit0r]

@8 Bit Dreams what is that little board? Could you please link me one on Amazon, I can0t find it on Ali Express.

>> Looks like that board << but would be good if @8 Bit Dreams can confirm that, or has a better/cheaper link?

 

[fpmpaolo]

I have another question.
Cables from the main cable are very short, can I solder longer cables on that?

 

[darefail]

Ideally the measurement of 5V on the meanwell and on the floppy connector should be the same. But in reality this is impossible.
Under load if it is close to 4.9V on the fdd connector it is ok.
For years i had it without dummy load but now i have added a 75 and 100 Ohm resistors. No difference..

 

[fpmpaolo]

Ideally the measurement of 5V on the meanwell and on the floppy connector should be the same. But in reality this is impossible.

Right. If I have plain 5V on the PSU, I will get 4.70V on FDD

For years i had it without dummy load but now i have added a 75 and 100 Ohm resistors. No difference..

Why 75 and 100 ohm? Could you please send pic of what you did?

Since PSU cable are terribily short, did you lengthen them soldering?

 

[miggymad]

Yes, you can extend the shorter cables with extra lengths of similar stock and colour (to avoid confusion). If soldering, use heat shrink tubing to isolate each join from the others or use something like block connectors if you have room inside the case.

 

[darefail]

Right. If I have plain 5V on the PSU, I will get 4.70V on FDD

Why 75 and 100 ohm? Could you please send pic of what you did?

Since PSU cable are terribily short, did you lengthen them soldering?

In mine 5V is set to 5.08V and i have 12.1-12.2V. IIRC on the fdd connector i have 4.87V but i have to measure again.
Generally you need a small load on the 12 and -12V rails to regulate the voltage correctly.
Without a load these rails might not output stable voltage or could even shut down. But i never noticed any problem without these loads.
As miggymad suggested, use block connectors. IMO soldering and shrink tubes is a sloppy job. But works anyway.
I will upload some pics when i am at home.

 

[darefail]

Found some old pictures without the dummy loads fitted.

 

[fpmpaolo]

Now because of that You need to install some kind of additional DC-DC converter. I've took these:
View attachment 2525941
And set them to 12V. That's it, now 12V rail looks perfect no matter what is happening on 5V rail.

Can you please explain what you did?

Did you solder the +12V cable and then turned the knob so to get plain +12V?

 

[darefail]

Can you please explain what you did?

Did you solder the +12V cable and then turned the knob so to get plain +12V?

As you are going to increase the 5V, you have to stabilize the 12V by adding this DC/DC converter.
Without it, increase the 5V until you have the 12V up to 12.5V. Then measure the 5V at the fdd connector.

 

[fpmpaolo]

As you are going to increase the 5V, you have to stabilize the 12V by adding this DC/DC converter.
Without it, increase the 5V until you have the 12V up to 12.5V. Then measure the 5V at the fdd connector.

If so, when I reach plain +5V on the FDD, I have +12.70

 

[darefail]

If so, when I reach plain +5V on the FDD, I have +12.70

A bit too much. You have to buy the converter.

 

[fpmpaolo]

A bit too much. You have to buy the converter.

that's what I'm doing. But I don't understand how to install it.
I found a couple on Amazon.

This has a 100Ohm resistor.

This has a 47 resistor

 

[darefail]

that's what I'm doing. But I don't understand how to install it.
I found a couple on Amazon.

This has a 100Ohm resistor.

This has a 47 resistor

This is a power inductor.
I think both of them give a fixed output of 5V.
The one that 8bitdreams suggested has many options for the output.

Google "12v fixed output buck converter" and you will find for about 2€ in Italy. Just read carefully the specs before you buy it.

 

[darefail]

But I don't understand how to install it.
I found a couple on Amazon.

You connect to the input your 12.7v and as the output is fixed at 12v you are done.
The output goes to your Amiga.