Alternative 2 prong PSU

[mrr19121970]

It's really for @ken, but if anyone else has an opinion here. There are 2 models of "2 prong" PSU and this means without butchering an existing PSU it's pretty hard (impossible) to make your own PSU. Impossible if you don't have a PSU at all. Maybe you have a 110v PSU and live in a 220v country or the other way around.

The Arfon Micro expander powers the 9vAC VIC20 with it's own PSU over the userport (pin 10 & pin 11).

So ken, you seem to have a good supply of userport edge connectors and little housings to hold them in. Do you think you can try it? Either direct soldering, or installing a 'barrel connector' are the ways that spring to mind for me.

[ken]

I am not to sure about backfeeding 9v into the userport to power a vic
do you have a link to the Arfon Micro expander ?
and yes I do have lots of connectors , I purchase them 500 at a time

[mrr19121970]

I am not to sure about backfeeding 9v into the userport to power a vic
do you have a link to the Arfon Micro expander ?
and yes I do have lots of connectors , I purchase them 500 at a time

http://sleepingelephant.com/ipw-web/bul ... f=1&t=7313

[ken]

well I pulled a 2 prong vic off the shelf and took a look and yes the 9v on 10-11 is pulled directly from the power supply line with no filters or anything
only thing I see is it bypasses the fuse and power switch so you would need to add a fuse and switch to the userport connector
sounds like a fun project

[mrr19121970]

Please do it. I'll be taking one from you, and I know of one other guy who also wants one...

This is a much better way to repair a broken ON/OFF switch too? Just leave it.

[ken]

yah I could build that into the reset switch box
would be a clean little box
best way would draw up a userport bypass board so you can still use the userport


great yet another project to add to my list ...lol

[ken]

I spent a few min throwing this together just for fun

powers a flat plug vic20 through the user port
and its a (passive) device, it does not hog the userport , I extended it out the back
I added a on/off switch and a fuse as this bypasses both on the board
and added a reset

[mrr19121970]

Cool. The pass through looks like a 2nd edge connector, not an "edge". Is this correct ??

[eslapion]

Although the 9VAC on the user port is a direct connection to the 9Vac PSU feed (save for the fuse) I would be really wary of powering a VIC that way.

The NTSC VIC-20 with PET style keyboard I have here draws a generous 1.1A on the 5V regulator and these are lossy linear types.

I wonder what the rated current limit is on the gold tabs of the 0.156" edge connector on the VIC-20's PCB.

I suspect powering the VIC through there could overheat traces on the VIC-20's mainboard.

Assuming the Arfon Micro Expander powers everything that could be connected to the cartridge port, connecting a datasette and Wico trackball to the VIC might increase the power load to a point some damage can occur.

[mrr19121970]

The Arfon also gives 5vDC to the expansion port too. Here there are 7 cart slots.

[eslapion]

The Arfon also gives 5vDC to the expansion port too.

I assumed it would be like that and that's why I mentioned the Datasette and Trackball (on the joystick port) only.

Since these aren't on the cartridge port but require 5Vdc, they end up being powered through the 9Vac that comes from the user port. Add that to the normal VIC-20 power and you're in for a generous amount of current flowing in from the user port.

I suspect it may be too much for the user port gold plated tabs.

[ken]

well I opened up the cad program to check on trace size to check load

0.025 trace is 1.65A
and
0.156 trace is 6.23A
so I am sure you are correct in saying it cant be done or is bad or shouldn't be done
or what ever negative thing you are going to say
I will just agree with you so you can feel good

[ken]

Cool. The pass through looks like a 2nd edge connector, not an "edge". Is this correct ??

yes
this is just a hand built unit that was done for fun so I used a edge connector , I forgot to incest the extender board before I took a pic
I should add my flexible usb fan/light to it , so I can really have something cool ...
adding a simple barrel connector or solder pads would allow for easy use of a wallwart
I think adding a USB charging port would be going to far

[eslapion]

well I opened up the cad program to check on trace size to check load

0.025 trace is 1.65A
and
0.156 trace is 6.23A
so I am sure you are correct in saying it cant be done or is bad or shouldn't be done
or what ever negative thing you are going to say
I will just agree with you so you can feel good

I don't know how you came up with these numbers...

AFAIK, the copper traces on the VIC-20 mainboard topside are standard 1 oz/ft2 copper.

The 0.156" spaced tabs of the user port are actually about 0.1" wide but they get narrower on the board so...

According to this calculator: http://www.4pcb.com/trace-width-calculator.html

The tab themselves should experience a temperature rise of 7C with a current of 2A.

The traces on the board are about 0.050" wide (between the edge connector and the wiring connector) and the same current should cause a rise in temperature of 22C. I think this is quite significant.

That being said, since old VIC-20s use a linear regulator, diode bridge and a large filter capacitor, they draw current in a very irregular manner (successive spikes) similar to the load waveform of a compact fluorescent but, of course at a much lower voltage but higher current.

These spikes can reach up to 5A in the early generation VIC-20 but the average current is effectively much lower and I won't go in the details of calculating an RMS value. I'm just trying to explain the general idea.

Can this really set your VIC-20 on fire? I don't think so.

Can it cause damage to traces or the soldermask of the PCB? In the long run, there is a risk.

The VIC-20 Programmer's Reference Guide says the current limit on these tabs is 100mA and that is more than likely grossly underestimated but powering the whole VIC through there represents more than 10 times this recommended limit. I know I wouldn't do it.

[ken]

ah so now you will change your answer again ......
now its a smaller trace and it gets smaller and what ever is next
so lets see the new size of .050 , I show max current 2.73A still better than the 1.5A fuse
and it narrows to what?

Go argue with the maker of the Arfon Micro expander.

mrr19121970 asked if it could be done and I did it just to see.......
I already know its not the (best) way or even a (great way) , I was just showing A way
thank you for taking something that was fun to throw together and make me wish I has never fukin did it
I guess I should just go build a 12V DC power supply to plug into the 9V AC port because that is a good idea.....