Commodore 64 New Powersupply 2

This is just a little follow up to my C64 power supply post. Since I built that supply I have acquired a second Commodore 64 and I wanted to be able to hook up both. I decided to build a second supply based basically on the same design as the first. You can review the earlier post from the link below:

https://hobbytronics.home.blog/2019/02/11/commodore-64-new-powersupply/

I used the same case, same Meanwell 5Volt DC Supply, another salvaged IEC power port and switch. With a fuse. This time I didn’t have a spare transformer around so I had to order one. The new transformer is a Jameco 105524 9 Volt power supply. I wasn’t happy that it really didn’t arrive with useful info on what wire was which. I went back to Jameco’s listing for it to look up the wiring, which while the information was there, it was not posted in a clear manner. They have a scanned transformer diagram with 1-6 marked on it, then below it typed text saying what the various wires are by the “colors” of the wires. So go by the wire colors. It turned out that the 4 wires I needed were the same color as the other transformer (which only had 4 wires as it was a 110 to 9.5V only transformer). The new transformer was larger, I guess because of the 230V supply support? It still fit into the case I used previously. I also still mounted the transformer and Meanwell supplies to a piece of raw circuit board material. I did run a ground wire down to the one bolt on the transformer. Still it was grounded already due to the Meanwell case being grounded as well as the copper on the circuit board material.

The thing I still didn’t do that should have been done is grounding the metal screws and metal screen on the top of the case, if the Hot wire every pulled and contacted to the screen that would not be a good thing if it was then touched.

This time I did use crimp terminals on the wires going into the Meanwell screw terminals as I had them around, and I think if they are tight they are a little safer that way.

I again did not include a “Computer Saver” or “C64 Saver” overvoltage protection circuit. With the larger transformer I didn’t have room for sure this time. The Meanwell does have overvoltage protection, but it won’t kick in until well after the damaging 5.4 Volts DC..

The new supply. Sorry for the poor picture quality..

The screen is a little smaller this time around, it didn’t need that much of a vent. Really it was just I thought it looked better that way than the larger screen. I put the fuse on the bottom, as having it in the lid, I couldn’t put the nut on it before. The Hot/Line/Live wire goes first to the switch, then the back of the fuse holder from there, then through the fuse back over to the Meanwell supply terminal where the Transformer is also connected to it.

I wanted to do a power led… I forgot to. This thing is very tight, it would take a good bit for me to get the board loose so I could get back at the screw terminals.. I have to take the 5 screws out holding the board down, pull the fuse holder out the back, and feed in some of the output wire cord to lift that end of the board.. I am not wanting to risk pulling any of the rather short wires out of the crimp terminals, or making them loose and dangerous later on. I may go back and do it at some point. I would like them on both supplies. Basically some wires and a resistor to an LED off of the 5Volt output..

Here you see the new supply on the left with fuse holder on the bottom.
Another view of the back and top. The new one is a fraction darker plastic, be great a few shades darker though.
Here is the top front view of the supplies. The new one on the left again. I added the metal sticker I had ordered as well.

Above you see the finished supplies side by side. The metal stickers that I ordered from “marstickers” on Ebay turned out amazing. I believe they sell them on Etsy as well, as I found the listings there, the pricing is similar. That is also who I ordered the reproduction Commodore 64 Gold case badges form for my second C64. These are cut metal foil sticker, mirror finish. They came with a backer and clear top piece that holds them into position to get them placed properly.

A few little things, make sure the supply isn’t a bit under voltage at the connector. If the wire is too long (and possibly to thin), you get some voltage drop on the cable and that can be bad for the operation of the computer. I went with a wire around 4′, but some people go longer. So I get a slight bit over 5Volts (5.1V max) on both of my supplies at the power connector.

The wire I used is virtually the same diameter as the pins. It is stranded security wire, it is not very flexible and doesn’t have many strands in it. It is not perfect, flexing it too much will likely cause it to break. Still it is real copper and is stranded, and a good diameter for the power lines.

The 5Volt 3Amp Meanwell supply should be 15Watts
The 9Volt 1.5Amp transformer should be 13.5Watts.

28.5Watts/110Volts = 0.259 Amps. Then the fuse should be rated at 125% of that. So 0.259*1.25=0.3238 Amps for the fuse at 110Volts

28.5Watts/220Volts = 0.1295 Amps. Then 0.1295 * 1.25 = 0.1619 Amps for the fuse at 220Volts

If you figure the Meanwell’s 77% efficiency that should move it to .366 Amps at 110Volts and .183Amps for 220Volts.

You should get the closest Amp fuse that is above the value calculated. Probably 400mA if you can find one at 120Volts or 200mA at 220Volts if that is your voltage there. If the rating is to close, then the inrush surge when plugging in could blow the fuse. You want to use normal (fast) acting fuses not “Slow Blow” fuses.

I am no professional at calculating fuse values. I believe that is correct though. The trick is you are figuring the Wattage usage of the supply at the top safe level of it (at the supplies efficiency level), so that you can then relate that power usage to the 110/220 AC, as that directly translates back to there.

The C64 won’t be drawing 28.5Watts out of the supply ever, unless something is wrong.

The factory supply (output) should be 16.5Watts 5Volt 1.5Amp (7.5Watts) plus 9Volts 1Amp (9Watts). So I expect the C64 won’t end up drawing more than that.

Factory supplies seemed to have 120mA or 200mA fuses on the AC line for 220Volt supplies. That seems to indicate they went with higher numbers, but they had 7805 regulators. With the 7805 to give out 1.5 Amps at 5 Volts actually used 1.5Amps at the input voltage, 9-14Volts probably. So they were using more nearing 21Watts (at 12Volt input) at full load. Well as the load increases the input voltage to the 7805 should in theory drop to close to 9Volts. Figuring that 120mA would be right for 21Watts.

The Meanwell has over voltage protection, I did not include a fuse on the 5Volt DC after it. If you did, you would want a 1.5Amp fuse probably there as the Commodore 64 should not pull that much safely anyways although it may blow before the protection on the Meanwell trips, although the Meanwell may still trip faster than the fuse will blow.

Power connector. You can see the wires aren’t tiny compared to the pins, 2 strands are also removed to get them to fit.

This is just what I did, I have not included any wiring diagrams or detailed parts list. It is a rather simple build really. The Meanwell gets the direct 110Volt AC to it, along with ground. The Transformer gets the same direct110Volt AC. Everything else is sending the right wire to the output on the Din power connector hta goes to the Commodore 64. This same setup could be used for a Commodore 128, swapping in the proper power connector, as the 9Volt AC transformer I used and and the 5Volt Meanwell supply I used can handle the additional current load. While this is a simple supply working with AC mains from the wall outlet isn’t a safe thing to do if you don’t know what you are doing. Like I mentioned above, the metal screen and the metal screws that hold it on SHOULD be wired to Ground for safety, if built into a metal case or having any external metal should be grounded, such as the screw heads. The enclosure’s metal corner screws are electrically isolated so they aren’t a problem in this exact case. I expect if I go back and add the Power LEDs that I will be grounding the metal screens in my case. I have been building supplies off and on for a couple decades and have a few years of electronics training having worked with open chassis and vacuum tube electronics back in school. Doing a supply like this is something you should really look at carefully if you go to make one of your own.

There is a simpler way than to work directly with the AC directly and wiring things up. You can get a good quality 5Volt DC AC Adapter, and if you look carefully you can find some 9 Volt “AC” adapters (often used for older security systems I think, but what for in them I don’t know, but you can still find them). Then you can take an extension cord (even a 2 wire one if both Adapters are 2 prong plugs, be sure it is heavy duty enough though), plug those two adapters into the extension cord and hide that inside an enclosure, cut the cords and wire in a cord with the Din power connector for the C64. Jan Beta had has done just that, it is likely a safer project. Retro Recipes has as well.

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