CoCo2 26-3134A with 230V~ ???

Hardware Hacking, Programming and Game Solutions/Cheats
jedie
Posts: 655
Joined: Wed Aug 14, 2013 12:23 pm
Location: germany
Contact:

CoCo2 26-3134A with 230V~ ???

Post by jedie »

Did anyone know a power supply solution for a CoCo2 26-3134A with 230V~ ?

In http://www.colorcomputerarchive.com/coc ... ndy%29.pdf i found some informations:

* power transformer provides 17,2 VAC, center-tapped, ad 1.8 amps RMS
* -5V are only for RS-232C and not used anywhere else.

Must i have a transformer with AC output? Or can i use a Switching Supply solutions with DC output?
What ampere is needed for +5V and -5V ?

It's seems that a power supply with -5V is hard to find.
I found theses Switching Supply solutions:

* MeanWell PD-2505: 25W 5V/2.5A -5V/2.5A
* MeanWell RT-65A: 66.1W 5V/6A 12V/2.8A -5V/0.5A
* RECOM Power RAC10-05DC/277: +5V/1A -5V/1A
* TDK-Lambda KMD15-55: +5V/1.5A -5V/1.5A

But they are not really cheap and it seems that i can't buy every of them easily in germany.

The MeanWell RT-65A costs ~20€

Maybe a simple transformer is cheaper... I found this:

* Block NT 12VA 2X6: 2x6V 12VA 1,08A - 11€
* Block EL 54&18,8 : 2x6V 16VA 1,3A - 7€
* Block EL 18/6 : 2x6V 18VA 1.5A - 16€
* Weiss UL 506 : 2x6V 18VA 1.5A - 7€
* Block EL 60/25,5 : 2x6V 25VA 2A - 9€
... too many ideas and too little time ... Related stuff written in Python:
Dragon 32 emulator / PyDC - Python Dragon 32 converter: https://github.com/jedie/DragonPy
DWLOAD server / Dragon-Lib and other stuff: https://github.com/6809
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: CoCo2 26-3134A with 230V~ ???

Post by sorchard »

It would be easier, safer and possibly cheaper to use a step down adaptor. Something like this:

http://www.amazon.co.uk/High-Quality-10 ... B000KGHOGM

The 'step down' part is the important part. There is a transformer inside to reduce the voltage.

Perhaps a European version is available?
Stew
jedie
Posts: 655
Joined: Wed Aug 14, 2013 12:23 pm
Location: germany
Contact:

Re: CoCo2 26-3134A with 230V~ ???

Post by jedie »

I can't use it, because the origin transformator was removed before shipping to save weight ;)
... too many ideas and too little time ... Related stuff written in Python:
Dragon 32 emulator / PyDC - Python Dragon 32 converter: https://github.com/jedie/DragonPy
DWLOAD server / Dragon-Lib and other stuff: https://github.com/6809
User avatar
tormod
Posts: 416
Joined: Sat Apr 27, 2013 12:06 pm
Location: Switzerland
Contact:

Re: CoCo2 26-3134A with 230V~ ???

Post by tormod »

The -5V on this CoCo is only for the RS232, so you don't really need it. I guess without the -5V the serial port will deliver 0/5V which will work fine with for instance your Dragon DriveWire adapter :)

This leaves you with +5V DC which you can get from a PC power supply or some other simple power adapter. This should be fed to the board instead of the output from the SALT (pin 3), which can get tricky because you don't want to impose this to the SALT output. Or you can inject a higher voltage (I think 9V or 12V is safe, considering the 17.2Vrms / 2 from the original transformer which rectified and flattened is more like 12V) past the rectifier bridge, at the entry of the SALT chip (pin 16). Going through the SALT chip adds the advantage of the SALT current limiter in case of some mainboard short circuit. But some CoCo guys may have first hand experience on this.

An alternative would be to get the same transformer as for a Dragon, like the Noratel AA-18120-TI-B you can get at distrelec.de for ~30€ (or use a Dragon PSU). You can probably feed the 8.5VAC to the CoCo rectifier (one leg to ground). Also, one of the 14.4VAC outputs could be used to generate -5V like on the Dragon, however it might be too high voltage for injecting it into the other side of the rectifier bridge (middle tap leg to ground), so I would have added a separate rectifier bridge and a 7812 voltage regulator instead and fed 12V to this SALT input (pin 15). Well, a lot of work considering you don't really need the -5V.
jedie
Posts: 655
Joined: Wed Aug 14, 2013 12:23 pm
Location: germany
Contact:

Re: CoCo2 26-3134A with 230V~ ???

Post by jedie »

tormod wrote:The -5V on this CoCo is only for the RS232, so you don't really need it. I guess without the -5V the serial port will deliver 0/5V which will work fine with for instance your Dragon DriveWire adapter :)
My origin Dragon DriveWire adapter will work, without any modification? I need only a Adapter? Geat!

Then it makes no sense to look at a -5V supply... But a old PC power supply has IMHO -5V (The newer one not.)
But i would like to have a "buildin" power supply and a PC power supply is to big.

The Noratel AA-18120-TI-B is also not really cheap, costs ~30€

From the
jedie wrote:In http://www.colorcomputerarchive.com/coc ... ndy%29.pdf i found some informations:
* power transformer provides 17,2 VAC, center-tapped, ad 1.8 amps RMS
What does it really mean?
The output is: 17,2 / 2 = +8,6V AC and -8,6V AC at 1.8A/2=0.9A both?

So 9V AC would be ok, isn't it?

The https://www.distrelec.de/ringkern-trans ... 0-9/352934 costs ~12€ (without shipping): 2x 9V AC - 2x 1,67A

A switching supply solutions has some charm. If i inject voltage after the rectifier bridge, then i will lost the main power switch, isn't it? That's a little bad.
So if i use a DC solution, then i will inject it on the same place as the tranformator output.
... too many ideas and too little time ... Related stuff written in Python:
Dragon 32 emulator / PyDC - Python Dragon 32 converter: https://github.com/jedie/DragonPy
DWLOAD server / Dragon-Lib and other stuff: https://github.com/6809
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: CoCo2 26-3134A with 230V~ ???

Post by sorchard »

jedie wrote:I can't use it, because the origin transformator was removed before shipping to save weight
Bold strategy! I hope you saved a lot on the shipping ;)

The 2 x 9VAC 30VA transformer you've found should work OK. The voltage is slightly high but if Q1 doesn't get too hot then it shouldn't be a problem. You could always put a bigger heatsink on if it did get too hot.

As you say, the original transformer is effectively 2 x 8.6 VAC. Max current is 1.8A per output coil. Power rating is 17.2 x 1.8 = 31VA.

As tormod suggested, you can inject DC directly between ground and one of the transformer pads on the PCB but I would say *9V max*. The full wave rectified/smoothed output from one half of the original transformer could be as high as 12V under no load but should be 8.6V - 2 x diode drops = approx. 7V under full load*.

*Edit: It's actually 1 diode drop giving approx. 8V under full load.

I don't know how happy the power switch will be with DC. Switches often have a higher AC current rating than DC but it'll probably be OK at this low voltage.

I don't know if you've used toroidal transformers before but you need to be careful with the clamp screw through the middle. There is sometimes a warning label. If both ends of the screw touch a metal chassis then you will have a single turn on your transformer and a large current. This could mean a blown fuse or a burned out transformer.
Last edited by sorchard on Tue Oct 07, 2014 3:24 pm, edited 1 time in total.
Stew
jedie
Posts: 655
Joined: Wed Aug 14, 2013 12:23 pm
Location: germany
Contact:

Re: CoCo2 26-3134A with 230V~ ???

Post by jedie »

sorchard wrote:The 2 x 9VAC 30VA transformer you've found should work OK. The voltage is slightly high but if Q1 doesn't get too hot then it shouldn't be a problem. You could always put a bigger heatsink on if it did get too hot.

As you say, the original transformer is effectively 2 x 8.6 VAC. Max current is 1.8A per output coil. Power rating is 17.2 x 1.8 = 31VA.
Hm. OK there are also transformators with 6V, 7V and 8V AC output.

But not with ~30VA...

e.g.: 2x 6V AC with 20VA or 50VA:
20VA: https://www.distrelec.de/universal-tran ... 145/366790 ~10€ - 0.55kg
50VA: https://www.distrelec.de/universal-tran ... 152/366797 15€ - 1kg

Maybe this is good: 2x 7V AC - wx2.14A 30VA:
https://www.distrelec.de/ringkern-trans ... -rm/354159
but 30€

Too many options :?
sorchard wrote:I don't know if you've used toroidal transformers before
No, never used before. Must i have some "upstream electronics" ???
Should i better use non toroidal transformers?
... too many ideas and too little time ... Related stuff written in Python:
Dragon 32 emulator / PyDC - Python Dragon 32 converter: https://github.com/jedie/DragonPy
DWLOAD server / Dragon-Lib and other stuff: https://github.com/6809
jedie
Posts: 655
Joined: Wed Aug 14, 2013 12:23 pm
Location: germany
Contact:

Re: CoCo2 26-3134A with 230V~ ???

Post by jedie »

On the page http://tandycoco.com/coco2.shtml i found the image http://tandycoco.com/images/26-3134-koreanmobo.jpg it looks exactly like my one.

Here i marked A1, A2 and A3:
Image

A3 is mass/center. A1 and A2 the two two ends of the coil (the 8.6V AC)
... too many ideas and too little time ... Related stuff written in Python:
Dragon 32 emulator / PyDC - Python Dragon 32 converter: https://github.com/jedie/DragonPy
DWLOAD server / Dragon-Lib and other stuff: https://github.com/6809
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: CoCo2 26-3134A with 230V~ ???

Post by sorchard »

2 x 9VAC / 30VA is the closest. The voltage is just a little bit high so you would need to check Q1 doesn't get too hot.

2 x 8VAC is a little low but it could work.

2 x 7VAC is definitely too low. Not enough margin for the regulators.

You don't need to do anything special with a toroidal transformer compared to a normal EI transformer. Just be careful with the screw through the middle.

If your house doesn't have circuit breakers you should probably include an inline fuse on the 230V side. Something like T2A with >1000A breaking capacity.
Stew
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: CoCo2 26-3134A with 230V~ ???

Post by sorchard »

:oops: I made a mistake... I would normally allow for 2 diode drops in a bridge, but that's not true for the way the Coco supply is configured.

I should have said the full wave rectified/smoothed output from one half of the original transformer could be as high as 12V under no load but should be 8.6V - 1 diode drop = approx. 8V under full load.

A 2 x 8VAC transformer might be just enough. Can't guarantee it though.
Stew
Post Reply