CGS Power Supply Questions

hopelessennui · Joined: Mar 23, 2008 Posts: 17 Location: Los Angeles

Hello all!
I had a couple questions about the CGS66 PSU.

When i bought it i thought it i thought it was like the MFOS psu where you just use an AC wall wart adapter, but in the directions Ken talks about using a center tapped transformer. Its a bit over my head. I tried finding a center tapped transformer on mouser and got lost. Can someone point me in the right direction, or even better a link to the right one? Also how would I wire the transformer to the AC mains?

Ken mentions "where possible use a wall wart"

Can i use a wall wart instead?

Thanks a million.

andrewF · Posted: Sun Jun 29, 2008 3:10 am Post subject:

Hi
sounds like you will be better off with a 18VAC wallwart for now.
from Ken's page -
"it is possible to use a wall-wart between CT (the 0V connection on the PCB) and one 18V AC connection. The required pads are marked with large white circles. The result will be half wave rectification. If you use larger caps (3300uf) and limit the loading, you will be okay."

hopelessennui · Joined: Mar 23, 2008 Posts: 17 Location: Los Angeles

is half wave retification bad? any idea of how much load it could handle? or how many mA wall wart i should use?

Thanks

otherunicorn · Joined: May 11, 2008 Posts: 136 Location: Australia

Full wave is better than half wave, but that doesn't mean half wave is "bad". You would want a wall wart with at least 700ma. The higher the better. If you can find a 1A or a 1.2A, all the better.

Kartoshka · Joined: Jan 13, 2008 Posts: 28 Location: Toronto, Canada

Another cgs66 question: does those lines (enlightened on the picture) meant to be bridged with piece of wire?

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otherunicorn · Joined: May 11, 2008 Posts: 136 Location: Australia

Yes. Those are links.

zthee · Joined: Feb 20, 2008 Posts: 414 Location: Stockholm

You might wanna flip that capacitor; as it says on the CGS website "The 10uF capacitor beside the -15V pin of the 4 pin MOTM style connector is also shown on the overlay backwards."

I think?

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otherunicorn · Joined: May 11, 2008 Posts: 136 Location: Australia

Kartoshka · Joined: Jan 13, 2008 Posts: 28 Location: Toronto, Canada

true, how could i miss that. thanks guys again.

Tronato · Posted: Wed Aug 13, 2008 5:04 pm Post subject:

Hello!

Ken mentions that he cut a track and I can see that he did. However he also mentions that a link has to be added right next to the cut that is indicated by a black marker line.

Did you add that link?

Thanks!

TRON

otherunicorn · Joined: May 11, 2008 Posts: 136 Location: Australia

Tronato · Posted: Tue Oct 07, 2008 12:13 pm Post subject:

Hello!

Any good electronic practice requires protecting your equipment... so where should I install fuses for the CGS66 and which should their value be?
I am feeding it with a 117V/36VAC CT 2 Amp transformer... actually a Stancor P-8672...

Oh... and are the LEDs absolutely necessary?

Thanks!

TRON

andrewF · Posted: Tue Oct 07, 2008 4:45 pm Post subject:

It is important to have a fuse on the 115V side of your transformer, this is for your personal safety. A fast-blow 0.5A should be fine.

Some designs also put fuses on the DC rails at the output of the regulators, others have fuses between the diode bridge and the regulators.
Have a google for images "regulated power supply", you should see lots of examples.

You don't need the leds and 1k resistors, but they don't cost much and will always let you know if the PSU is switched on and operating properly.

Make sure all the 115V wiring is securely clamped down so it can never be pulled loose. Another good safety technique is, once everything is working properly, drown all the 115V solder connections in silastic/sealant goo, so nothing can touch them and it helps hold all the wiring in place.

Tronato · Posted: Tue Oct 07, 2008 5:06 pm Post subject:

Hello!

Thanks AndrewF!

TRON

otherunicorn · Joined: May 11, 2008 Posts: 136 Location: Australia

If you ever intent to power your supply without a load attached, for testing etc., the LEDs do become necessary. The provide the minimum load needed to make the regulators function.
If you don't want the LEDs, install the resistors, and put jumpers where the LEDs go so the minimum load remains.

Tronato · Posted: Sun Oct 12, 2008 2:18 pm Post subject:

Hello!

So how should the LEDs be installed here?
The PC Board has a small triangle where the LEDs should be insatalled... does the long leg of the LED go in the base of the triangle?
Thanks!

TRON

Luka · Joined: Jun 29, 2007 Posts: 1003 Location: Melb.

http://en.wikipedia.org/wiki/LED

wiki is great for working out simple problems like component orientation

Tronato · Posted: Fri Dec 12, 2008 1:38 pm Post subject:

Hello!

I am feeding 20VAC into the CGS66 from a supposedly 120/36VAC CT transformer, no load, leds light as expected but after adjusting the trimmers the maximum that is being output is (+/-) 12.75VDC.

Isn't it supposed to be (+/-) 15 VDC at least?

Thanks!

TRON