[chum_2000_uk]

Hi guys,

I've just bought a PSU board and R-core transformer from Kingwa at Audio-GD to power a Jaycar headphone amp kit that I am in the middle of building. I'm not quite 100% sure on how the r-core is wired to the PSU, so if anyone could help me out a little that would be great

Here are pics of the PSU and R-core:

As you can likely tell from my user name I am based in the UK, so I need 230V. Kingwa at Audio-GD already soldered the yellow and green wires together for me for the primary so that is sorted. Its just the secondary that I am unsure about, because as you can see for 18-0-18V it says to use blue and brown.

If you look at the A-GD PSU, it has 4 AC solder points at the bottom, and as I see it there are 5 wires to connect to these; 2 blue, 2 brown and the green/yellow ground wire seen between them in the pic.

So.... I'm thinking that they need to be soldered like this:

both brown to one solder point, both blue to another, then the green/yellow wire to one of the inner solder points, and a common ground wire across to the other inner solder point. That's my thoughts on how the secondary should be wired, any input will be so much appreciated.

Ok, while I'm here... I may as well make sure that my understanding of the primary wiring is correct too (this will be the first time I have wired a transformer up). While testing at least, I am probably going to wire the primary up to a switched IEC inlet, like this:

Bulgin | Connectors | Electrical/Power | IEC Connectivity | |BZM27/Z000/53B

So I assume the red and orange go to live and neutral (does it matter which goes to which, is either way fine?) and the centre tapped yellow and green wires go to earth, correct?

And with that connector that I have linked to above, I assume the switch will already be pre-wired to the IEC socket, so WONT have to be wired separately?

Sorry for the lengthy post, I just want to make sure I know exactly what I am doing before I start. Thanks so much for your help

 

[spritzer]

For the primary you connect red/orange to the fuse/switch and connect yellow and green together. The secondary wiring should be the blue and brown wires going to each side of the AC input for each side of the supply. On the last pic you posted it would be, from left to right, brown - brown - blue - blue. The yellow and green wire should be connected to the chassis ground and the other secondaries safely tucked away where they can't short out.

 

[chum_2000_uk]

Thanks spritzer!

I've got the secondary all figured out now with your help

for the primary, the IEC connector I was going to use doesn't have a fuse. Yellow and green are already connected together. Do the yellow and green wires also have to go to the earth pin for the IEC inlet?

so like this:

Cheers

 

[chum_2000_uk]

Oh, just for anyone else's benefit who is searching for similar info.... here is a revised pic showing how the R-core should be wired, based on info by spritzer:

Each of the brown and blue wires going to an AC point, and the yellow/green wire going to a chassis earth point.

Thanks

 

[FallenAngel]

1) Add a fuse. The funny saying about this is that a $50 transformer will always sacrifice itself to save a 50c fuse.
2) Do not connect Green/Yellow to Earth Ground, simply connect the wires together and isolate from everything else.

 

[Currawong]

If it's the same R-Core transformers as used in the Audio-gd products, it will have a fuse built in. It'd be worth checking this with Kingwa.

 

[spritzer]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif 1) Add a fuse. The funny saying about this is that a $50 transformer will always sacrifice itself to save a 50c fuse.

Yeah, always install a fuse and also a DPST mains switch to fully isolate the component from the mains. If your IEC socket doesn't have a fuse built in, then just use a separate fuse holder.

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif 2) Do not connect Green/Yellow to Earth Ground, simply connect the wires together and isolate from everything else.

Indeed, the yellow and green wires should only be connected together and not to anything else. Now the wire with yellow and green stripes should be connected to the chassis ground. The ground lug of the IEC should also be connected to the same point on the chassis but you might want to install some sort of ground loop breaker. A 10R/2W resistor would do the trick but it isn't really needed.

Quote:

Originally Posted by Currawong /img/forum/go_quote.gif If it's the same R-Core transformers as used in the Audio-gd products, it will have a fuse built in. It'd be worth checking this with Kingwa.

It's a thermal fuse and will not kick in unless the transformer overheats. Useless when it comes to excessive current draw.

 

[chum_2000_uk]

Really appreciate the info guys, this is just what I needed - thanks.

Spritzer, I haven't actually bought the iec inlet yet, so now i'm thinking to get one with a fuse and a switch. I assume the built in switch will be dpst, seeing as it's a mains switch. Will this suffice do you think?

I haven't actually got a case yet either, so when testing, what do you guys recommend I use as my earth point for the transformer and iec lug?

Thanks!

 

[spritzer]

Mains switches are either SPST or DPST so I'd spring for the more expensive switch.

I never bother with earth when I'm testing something new but if you are going to touch any metal parts then by all means ground them.

 

[Currawong]

Quote:

Originally Posted by spritzer /img/forum/go_quote.gif It's a thermal fuse and will not kick in unless the transformer overheats. Useless when it comes to excessive current draw.

From his email, months ago, when I asked him about this:
Quote:

We order the transformers inc the fuse in it. Transformers fuse can protect by heat and over current, I think this can offer the best protect.

Good of you to be concerned about it though.

 

[spritzer]

The thermal fuse will kick in due to excessive current but not as quickly as the other fuses. Most of the cheap R-cores made in China have a thermal fuse as standard. The R-core here in question can be easily bought off ebay so it isn't a custom unit.

 

[Beefy]

Quote:

Originally Posted by spritzer /img/forum/go_quote.gif Mains switches are either SPST or DPST so I'd spring for the more expensive switch.

Slightly O/T, but I would be inclined to recommend only double pole switches on the mains for safety reasons.

If an idiot electrician has wired the live and neutral wires backwards in the GPO, a single pole switch will only be switching the neutral. So when you think your switch is turned off, you can still easily have a fault from live to earth.

Rare problem perhaps, but very easy to prevent by switching both sides of AC mains.

 

[spritzer]

Indeed, that's why I pointed out above that he should go for the DPST switch.

 

[chum_2000_uk]

Thanks for all your help guys, when I buy the IEC inlet I am going to make sure it either has a DPST switch, or wire one separately. I'll also make sure to get one with a fuse.

What fuse rating would you guys recommend? The usual 3A or less?

 

[spritzer]

According to this then the transformer is 50VA and for 230V you would only need 1/2A for some extra headroom. Inrush current isn't really a problem with R-cores so you could use a normal fast fuse.