115V - 230V Isolated Power Supply

[AM]

I opened a copy of a T-Rex Power Plant Jr and found out that there is an 115V in next to the 230V one. The circuit board appear to be a double side tinted one. Please see attached images.

Is it possible to just solder the wire that now goes to the 230V in to the 115V one or install a switch (and what kind?) so I can use it with 115V? I don't know if the transformer and fuse would work or get damaged.

[antonis]

IMHO, it won't work..

Transformer clearly states that it's 230V rated (NOT 115/230) so most possible for transformer is to be single input (not multiple inputs for various mains voltage..)

You can easily verify it by measuring between any of 230V pin & 115 pin.. You should read "open" ..!!

In case of very low resistance measurement, verify it by measuring between the 2 230V pins in a rough analogy..
About 115 fuse rating, you should overdouble existing 230V fuse..
(e.g. about 2.5 times, at least..)

P.S.
No need to tell you that messing up with mains without skilled precautions should be life-time consuming action..

[ElectricDruid]

I certainly wouldn't assume that would work. It could be that they use the same PCB for both a 230V and a 115V version of the product and simply fit the correct transformer for a given version.

Transformers that can do either 230V or 115V tend to have two primary windings and are often marked "2 x 115V". You connect them in series for 230V and in parallel for 115V, and you do get circuits which provide a switch for this. However, the transformer you've got isn't marked like that. On the other hand, it does seem from the number of pins to have more than a simple single primary winding.

Overall, it doesn't look straightforward to me. Perhaps with some tracing out and testing of the transformer you could work out what they've done, but I wouldn't just wade in and try it. That sounds like an invitation for the magic smoke to escape and your power brick to become more "brick" than "power".

[antonis]

Much more detailed answer, by Tom.. 

[Ben N]

I certainly wouldn't assume that would work. It could be that they use the same PCB for both a 230V and a 115V version of the product and simply fit the correct transformer for a given version.

That would be my guess/assumption.

[AM]

Thanks for the replies guys. It sounds like more trouble (and potential disaster) than what it's worth. I'll leave it alone.

[Rob Strand]

Thanks for the replies guys. It sounds like more trouble (and potential disaster) than what it's worth. I'll leave it alone.

That's the best plan.

If your soldering isn't good it's not a good idea to mess with it from a safety point of view.

If you know how to do this safely you wouldn't need to ask! (no offense).  It's actually very easy to check.
----------------------------------------------------------------------------------
So having said that.

To me I can see the transformer has three input pins, not the four you would see on a split 2x 115V wired in series. 
The PCB has the following tracks:
- The fuse is on the 0V line, then goes to the transformer
- The 115V terminal has a track to the transformer
- The 230V terminal has a track to the transformer
So to me it does look like you just solder the wire to the 115V terminal instead of the 230V.
It doesn't make sense to even have the 115V terminal there otherwise;  except in the remote chance
that the 230V and 115V both have three pins and use different pairs.

But the main point is without testing the transformer you don't *know* that the winding is 115V.  What if it's 220V and 230V, or 230V and 240V? (with a risk of connecting across 10V!)  At the end of the day the PCB marking can say anything and does not have to match what the transformer *is*.

In some cases you need to change the fuse for 115V vs 230V.

You might be able to find data on a DCT-5 transformer.

[merlinb]

There's one here that appears to show the 115V tap being used exactly as you suggest (post #3):
https://musikding.rocks/wbb/index.php/Thread/22357-Unterschiede-Palmer-MI-PWT-05-und-HB-Powerplant-Junior/

[AM]

Thanks Rob and Merlin. My soldering skills are good so I'm confident to do the soldering part. My theoretical knowledge is poor and this is why I have to double and triple check with guys like you who have good understanding of circuits. I will translate what people wrote in that forum and find out what's the deal.

[AM]

From what I understand using google translate, the consensus in that forum is that the two power supplies are identical. The differences are that one of them has the voltage switching implemented, plus a detachable cable and an on/off switch. But the transformers and circuit boards are the same. On the other hand, if you look at the Palmer PWT 05 MKII on the net, you'll find pictures and it's clearly visible where it reads 250 mA per output. The other one (which is what I have too) is rated at 120 mA per output.

[Rob Strand]

There's some criticism regarding the ratings in the thread.  One guy says 300mA *total* (maybe) and clearly produces ripple (ie. loses regulation) with 100mA on each outlet.

For a supply like that you will have two ratings
- the maximum current  of an individual outlet, and
- the total current = the sum of all currents.   
  The total must be below the total limit regardless of the individual ratings.

A worst-case scenario is the maximum for single outlet is equal to the total outlet limit.
The best case is the total is n times the single rating.

If that transformer is only 5VA then the total current might only be 250mA to 300mA.   Getting in the ball-park of what the guy says in the thread.

Another point is with a tapped primary winding (instead of two separate primary windings wound in series for 230V and parallel for 115V) the tru output power for 230V input is higher than the rating at 115V.  That comes about because the only part of the primary winding get utilized on the 115V tap.