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I recently received a Soldering Station, mine is labeled Huayu 898D+.

It has a nice digital display for PID temperature controller.

Of course, I took it apart.

The only problem is that I got the 220v version, which is quite inconvenient here in the USA where 110v is the norm. I tried it out without modification and it sort of worked. The iron wouldn't go above 250 degrees C and the hot air was also quite under powered.

Unfortunately, there is no switch to easily change between 220v and 110v, so we'll need to do some hacking. After thinking a bit about how to fix this, I decided to try to reduce the number of terms on the primary coil of the transformer.

From what I understand, transformers usually have about the same number of turns on the primary as the expected input voltage. For example, a 110v transformer might have 110 turns on the primary. From there, depending if the voltage is stepped up or down, the secondary's number of turns is directly related to the change in voltage. For example, to step up the voltage from 110 to 220, we would have double the number of turns on the secondary as on the primary.

Ok, so back to my fix for the soldering station.

A quick check of the PCB shows how power comes in from the mains and is routed to the red wires:

I assumed the primary on the transformer has around 220 turns, so I started by removing 100 turns by cutting the tape off the bottom of the transformer (where the red wires attach and carefully unwinding 100 turns. I did 5 turns at a time, cutting off each section of wire so I could easily see how many turns I had removed.

The PCB clearly marks some 24v inputs, so I disconnected one of those and measured the AC voltage. It was only 15.5v

I removed 10 turns more then 40 turns more, measuring the voltage each time. I then plotted these points and projected the best fit line forward to 24v. Using this estimate, we'll need to remove just under 400 turns of wire in total. Here's after I removed 300 turns of wire.

I ended up removing a total of 350 turns for a final voltage of 24.2v on the 24v output, I checked every 20 turns towards the end. En total, the removed copper weighed 16g.

When I was done, I taped the transformer back up, but I didn't run the tape inside the iron core. Just taped around the outside and it works great!

The iron heats up to 400 degrees C almost instantly as does the hot air gun. 220v to 110v conversion complete!

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