TS100 Soldering Iron - Earthing the tip

[bagunceiro]

After all the positive reviews for it I thought I'd better get myself a TS100. Up to now it all seems very good.

There's one small exception to this and I could use some advice. The PSU I am using is a universal laptop job set to 20V and seems to be nice and stable. But it's not earthed, and there is AC leakage onto the tip of the iron at 120V (more or less the supply here). So I earthed it, using a wire from the earth connector on the iron to the earth pin on the mains plug. When I do that the iron's temperature (as measured by itself) goes haywire, swinging wildly from 200ishºC to nearly 400. I doubt it is actually doing that as the change is far too rapid so I think the earthing is screwing up the thermocouple. Disconnect the lead and it settles down to a nice steady 300ºC again.

My best solution is, I think, to find a more suitable supply. But nevertheless I'd like to understand what's going on. Does anyone have an explanation?

[Gyro]

Welcome to the forum,

Your conclusion is the right one I'm afraid, your PSU has a higher than normal leakage current. Those cheap universal laptop supplies are generally poor quality, sometimes even unsafe (impossible to say without seeing the internal construction). If you are actually seeing 120V on the tip (when not earthed) with an ordinary DMM then the leakage is bridging the insulation inside the tip and upsetting the sensitive thermocouple voltage sensing circuit, causing it to misread temperature.

This problem has been reported before, but appears to be a rare occurrence...

https://www.eevblog.com/forum/reviews/ts100-doesn_t-function-properly-when-earthed/

Try getting a second-hand decent brand name genuine original laptop adapter off ebay, eg. Lenovo, Dell, HP etc. They tend to be cheaply available and are much better quality (ie. they have passed real approvals!). Don't be fooled by listing that say "Adaptor for xxx", check the labels in the photos.

A couple of other threads that may be helpful to you...

https://www.eevblog.com/forum/beginners/choosingunderstanding-the-right-powersuply-for-the-ts100/

https://www.eevblog.com/forum/projects/silicone-lead-for-soldering-iron-recommendations/

I hope this helps.