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I bought one of the Jingda ‘XL-150A’ leather irons from Aliexpress and did an examination.
Before even powering it on, I took it apart.
The first thing I noticed was the power cable was bogus. It had a 3 prong ‘Y’ grounded Chinese Type I plug molded to the cable. The plug was marked “JS-03 10A 250V”. The cable was embossed with “3×0.75mm2” along with safety ratings. That should be a three conductor earthed 6 amp cable. But coming out of the cable end was only two conductors, and they appeared to be 0.50mm or less. Any impression of grounded safety was only an deliberately mismarked illusion.
The control circuit is a basic thermistor feedback type based on a LM358 dual opamp controlling a BTA06 triac. I measured a heating element resistance of 337 ohms. This type of heating element isn’t likely to change much with temperature, so applying 100% power gives 150 watts at 240V, but less than 40W at 120V. You really want to run it at 240V, preferably using an isolation transformer if you keep the original ungrounded power cord.
I measured the warm-up cycle with the iron set to the highest dial temperature. At 237V the iron took 1:15 from 30C to 100C, and 2:54 from 30C to 200C. Even discounting heat loss from convection, which is going to be significant, it would take about 12 minutes to heat up at 120V.
I didn’t do enough measurements to check the overshoot, or how long it the iron takes to stabilize. When I marked the time for the target temperature, the face temperature was rapidly rising. That suggests the interior might have been considerably hotter. I might do some additional runs to check the time constant.
I’m otherwise pretty confident in the accuracy of my measurements. I was measuring using four probes, two sensors (thermistors) with multimeters, and two K-type thermocouples. They were taped at different points on the hot face using a single layer of Kapton tape. They all had very close readings, so the measurement point was not much of a variable. Future tests will likely just use a single thermocouple.
Bottom line: this iron is really only suitable for 240V.
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I say 240V only solely because it has so little heating power at 120V. It will take a long time to heat up, and the iron won’t be able to maintain a stable temperature in use. The temptation will be to run it hot (or at least as hot as it gets) and rely on thermal mass, rather than feedback temperature regulation.
Even at 240V the iron has a pretty slow regulation loop. It was frustrating trying to calibrate the dial which is *way* off on the slope — setting the position so that 150C is correct results in a setting of 200C being around 185-190C.
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