| Electronics > Projects, Designs, and Technical Stuff |
| JBC-mini - a low cost T245 handle controller |
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| poorchava:
I think that for maximum rms currents over 6A the filter would be seriously large, but I'll look into that. AC signal is offset from system ground only by the thermocouple voltage. The voltage drop across wires is around 25mV or so at 2A through the heater. As for the heater resistance temperature coefficient, I'll check and see. |
| 0xdeadbeef:
Probably not what you want to hear, but but just for info: you can get a new JBC station with T245 handpiece plus two cartridges for less than 250€... Ok, it's analog but still tempting. eBay (including VAT and shipping in Germany) http://www.ebay.de/itm/JBC-Lotstation-BT-2BWA-analog-mit-Lotkolben-T245-A-und-Zubehor-/231246976280 Webshop (including VAT, excluding shipping) http://www.chiemtronic.de/produkte/jbc-loetstationen-loettechnik/analoge-jbc-loetstation-bt-2bwa/ |
| poorchava:
A small development: The ac switch and zero crossing detection is fully working. I also wrote software to control the display and the encoder (which turned out to be really crappy and required additional filtering and an external schmitt trigger). I still have some glitches at minimal and maximal duty cycles, but those are only software quirks. Now I have the analog part left. |
| poorchava:
Yesterday I found some time to work on the project. Right now the setup looks like this: I have put entire circuit together more or less. Some conclusions: -zero crossing should be sensed from the same winding which powers the tip. Sensing from another transformer (the small one that powers logic) introduced phase shift between the zero signal and the actual zero. -the opamp behaves well when driven into saturation and desaturates reasonably quickly. I may add some load th the opamp output to speed up coming out of positive saturation -replacing BAT54 with 1N4148 as opamp input clamping diodes helped. -I must have miscalculated necessary gain, because the opamp hits the rail at about 300 degrees -powered from 12V transformer, this is already powerful as hell and heats up fast -analog part is quite stable even without software avaraging , i'm getting about +/- digit readout fluctuation Interesting part: JBC tip CAN be used as a weak substitute for a light bulb. By some software bug I have managed to get the tip glowing hot. And it still works wihtout proble and is still getting wetted by solder perfectly. This stuff is really impressive... I added a block of power resistors in series though, to limit the power. |
| poorchava:
It works! Right now only with very crude proportional regulator, but it keeps the temperature within 2 degrees from setpoint. I will now look for an enclosure and design the board for ordering :-) Would anyone be interested in buying a pcb, a kit or a fully built station? I won't be asking alot, just to return the material and shipping costs. |
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