diff --git a/content/posts/2018-06-25-Saike-858D-Measurements.md b/content/posts/2018-06-25-Saike-858D-Measurements.md new file mode 100644 index 0000000..df11e0b --- /dev/null +++ b/content/posts/2018-06-25-Saike-858D-Measurements.md @@ -0,0 +1,67 @@ +--- +title: "Saike 858D Rework Station - Measurements" +date: 2018-06-25T13:20:00+02:00 +author: eNBeWe +type: post +categories: + - Allgemein + - Bastelkram +tags: + - 858D + - DIY + - Arduino +--- + +The next part in the series about reverse engineering the Saike 858D rework station ([Overview][1]) brings a few +measurements, I did in my device. +It presents me with the problem, that I am not sure anymore if I want to keep the transformer, +currently used in the station. + + + +I soldered some wires to the connector of the transformer, allowing me to hook up my Oscilloscope to the transformer output. + +## 10VAC Rail + +![10V Rail Without Load](/posts/images/858D/10VAC_No_Load.png) + +The first measurement is the 10V rail in idle state, without the heater or fan running. +The "sine wave" is not really pretty but I don't really care, given the fact that it will be rectified anyway. +The peak output voltage is 16.6 volts, and the RMS output is 12 V instead of 10 V. +This means the transformer produces a voltage a bit higher than rated. + +![10V Rail With Fan Running](/posts/images/858D/10VAC_Fan_Running.png) + +If the fan is running, the 10V rail degrades a bit more and slightly drops in voltage. +Again, given the fact that it it fed through a rectifier and then a voltage regulator, that is almost fine. + +I don't really like that we use a voltage of about 12V as the input for the 7805 voltage regulator. We power the microcontroller, the display, the EEPROM and a bit of other stuff from the regulator so I would guess the current is not too high, probably in the few hundreds of mA. + +## 30VAC Rail + +![30V Rail Without Load](/posts/images/858D/30VAC_No_Load.png) + +The second rail of the transformer should supply 30VAC. In reality it overshoots quite a bit and delivers 34VAC RMS, peaking at 47 volts. The diodes in the full-bridge rectifier have a 1 volt drop each, so the rectified voltage is probably somewhere close to 45 volts. + +![30V Rail With Fan Running](/posts/images/858D/30VAC_Fan_Running.png) + +With the fan running, the voltage drops a bit, peaking at 43 volts. This is the voltage, the control circuit for the fan has to regulate to not overload the fan. +The fan is labeled with a consumption of 0.35A, which means the transistor has to sink about 4 Watts (11 volts at 0.35A) of heat. As a result, with the fan running, the transistor almost instantly heated up to about 50°C. + +## Fan output + +![Fan voltage sweep](/posts/images/858D/Fan_Sweep.png) + +Additionally, I measured the voltage at the output terminal of the fan. +At the minimal potentiometer position, the fan has a voltage of 11.4 volts applied to it. +At the maximal position, the voltage rises to 28.2 volts, more than 4 volts over the fan specification + +## Conclusion + +I am not really happy with the transformer in the device. The rating is dodgy at best, and lots of energy is wasted in heat in regulation circuits. + +At the moment I tend towards replacing the transformer with a 24 volts switching power supply and a small buck converter for the 5 volts logic circuts. The fan regulation could then be done through simple PWM. + + + [1]: {{}} + diff --git a/content/posts/images/858D/10VAC_Fan_Running.png b/content/posts/images/858D/10VAC_Fan_Running.png new file mode 100644 index 0000000..1b3f9fb Binary files /dev/null and b/content/posts/images/858D/10VAC_Fan_Running.png differ diff --git a/content/posts/images/858D/10VAC_No_Load.png b/content/posts/images/858D/10VAC_No_Load.png new file mode 100644 index 0000000..0ee4288 Binary files /dev/null and b/content/posts/images/858D/10VAC_No_Load.png differ diff --git a/content/posts/images/858D/30VAC_Fan_Running.png b/content/posts/images/858D/30VAC_Fan_Running.png new file mode 100644 index 0000000..fff67ac Binary files /dev/null and b/content/posts/images/858D/30VAC_Fan_Running.png differ diff --git a/content/posts/images/858D/30VAC_No_Load.png b/content/posts/images/858D/30VAC_No_Load.png new file mode 100644 index 0000000..fb11a6a Binary files /dev/null and b/content/posts/images/858D/30VAC_No_Load.png differ diff --git a/content/posts/images/858D/Fan_Sweep.png b/content/posts/images/858D/Fan_Sweep.png new file mode 100644 index 0000000..8169a1b Binary files /dev/null and b/content/posts/images/858D/Fan_Sweep.png differ