68 lines
3.1 KiB
Markdown
68 lines
3.1 KiB
Markdown
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---
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title: "Saike 858D Rework Station - Measurements"
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date: 2018-06-25T13:20:00+02:00
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author: eNBeWe
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type: post
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categories:
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- Allgemein
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- Bastelkram
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tags:
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- 858D
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- DIY
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- Arduino
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---
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The next part in the series about reverse engineering the Saike 858D rework station ([Overview][1]) brings a few
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measurements, I did in my device.
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It presents me with the problem, that I am not sure anymore if I want to keep the transformer,
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currently used in the station.
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<!--more-->
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I soldered some wires to the connector of the transformer, allowing me to hook up my Oscilloscope to the transformer output.
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## 10VAC Rail
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The first measurement is the 10V rail in idle state, without the heater or fan running.
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The "sine wave" is not really pretty but I don't really care, given the fact that it will be rectified anyway.
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The peak output voltage is 16.6 volts, and the RMS output is 12 V instead of 10 V.
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This means the transformer produces a voltage a bit higher than rated.
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If the fan is running, the 10V rail degrades a bit more and slightly drops in voltage.
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Again, given the fact that it it fed through a rectifier and then a voltage regulator, that is almost fine.
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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.
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## 30VAC Rail
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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.
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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.
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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.
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## Fan output
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Additionally, I measured the voltage at the output terminal of the fan.
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At the minimal potentiometer position, the fan has a voltage of 11.4 volts applied to it.
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At the maximal position, the voltage rises to 28.2 volts, more than 4 volts over the fan specification
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## Conclusion
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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.
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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.
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[1]: {{<relref "2018-06-20-Reverse-Engineer-a-Saike-858D.md">}}
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