67 lines
3.1 KiB
Markdown
67 lines
3.1 KiB
Markdown
---
|
|
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.
|
|
|
|
<!--more-->
|
|
|
|
I soldered some wires to the connector of the transformer, allowing me to hook up my Oscilloscope to the transformer output.
|
|
|
|
## 10VAC Rail
|
|
|
|
|
|
|
|
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.
|
|
|
|
|
|
|
|
If the fan is running, the 10V rail degrades a bit more and slightly drops in voltage.
|
|
Again, given the fact that it is 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
|
|
|
|
|
|
|
|
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.
|
|
|
|
|
|
|
|
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
|
|
|
|
|
|
|
|
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 supply. The fan regulation could then be done through simple PWM.
|
|
|
|
|
|
[1]: {{<relref "2018-06-20-Reverse-Engineer-a-Saike-858D.md">}}
|
|
|