content/ZPB30A1.rst

Tue, 28 Aug 2018 15:05:01 +0200

author
David Douard <david.douard@logilab.fr>
date
Tue, 28 Aug 2018 15:05:01 +0200
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improve hgignore

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1 =========================
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2 ZPB30A1 Electronic Load
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3 =========================
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4
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5 :Author: David Douard
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6 :Category: Electronics
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7 :Tags: ZPB30A1, electronic load, test equipment
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8
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9 A few weeks ago, I purchased a cheap electronic load from AliExpress
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10 (`this one`_ to be precise). It's a ZHIYU model ZPB30A1. It's
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11 specifications are:
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12
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13 - constant current mode
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14 - max voltage: 30V
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15 - discharge current: 0.2A to 9.99A (+/- 0.7% + 1 digit)
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16 - max dissipated power: 60W
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17 - voltage measurement error: 1% + 2 digits
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18
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19 It supports 2 operation modes:
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20
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21 - electronic load: in this mode, you can set the current and the
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22 minimum voltage above which it beeps; in this mode, it display the
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23 measured voltage and set current.
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24 - battery capacity test mode: in this mode, you set the discharge
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25 current and the lower voltage limit at which the discharge test
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26 stops. It displays the total discharged capacitu (in Ah) and energy
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27 (in Wh).
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28
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29 .. image:: {filename}images/ZPB30A1/zpb30a1.jpg
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30 :alt: Overall view of the ZPB30A1 electronic load
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31
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32 The device looks pretty nice and reasonably well built. It can do 4
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33 wire measurements.
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34
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35 The device itself is built around a single ST W60N10 N channel MOS
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36 transistor (100V, 60A, 200W) and a STM8S005K6 microcontroller.
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37
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38 .. image:: {filename}images/ZPB30A1/zpb30a1_board.jpg
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39 :alt: Main PCB of the ZPB30A1 electronic load
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40
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41 The shunt resistor is a 10mΩ wire. A very small value that explains
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42 the rather big minimal current of 200mA (which means a voltage drop as
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43 low as 2mV).
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44
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45 .. image:: {filename}images/ZPB30A1/zpb30a1_mosfet.jpg
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46 :alt: Main transistor of the ZPB30A1 electronic load
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47
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48 One nice thing with this device is the fact that every component value
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49 is written on the PCB: no need to use the magnifier to read the SMD
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50 parts values.
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51
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52 The bottom side of the PCB is pretty empty besides the ground plane.
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53
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54 .. image:: {filename}images/ZPB30A1/zpb30a1_bottom.jpg
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55 :alt: Bottom side of the PCB of the ZPB30A1 electronic load
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56
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57
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58 The most annoying thing is the minimum current of 200mA, which pretty
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59 hight. It's obviously not designed for small battery or PSU
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60 testing.
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61
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62 Another thing is that its limited to CC mode only (does not provide
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63 constant resistance mode nor constant voltage). It's a bit unfortunate
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64 since it's probably only a matter of software.
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65
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66 Also, the usability is quite rough. For example, to choose the
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67 operating mode (between CC charge and battery capacity test mode), you
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68 have to power off the device and power it on holding the start/stop
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69 button down.
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70
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71 The last missing feature, for me, is that there is not "output" port
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72 allowing to capture the values when doing a battery discharge
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73 test. The good news is that there is unpopulated port. Looks like some
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74 ISP/serial port directly connected to the microcontroller. Pins are
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75 labelled as G, R, T, L, F and Vc. G stands for ground, and Vc is
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76 obvious. R and T might be Rx and Tx of a serial port. F and L are not
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77 obvious.
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78
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79 So I've probed a bit to see if there are any signals.
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80
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81 The overall (messy) setup was:
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82
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83 .. image:: {filename}images/ZPB30A1/overall_setup.jpg
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84 :alt: Overall testing setup for the ZPB30A1.
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85
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86 During this test, the electronic load was sunking almost 1A at 30V,
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87 thus dissipating around 30W. The MOSFET transistor was getting a bit
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88 hot. I measured 65°C with my cheap IR thermometer.
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89
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90 The F pin shows a square signal at 50kHz, and there is some activity on
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91 the T pin. I've used my new Rigol DS1054Z scope to try to find out if
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92 the signal is meaningful. And after playing a bit with the Serial
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93 decoder, I finally found that:
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94
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95 .. image:: {filename}images/ZPB30A1/DS1Z_serial.png
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96 :alt: Serial signal on the T pin.
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97
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98 When the ZPB30A1 was actually set up like this:
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99
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100 .. image:: {filename}images/ZPB30A1/zpb30a1_setup.jpg
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101 :alt: Testing setup for the ZPB30A1.
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102
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103 So the measured voltage is constantly written on the serial port at
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104 115200 baud, 8N1. The third value is 1 when it is normally operating,
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105 and 0 when the voltage is below the limit.
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106
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107 However, in battery discharge mode, there is nothing on the serial
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108 line.
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109
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110 Now, I have to solder a socket in there. Then the next step will be to
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111 see if we can send commands to the ZPB30A1. I may need to learn a bit
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112 about the ST microcontroller...
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113
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114
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115
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116 .. _`this one`: http://fr.aliexpress.com/item/New-Constant-current-electronic-load-9-99A-60W-1-30V-battery-capacity-teste-free-ship/32571919265.html
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117
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118

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