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Advertising Index Altronics.................................. 70-73 Element14.................................... 25 Emona Instruments........................ 3 Front Panel Express....................... 6 Gless Audio................................ 103 Harbuch Electronics..................... 77 Hare & Forbes.......................... OBC High Profile Communications..... 103 Icom Australia................................ 7 Jaycar .............................. IFC,49-56 Ask SILICON CHIP . . . continued from page 103 has a small drain and consequently the battery slowly discharges when the van is not in use. So it seemed reasonable to increase the output of this power supply and connect it in parallel with the solar panel input (120W) to the MPPT, using a MOSFET as a protection diode in the power supply’s output. I guessed at setting the supply output to 17V since this is just below what the panel would produce when charging via the MPPT. It was not my intention to have both power supply and panel charging simultaneously although it will depend on the software as to whether this will be OK. In fact, the input to the MPPT from the panels is 15.8V during bulk charging and this seems to charge the battery more quickly than using the power supply. The results were interesting. Using the power supply, the MPPT went into bulk charging mode as expected but the bulk charging LED flashed off briefly about every four seconds. In the description, it says that if the battery voltage is lower than 10.5V, the MPPT will charge in bursts with the LED flashing every four seconds before bulk charging begins. By this, I presume that the word “flashing” means it is on briefly every four seconds but in this case, it is off briefly every four seconds. In fact, the battery voltage was around 12V so perhaps this is a coincidence. So I have two questions. Is my arrangement to have the power supply charge the battery via the MPPT reasonable? What could be the reason for the brief flash off every four seconds until bulk charging ends? 104  Silicon Chip Keith Rippon .............................. 103 DOWNLOAD OUR CATALOG at www.iinet.net.au/~worcom WORLDWIDE ELECTRONIC COMPONENTS PO Box 631, Hillarys, WA 6923 Ph: (08) 9307 7305  Fax: (08) 9307 7309 Email: worcom<at>iinet.net.au KitStop.......................................... 41 LD Electronics............................ 103 LED Sales.................................. 103 Low Energy Developments........ 103 Microchip Technology................... 17 Mikroelektronika......................... IBC By the way, I particularly liked the series on TV dongles. What a superb and interesting set of articles. (D. W., via email). •  The MPPT charging assumes that a solar panel is connected rather than a power supply. If using a power supply instead of a solar panel, it would be best to use a current-limited supply set for around 6.6A at 18V. That is because the MPPT charging works on the fact that the current will drop as the solar panel is loaded. The solar panel output follows the VI curve as shown in the article – see Fig.1 in the February 2011 issue. The flashing of the LED during bulk charging is indicating the way the MPPT system works by periodically checking the panel to set up for maximum power from the panel. The LED indicates when this is happening. 12/24V switching for a solar panel regulator I write concerning the “12V/24V Regulator for 70W Solar Panels” in the September 2013 issue. I have a query relating to the use of links L1 & L2 for the 24V and 12V versions, respectively. Could these links be replaced by a single DPDT switch (eg, Jaycar’s ST-0575 or ST-0576 etc) to enable me to switch between the 12V and 24V modes, depending on the proposed usage at the time? If so, what switch type etc, would Ocean Controls.............................. 9 QualiEco Circuits Pty Ltd............. 59 Quest Electronics....................... 103 Radio, TV & Hobbies DVD............ 41 RF Modules................................ 104 Sesame Electronics................... 103 Silicon Chip Binders..................... 10 Silicon Chip Bookshop................. 97 Silicon Chip Online Shop........ 26-27 Silicon Chip Subscriptions........... 65 Television Replacements........... 103 Tenrod Pty Ltd.............................. 13 Trio Test & Measurement.............. 45 Wiltronics...................................... 81 Worldwide Elect. Components... 104 xLogic............................................. 6 you recommend? (P. M., Karabar, NSW). •  That’s a good suggestion. Since the switch effectively has to carry the full output of the charger, it should have a heavy current rating. Jaycar’s ST-0576, a 10A DPDT switch with a centre-off position, would be the better choice. Mind you, the switch should not be operated while a battery is connected, otherwise the Mosfets might be damaged. In fact, disconnecting the battery between uses and not using the centre “Off” position on the switch would SC be prudent. siliconchip.com.au