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Advertising Index Ask SILICON CHIP . . . continued from page 111 best to use a current-limited supply set for around 6.6A and 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 Fig.1 of the February 2011 issue. The flashing of the LED during bulk charging indicates the way the MPPT system works. This system periodically checks the panel to set the circuit up for maximum power transfer. The LED indicates when this is happening. Queries on the Jacob’s Ladder My son and I are looking at building the Jacob’s Ladder Mk3 (SILICON CHIP, February 2013) project together and among other things, learning how it works. I have a few questions as this is our first foray into high-voltage electronics. What is the minimum safe distance from the electrodes that one can safely enjoy the arc without a decent acrylic tube barrier? While the project recommends a car battery, after a scan over the circuit diagram, could the project be run from a 12V 5A (or better) DC power supply? And how long can the ladder be in operation before it overheats, if it overheats? (A. F., via email). •  The spark voltage will jump across a 30mm gap. If the gap is made too large, the spark will simply jump across the terminals of the coil itself. However, you should avoid putting your hands or any other body part within about 10cm of the spark wires, merely to avoid the possibility that you might inadvertently go too close and 112  Silicon Chip 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 come into contact. If you do that, you won’t do it again! A power supply capable of more than 5A would be needed; preferably 8-10A. The unit should not overheat, even if it is used continuously. After all, this unit is merely a variant of our ignition system which is intended for continuous use in the engine bay of a vehicle. Super Jacob’s Ladder with two transformers I would like to connect the outputs of a 15kV neon transformer to the output of a 10kV oil fire transformer to produce a 25kV Jacob’s Ladder. Would this be OK or would I need high-voltage diodes to stop feed from one transformer getting into the other transformer? If so, what diodes would I need? At the moment I have two Jacob’s Ladders but would like to boost it up if possible. (A. F., via email). •  You can connect the two secondary windings of your transformers together to get a theoretical total of 25kV. However, you must do it so that the voltages add instead of subtract (there the result would be only 5kV). In effect, you have it connect the start of one secondary winding to the finish of the other. Since there is probably no easy way of identifying the starts and finishes, you would have to do it by trial and error. If you get it right, the total voltage will jump a Altronics.................................. 80-83 Core Electronics............................. 8 Emona Instruments...................... 38 Freetronics................................... 10 Gless Audio................................ 111 Hammond Manufacturing............. 77 Hare & Forbes............................. 2-3 Icom Australia................................ 7 Jaycar .............................. IFC,51-62 Keith Rippon .............................. 111 KitStop.......................................... 79 LD Electronics............................ 111 LED Sales.................................. 111 Low Energy Developments........ 111 Master Instruments........................ 5 Microchip Technology............... OBC Mikroelektronika......................... IBC Ocean Controls............................ 49 QualiEco Circuits Pty Ltd............. 50 Quest Electronics....................... 111 Radio, TV & Hobbies DVD............ 79 RF Modules................................ 112 Sesame Electronics................... 111 Silicon Chip Binders................... 102 Silicon Chip Bookshop................. 95 Silicon Chip Online Shop.... 104-105 Silicon Chip Subscriptions........... 25 Television Replacements........... 111 Tekmark Australia........................... 9 Tenrod Pty Ltd.............................. 17 Virtins Technology........................ 11 Wiltronics...................................... 41 Worldwide Elect. Components... 112 much bigger spark gap than it otherwise would. However, you should remember that the maximum output voltage you actually obtain will depend on the dimensions of the spark gap in the ladder and the insulation of all the wiring leading from the transformers to the Ladder itself. Even so, the resulting Jacob’s Ladder display will be limited by the less powerful transformer. In practice, the display might not be any better than that produced by the high-energy ignition coil we employed in the Jacob’s Ladder featured in the February 2013 issue. And since it is battery-powered, we think it would be safer than your SC transformer-powered version. siliconchip.com.au