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"Inductive Candle" is an inductively charged (similar to smart phone or watch "cable free" chargers) candle that automatically "lights" when removed from the charging base and "extinguishes" when returned to the charging base.

The base assembly contains an inductive transmitter and coil and a 12mm diameter by 3mm thick neodymium magnet.

The candle assembly contains an inductive coil and receiver, a lithium polymer battery charger, a lithium polymer battery, a 6mm diameter by 2mm thick neodymium magnet, a normally open reed switch, and a flickering LED.

When the candle assembly is removed from the base assembly, the neodymium magnet in the candle assembly activates the reed switch which illuminates the LED using the LiPo battery as the power source. When the candle assembly is returned to the base assembly, the neodymium magnet in the base assembly alters the magnetic field of the neodymium magnet in the candle assembly deactivating the reed switch and extinguishing the LED while the inductive charging system charges the LiPo battery. Since the charging system utilizes air coil induction which is not as efficient as cable charging, the design extinguishes the candle when the candle assembly is returned to the base assembly for charging.

I purchased the inductive charging system from Adafruit.com (I really like that place) who indicates the system will operate from 9 to 12vdc. When operated at 12vdc however, the inductive charging system generates heat that may be excessive for most PLA filaments. Using an IR thermometer I measured the temperature on "Base, Cover.stl" at 56° C (approximately 133° F) when using a 12vdc power source. Thus if you decide to use a 12vdc power source I recommend printing "Base, Cover.stl", "Base.stl" and "Lamp, Base Interface.stl" using Ultimaker CPE+ or equivalent filament having a higher temperature rating than PLA.

And as usual, I probably forgot a file or two or who knows what else, so if you have any questions, please do not hesitate to ask as I do make plenty of mistakes.

Designed using Autodesk Fusion 360 and Meshmixer 3.5.474, sliced using Cura 4.1 and printed in Ultimaker PLA and CPE+ filament on an Ultimaker 2+ Extended and an Ultimaker 3 Extended.

One final note, I receive no compensation in any form whatsoever for the use of any of the components and/or materials used in this design.

Step 1: Purchase, Print and Prepare the Parts.

I purchased (or salvaged) the following parts:

  • One Inductive Charger Set (https://www.adafruit.com/product/1407).
  • One USB LiIon/LiPoly charger (https://www.adafruit.com/product/259).
  • One LiPo Battery (https://www.adafruit.com/product/258).
  • One reed switch (2 by 12mm, Gikfun 20pcs Reed Switch Normally Open N/O Magnetic Induction Switch Electromagnetic for Arduino (Pack of 20pcs) EK1621x2, available on line).
  • One neodymium magnet (12mm diameter by 3mm thick, local hobby shop).
  • One neodymium magnet (6mm diameter by 2mm thick, local hobby shop).
  • One salvaged 9 - 12vdc 500ma power supply (note using a 12vdc power supply will decrease charging time at the expense of increased heat, while alternatively using a 9vdc power supply will increase charging time but with reduced heat).
  • One salvaged tea lamp LED (https://www.amazon.com/gp/product/B00T28FWVS/ref=ppx_yo_dt_b_asin_image_o00_s00?ie=UTF8&psc=1).
  • One salvaged 100 ohm resistor.
  • One white drinking straw ("borrowed" from a local restaurant) cut to 180mm in length This piece is optional in order to disguise the wiring in the candle if the candle is printed with translucent / transparent material.

Parts I Printed:

  • I printed one each of all parts at .15mm layer height, 20% infill (well, ok, except for "Lamp, Candle.stl", which I printed in Ultimaker Translucent filament at 100% infill for the cover photo which required some 14 hours to print). Since the inductive charging system generates heat, I printed "Base, Cover.stl", "Base.stl" and "Lamp, Base Interface.stl" using Ultimaker CPE+ filament. The remaining parts were printed in Ultimaker PLA filament.
jeanniel112 days ago
OK, you had me at magnets, but with LIGHTS! Super great project, and thanks for sharing!
gzumwalt (author)  jeanniel110 days ago
Hi jeanniel1,

Thank you so very much, and I'm truly pleased you enjoyed this Instructable!

I enjoy showing people how to use materials in unique ways, and this Instructable shows how to use magnetic interference to convert a commonly available "normally open" reed switch to a not so commonly available "normally closed" reed switch thanks to magnetics.

Again, I'm sincerely glad you enjoyed this Instructable, and hope you, as I, learned from it!

Greg
It's instructible like your's that keep me reading and creating!
megapix13 days ago
Nice project!
gzumwalt (author)  megapix10 days ago
Hi megapix,

Thank you very much, I hope you enjoyed it!

It was a learning experience for me regarding magnets!

Greg
curiosity3620 days ago
Quaint country touch. Do the rare earth magnet in the center of the coils effect the resonance of the coils thereby effectingcharging circuits? Possibly reducing their already fairly low efficiency? Thanks for posting.
The magnetic field from the magnets won't affect the coils, but because the magnets are coated with metal, there will be some current generated in the metal plating, therefore using a little more energy from the charging coil.
gzumwalt (author)  curiosity3620 days ago
Hi curiosity36,

Thanks, I hope you enjoyed it!

I ran two simultaneous charging tests; one with the magnets and one without (in doing so the one without magnets required a quick disconnect to extinguish the LED for the charging test). After completely charging both candles, then running both candles off their bases for 12 hours, I returned each candle to their respective base and video recorded the charge status LEDs on the LiPo charging boards. The charge time deltas between the two averaged 8 minutes after 6 tests, where sometimes the magnet base charged first, and sometimes the non-magnet base charged first. Thus I noticed no negligible difference between the two regarding charging time.

However, during the charging process I also recorded the transmitter circuit currents and detected an average 1.2ma additional current draw in the transmitter where the magnets were present. Since this highly repeatable observation occurred only during charging, the additional current would not effect the run time when the candle was off its base so I went with the design.

Again, thank you and I hope you enjoyed it!

Greg
jmontoya722 days ago
This is such a super cool -and still quite simple- project. Just quite genius!
Thanks for sharing! Look forward for a weekend to give this a try!
gzumwalt (author)  jmontoya721 days ago
Hi jmontoya7,

Thank you so very much, I'm glad you enjoyed it, and you are very welcome!

Greg
This is great! I love it :)
gzumwalt (author)  Penolopy Bulnick22 days ago
Hi Penolopy!

Thank you very much, I'm glad you enjoyed it!

Greg