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Registered Member #350
Joined: Mon Mar 27 2006, 05:14PM
Location:
Posts: 106
mikeselectricstuff wrote ...
I wonder if another approach might be a construction of a very large number of very very small battery structures - this sort of thing was used for driving image intensifiers in WW2. With clever application of modern materials this could actually give the best power/weight ratio as there would be no conversion losses, but may need some serious development on the materials and structure of the battery - DIY Li-Po batteries are possibly a bit ambiitous..! Or perhaps a hybrid of this and a CW multiplier - e.g. a few 1kv battery stacks and some HV MOSFETS driving a CW or marx type multiplier.
The oxford electric bell is powered by such a high voltage battery.
It has been continually ringing since 1840 and the battery was never replaced. It's an electrostatic bell. The battery produces several thousand volts and is working now for nearly 170 years. The battery is probably a stack of paper that was covered with zinc on one side and manganese dioxide on the other. But I don't think such a battery could have a sufficient power density no matter what kind of electrolyte you soak the paper in. You would need to build a high voltage lithium battery but that's too difficult to do it yourself.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Perhaps it would be helpful to calculate the energy needed to lift a given vehicle of given mass through 1m using ion reaction, and then calculate the power density that a power source must have to lift its own weight and that of such a craft.
Once you have a fair guesstimate of required energy source power density, you will be able to test it against possible engineering solutions.
Where would I start, were it my problem? A very energetic micro RTG driving directly a high voltage piezoelectric crystal might be worth a look. 'Big' science!
Registered Member #350
Joined: Mon Mar 27 2006, 05:14PM
Location:
Posts: 106
What's a micro RTG?
If you use ultracapacitors you can even build a wingless lifter. There are 70F 2.5V caps that weight 15g. If you connect 20,000 of them you have a 50kV power source that weights 300kg. However that power source could easily deliver several amps. That means you can get more then 1 Watt per gram out of those caps. The lifter would then weight maybe 400kg, cost $200,000 and fly for 10 to 20 seconds without an external power supply. Not the most practical device but it might work.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
DrZoidberg wrote ...
What's a micro RTG?
A Radioisotope Thermoelectric Generator. - such as are used in some space probes and remote, untended maritime navigational buoys on the Russian coast.
Early heart pace-makers were driven by Pu-238 micro RTGs, and I believe some of these are still functioning to this day in those patients yet living.
Whilst considered too active for RTGs nowadays, isotopes like Po-210 have such a phenomenal energy density - about 140W/gm - that a small chunk will liquefy and then vapourize through its own emission of heat.
I am not suggesting that this is necessarily the way ahead for the 'ionocraft,' but that it is difficult (for me, at any rate! ) to think of any other power source with sufficient energy density to make the scheme even remotely feasible.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
I did look into connecting several PZTs in series with ex-laser printer HV diodes, kinda like the "diode split transformer" system.
The possibility exists to drive the primaries from a single large toroidal transformer with multiple windings (wouldn't need to be very big either) to provide galvanic isolation for the ascending stages. Insulation of wire needs to be the thickest for the highest stage...
Also might be possible to get it off the ground initially via a tether, then detach once its flying, as there are issues with electrostatic attraction to the ground plate.
EDIT:- If you want to obtain small LiPoly batteries cheaply, check out HMV's MPman micro MP3 player. Contains a nice neat little 150mAh Lipo cell, that isn't much bigger than a stick of gum rolled up.
Four of those would be 14.4V@150mAh, enough for a small model helicopter. In fact you could possibly use motor + propeller to suck air through your ionocraft stack from underneath (so no motor drive issues) to multiply the thrust-weight ratio somewhat.
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Ionocraft
