[NewCandle] Energy Harvesting

[Keith Nagel]

Hi Horace + Nick,

This is basically a field mill. The problem with using them
is that the variation in capacity that we'd see from the
small displacements of the vibrating string would produce
very little power. Typically field mills use a rotating blade
design for more delta C. I have experimented with magnetic field
mills which can produce much larger delta L's, to achieve
parametric resonance. Even with the bigger variation, it's
hard to get this to work, and the results are less than exciting.

I'm looking at Nick's test setups and numbers, and I'm
not seeing a lot of love there. Did you load the generators
so as to establish efficiencies of conversion? To sustain
a couple of volts on an air capacity of a few hundred pf
takes very little power. I liked the setup using the "big
squishy cap" but again I wonder about how efficient something
like that would be in practice ( springy would be more
promising that squishy ).

Here you can read more about field mills.
http://a-tech.net/ElectricFieldMill/index.html

K.

-----Original Message-----
From: newcandle-bounces at ipdiscover.com
[mailto:newcandle-bounces at ipdiscover.com]On Behalf Of Horace Heffner
Sent: Wednesday, October 22, 2008 5:07 PM
To: New energy for the new world.
Subject: Re: [NewCandle] Energy Harvesting




On Oct 22, 2008, at 4:26 PM, Keith Nagel wrote:


So what else can we use? Yea olde magnetic pickup. I'm imagining
something like a speaker cone arrangement.


How about a plain old variable gap capacitor?


If you use mechanical energy to pull apart two plates having a charge then
work is done and the voltage necessarily rises. You can now discharge the
plates through a circuit to obtain the electrical energy. All you need in
addition is a trickle charge to maintain the average charge on the plates
and full wave rectification.


D1 V1
P---|>|---R1--o-------C2--o---B1--------Load
| | | |
G Mech.==>C1 G G
|
G


Fig 1 - Diagram of mechanically driven capacitor gap power supply


In Fig. 1 a HV DC power supply P and D1 maintains a high voltage by trickle
charge through on the plates of a variable gap capacitor C1, the gap of
which is varied by mechanical power. The AC power from generated by the
mechanically driven gap oscillations of C1 are transmitted through the DC
current blocking capacitor C2 and a rectifying bridge B1 to the load.


One advantage to this design is the RMS voltage V1 is only limited by the
gap breakdown voltage, thus the advantage is avoiding in many cases problems
obtaining sufficient voltage to effectively drive a bridge rectifier B1. If
a sufficient voltage V1 is difficult to obtain, it is still possible to
drive a FET bridge B1 (and diode D1 if necessary) using plate position
sensing or potential sensing circuitry to drive the gates provided the
energy required is not excessive.


An alternative to power supply P plus D1 is to eliminate them and make at
least one plate of the capacitor C1 a charged electret.
Best regards,



Horace Heffner
http://www.mtaonline.net/~hheffner/