|
Posted by Mark Rand on January 10, 2008, 2:29 pm
Please log in for more thread options
>
>These audio amps are designed to drive 8 ohms, and if you look at a
>speaker, the coil has quite a few windings, I think a coil of copper
>pipe, of maybe 10 - 15 turns?, will present a DC resistance of
>approximately nothing, and at 30 KHz the impedance will still be
>pretty low, I think it will just look like a short circuit to the amp.
To get 42uH in air would require between 20 to 35 turns for a reasonable sized
coil. That'd give you 8 Ohms at 30kHz with no iron anywhere near it. Put 1uF
of capacitance in parallel with it (series parallel stack of motor run
capacitors probably) and drop the frequency to about 24kHz and the impedance
goes towards infinity until you introduce a lump of metal into the coil.
Use a smaller number of turns and a larger capacitor and you can, within
reason, get any size coil you want.
At that point, you probably want a hall effect current sensor, potential
divider and PIC processor to measure the phase angle of the current and trim
the frequency to keep the whole lot close to resonance. None of that is
particularly challenging electronics or programming. I just don't know if it's
a meaningful thing to attempt...
So many ideas. So little time.
Mark Rand
RTFM
| 
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap
> bridge
> mode, can pump 2kW into 8Ohms at 30kHz. Said amps are about £275 with VAT.
>
> Is this an excuse to wrap a bit of microbore heating pipe into a coil,
> connect
> it to the amp and the suds pump, connect the amp to a signal generator and
> successfully do heat treating of small parts?