Re: 4000 watt Audio Amp to drive Tesla coil (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Tue, 11 Sep 2007 08:50:46 -0500
From: Daniel Hess <dhess1@xxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: 4000 watt Audio Amp to drive Tesla coil (fwd)

I've never heard of this being done before and there might be some good 
reasons why not. I'm not saying it couldn't be done but there are some 
significant obstacles to overcome.

For one thing, I'm assuming that this is a car amp, not a home or studio 
amp since home and pro audio equipment is usually rated for 8 ohm loads 
whereas car audio is rated for 4 ohms. If it is a car unit you should know 
that car audio is notorious for using 'funny math' to measure their output 
power. For example, how was the 4000 watts derived; RMS, peak power, music 
power? Unless you know this you don't really know how much power the amp 
really has. Among audiophiles, RMS power, at a specified impedance, at a 
specified frequency (or frequency range), at a specified distortion rate 
(THD & IMD), is the preferred method of comparison, apples to apples so to 
speak.

When an amp's output is specified in the above manner, change any one of 
these factors and you change them all. For example; What is the impedance 
of your primary? If it's less than 4 ohms the amp will become unstable and 
probably won't be long for this world. (And a device damaged in this 
manner would be considered abuse and neglect and technically, the damage 
would not be covered by warranty.) If the primary's impedance is greater 
than 4 ohms, the amp's power will fall off steeply.

The mosfet finals are most likely designed, selected, for audio frequency, 
typically 20 Hz to 20 kHz, So trying to drive a typical coil at say, 80 
kHz to 120 kHz, the outputs will probably not perform as well as their 
intended operating range. (Motorboating, unintended oscillations and/or 
unpredictable results).

I suppose it would be possible to design such an amp but with Tesla coil 
frequencies and primary impedance as the design goal. Such an amp would 
allow you to dial in any primary frequency giving you vastly more finite 
tuning control over simply tapping the primary at different points.

Daniel Hess




On 9/10/07, Tesla list <tesla@xxxxxxxxxx> wrote:
>
>
> ---------- Forwarded message ----------
> Date: Mon, 10 Sep 2007 10:57:28 -0700 (PDT)
> From: Timka <tomasdoc2002@xxxxxxxxx>
> To: tesla@xxxxxxxxxx
> Subject: 4000 watt Audio Amp to drive Tesla coil
>
> Hello all,
>
>   Did anyone ever used and audio amp to drive Tesla coil before?
>
>   I came across a few mosfet amps on EBay, new but relatively cheap. The
> one I was looking at is rated at 4000 watts bridged output into 4 Ohms 
load.
> Now, I figured if I would use copper tubing, the resistance wouldn't be 
a
> major factor after all.
>
>   Another good thing is that I can feed anything into it via signal
> generator or even audio to see how coil behaves.
>
>   Now, nasty things that I worry about:
>
>   1) It would really suck if I ended up blowing final mosfets due to TC
> secondary kick back and frying internal circuitry, which would be a 
total
> fiasco and probably would puzzle a lot of clerks at the return 
department.
> Ad states that amp employs overload protection but whoever designed them
> back in China never envisioned a million volts kickback from an ordinary
> speaker, so I'm not holding my breath there. Any suggestions here?
>
>   2) What kind of power supply is needed? In a car amp works off
> alternator and use around...... around a lot of amps! In fact, not every
> alternator can pull a 4000 watts amp as the most of them is in the area 
of
> 120 amps on average. Here is quick math for 4K watts amplifier:
>
>   1 channel with 4000 watts RMS per channel doubled to the account for
> amplifier inefficiency (4000 watts X 2 = 8000 watts), then divided by 
the
> average output Voltage of an alternator, 13.8 volts (8000 divided by 
13.8= 580 amps). Since the average signal requires about 1/3rd of the 
average
> power in a tone used to drive TC, dividing by 3 (580 amps divided by 3 = 
193
> amps). This is the result of the amplifier's approximate average current
> draw.
>
>   Soooooooo, how and where in the world do I get a source of 200 
constant
> amps at 13.8 volts? This is not your average power supply you can plug
> into a wall. I was thinking of getting a car booster/starter a.k.a 
battery
> charger, it's the size of small fridge, with 2 fat clammed cables, 
weights
> about 60lb and probably employs a very large transformer you can use to 
kill
> your mother in-law that can be plugged into a wall. Another ad claims 
that
> this car starter can give an instant 300 amps surge or so but how about
> using it for longer than instant or lets say 10 min? Can it pull this 
amp?
> Of course I can add a few 2 farad audio caps in between, but would it be
> enough?
>
>   The specks of amp are as follows:
>
>   Frequency Response: 15Hz- 35kHz (not too great but hey, it's audio)
>
>   It's on ebay listed under the folowing #150156590184
>
>   All suggestions are welcome,
>
>   Thanks in advance,
>
>   Tim
>
>
>
>
>
>
>
> ---------------------------------
> Moody friends. Drama queens. Your life? Nope! - their life, your story.
> Play Sims Stories at Yahoo! Games.
>
>
>