Open Loop Pulse Triggering
Results
Coil B
Fig
1 illustrates the dry firing for coil B. The voltage markers give a dV of 0.51V
resulting in a wire current of 51A. Coil
B data shows the wire diameter as 1.0mm so the wire and coil current densities
are 64.9Amm^{1} and 51Amm^{1} respectively. Note that this is
larger than the densities calculated for coil A. Fig 2 shows the current waveform
resulting from firing a projectile.
Fig
1. Coil current during dry firing
Fig
2. Projectile interaction with coil
The
specific shape of the modified current waveform depends on when the current pulse
is terminated. The shape in fig 2 is typical of current pulses close to the optimal
length.
Fig
3  5 illustrate the projectile speed and energy characteristics. Fig 6 plots
the three projectile speed curves for comparison.
Fig
3. Solid projectile No. 1 speed and energy data
Fig
4. 4mm cored projectile speed and energy data
Fig
5. 6mm cored projectile speed and energy data
Fig
6. Projectile Speed Comparison
Coil
Efficiency
Using
the same data processing techniques as described in the results from coil A we
can determine the efficiency of coil B. The data is tabulated below.
Projectile 
Peak Power (W)

Conduction Loss (mJ)

Commutating Loss (mJ)

Total Loss (mJ)

Kinetic Energy (mJ)

Efficiency (%)

Solid No.1 
1.350E+3 +/ 2.5E+1

1.0040E+4

8.16E+2

1.0856E+4

5.06E+2 +/ 1.5E+1

4.45E+0 +/ 1.4E1

4mm Cored No.1 
1.350E+3 +/ 2.5E+1

9.138E+3

8.03E+2

9.941E+3

4.72E+2 +/ 1.5E+1

4.53E+0 +/ 1.5E1

6mm Cored No.1 
1.350E+3 +/ 2.5E+1

8.847E+3

8.02E+2

9.249E+3

4.04E+2 +/ 1.5E+1

4.19E+0 +/ 1.6E1

Table
1. Energy and efficiency data
It's
still not clear if there is really any distinguishable difference in coil efficiency
with different projectiles. One thing you may have noticed is that I haven't included
and error value with the coil losses. The reason for this is that I don't know
what the error is likely to be from the integrations. I suppose I could guesstimate
a value of, say, 5% but it's not really important at the moment. I would certainly
argue that the efficiency of coil B is greater than that of coil A. Finally we
can see that the peak power is close to double that of coil A, it's quite a jump
however the energy dissipated only raises the coils temperature by around 0.2^{0}C.
Looks like there's plenty of room for more power!
