I'll be using the
three common types of energy sources; batteries, capacitors, and inductors.
Lead Acid Battery
This consists of
five 6V@10Ah sealed lead acid batteries giving a total supply voltage of 30V and
a pulsed current capacity of about 200A. Maximum power outputs from this arrangement
will be around 5kW (taking into account internal resistance), not exactly very
powerful but this is for preliminary testing. In the future I'll be increasing
the voltage substantially. A battery source is quite versatile since it can power
a coilgun system with any number of coils. The image below shows one of the batteries,
the white strip on the top is for tallying up the number of charge cycles the
battery has gone through.
1. 6V@10Ah sealed lead acid battery.
The internal resistance
of the five connected batteries can be found by looking at a current drain pulse
and the corresponding terminal voltage. Fig 2 shows the internal resistance over
a range of current values. The variation of current values is obtained from the
exponential growth of the pulse.
2. Variation of internal resistance with current drain.
This is a somewhat
crude method of characterising the battery behaviour. A better way might be to
show the time dependent resistance for specific current drains. In any case it's
sufficient to show that the internal resistance lies somewhere between 60 and
A larger value will be typical of larger current drains but the resistance will
also depend on the duration of the current pulse. In its simplest incarnation
a batteries circuit model can consist of an ideal voltage source in series with
a fixed resistance, however, this is only valid over a finite period of time for
any given current drain. The state of charge of the battery and its recent charge/discharge
history will also affect the model parameters.
will provide energy for all high power testing. I'll probably start off with a
This will consist
of several small mains transformers connected in parallel. The primary winding
will be the 'charging' side and needs to be run at a lower voltage than its a.c.
rating, this is because it's operating under a d.c. regime during charging.