MV CoilMaster Mark1.5 Upgrade

The charge time has been vastly reduced, you can actually see the environment light dim with each charge cycle. Also the red glow from the halogen tubes looks amazing in the dark.

At the moment the only limiting factor for fire rate is the charge time, this is the time the capacitor bank takes to get fully charged. This time can be influenced by the charging resistor, a lower value charge resistor will reduce the charge time but increase the charge current.

The first version of the CoilMaster has a 150W bulb as charge resistor, at the time I was pretty fond of the (relatively) short charge time. But I recently realized that it could be improved by a LOT. This upgrade takes charge time to the next level. In stead of one 150W bulb now  2x1000W halogen tubes are used, the entire charge circuit had to be upgraded to handle the peak currents.

The 1000W halogen tubes both have a 'cold' resistance of 3.6 Ohm, the 'hot' resistance should be R= u^2 / P = 230V^2 / 1000W = 52.9 Ohm. The replacement values of the cold resistor is 1.8 Ohm and the hot is 26.45 Ohm. This means the charge resistor is highly variable, and thus is the charge time. A minimum and maximum charge time can be calculated.

Cold: T=R*C = 1.8*8800u = 0.01584 sec, 5T = 0.0792 sec
Hot:   T=R*C = 26,45*8800u = 0.2328 sec, 5T = 1.164 sec

The peak charge current would be I=U/R = (270*root2)/1.8 = 212.1 Amp in cold start up (neglecting the internal resistance of the relay and capacitor bank). This does explain why all the lighting around dims at the first charge cycle. Normal relay's cant handle this kind of surges, that's why I used a solid state relay of 25A. These relays can handle surges up to 10X the nominal current.

To verify these numbers I taped the gun when charging from cold to hot. The peak voltage = root2 * 270V = 382V. I consider the capacitor bank charged at ~ 90% of this value = 340V (not the 5T value).

Charge time cold: ~ 0.9 sec
Charge time hot: ~ 1.12 sec

These numbers seem pretty plausible with the calculations, the resistor doesn't stay 'cold' but warms up at the first charge cycle. Also the internal resistance from the capacitors wasn't taken into account. The cold charge time in a combat situation would apply for the second shot (if you run around with a charged gun), the hot charge time applies for the next shots. (of course running would be a problem if you need a mains connection).

Video:

All the other specifications (kinetic energy, muzzle speed and charge time from the internal battery remain unchanged (Mark1). Only the charge system was altered, the modified schematic: Download the schematic (pdf)

The bulb is no longer connected, but is left on for decoration. Future versions of the gun won't have the bulb at all. The speedometer was also modified, now it is able to handle larger projectiles. Max diameter projectiles are 16mm.

After this upgrade I feel pretty confident the charge time can be farther reduced to at least 0.5 sec. This probably isn't achievable with halogen tubes (at a 16Amp connection). Using an oil cooled resistor wire of ~ 2 or 3 Ohm would probably do the job. A few more detailed pictures of the upgrade: