I plan to build a battery+relay electrical launch system to boost the effective delivered current and voltage to fire big clusters. This would be a relay box triggered by the club launch system.
Looking for input on design.
When I was firing clusters of 8 or less engines, was achieving about 99% success rate igniting engines with club launch systems.
Even using creative methods with ematches to reduce total current, the 8 flights I have attempted with 11 to 30 motors have had much lower success rate. Details at www.bpasa.com.
Voltage sag due to 16 awg launch leads, connectors, and anything less than a very strong battery becomes very significant. While most ematches still seem to fire, some are delayed until the rocket has pulled away from the pad.
The relay+battery system needs to be able to deliver very high current bursts without major voltage sag. Some of the flights I have done have attempted to draw 60 to 70 amps from a 12V system.
Components I am considering:
> 200A automotive relay
> 8 awg leads
> Lipo battery pack: 14.8V (4 cell) 5Ah (40C continuous, 50C for 10 second bursts)
> 200A automotive relay: One reference (at rocketflite.com) advises using a relay with a clamping diode to dampen the voltage created by the relay coil when it is deactivated. If I only trigger my relay box with the club's relay launch system, I would not expect this to be an issue? I also assume that if I did use a relay with a clamping diode, that I would have to determine the polarity of the club's launch leads each time I use them? and would prefer not to do this.
> Lipo battery: Rated for 200A continuous (5Ah x 40C) it should be able to give me all the current I'll ever need in a 1.3 lb battery. With 14.8V at no load, using extremely heavy gauge leads (jumper cable wire) I would expect to put 12 or 13V into the rocket's ignition setup even for very big clusters.
> Suggestions about the battery? Relay? Anything else?