Decades ago smallest on board electronics used A23 (12v 55mAh) battery with
storage capacitor to fire upper stage igniters.
They only worked with low current (<50ma safe) e-match type, or photo flash
bulb/thermite. Internal resistance on stack of button cells inside A23 was too
high to fire ~1.5-2 ohm low current initiator directly, but with capacitor
storage they worked well with fresh battery.
Sadly low current e-matches types became hard to obtain by unlicensed rocket
hobbyist in US after 9/11, due new DHS sales restrictions. The small A23
battery became less popular in on-board electronic designs about same time.
If I were going ultra small on board electronics today, might use CR11108 (1/3
N) lithium cells with 3v and 160mAh? Three fit inside same "N" sized alkaline
cell battery holder for 9v equivalent, but less space. Key to success with any
small batteries is capacitor storage to boost short circuit current the bridge
wire creates. A fresh single 1/3N battery would probably fire low current
e-match without capacitor if extra volume was crisis?
PS - if using any relays inside rocket, make sure they are vibration safe. The
cheap PC board 1A relays are not vibration safe and should not be used for
firing on-board igniters. Use solid state 1A switch, as it is cheaper/smaller
option compared to never close due vibration relay. DAMHIK
Cheers!
On January 5, 2021 at 8:16 PM Peter Fairbrother <peter@xxxxxxxxxx> wrote:
On 05/01/2021 21:00, Dr Edward Jones wrote:
[...]
What's common practice with small battery ignition, even with a relay?
4 x AA, fresh Energiser or Duracell preferred.
Maybe 6 x AA if you are igniting up to four ematches at once over a
distance with diodes in circuit. Chap I know recommends 3+n AA, where n
is the number of ematches.
2x18650 is overkill if you want to go rechargeable.
This is mostly for firework displays where I'll fire maybe 30-100
ematches in 20 minutes.
Smaller cells will work too, in fact a single AA will fire an ematch. I
just tried. :)
Peter Fairbrother
My main box has 4xAA to run the arduino and 6xAA for the matches. 36
relays, the unpowered breakout boxes have 3A diodes for the matrix.
Maximum firing wires would be 50m long, though 20m is more usual max. I
seldom fire more than 2 ematches at once but it is built for firing up
to 4 (and I could easily add more AAs if needed).