Electronics > Projects, Designs, and Technical Stuff
My arduino powered firework sequencer. 2018 version!
<< < (12/13) > >>
Dubbie:
That’s an interesting idea re. The AC gate signal.
Yansi:

--- Quote from: usagi on March 10, 2019, 01:18:37 am ---so my design currently uses port expanders driving darlington arrays.

i'm thinking i can get better integration with high power shift registers like tpic6b595...

--- End quote ---

Very substandard solution.  You will get a pretty firework on a shorted channel too. But not from the business end, but from your transistor array.

Any output should be short circuit protected, and preferably shorted at the driver side when inactive.

Any fault on any output shall never cause any other output to misfire. Neither may excessive current draw from a channel cause the supply voltage to droop to cause further damage or circuit mis-behavior.

Think about it. Solutions may get complicated pretty fast. Hence why the professional firing devices are not simple arduino toys!
texaspyro:

--- Quote from: Yansi on March 10, 2019, 08:06:20 pm ---
Any fault on any output shall never cause any other output to misfire. Neither may excessive current draw from a channel cause the supply voltage to droop to cause further damage or circuit mis-behavior.


--- End quote ---

Number 1,2,3... rules in my launch controller design is: no single component failure can cause a launch condition.  Hence the AC coupled, dual FET switches.  All the components in the firing circuits (particularly the continuity / monitoring parts) are through hole... SMT parts are much more likely to fail short-circuit and shorts tend to cause excessive current to flow.   Critical resistors are use two in series so a shorted one will still limit currents to a safe level,  Although the output FETS can handle 1000 amps, the output current is limited by a 2.4 ohm, 20 watt resistor... that limits the max current to around 20 amps per channel.   Timers limit the output pulse to a max of 3 seconds.

Yansi:

--- Quote from: texaspyro on March 11, 2019, 02:12:43 am ---
--- Quote from: Yansi on March 10, 2019, 08:06:20 pm ---
Any fault on any output shall never cause any other output to misfire. Neither may excessive current draw from a channel cause the supply voltage to droop to cause further damage or circuit mis-behavior.


--- End quote ---

Number 1,2,3... rules in my launch controller design is: no single component failure can cause a launch condition.  Hence the AC coupled, dual FET switches.  All the components in the firing circuits (particularly the continuity / monitoring parts) are through hole... SMT parts are much more likely to fail short-circuit and shorts tend to cause excessive current to flow.   Critical resistors are use two in series so a shorted one will still limit currents to a safe level,  Although the output FETS can handle 1000 amps, the output current is limited by a 2.4 ohm, 20 watt resistor... that limits the max current to around 20 amps per channel.   Timers limit the output pulse to a max of 3 seconds.

--- End quote ---

(text in bold) Not true, at all. Anything to back your statement?

Also your solution seems irrational in both design and economical point of view. Strongly, very, very strongly doubt your 1kA rating anyway.

Could be probably done much differently but still safely.
texaspyro:

--- Quote from: Yansi on March 11, 2019, 01:48:32 pm ---
--- Quote from: texaspyro on March 11, 2019, 02:12:43 am ---
--- Quote from: Yansi on March 10, 2019, 08:06:20 pm ---
Any fault on any output shall never cause any other output to misfire. Neither may excessive current draw from a channel cause the supply voltage to droop to cause further damage or circuit mis-behavior.


--- End quote ---

Number 1,2,3... rules in my launch controller design is: no single component failure can cause a launch condition.  Hence the AC coupled, dual FET switches.  All the components in the firing circuits (particularly the continuity / monitoring parts) are through hole... SMT parts are much more likely to fail short-circuit and shorts tend to cause excessive current to flow.   Critical resistors are use two in series so a shorted one will still limit currents to a safe level,  Although the output FETS can handle 1000 amps, the output current is limited by a 2.4 ohm, 20 watt resistor... that limits the max current to around 20 amps per channel.   Timers limit the output pulse to a max of 3 seconds.

--- End quote ---

(text in bold) Not true, at all. Anything to back your statement?

Also your solution seems irrational in both design and economical point of view. Strongly, very, very strongly doubt your 1kA rating anyway.

Could be probably done much differently but still safely.

--- End quote ---

Yes, I have info on failure mechanisms of SMD resistors but am not a liberty to comment further.   One thing I can mention is the small spacing between pads that can short during faults that cause solder to melt.

The design was based upon over 40 years of experience with pyrotechnic systems and observed, real-world faults that caused unintentional firings.  It may appear to be over engineered, but every feature was designed in with special attention to how to prevent those things from happening.  Cost was at the very bottom (well, actually totally missing) from the list of requirements.   Have you ever designed safety-of-life critical systems?

As far as being able to handle 1000 amps... it can for a couple of seconds.  Tested with 4S16P A123 LiFePO4 battery.  Actually around 2/3 of the power at that level gets absorbed into the wiring and the 2.4 ohm current limiting resistors on the standard firing boards limits the current to around 20A per channel.  If you are doing a large cluster you can spread the igniter wiring across multiple channels or short/reduce the current limiting resistor.   Applying two much current (or ramping the current too quickly) across an igniter can pop the bridgewire without lighting the pyrogen.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod