hey great thread.
Old. but good - not sure if you guys read Rob's ignitor testing ...
https://web.archive.org/web/20121119015627/http://www.gwiz-partners.com/igniters.pdf
You'll find the DF N28F is very much equivalent to an MJG J-tek and there
is a good
reason for that - your standard Automotive airbag used to have 2 of these
babies in it.
Kind of crazy when you think that in an accident you're Airbag deployment
is relying
on 2 Ohms of load and a one dollar e-match. :-)
On Tue, Jan 24, 2017 at 3:23 PM, Chris Spurgeon <chris@xxxxxxxxxxxxxxxxx>
wrote:
I wonder if it could also be the case that at the instant when one of the
igniters burns through, all of them are already so hot that they’ve reached
a point of no return and are going to ignite even without further electric
current?
On Jan 24, 2017, at 1:02 PM, R Dierking <applerocketry@xxxxxxxxxxx> wrote:
Yup, I know, hard to believe series is better. But, it is. It took a lot
of convincing (Allen) and testing for me to swallow that, but it works
great.
However, you have to test before you launch! I provided test points on
the airframe to test the amount of resistance of the series before
launching.
Now, if I could only get the damn hatch to blow off. ☹
*From: *Alexander Jones <uscjones@xxxxxxxxx>
*Sent: *Tuesday, January 24, 2017 12:06 PM
*To: *roc-chat@xxxxxxxxxxxxx
*Cc: *R Dierking <applerocketry@xxxxxxxxxxx>; Chris J Kobel
<chris.j.kobel@xxxxxxxx>
*Subject: *Re: [roc-chat] Re: Resistance for Electric Matches
Excuse me if I'm misunderstanding the situation, but wouldn't it be a bad
idea to wire them in series? Bc they're designed to kill their own circuit
(or at least add a LOT of resistance to it) when they blow, so if you're
trying to get more than one charge to blow, and they're not backups to each
other (i.e. you need all of them to fire), you'd have one blow, then the
current would drop drastically across the other two and they may not
fire....I would think it'd be better to wire them in parallel so they all
have current available to them at all times, then just limit the current
with a resistor, or, if your concern is destruction of your electronics,
then put some other kind of current limitation circuitry in the line....
something like this: http://www.instructables.com/id/World-
simpliest-DC-current-limiter/ ....if you don't want to drag yourself
through the math to get the fixed resistor value analytically (so you don't
have a potentiometer in your rocket), you could build the circuit first
with the potentiometer in place to determine what resistance = the current
you want, then replace it with an equivalent fixed-value resistor. It's a
decent amount of work, but it's better than destruction of your avionics
board due to overcurrent or a recovery system failure on what I assume is a
pretty big project, if it has 3 parachutes.
....or just check and see if your avionics board has a current limiter or
overcurrent protection built in....some of them do.
On Tue, Jan 24, 2017 at 11:43 AM, Adrian P. Bailey <adrian@xxxxxxxxxxxxxxx
wrote:
This may be a silly question but have you tested the resistance of the
test leads (by holding the ends together)… ;)
*From:* R Dierking [mailto:applerocketry@xxxxxxxxxxx]
*Sent:* Tuesday, January 24, 2017 11:41 AM
*To:* Adrian P. Bailey <adrian@xxxxxxxxxxxxxxx>; roc-chat@xxxxxxxxxxxxx;
Chris J Kobel <chris.j.kobel@xxxxxxxx>
*Subject:* RE: [roc-chat] Re: Resistance for Electric Matches
Looks like the San Marcos store for me.
Are Cat 3 test leads OK for our purposes? Perhaps I just need better
test leads with clips?
*From: *Adrian P. Bailey <adrian@xxxxxxxxxxxxxxx>
*Sent: *Tuesday, January 24, 2017 11:25 AM
*To: *roc-chat@xxxxxxxxxxxxx; Chris J Kobel <chris.j.kobel@xxxxxxxx>
*Subject: *[roc-chat] Re: Resistance for Electric Matches
Fry’s in Woodland Hills has quite a selection. Check online – it will
tell you what they have in the store nearest you: http://www.frys.com/
*From:* roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-
chat-bounce@xxxxxxxxxxxxx <roc-chat-bounce@xxxxxxxxxxxxx>] *On Behalf
Of *R Dierking
*Sent:* Tuesday, January 24, 2017 11:20 AM
*To:* Chris J Kobel <chris.j.kobel@xxxxxxxx>; roc-chat@xxxxxxxxxxxxx
*Subject:* [roc-chat] Re: Resistance for Electric Matches
OK, JK, but RSO’s, if you ever see wires sticking out of one of Chris’s
rockets… 😲
He does know his igniters!!!
So, glad I asked about this before conducting my ground test. I had 2
matches with 1.6 ohms and one that was 3.2 ohms that would have invalided
my test. Particularly bad if I would have found out about this later.
Learned: When doing multiple charges in series measure each match (or
igniter), and then all together to check for problems.
Going OT a bit, but does a place like Fry’s have a good selection of
meters? I wonder if I can get a meter that reads resistance better. Maybe
the leads have to be higher quality too?
*From: *Chris J Kobel <chris.j.kobel@xxxxxxxx>
*Sent: *Tuesday, January 24, 2017 10:53 AM
*To: *R Dierking <applerocketry@xxxxxxxxxxx>; roc-chat@xxxxxxxxxxxxx
*Subject: *RE: [roc-chat] Re: Resistance for Electric Matches
Sticks and stones….
*From:* R Dierking [mailto:applerocketry@xxxxxxxxxxx
<applerocketry@xxxxxxxxxxx>]
*Sent:* Tuesday, January 24, 2017 10:51 AM
*To:* Chris J Kobel <chris.j.kobel@xxxxxxxx>; roc-chat@xxxxxxxxxxxxx
*Subject:* RE: [roc-chat] Re: Resistance for Electric Matches
Wow, not bad for a wire twister Chris. 😊
*From: *Chris J Kobel <chris.j.kobel@xxxxxxxx>
*Sent: *Tuesday, January 24, 2017 10:33 AM
*To: *roc-chat@xxxxxxxxxxxxx
*Subject: *[roc-chat] Re: Resistance for Electric Matches
Some info on igniters that I gathered a few years back.
Chris
*From:* roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-
chat-bounce@xxxxxxxxxxxxx <roc-chat-bounce@xxxxxxxxxxxxx>] *On Behalf
Of *R Dierking
*Sent:* Tuesday, January 24, 2017 10:08 AM
*To:* Andrew Wimmer <xenonrocket@xxxxxxxxx>; roc-chat@xxxxxxxxxxxxx
*Subject:* [roc-chat] Re: Resistance for Electric Matches
To be honest, I don’t know the brand. They are not in the box. They are
however the same color lead wire (black) and appear to be the same make. A
single one is 3.2 ohms.
Richard
*From: *Andrew Wimmer <xenonrocket@xxxxxxxxx>
*Sent: *Tuesday, January 24, 2017 9:56 AM
*To: *roc-chat@xxxxxxxxxxxxx
*Subject: *[roc-chat] Re: Resistance for Electric Matches
What brand electric match?
3 in series should have 3 times the resistance of a single match.
http://www.pyromate.com/Basics-of-Electrical-Firing.htm
-Andrew
On Tue, Jan 24, 2017 at 9:45 AM, R Dierking <applerocketry@xxxxxxxxxxx>
wrote:
What’s a good range for the resistance of electric matches?
For my project, there will be 3 parachutes deployed from separate
side-bays and initiating the charges at apogee.
Connecting the matches up in *series* and testing today.
I know the resistance will go up with the series connections, but would
like to get an idea what the range should be.
Thank you,
Richard Dierking
