Safety First

Electric Matches like Davey Fire which is what is supplied with Pro38 motors.

Les

Its an issue about safety :)

we've had a relay controller fail in the closed position, luckily it was durign storage and drained teh battery, without accidentally lighting off a rocket while a roclketeer was underfoot.

best way to avoid this is to know your equipment. keep it simple and have failsafes

I notice that in this cautionary tale, no mention is made of just exactly what was wrong with the launch controller which leaves me with far more questions than answers.

1) Just what was the circuit design and how was it intended to operate? 2) How much current was available? 3) At what voltage? 4) Did the circuit operate as designed or was there a failure?

This is of more than academic interest as I assist with the design and construction of my clubs equipment.

The electric matches supplied with Pro38 motors have a maximum safe test current of a few tens of milliamps.

snipped-for-privacy@gmail.com wrote:

And to add, always touch the clips together to verify no current. Saved my ass last Aug. Wish I could say the same for guy on the pad next to me ;/

Simplest thing in the world to do yet so many overlook it.

Ted Novak TRA#5512 IEAS#75

I can't remember where I heard it (think it was here...) but there was a suggestion that igniters should be connected to the controller,

*before* being inserted into the motor. That way, if the controller is indeed faulty, all you've gotten is a scare... instead of first- or second-degree burns.

(Wish I could remember where I saw it posted before, so I could give the original poster credit...)

I prefer attach the igniters to the (shorted) launch leads and then at a safer distance plug those into the controller then your hands are never in the flame path at the critical moment. And always continuity test the igniters outside the motor.

Stephen.

Also the measurement of '8 volts' across people isn't especially meaningful - if indeed it is a valid test (I remember meters we had a school that indicated that I was a 60v source!) - it gives no idea of how much current.

Others have pointed out that sticking ignitor leads in ones mouth is not a good idea, since there is no telling what is connected at the other end. I wouldn't want 12v across my tongue, but what if someone had erroneously connected the launch controller to an inverter ? (unlikely one would hope but possible, some people use mains connectors on LCs)

Would static charge not be a more likely explanation? The oxral igniters supplied with Pro38's have been fired by continuity tests before, does anyone know conclusively of e-matches being fired by static?

I remember seeing this suggestion proposed in an issue of Extreme Rocketry.

Anyone come up with a downside to this idea?

George Rachor

Len Lekx writes:

-- ========================================================= George L. Rachor Jr. snipped-for-privacy@rachors.com Hillsboro, Oregon http:rachors.com United States of America Amateur Radio : KD7DCX

A safety key eliminates the need?

It was in the Extreme Rocketry December '04 issue Aft Closure by Brent McNeely.

Safety keys can experience fused contacts, too... ;-)

Isn't a little extra caution better than a whole lotta hurt?

One little modification I'd make to the procedure, though. After connecting the igniter outside the motor, and making sure it didn't go off in my face, I'd short the two igniter wires together temporarily while inserting the igniter into the motor. In the event that the LCO triggers your pad by accident, the short will prevent current from setting off the igniter when it's halfway into the motor.

Thanks, Kath.

>

re-read the article, the faulty controller passed that test. better to have a bevice in parralel with the clips that give indication of power.

C'mon just stick an LED with resistor in there. two extra parts that are worth pennies to keep this from happeneing.

Make sure the LEDs are bright enough to see in direct sunlight.

I once worked in an electronics shop that had an antenna on the roof. One very windy, low humidity, day, about this time of year, I heard some popping from near the wall. Tracing it down, I found that a arc, or spark, would jump across the PL-259 connecter. That was a distance od about 1/4". The wind, blowing on the antenna wire, was producing some very high voltages on the coax cable. The article states that it was a very windy day. It may be possible that the wind had built up a very high voltage on the ignition wire, which discharged through the igniter when the person touched the other lead. It would be a rare event, since conditions would have to be just right.

Ed Mallory

Or use a blinking LED -- the human eye sees the difference much better in any lighting conditions.

David Erbas-White

How about a buzzer?

Ted Novak TRA#5512 IEAS#75

Maybe it's just me, but I find a buzzer pretty irritating -- so it could lead one (well, me) to 'hurry up' doing something that I don't want to 'hurry up' on.

What I mean is, sometimes the buzzer is irritating enough that the continuity is only tested very briefly - when in fact it ought to be monitored most (or all) of the time.

I understand and agree that this is a personal preference issue, but thought I'd add my two cents worth.

David Erbas-White

I assume Ted means a buzzer connected across the output of the launch controller firing circuit, or from a multi-contact relay that switches the output, so that if the buzzer is going you know the clips are energised. Across the clips would be better in that case, but I'd be inclined to put a large (say 10K) resistor in parallel with the buzzer and igniter, so that any capacitance in the buzzer (which will likely have some kind of drive circuit) or static charge on the clips can discharge.

Alternatively, how about a small box, with a buzzer inside and a couple of terminals. Connect it to the clips, if it buzzes you're live. You'd just have to make sure that the current required by the buzzer was less than the safe level for an e-match.