NAR L3 WIRING - HELP!!

[neond7]

I had originally planned on flying my L3 cert attempt with TRA. Due to a preference of launch fields and the unavailability of TAP's at that location, I was changing my L3 cert attempt to NAR.

I've read some threads on here about the NAR "six switch rule" no longer being in effect. Section 2.4 of the NAR L3 Cert requirements document states:

The capability must exist to externally disarm all pyrotechnic devices on-board the rocket. In this context, 'disarm' means the ability to physically break the connectin between a pyrotechnic system and its power source. Simply turning off the device controlling the pyrotechnic(s) may not be sufficient.​

I forwarded my wiring diagram to my LL3C for review. He said it looks good but I need to be able to disconnect the charges as well. My thought is that the external rotary switch wired on the power line actually physically removes the power when the circuit is open, it isn’t using the “logical” power switch on the device itself. The switch isn’t just turning off the device, it is physically removing power from the system.



Should this layout satisfy the NAR requirements? Adding a bunch of extra switches or breakable connections seems like it will add a lot of extra opportunities for something to go wrong and will not add anything to safety.

 

[rharshberger]

I had originally planned on flying my L3 cert attempt with TRA. Due to a preference of launch fields and the unavailability of TAP's at that location, I was changing my L3 cert attempt to NAR.

I've read some threads on here about the NAR "six switch rule" no longer being in effect. Section 2.4 of the NAR L3 Cert requirements document states:

The capability must exist to externally disarm all pyrotechnic devices on-board the rocket. In this context, 'disarm' means the ability to physically break the connectin between a pyrotechnic system and its power source. Simply turning off the device controlling the pyrotechnic(s) may not be sufficient.​

I forwarded my wiring diagram to my LL3C for review. He said it looks good but I need to be able to disconnect the charges as well. My thought is that the external rotary switch wired on the power line actually physically removes the power when the circuit is open, it isn’t using the “logical” power switch on the device itself. The switch isn’t just turning off the device, it is physically removing power from the system.

View attachment 288606

Should this layout satisfy the NAR requirements? Adding a bunch of extra switches or breakable connections seems like it will add a lot of extra opportunities for something to go wrong and will not add anything to safety.

It should as long as the switch is on the proper leg of the battery. Verify with your altimeter manufacturer which polarity you need the switch on to totally sever power. iirc Missleworks and Eggtimer products its the negative battery lead you put the switch on. This is the method I am going to be using as well.

 

[mikec]

Should this layout satisfy the NAR requirements?

IMHO it should, and this is the layout that I used on my L3, but there has never been a clear directive from NAR on this and it's up to your L3CC member in the end.

 

[mikec]

It should as long as the switch is on the proper leg of the battery.

I'm not seeing how it matters which side the switch is on, unless you have unexpected ground paths from conductive structure and you tie the battery to them.

 

[rharshberger]

I'm not seeing how it matters which side the switch is on, unless you have unexpected ground paths from conductive structure and you tie the battery to them.

I believe that is exactly the reason for making sure the battery is switched properly. Its all about eliminating the "what ifs".

 

[Dwatkins]

Because your altimeters have capacitors disconnecting the battery is not disconnecting the firing circuit for the charges. The capacitors are charged once you power up the units. The capacitor and not the battery is what is firing the charges and this may be his problem with your design. I would advise to talk with him so he can explain his reasons.

 

[jderimig]

Because your altimeters have capacitors disconnecting the battery is not disconnecting the firing circuit for the charges. The capacitors are charged once you power up the units. The capacitor and not the battery is what is firing the charges and this may be his problem with your design. I would advise to talk with him so he can explain his reasons.

That is a good point. Good design practice is to include discharge resistors on all the caps. You can check with your altimeter manufacturer to check if the capacitors are discharged when no battery is connected an how long that would take. Based on that answer you can lobby for a simple battery switch + delay to safe the pyro circuit.

 

[tim cubbedge]

The caps on the stratologgers are brown out caps and they discharge a few seconds after powering off.
The only purpose is to keep power running to the altimeter in the event of a brownout or momentary power loss. When you turn the altimeter on, it will start beeping out the settings, etc. Wait a second or so for the capacitor to charge, then disconnect the battery or turn the switch off. The altimeter should continue to beep for a second or two. It will keep running longer with higher battery voltage, so bear this in mind -- 9 volts should be about 2 seconds, 12 volts 3 seconds, and 5 volts about one second.

 

[Bat-mite]

That requirement was dropped.

 

[UhClem]

Even if you can argue that this switch arrangement meets the requirements of the current NAR L3 rules, it is bad practice.

What happens if the battery is wired in backwards and you turn power on?

What happens if the altimeter has failed (there are many different ways for this to happen) so that it activates its output shortly after turning the power on?

I like altimeters that include the ability to use an arming switch so that I can power up the altimeter and verify that it is operating as expected before arming the outputs. I used a AltAcc2 and RDAS for my L3 flight which required four switches.

This doesn't control all of the failure modes but it does get a bunch of them.

 

[g zilla]

Normally you should put the switch on the positive side. Thats how it is done with light switches and outlets

 

[soopirV]

Normally you should put the switch on the positive side. Thats how it is done with light switches and outlets

I think the reason the negatives are switched is because the MOSFETs that are almost universally used now in place of BJT transistors (redundant, I know) are most commonly N-channel, so they complete the "ground" leg of the circuit when current is applied to the gate. If the negative path is interrupted, then even if a positive potential is applied to the gate, there can be no bang. DC is a lot different from AC, but you're absolutely right about the light switch wiring! This way the fixture doesn't have any current applied when the switch is off.

 

[Steve Shannon]

Normally you should put the switch on the positive side. Thats how it is done with light switches and outlets

No, light switches and switched outlets have the switch in the powered conductor of a single phase, but voltage alternates between positive and negative relative to the neutral conductor.

To the OP, talk to your L3CC and find out what is needed. Unless you intend to switch L3CCs, which I don't recommend, nothing said here makes any difference except to educate others.
For the record I put switches in the output circuits as well as the battery circuit, and I felt comfortable doing so.


[emoji1010] Steve Shannon, L3CC [emoji1010]

 

[cbrarick]

Why not use the supplied switch connection? That was good for my L3.....seems like you're reinventing the wheel.

 

[Getmore]

Bet me to it. That's what it was design for.

Why not use the supplied switch connection? That was good for my L3.....seems like you're reinventing the wheel.

 

[neond7]

Why not use the supplied switch connection? That was good for my L3.....seems like you're reinventing the wheel.

The supplied switch connection is a "logical" switch. The altimeter still has a live battery hooked to it at that point. The funny thing is, that is how Perfectflite recommends they get hooked up, and I've got a ton of successful dual deployment flights with zero failures as my data point. Many of those flights were with redundant altimeters as well.

I changed the connection for this L3 attempt to have the capability to totally remove power from the system. My LL3C didn't seem to think this meets the NAR requirement. People keep saying that requirement was removed - but it is still in the L3 cert handbook!!

 

[rharshberger]

Why not use the supplied switch connection? That was good for my L3.....seems like you're reinventing the wheel.

When all the L3CC/TAPs agree on the exact same method these discussions won't happen anymore. There are posts on TRF where two TAPS/L3CC's can't even agree on the interpretation of a set of rules what makes anyone else different, L3CC/TAP or otherwise.

 

[ksaves2]

Jeff,

Switches on each ematch channel were disavowed years ago. There were misguided individuals who "thought" they added "safety" but were just plain stupid for not logically thinking the failure modes through. If you can't find another L3CC to approve it,
go to TRA and do the certification there. If your L3 rocket ends up in a tree or hanging from wires, it can still be considered successful whereas in NAR it's not.
I've been told that officially both the NAR and TRA dropped ematch channel safety switches so the particular L3CC is misinformed. Kurt

 

[watermelonman]

Certify through Tripoli and skip the headaches.

I know NAR formally removed the silly rules but the individual certifiers still get a say, and NAR is clearly farther behind in this regard.

 

[Steve Shannon]

The supplied switch connection is a "logical" switch. The altimeter still has a live battery hooked to it at that point. The funny thing is, that is how Perfectflite recommends they get hooked up, and I've got a ton of successful dual deployment flights with zero failures as my data point. Many of those flights were with redundant altimeters as well.

I changed the connection for this L3 attempt to have the capability to totally remove power from the system. My LL3C didn't seem to think this meets the NAR requirement. People keep saying that requirement was removed - but it is still in the L3 cert handbook!!

No, the requirement was not removed. It was clarified because some people thought shunts were needed, some thought six switches were needed, and some didn't understand what was needed. We tried to make it easier to understand without having people read too much into it. What you see is the result. Talk to your L3CC.


[emoji1010] Steve Shannon, L3CC [emoji1010]

 

[ksaves2]

No, the requirement was not removed. It was clarified because some people thought shunts were needed, some thought six switches were needed, and some didn't understand what was needed. We tried to make it easier to understand without having people read too much into it. What you see is the result. Talk to your L3CC.
[emoji1010] Steve Shannon, L3CC [emoji1010]

His wiring is fine. Unless the switches are cheap 2 bit stuff he doesn't need to talk to the same L3CC who said he needs switches on the ematch circuits. Get another L3CC or since Jeff has a TRA number, make arrangements and travel to a TRA site and do the L3 under their auspices. Me suspects he has an NAR group nearby or has some emotional attachment to same.

Oh, shunts are stupid useless safety devices too. Putting them in place without ACTUALLY testing them in the
FAILURE MODE they are supposed to be guarding is a total, inept, fallacy. Problem is with testing, one may dork their electronics by the process of the test plus, if they are using an augmented ematch, the parallel shunt may do nothing to protect it against going off.

The saving grace here are the newer devices that can be activated remotely from a safe distance. Kurt

 

[Steve Shannon]

I'm trying to avoid "L3CC shopping" here, Kurt, not discuss the use of shunts. This may be a simple misunderstanding. L3CCs and TAPs talk behind the scenes and try to avoid debating each other's advice on a public forum.


[emoji1010] Steve Shannon, L3CC [emoji1010]

 

[cherokeej]

L3CC's and TAPs certainly do discuss issues behind the scenes. That is a fact.

The rule was clarified and the language changed. It used to say disconnecting the battery from the unit "shall" not be enough. It now reads "MAY" not be enough.

Input capacitors are for de-bouncing the power to the unit. They have nothing to do with any capacitive discharge circuit that may exist in the output circuitry of any given altimeter/accelerometer unit.

But the bottom line is that it is up to your L3CC. If he says you need to switch the outputs, then you need to do some switch shopping.

 

[Zeus-cat]

Jeff,

Switches on each ematch channel were disavowed years ago. There were misguided individuals who "thought" they added "safety" but were just plain stupid for not logically thinking the failure modes through. If you can't find another L3CC to approve it,
go to TRA and do the certification there. If your L3 rocket ends up in a tree or hanging from wires, it can still be considered successful whereas in NAR it's not.
I've been told that officially both the NAR and TRA dropped ematch channel safety switches so the particular L3CC is misinformed. Kurt

I know someone who just joined Tripoli just to get his L3 because of this switch requirement.

 

[mikec]

The rule was clarified and the language changed. It used to say disconnecting the battery from the unit "shall" not be enough. It now reads "MAY" not be enough.

Changing a shall to a may is certainly a model of brevity, but clarity, not so much.

When I did my L3 I convinced my L3CC that one switch was enough by pointing out the "may", but a clearer statement would be better IMHO. I don't know of an altimeter still in production that powers its outputs from capacitors (the Perfectflite MAWD was one example).

 

[Bat-mite]

I know someone who just joined Tripoli just to get his L3 because of this switch requirement.

It's great to belong to both organizations, but I just got my L3 thru NAR with a simple wiring diagram and two switches for power on/off.

 

[ksaves2]

I'm trying to avoid "L3CC shopping" here, Kurt, not discuss the use of shunts. This may be a simple misunderstanding. L3CCs and TAPs talk behind the scenes and try to avoid debating each other's advice on a public forum.


[emoji1010] Steve Shannon, L3CC [emoji1010]

Well if the L3CC is inappropriately requiring Jeff to add four stupid switches to his project to certify, I'd say it's time to L3CC shop or go to the other organization.
Someone used the word shunt in the thread and that is another pet peeve. I'll drop it there and will not continue it. With some of the newer remotely activated
devices coming on the market, that can eliminate that problem which is an issue with staging and air starting, not certification. Kurt

 

[ChrisAttebery]

I'm wiring my RRC2+ the same way you are for my TRA L3 attempt. The Stratologger manual states that that is one of the ways it can be hooked up safely. If you've flown it in that configuration I would have an logical discussion (not an argument) , with the L3CC. I'd show him the manual for the altimeter and the fact that you've flown these exact altimeters in the past. The outputs are reverse voltage protected. Its in the manual. If he can give you a LOGICAL reason to do it, fine. But don't change something just because it's on a piece of paper that was written in the days when altimeters were still fairly new and occasionally had misfires.

 

[ChrisAttebery]

Let me add one more thing. Ask him to show you one of his altimeter days where he's added the switches to the outputs. Is he practicing what he's preaching?

 

[Steve Shannon]

Well if the L3CC is inappropriately requiring Jeff to add four stupid switches to his project to certify, I'd say it's time to L3CC shop or go to the other organization.
Someone used the word shunt in the thread and that is another pet peeve. I'll drop it there and will not continue it. With some of the newer remotely activated
devices coming on the market, that can eliminate that problem which is an issue with staging and air starting, not certification. Kurt

Kurt,
There is no requirement to have switches for each charge and never has been. Likewise some people incorrectly interpreted a need for shunts. Shunts may help with static but simply complicate things and to the best of my knowledge were never required.
Go back and reread the original post; his L3CC said there must be a way to disconnect his charges. Nothing more. This is due to the need to safe unfired charges. We don't know what the real objection was: whether it was not possible to positively see that the charges were disconnected (some rotary switches are disliked by some taps and l3ccs for this reason) or what.
He just needs to find out what his L3CC is really requesting. If his L3CC is REALLY asking for six switches then he should ask for help, but I doubt that's what he's expecting.


[emoji1010] Steve Shannon, L3CC [emoji1010]