Just torched my new RRC2+.... what did I do wrong

[kjkcolorado]

I'm glad this has turned to some discussion regarding parallel vs series wiring of e-matches. As I mentioned earlier, I have been in the camp of dual e-matches in parallel to add redundancy in the event of one match failing. Let me be clear explaining my limited experience to date. I have done a fair amount of ground testing (with traditional 9V battery up to this point), with only 3 successful DD flights to my name in this configuration. That's it....

My thought was that if you test your e-matches when prepping, you have a high likely-hood of getting all your e-matches to the pad in good shape. At that point I would think an e-match failure would happen due to forces during launch/flight or prior deployment charge (apogee charge forces disrupting e-match in main chute charge). So, in parallel, you can lose one e-match and still have a nominal deployment. Well, from the knowledge shared here I've learned that this may not necessarily hold true. And, as several others have pointed out, I'm asking my electronics to do something they are not designed to do. So, now I am considering trying a 1S LiPo and series wired dual e-matches.

One question, if you get to the pad with dual e-matches in series and my altimeter verifies continuity, haven't I just doubled my chance of a deployment failure needing only one of two e-matches to lose continuity during launch/flight? What am I missing?

 

[rcktnut]

Parallel is the correct way to wire them. If your first e-match "opens" the circuit without firing the charge in a series connection, you will not have power to the next e-match inline. I have a MAWD and the instructions say to wire in parallel and it supposedly can fire up to 10 e-matches that way. Never used it yet, my Missle works alts. are serving me fine yet. Best to follow directions according to what alts. you have I guess.

 

[catman001]

One point that seems to confuse people is the "C" rating. This is the amount of current that a battery can deliver without damaging itself. It is not, the amount of current the battery can deliver in a short circuit condition. That is determined by its internal resistance.

After first reading this post, I went and measured the resistance of a small, 2s, 260mah, battery from Hobbyking, which I use with some of my altimeters. Using the internal resistance function on my battery charger, I recorded one cell at 88 milliohm's, and the other cell at 85 milliohm's, for a total of 173 milliohm's, or .173 ohm's.

Using ohm's law, which states that current is equal to the voltage, divided by the resistance, I have 8.4 volts divided by .173 ohms, or 48.55 amps. Yes, that little battery only about 1/3 the size of a nine volt can deliver almost 50 amps in a short circuit condition.

A 9 volt battery has a internal resistance of about 1.8 to 2 ohms, so 9 volts divided by the resistance, gives you 4.5 to 5 amps in a short circuit condition. They cannot deliver any more current than that due to the resistance of the battery itself. That is one of reason's that many people still like 9 volt battery's. Even if the ematches are shorted, most if not all altimeters can take a 5 amp current draw without damage.

While I use Li-Po's for altimeter's, I do so knowing that if I have a short somewhere, things are not going to end well. Just remember, the "C" rating is what the battery can deliver without damage, not what the battery will deliver under a short.

Mike

 

[dixontj93060]

Parallel is the correct way to wire them. If your first e-match "opens" the circuit without firing the charge in a series connection, you will not have power to the next e-match inline. I have a MAWD and the instructions say to wire in parallel and it supposedly can fire up to 10 e-matches that way. Never used it yet, my Missle works alts. are serving me fine yet. Best to follow directions according to what alts. you have I guess.

I'm guessing you didn't read any of the earlier posts including ones from two altimeter experts/designers that recommend series wiring along with the explanation as to why this works for ematches.

 

[UhClem]

Here's the data sheet for the specific FET's I use: https://aosmd.com/res/data_sheets/AO3404A.pdf .

This is not the best choice for use here.

The datasheet specifies Rds(on) only for a Vgs of 4.5V while the altimeter is driving it with less than that. Probably 3.3V. This means that the resistance of the MOSFET will be higher than expected resulting in greater power dissipation. Since these are SOT-23 packaged parts they cannot dissipate a lot of power. Reading between the lines of the data sheet I think that a current of 3A would be outside of the Safe Operating Area. The data sheet doesn't say but I suspect that the continuous drain current specification is for Vgs = 10V.

It is easy to find parts in this package that do have Rds(on) specified at 3.3V and lower. A quick search at Mouser turned up devices with a lower Rds(on) at 2.5V than this part has at 4.5V. Cheap too.

This might not have helped in this particular case but it would certainly help to make them more robust.

Because of that SOT-23 package and 1 second on time I would recommend using a series resistor to limit fault currents when using a low resistance battery. You want something high enough to limit the fault current to a safe level but not so high that it doesn't allow it to deliver the all fire current to the load. 1 Ohm would probably be a good starting point. A nice 5W wire wound part should work well because it has very high pulsed power dissipation capability.

You can either put a resistor in series with each output or just one in series with the battery.

 

[soopirV]

This thread is timely, as I'm just about to start into the world of Dual Deploy. I have 1S, 2S and 3S lipos that I've used for various purposes in rocketry, but now know to use 1S or 9V on the deployment charges. I still am a little unclear on how series wiring is better than parallel- I get that parallel will increase the amount of current you dump, but series seems susceptible to open circuit, curious how this actually works in Pyro shows? Regardless, it makes me realize that what I really need for redundancy, as someone mentioned previously, is to have two altimeters.

 

[watermelonman]

My current igniters report continuity after firing. I imagine that means enough current flows through to continue in a series after each fires.

I have been using 9v batteries with my RRC2, with great success. I would like to move to lipos at some point but frankly the 9v works so well that it is tough to even bother looking at other solutions.

 

[dixontj93060]

...but series seems susceptible to open circuit, curious how this actually works in Pyro shows?

The presentation Safety and Wiring Techniques in Electrical Pyrotechnic Ignition by Dr. James Beeghly says this:

For low energy systems, the pyrogen in the match usually fires before the nichrome melts and thus all the matches in a series circuit have time to fire.
​

Where low energy is defined as <24VDC.

 

[mpitfield]

I thought this too, but Mr. Derimiggio schooled me on this back here: https://www.rocketryforum.com/showt...lace-to-get-e-matches&highlight=ematch+series. As it turns out e-matches are designed to be run in series (think dynamite locations along a ridge, or fireworks spread out across a large outdoor stage). I never knew this and did my own research after the post above--turns out it is a very accepted and standard practice. Saying that, the MJG Firewire (non-regulated) initiators used by the OP do have some limitations compared to normal e-matches, but I believe the spec is still 4 or 5 in series.

Not to hijack this thread but I can see Kendal is getting some good information pertinent to his needs, but we are also getting some good stuff on the never ending series vs. parallel debate. To that end, I can see that it has been mentioned in at least two posts here that the pyro industry regularly runs series circuits and is the norm for what some called commercial e-matches or igniters. One thing I am not sure of is, does this apply to our hobby e-matches and if so all of them? Traveling to US launches from Canada, I normally just pick up e-matches at the launch and it is normally whatever the on-site vendor has in stock, so I cannot always control what I use.

BTW, if the OP would like us to take the "series vs. parallel" discussion to another thread I can do that but I think there is some good stuff being said here. As far as expanding this conversation to a full discussion on redundancy I can see benefits to that discussion however we should maybe have a dedicated thread or resurrect a previous thread where it has been discussed for anyone wanting to have that discussion.

The other thing that I would like to better understand is the following "take away" made by Jim Amos:

"2S batteries are a better choice for brown-out prevention as the brown-out cap has a higher voltage potential"

Based on my discussions and experiences, my interpretation is that this does not to a Li-Po due to it's low internal resistance, normal operating temperature range aside. I understand that a 9v alkaline battery can have issues delivering power right after it has delivered power, to simplify this I will call this recovery time. Li-Pos on the other hand can deliver multiple bursts or current back to back.

I have tested this and in fact witnessed this using a 1S on both the StratoLogger 100 and the StratoLogger CF, which both require a min 4v and have a nominal operating range of 4-16v. Between actual flights and bench testing I would guess that I have at a minimum a few dozen dual e-match on a 1S Li-Po events to draw on. With the back to back tests being extreme, not possible in the real world, bench testing. These tests have literally been back to back then loaded up again back to back, etc. performed on the same battery and from start to finish the recorded voltage drops are less than 1volt. I have since measured the voltage drop using my bench tester which allows me to record tests and the voltage barely moves.

So although I would be the first to say that Jim most definitely has much more knowledge on the general topic of Altimeters, and likely electronics, his take away does not fit with my experience and how I have interpreted other posts. Obviously I am missing something in this regard so if anyone can provide clarification I would appreciate it.

 

[Viking]

Worth considering transient black-outs. If, for example, a battery(of any chemistry) plug/terminal connection is sub-optimal, or a switch loses contact briefly during a high-g boost, the more energy stored in that cap the better.

 

[FredA]

Re-Read post #33.

9V batteries are the ticket.
Few, if any, altimeters are really setup to deal with the current LiPo's can deliver.

 

[kjkcolorado]

Well, I thought I didn't want to go through the series vs parallel e-match debate, but I'm learning a lot and it's really a significant part (if not the most significant part) of why I fried my altimeter. It's now obvious to me that the electrical equation for wiring dual e-matches in series is safer for your electronics. However, I'm still wondering if this method really provides a significant level of redundancy. Is there any hard data that if an e-match in series fails when the electrical current is applied that it will conduct enough to fire the other e-match? Do we know that this is the most common time/cause of e-match failure? If any of you have heard the phrase 'paralysis by analysis'... I think I'm there.

 

[kjkcolorado]

Re-Read post #33.

9V batteries are the ticket.
Few, if any, altimeters are really setup to deal with the current LiPo's can deliver.

After frying my altimeter and all this discussion/debate, it's hard to argue with theses two sentences.

 

[Random Flying Object]

What was the pyro channel duty cycle set to?

 

[rcktnut]

I'm guessing you didn't read any of the earlier posts including ones from two altimeter experts/designers that recommend series wiring along with the explanation as to why this works for ematches.

I read all the posts, and Perfect Flight suggests using parallel wiring. The series wiring makes sense also. I guess that is why this is highly subject to debate.

The presentation Safety and Wiring Techniques in Electrical Pyrotechnic Ignition by Dr. James Beeghly says this:
For low energy systems, the pyrogen in the match USUALLY fires before the nichrome melts and thus all the matches in a series circuit have time to fire.

If you are comfortable with this sentence using the word USUALLY instead of ALWAYS, go with series.

 

[FredA]

If you are serious about wanting more than one chance to fire the charge, then go with a four channel altimeter and use one e-match per output.

 

[rcktnut]

If you are serious about wanting more than one chance to fire the charge, then go with a four channel altimeter and use one e-match per output.

Best answer yet, or 2 altimeters, redundant system.

 

[Onebadhawk]

If you are serious about wanting more than one chance to fire the charge, then go with a four channel altimeter and use one e-match per output.

+1...

By doing this any other way I think you're introducing more possible fails then you're eliminating...

Teddy

 

[vance2loud]

Best answer yet, or 2 altimeters, redundant system.

I personally go with this logic. Rather than relying on 2 e-matches on 1 altimeter a second altimeter with it's own separate battery is considerably more redundant.
My Darkstar Jr that I used for my L2 had a Raven (Apogee and main 600 feet) as the main altimeter and an AltiDuo (main only at 492 feet) as the backup for main. I used the Ejection charge in the motor for a backup for drogue. It would have taken 3 totally independent failures to allow for no parachute at all.
I also oversized my drogue (understandably not always an option, but this was a cert attempt) just in case.
A second altimeter doesn't require recording or any of the other nice features that we are used to, so there are a lot of options that are cheaper than a 'H' size motor and that can fit into tiny amounts of room.

 

[ksaves2]

Thanks for posting Kendal. Great thread and opinions from all. I've learned a lot of cautions. If it's any consolation, I tried a second bench testing of an EasyMega and toasted it with a reverse polarity situation. I should have referred to the instructions line by line like I did for my first test. I think one take away is the only place one should consider a large capacity battery is if they want a longer run time for a nose mounted Rf tracker and "useful" nose weight! Other than that, unless a device maker recommends a particular battery than a 9V stick to that. Kurt

 

[soopirV]

VanceCloud- you're the first person I've seen (albeit I haven't looked very hard) to fly an altiDuo. I assume it's successful, and not to hijack the thread, part of "true redundancy" is not relying on the same technology twice. I fly eggtimers only- don't have anything else in my hanger. Would including an altiDuo be safe,
Given that both fly off the atmega micro controller? Different program, I'm sure, but same backbone/architecture.

 

[vance2loud]

VanceCloud- you're the first person I've seen (albeit I haven't looked very hard) to fly an altiDuo. I assume it's successful, and not to hijack the thread, part of "true redundancy" is not relying on the same technology twice. I fly eggtimers only- don't have anything else in my hanger. Would including an altiDuo be safe,
Given that both fly off the atmega micro controller? Different program, I'm sure, but same backbone/architecture.

As it has only been used twice so far and only as backup, so far so good.
The backup charge was clearly audible at around the expected time.
The only missing feature that I feel is required for a backup altimeter would be a delay so that for apogee I could set it to fire 1-2 seconds after apogee (which the Quark has).
It also is not rated to use a 9v battery (4.5 - 7.4 v recommended) but when combined with a 200mA 2s lipo it can into a tiny amount of room. YMMV
Personally I mix it with a Raven so I had a more 'proven' Altimeter but I think that the reason for using 2 different types of altimeter is more about reducing the chance of user error rather than chipset error.

 

[soopirV]

As it has only been used twice so far and only as backup, so far so good.
The backup charge was clearly audible at around the expected time.
The only missing feature that I feel is required for a backup altimeter would be a delay so that for apogee I could set it to fire 1-2 seconds after apogee (which the Quark has).
It also is not rated to use a 9v battery (4.5 - 7.4 v recommended) but when combined with a 200mA 2s lipo it can into a tiny amount of room. YMMV
Personally I mix it with a Raven so I had a more 'proven' Altimeter but I think that the reason for using 2 different types of altimeter is more about reducing the chance of user error rather than chipset error.

That is a terrific point! User error vs chipset error is a great way of putting it, too. Thanks for helping reframe the discussion!

 

[kjkcolorado]

Thanks for posting Kendal. Great thread and opinions from all. I've learned a lot of cautions. If it's any consolation, I tried a second bench testing of an EasyMega and toasted it with a reverse polarity situation. I should have referred to the instructions line by line like I did for my first test. I think one take away is the only place one should consider a large capacity battery is if they want a longer run time for a nose mounted Rf tracker and "useful" nose weight! Other than that, unless a device maker recommends a particular battery than a 9V stick to that. Kurt

It is some consolation that my mistake has stimulated this discussion and it appears quite a few peope have benefited. Sorry you lost an EasyMega ($$$ compared to my RRC2+!!!). I'm firmly back to the 9V for this altimeter for a while. If I decide to venture back to trying out a LiPo, it will be with a single e-match per channel and 2 altimeters if a significant level of redundancy is desired.

Funny you should mention the tracker and a larger capacity battery. The same day I got the LiPo that helped me toast my RCC2+, I puchased a 1S, 750mAh LiPo for my future Missile Works RTx!

 

[Buckeye]

Re-Read post #33.

9V batteries are the ticket.
Few, if any, altimeters are really setup to deal with the current LiPo's can deliver.

Yeah, I am in no hurry to switch to LiPos. The $60 charger is another turnoff for me!

My big rockets use a 9V Duracell which I fly up to 12 times DD with my good ol' Perfectflite MAWD. OK, before you guys start berating me with "You idiot! A new battery is needed for every flight and is cheap insurance!" keep in mind that the MAWD has a honking big capacitor to fire the pyro channels.

My little rockets use a 9V A10 which can probably fly 3 times DD, but I only use them once at $1 each.

 

[michigander]

I recently did a flight 3 channels on eggtimer , aux 1 drogue at apogee , B drogue 2 sec delay backup . Motor deploy 17 sec left in , sim called for 13 sec


No backup on main as flying in muddy cornfields

 

[ksaves2]

You going to see if it can be repaired? Lifting off the FETs isn't that much of a problem. The question is did any of the other associated circuitry get zapped out of spec? Might be worth fixing and test in a two bit vacuum chamber. If it passes, fly it in
a "beater" rocket. I have a few of those and it's nice that I just don't worry about them anymore. I mean I'm careful with prepping but if God decides to keep them, I'm not going to cry about it, especially if an SU motor is involved. Kurt

 

[Handeman]

... My big rockets use a 9V Duracell which I fly up to 12 times DD with my good ol' Perfectflite MAWD. OK, before you guys start berating me with "You idiot! A new battery is needed for every flight and is cheap insurance!" keep in mind that the MAWD has a honking big capacitor to fire the pyro channels...

I'm with you on the multiple fights on a 9V Duracell. I fly them on my Perfectflite HiAlt45, SL100, and CF until the altimeters report below 8.9V since my meter actually measures about 0.1V higher then the altimeters report. I think the most likely time for a failure is the first flight on an untested battery.

I do replace the battery regardless of the voltage if there was some sort of anomaly with the flight like a failed apogee or main deploy, hard landing due to fouled main, etc. although I haven't had anything like that in 7 years or more. (knock on wood)

An interesting side note about battery draw. I hung a rocket in a tree for 5 days and when I got it down, the HiAlt45 was still beeping altitude and had about 7.5V left on the 9V Duracell. The CF was also beeping altitude and speed but only had about 5V left on the 9V Duracell.

 

[soopirV]

I recently did a flight 3 channels on eggtimer , aux 1 drogue at apogee , B drogue 2 sec delay backup . Motor deploy 17 sec left in , sim called for 13 sec


No backup on main as flying in muddy cornfields

What did you use as a power source, a 9V? I have several Eggtimer products, and all the documentation (with the exception of an older RevC Eggtimer) specifically call out LiPo as a suitable (sometimes recommended) option.

 

[dixontj93060]

What did you use as a power source, a 9V? I have several Eggtimer products, and all the documentation (with the exception of an older RevC Eggtimer) specifically call out LiPo as a suitable (sometimes recommended) option.

Post #1, point #1 from O.P.,

"1) Connected it to the new LiPo I am testing it with (2S, 225mAh, 10C)."