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

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

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

How on Earth did you make that deduction? OP and the person I asked my question of are two different people...am I missing something?
 
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

I sent it back to Jim at Missile Works. I don't have the expertise or equipment to test and fix it (if it's fixable).
 
Oh, sorry, my mistake.

This pisses me off- guys get sanctimonious enough to bother to go back to reference AND quote a previous thread, instead of actually paying attention and understanding what's going on. Don't mean to hijack the thread, but this is a rare opportunity to call a spade a spade when it comes to the devolution of Internet discourse.

To the guy I originally asked an honest question about, can you share more about your eggtimer battery configuration before nosy-pants here busted in and ruined it?
 
This pisses me off- guys get sanctimonious enough to bother to go back to reference AND quote a previous thread, instead of actually paying attention and understanding what's going on. Don't mean to hijack the thread, but this is a rare opportunity to call a spade a spade when it comes to the devolution of Internet discourse.

To the guy I originally asked an honest question about, can you share more about your eggtimer battery configuration before nosy-pants here busted in and ruined it?

Look. Did say I was sorry. This thread was about the RRC2+ altimeter, then moved to LiPo batteries and now Michagander & you have it on a third (Eggtimer) track. Hard to keep up, especially answering on a phone in an airport.
 
Look. Did say I was sorry. This thread was about the RRC2+ altimeter, then moved to LiPo batteries and now Michagander & you have it on a third (Eggtimer) track. Hard to keep up, especially answering on a phone in an airport.

Fair enough, apology accepted.
 
Hi,

I will say I didn't quite understand how the adverse event happened with Kendal but I've had things happen like metal contacting the bottom of a board and... POOF!!!!!! This happened to me twice when building EggFinders and it turned out a stray lead cut-off was loose and shorted across the board! Stupidhead here was not prudent enough not once but twice! Turned out in my case the lead shorted across an LED and whacked the LEDs in question and both units were fine. I replaced the LEDs and no problem. I don't think in my case the type of battery had anything to do with it. A Nicd, Nimh or Alkaline is probably going to be able to source enough current to whack these tiny components given the right conditions.

Some years ago, I made some of those three transistor wireless transmitters/microphones and put one on the roof to do a range test. I took a 12V lead calcium cell up there (the rigs were designed for 12V) and I managed to connect the battery up with reverse polarity (ie. + to - and - to +). Let's just say, "Don't do that!" A capacitor exploded like a very large firecracker and bits bounced off the side of my head. Weird thing was I just replaced that capacitor and the dern'd thing worked!! Kurt Savegnago
 
I wanted to post a follow-up for everyone that's bothered to read thru this thread.

I'm only going to touch on the redundancy subject briefly as the ongoing conversation is still ongoing... I think it's useful to start with definitions, hence I refer you to what I believe is the most applicable definition when it comes to HPR redundant systems:

https://en.wikipedia.org/wiki/Dual_modular_redundancy

Dual modular redundancy/ From Wikipedia, the free encyclopedia:
"In reliability engineering, dual modular redundancy (DMR) is when components of a system are duplicated, providing redundancy in case one should fail. It is particularly applied to systems where the duplicated components work in parallel, particularly in fault-tolerant computer systems. A typical example is a complex computer system which has duplicated nodes, so that should one node fail, another is ready to carry on its work."

With that definition as a foundation, anything short of completely independent and duplicated systems is not a *truly* redundant system. If you're not going to implement truly redundant systems, you can reduce the chance of single-mode failures by implementing lesser degrees of redundancy. There are many factors that drive these lesser degrees of redundancy, primarily, monetary budgets, project investment, mass or payload budgets, physical space, personal preferences, personal comfort levels, etc. Each flyer needs to assess what is most appropriate per-project and be cognizant of the "collection-of-trades" that such decisions imply.

Bob Krech made a great post titled "Avoid the death penalty for your rockets: Always follow Ohm's Law!!!!!!". The post is located here:
https://www.rocketryforum.com/showt...ot-thing-and-redundancy&p=1569275#post1569275

What's contained therein is directly applicable to this specific thread, and with that I'd like to make some recommendations on batteries and ematches for the RRC2+ (and RRC3):

- When using 9V alkalines, you can safely run 1 ematch per event, or 2 ematches per event (parallel or series based on your preference). You should understand the implications of parallel/series connections when running dual ematches per event. The most reliable means of dual-ematch connection is series.

- When using 1S or 2S Lipo batteries you can safely run 1 ematch per event, or 2 ematches in SERIES ONLY.

- Avoid metallic canisters if possible and always pre-measure ematches to ensure resistive compliance.

(NOTE: what I found most alarming when it comes to reliability was the statement made in the same thread cited above by mpitfiled - "Doing nothing more than unwinding an e-match and firing it off with a 9v battery, out of less than 100 I have had 2 fail. If this is the reliability of the cheap Chinese imports, I'd not trust my rockets to them. jderemig said" - MJG J-Tek, 1/10000 failure rate based on fireworks guys experience." YMMV)


Addressing additional points made in the thread:

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.

The Rds of this device is 62mOhms with a 3.3Vgs @ 25C. The additional junction resistance vs. the published 4.5Vgs @ 25C is 27mOhm. At a typical 1A all-fire current this nets an additional power dissipation of 0.027W, and factoring in a worst case Rtheta, a resultant 2.43C temp increase (with typical Rtheta, only 1.75C). Even at 3x the all-fire current, junction temp increase would be 15.7C typically and worst case 21.8C, which is well within the 150C thermal incineration temperature of the FET. Based on the thousands of RRC2+ and RRC3 altimeters in service and the 10's of thousands of flights made by the collective using all different battery types, I'd say the choice is quite satisfactory. I use these FETs in other products I manufacture thereby leveraging higher economies of scale. I consider the trades a net win.

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.

This statement is made in terms of voltage level only... while your test netted a worst case 1v drop over the extremes you cite, you didn't operate your altimeter with a potentially shorted output which would have dropped your battery voltage much lower. The higher the voltage in the brownout cap, the longer it can keep the logic afloat should your battery voltage levels drops into the mud due to unforeseen circumstance.

It is some consolation that my mistake has stimulated this discussion and it appears quite a few people 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.

All the choices you cite will work... avoid parallel connections with Lipo's and they too will work.
 
(NOTE: what I found most alarming when it comes to reliability was the statement made in the same thread cited above by mpitfiled - "Doing nothing more than unwinding an e-match and firing it off with a 9v battery, out of less than 100 I have had 2 fail. If this is the reliability of the cheap Chinese imports, I'd not trust my rockets to them.)

Jim it is funny you just posted this because I have been thinking about this a lot since coming to the realization that my experience is uncommon. If you sell decent e-matches, and can deliver them to upstate NY then I will place an order immediately. I have done a bit of research and it appears that there my be some restrictions in place that prevent me from purchasing them on-line and shipping them. That is except for the new MJG Firewire Initiator that jderemig mentioned something along the lines that the jury was out. I would like to know more about those from a reliability point of view, as it relates to our application.

I agree this conversation has been one of the more productive ones. For me it has been in that my reasons for dual e-matches has been largely predicated on my limited personal experiences with e-matches, most of which have been bench tests. That being said my new strategy is to source better quality e-matches with the reliability that jderemig cited, and use one e-match with my fully redundant Av bays and two in series on my single Av bays...yes I have fully redundant Av bays.

BTW the example of redundancy that you selected is my field. My company designs, monitors and administers fully redundant and high available systems, from the firewalls, routers, local network, server hardware and the core services that run on them. This partly explains my desire to mitigate failure.
 
I agree with onebadhawk regarding redundancy- for a couple of my rockets I chose to install dual altimeters. Past that, I don't understand a tenth of what you guys are discussing here- I clearly need to read "Electronics for Dummies".

Mike Momenee
TRA #12430 L3
 
mpitfield,
In terms of the MJG Firewire Initiators that are non-regulated by the ATF, there is no concern from my perspective about their reliability. I believe the earlier comment about 'the jury was still out' comes from a less than ideal start at this products launch. As I understand from communication I had with MJG, there was a production problem identified with some (possibly all) of the first few batches. I purchased these early on and recieved one of those 'bad batches'. Fortunately, I did not employ them in flight and found poor reliability during ground testing. About the time I contacted MJG there were several others who were experiencing the same thing. MJG shared the information about the production problem and replaced my entire order (and I believe they did the same for anyone else who contacted them with this problem). My numbers are still pretty small (just under 40), but so far I have had zero failures in flight and ground testing with the replacements. More convincing than my limited experience is the multiple threads/posts I have seen confirming their reliability since the initial problem.
 
I've been using the Firewire initiators for the last two seasons and I haven't had any failures.
 
The Rds of this device is 62mOhms with a 3.3Vgs @ 25C. The additional junction resistance vs. the published 4.5Vgs @ 25C is 27mOhm. At a typical 1A all-fire current this nets an additional power dissipation of 0.027W, and factoring in a worst case Rtheta, a resultant 2.43C temp increase (with typical Rtheta, only 1.75C). Even at 3x the all-fire current, junction temp increase would be 15.7C typically and worst case 21.8C, which is well within the 150C thermal incineration temperature of the FET. Based on the thousands of RRC2+ and RRC3 altimeters in service and the 10's of thousands of flights made by the collective using all different battery types, I'd say the choice is quite satisfactory. I use these FETs in other products I manufacture thereby leveraging higher economies of scale. I consider the trades a net win.

You may consider those trades a win but it still means that the device cannot meet the specifications you claim. Namely the ability to output 5A for 1 second. Unless you mean that it will do it only once.

I have concerns about the 90C/W figure used because the data sheet does not fully specify the test conditions. Just how much copper is on the 1 sq. in. circuit board and how is it connected to the device? I suspect that most of it is copper and it is connected to the drain. If so, the correct figure for the RRC2 is going to be worse.

As temperature increases so does Rds(on). The data sheet shows that it increases by a factor of 1.6 between 25C and 150C.

Assume an ambient temperature of 40C, a not unreasonably hot day, and work backwards to the maximum current:

(150C - 40C)/90C/W = 1.22W
sqrt(1.22W/(.062*1.6)) = 3.5A

So with the generous 90C/W value, 5A results in the maximum junction temperature being exceeded.
 
Jim Amos got back to me today regarding this RRC2+ unit. Unfortunately my error scorched it too badly to make replacing the FETs a possibility. It tested OK in his vacuum chamber, and I will be able to use it as a simple ride along altimeter. Along with not charging me for evaluating and testing this unit, he made me an offer for a new RRC2+ at a discounted price. I took him up on his offer and he also did not charge me for shipping both units back to me. Can't say enough good about his customer service on this. Clearly I didn't expect any of this based on the whole event being a result of my error/ignorance.
 
Jim Amos got back to me today regarding this RRC2+ unit. Unfortunately my error scorched it too badly to make replacing the FETs a possibility. It tested OK in his vacuum chamber, and I will be able to use it as a simple ride along altimeter. Along with not charging me for evaluating and testing this unit, he made me an offer for a new RRC2+ at a discounted price. I took him up on his offer and he also did not charge me for shipping both units back to me. Can't say enough good about his customer service on this. Clearly I didn't expect any of this based on the whole event being a result of my error/ignorance.

Kendal,,

That's is what you call-- "I truly care customer service"......

Teddy
 
Jim Amos got back to me today regarding this RRC2+ unit. Unfortunately my error scorched it too badly to make replacing the FETs a possibility. It tested OK in his vacuum chamber, and I will be able to use it as a simple ride along altimeter. Along with not charging me for evaluating and testing this unit, he made me an offer for a new RRC2+ at a discounted price. I took him up on his offer and he also did not charge me for shipping both units back to me. Can't say enough good about his customer service on this. Clearly I didn't expect any of this based on the whole event being a result of my error/ignorance.

I have similar experiences with Jim Amos, and he gets my business every time! Pleasure to deal with.
 
Jim Amos got back to me today regarding this RRC2+ unit. Unfortunately my error scorched it too badly to make replacing the FETs a possibility. It tested OK in his vacuum chamber, and I will be able to use it as a simple ride along altimeter. Along with not charging me for evaluating and testing this unit, he made me an offer for a new RRC2+ at a discounted price. I took him up on his offer and he also did not charge me for shipping both units back to me. Can't say enough good about his customer service on this. Clearly I didn't expect any of this based on the whole event being a result of my error/ignorance.

That's nice. I had a similar experience with a product from another vendor and was offered a discounted price for a replacement. My case was my own stupidhead fault too. Kurt
 
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