[NRVR-Members] Rocket PSA: Problems with 110/220 Rotary Switches & LiPo Probs with "Protection PCBs"

Thomas Tweeks Weeks tweeks-junk2 at theweeks.org
Mon Mar 13 20:57:57 CDT 2017

On Monday, March 13, 2017 8:45pm, "Bob Schoner" <bob.schoner at gmail.com> said:
> Wow hadn't heard either of
> those before. Thanks for passing that on. I know
> it isn't elegant but I still am a fan of the simple "twist and tuck"
> method. I prefer to leave the wires sticking out and tape them to the
> outside of the body tube.

Twist and tuck altimeter arming sounds about is simple as it gets Bob (and sounding more and more appealing ;). I'll have to keep that in mind as I finalize my avionics bay. :) Although for this L3, I would have three things to twist and tuck (two altimeters and one dedicated pyro supply).. it would be a shame if it turned in to twist, tuck and touch. <zzzzzap!>  ;)

> I guess unless you buy some military or aerospace grade of switches there
> is probably a chance of failure. 

Might be able to ping Dr. Shinpaugh (or other friends I have in the cubesat industry) on sourcing some high-G switches.

> I have several rockets with those
> switches. I would suspect they are more like Kelly to fail after a hard
> landing or some other traumatic event. Not really sure if I will replace
> them or take my chances

Well.. the root cause of those switch failures hasn't been stated AFAIK. It could be user error (inexperienced folks not rotating them far enough), or some cheap Chinese source that's recently released inferior switches that fail in high G scenarios. Who knows. Like the 9V battery failure experiment I've told you I want to try,  this could represent another cool arduino data gathering experiment for capturing switch contact data watching for high-G contact bounces or faults. Now that I have a bay that's big enough to carry such payloads.. I can finally start getting some useful data out of some of my flights. :)

(which is part of why I got into arduinos in the first place)


> Thanks
> Bob
> On Mon, Mar 13, 2017 at 7:43 PM Thomas Tweeks Weeks <tom at theweeks.org>
> wrote:
>> Hey all.. esp you L3 guys.
>> So I'm designing my ebay for my L3, and I just got the brand new
>> PerfectFlight StrataLoggerCF in the mail (the new one with the speaker/LED
>> connector).. and there's a little warning handout about common critical
>> failure modes they're seeing back from their customers.
>> Failing 110/220 Power Switches:
>> There is new StrataLoggerCF power check feature & very surprising warning
>> about using 110/220 AC style switches of this type:
>> https://www.apogeerockets.com/Electronics-Payloads/Electronics-Accessories/Electronics-Rotary-Switch
>> I know these are very popular arming switch styles and have been for at
>> least a 15-20 years or so (I have a couple in my own parts bin), but check
>> out what this leaflet from Perfect Flight is saying about them now:
>> "We have had numerous reports of failures of the 110/220 rotary switch
>> that is sometimes used [...] in rocketry applications. The failures
>> typically in one of two ways, either as:
>> *  a switch that turns off when tapped or wiggled, or
>> * a switch that exhibits a high resistance (several hundred ohms) when
>> turned on
>> [Our new WiringCheck] feature [... which performs a pre-flight
>> load/no-load comparative battery test] is intended to reveal the latter
>> type of problem, but we still do not recommend the use of this type of
>> switch in rocketry applications. [...]"
>> So in short.. I don't know if this is a NEW issue (e.g. from cheap Chinese
>> supply of rotary switches), or an old time gremlin that is just now being
>> revealed. Either way, since this info was nowhere on the PerfectFlight
>> website or on line documentation (it was thrown in as a warning card in my
>> latest purchase), I hope after this is archived in our mail list that it
>> will serve as a warning to others. (someone might want to re-post it to
>> RocketryForum.com, et al).
>> Warning About Some LiPos:
>> This little info card is useful, and also contains a warning about using
>> LiPo cells with over-current protection circuitry shink-wrapped into them,
>> as the short condition of some ematches will shut down such batteries..
>> causing another type of critical power failure to a critical recovery
>> component of your rockets.
>> Just wanted to share.
>> Tweeks
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