Blue Raven blew BP charges instantly when switched on

[Fireflash]

Was carrying out ground deployment tests for a rocket that my Uni team are planning on launching soon. This rocket has BP charges on both bulkheads of the Avi bay (Apogee charge on lower bulkhead, Main charge on upper bulkhead). We had the Avi Bay fully wired up with BP charges prepped and went to turn the board on to check continuity. All was good but we didn't have continuity on the main channel so we turned the board off to investigate, the e-match was loose so we fixed it and went to turn the board back on again with the screw switch. When we turned the board on again a second time both BP charges went off instantly. Luckily nobody was hurt but it definitely shock us up.

We checked over all the wiring afterwards and everything was as should be, we then decided to try turn on the board again this time with just e-matches in, it's behavior was all normal until we tried to fire the channels remotely, sometimes they would fire, sometimes they wouldn't , overall just strange behavior. We tried this again a couple hours later and everything was suddenly fine.

We've used this Raven before and had no problems, it was recently on a flight that had a hard landing (main parachute didn't fully deploy so came down under drogue only), unsure if this could have damaged it in some way. I checked over the board and all the components and solder joints look fine.

This ground test was a simple setup that we have used many times before, Raven was connected to a terminal expansion board, both charges were wired through the bulkheads to terminal blocks where the e-match was connected into the other side and then placed into our aluminium BP charge cups. We were using a 3s 550 mAh Lipo and the only other thing mounted to the bay at the time was a Telemetrum connected to a 1s. The raven had the latest firmware uploaded.

Interested to hear if anyone else has experienced a similar thing? Attached below is a picture of the bay (minus the body tube and upper bulkhead) just after it blew both charges encase someone can pick up on something.

 

[MarsLander]

I would contact featherweight and work through the issue with them directly.

@Adrian A

 

[Adrian A]

Sorry to hear you had a problem Charges blowing unexpectedly is never fun, but I'm glad you were in a safe configuration. It's important for me to understand what happened so that we can prevent this happening to anyone else.

The hard landing in a prior flight, and using a 3S battery (which should work, but 1S is recommended) are unusual aspects that might have been a factor. Would it be possible for me to get the av-bay in the configuration where the charges fired, so I can do a detailed investigation to see if I can reproduce the problem and find root cause?

 

[manixFan]

One of the changes that has been made to the Spaceport America Cup this year is that LiPos other than those recommended by the manufacturer are no longer allowed. So at least for the SAC, a 3S LiPo would not be allowed. I think in general it’s always important to follow the manufacturer’s battery recommendations.

But with all that said, even with a 3S, blowing the charges on startup is clearly a serious issue. I’ve had my share of hard landings, so if it is related to that, it would be nice to have a way to verify an altimeter’s integrity after such an event.

Kudos to the team for operating in a safe manner during testing. It’s all too easy to get complacent after a few tests.

Looking forward to hearing the findings.


Tony

 

[FredA]

One of the changes that has been made to the Spaceport America Cup this year is that LiPos other than those recommended by the manufacturer are no longer allowed.

Wow - finally somebody realizes that battery selection is not something done randomly or with the bigger-is-better attitude. Kudos to them.

 

[cerving]

Consulting with the altimeter vendor before buying a battery is always a good move.

 

[Titan II]

Just following the manual is appropriate (highlight added)....

 1S (3.7V) lipo are recommended. 9V batteries are o.k. A new feature of the Blue Raven is that ifthe output current goes over 4 Amps, the Blue Raven will now reduce the average current to 4Amps, so large capacity lipos are now o.k.

 

[manixFan]

Just following the manual is appropriate (highlight added)....

 1S (3.7V) lipo are recommended. 9V batteries are o.k. A new feature of the Blue Raven is that ifthe output current goes over 4 Amps, the Blue Raven will now reduce the average current to 4Amps, so large capacity lipos are now o.k.

Actually, the D.E.T.G. (the official rules for the SAC) is quite specific: “Lithium-Polymer (LiPo) batteries are not permitted due to fire hazard unless installed in the powered device by the manufacturer or recommended and supplied by the manufacturer.”

The only battery that Featherweight sells for the Blue Raven is a 1S battery, so that is the only one that would be allowed. The competition is in some respects more restrictive than either TRA or NAR. Other vendors have specifically added recommendations for batteries to make it easier for teams to figure out what is acceptable.

Student designed electronics can not use LiPos at all – they have to use a power source with a lower fire risk. This rule is based on past experience at the event.


Tony

 

[cerving]

Probably a front closure blowby that caught the AV bay on fire... yeah, I can see that happening at SAC. Not sure how a manufacturer-supplied LiPo would mitigate that vs. one that the team bought themselves...

 

[manixFan]

Probably a front closure blowby that caught the AV bay on fire... yeah, I can see that happening at SAC. Not sure how a manufacturer-supplied LiPo would mitigate that vs. one that the team bought themselves...

The rules mostly apply to SRAD (Student Research and Development) electronics and payloads. Teams routinely used 2000mAh LiPos, often times several, in AV bays and payload projects. None of the recommended altimeter batteries are anywhere close to that. Some GPS units do recommend somewhat large batteries, but again, nowhere near what teams typically used. The tiny 150mAh battery supplied by Featherweight are a much smaller fire risk than a 20x larger battery than needed ‘just because’ teams don’t want to think about it.

As a point of reference, most LiPos have been excluded from European competitions for several years and those teams were surprised we still allowed them here. There are plenty of other battery types that are safer and work well. LiPos can catch fire due to a puncture from a hard landing or ballistic recovery, which is not uncommon.

And of course a LiPo battery of the same rating and form factor is really the same whether it’s bought from an altimeter maker or a third party. The main point is the manufacturer tends to be very reasonable with recommended batteries vs what teams choose on their own. So the rule is designed to force teams to rationalize their choices and be sensible rather than just throw a huge LiPo battery in the AV bay and call it a day.


Tony

 

[bschultz32]

Someone in the thread above made a negative comment about "the bigger-is-better attitude".
My first L3 attempt at BALLS 2022 failed because my Raven3's sat on the launch pad, energized and drawing power, for two and a half hours before launch. They were powered by small 150 mAh LiPo batteries purchased from Featherweight, and just didn't have enough capacity to get 'er done after beeping & flashing for over two hours in 90+ heat out there. Once burned twice shy: I worked out a plan with Adrian Adamson to use much larger 3500 mAh Li-ion 18650 batteries on my second attempt. Worked great! All four ejection charges blew. (Admittedly, on this second attempt, the on-pad wait time was only about 20 minutes.)
My point is that harsh experience has taught me to go large on batteries. I'll gladly sacrifice a few feet of altitude in exchange for not slamming the playa with my expensive rocket.

 

[Mason T]

Someone in the thread above made a negative comment about "the bigger-is-better attitude".
My first L3 attempt at BALLS 2022 failed because my Raven3's sat on the launch pad, energized and drawing power, for two and a half hours before launch. They were powered by small 150 mAh LiPo batteries purchased from Featherweight, and just didn't have enough capacity to get 'er done after beeping & flashing for over two hours in 90+ heat out there. Once burned twice shy: I worked out a plan with Adrian Adamson to use much larger 3500 mAh Li-ion 18650 batteries on my second attempt. Worked great! All four ejection charges blew. (Admittedly, on this second attempt, the on-pad wait time was only about 20 minutes.)
My point is that harsh experience has taught me to go large on batteries. I'll gladly sacrifice a few feet of altitude in exchange for not slamming the playa with my expensive rocket.
View attachment 634438

Your point is absolutely valid and the the flight computers should be designed in a way where the internal resistance of the battery is not a critical parameter to prevent destroying the flight computer. There are certainly times where it is needed if it's going to be sitting on the pad for an amount of time. The problem is that a lot of what is out there is just a MOSFET from the battery to the igniter. There is nothing to current limit other than the internal resistance of the battery. This is dangerous because you can test it with a larger battery and will look good until you end up in a case where the igniter gets shorted or doesn't open right away and then it can burn up traces on the PCB or damage the MOSFET. This is why so many vendors recommend low mAh or 9V batteries.

The Eggtimer has current limited outputs so its not a problem.
The Blue Raven has added current limiting in a software update so make sure you are up to date.

These are the ones that I know have current limiting. If you know of others that do I would love to know about them.

 

[kavy8]

Actually, the D.E.T.G. (the official rules for the SAC) is quite specific: “Lithium-Polymer (LiPo) batteries are not permitted due to fire hazard unless installed in the powered device by the manufacturer or recommended and supplied by the manufacturer.”

The only battery that Featherweight sells for the Blue Raven is a 1S battery, so that is the only one that would be allowed. The competition is in some respects more restrictive than either TRA or NAR. Other vendors have specifically added recommendations for batteries to make it easier for teams to figure out what is acceptable.

Student designed electronics can not use LiPos at all – they have to use a power source with a lower fire risk. This rule is based on past experience at the event.


Tony

Was this rule related to the fire at 2022 SAC?

 

[bschultz32]

The BALLS story I told above has a lot of twists and turns that I left out for the sake of brevity. One of them is that the plan I worked out with Adrian includes using an inline resistor to prevent the 18650 from charbroiling the Raven3. That worked.
As Mason T correctly pointed out, the Blue Raven has current limiting and does not require a resistor. I own one Blue Raven already, and will have a second in time to fly at BALLS in September, no resistors needed!

 

[g.pitts]

Your point is absolutely valid and the the flight computers should be designed in a way where the internal resistance of the battery is not a critical parameter to prevent destroying the flight computer.

The altimeter designer does not own the electronics bay design, so I would state that the electronics bay should be designed in a manner to comprehend the limitations of the selected altimeter(s) (or any other component for that matter). The electronics bay is the system that the rocket builder can control, and the builder should understand any limitations of the subsystems being integrated into their work and mitigate them appropriately. Putting a 1.6 Ω 3 Watt pulse-rated resistor (or adjust the resistance value based on your own analysis) in series with one lead of each pair going to a BP initiator is a reasonable means of limiting the current provided by and/or seen by the altimeter.

 

[Mason T]

The altimeter designer does not own the electronics bay design, so I would state that the electronics bay should be designed in a manner to comprehend the limitations of the selected altimeter(s) (or any other component for that matter). The electronics bay is the system that the rocket builder can control, and the builder should understand any limitations of the subsystems being integrated into their work and mitigate them appropriately. Putting a 1.6 Ω 3 Watt pulse-rated resistor (or adjust the resistance value based on your own analysis) in series with one lead of each pair going to a BP initiator is a reasonable means of limiting the current provided by and/or seen by the altimeter.

Outside of the voltage of the battery the electronics bay design should be basically irrelevant to the flight computer. It is on the flight computer designer to ensure that it can not self destruct with a shorted output. Taking into account system protections is one of the differences between a hobbyist project and an engineered product. Adding the resistor is a work around and should not be needed. It adds complexity and more points of failure. They could incorporate the resistor into the flight computer and it would make for a much better solution. Is it elegant, no. There are better ways to go about it but at least it would be protected. The different vendors need to update to be compatible with modern batteries is my point.

 

[cerving]

A dead-short across the outputs is a failure mode that the altimeter designer should anticipate. Kudos to Adrian for mitigating this issue with his Blue Raven.

 

[jderimig]

These are the ones that I know have current limiting. If you know of others that do I would love to know about them.

Marsa's have had PWM controlled current limiting since 2009.

 

[BMcD]

OP - I am sorry I cannot help you with your problem.

Everyone else - thank you for your insight. There are at least a half dozen points in this thread so far I had not considered.

 

[g.pitts]

Outside of the voltage of the battery the electronics bay design should be basically irrelevant to the flight computer. It is on the flight computer designer to ensure that it can not self destruct with a shorted output. Taking into account system protections is one of the differences between a hobbyist project and an engineered product. Adding the resistor is a work around and should not be needed. It adds complexity and more points of failure. They could incorporate the resistor into the flight computer and it would make for a much better solution. Is it elegant, no. There are better ways to go about it but at least it would be protected. The different vendors need to update to be compatible with modern batteries is my point.

OP is happy, so you and I will have to agree to disagree. Overcurrent protection can be done either by Adrian's implementation (I'm not certain other altimeters have the horsepower or engineering selection in place to do it) or by placing a (large) resistor the small board of an altimeter (which there's no room for). IMO a large resistor is better suited in the larger environment provided in the electronics bay. And it isn't a "workaround" - it's good engineering practice (what happens if the e-match shorts?). Every component we work with has limitations, or better stated, specifications that we need to accommodate.

 

[tfish]

could it be an issue with the simple circuit?

Tony

 

[FredA]

98% of rocketeers have no idea why they would consider adding a resistor - electronics are magic.

Given that, altimeter designers MUST design to the market of basically clueless customers.

Those without output protection should be shunned as that feature is mature and should have universal adoption.

 

[bschultz32]

Include me in the 98% clueless crowd. I figured the solution to my pad wait problem was simply a bigger battery with more capacity. I didn't reach out to Adrian Adamson because I am an electronics genius (I'm certainly not) - I reached out to hm because I was about to do something that deviated from the recommendations in the Users Manual, and it seemed prudent to run it by the manufacturer first. Boy, am I glad I did. The moral of the story is: check with the manufacturer first before you get creative and do something obviously different from what the manufacturer intended.

 

[jderimig]

For those who want to put in line resistors ( 2 additional potential points of failure in your system ) to your matches please try not to wing it or get recommendations from people on the internet. Contact the manufacturer of the device you are using an get their recommendation for a suitable current limiting resistor (digikey or mouser part number) for their design.

 

[Tractionengines]

The capacity is separate from the voltage. The recommended type is a 1S battery (4.2V full charge), with 9V acceptable... they are using a 3S that has a full charge voltage of 12.6.

Replacing 1S 300mAh with 1S 3000mAh has the same voltage just a MUCH LONGER run time. Replacing it with a 3S 300mAh battery applies much more "stress" to the electronics from the higher voltage. While not adding any longer run time.

 

[manixFan]

The capacity is separate from the voltage. The recommended type is a 1S battery (4.2V full charge), with 9V acceptable... they are using a 3S that has a full charge voltage of 12.6.

Replacing 1S 300mAh with 1S 3000mAh has the same voltage just a MUCH LONGER run time. Replacing it with a 3S 300mAh battery applies much more "stress" to the electronics from the higher voltage. While not adding any longer run time.

You are missing a crucial factor – larger mAh batteries can dump far more current than smaller ones. Adrian specifically chose the 150mAh battery because its ability to dump current is limited by its size. If you connect a 3000mAh battery, it's likely going to be rated at 40C or so, and it can fry anything that doesn't have current limiting, regardless that it's still only 4 volts or so.


Tony

 

[rfjustin]

Sorry to hear you had a problem Charges blowing unexpectedly is never fun, but I'm glad you were in a safe configuration. It's important for me to understand what happened so that we can prevent this happening to anyone else.

The hard landing in a prior flight, and using a 3S battery (which should work, but 1S is recommended) are unusual aspects that might have been a factor. Would it be possible for me to get the av-bay in the configuration where the charges fired, so I can do a detailed investigation to see if I can reproduce the problem and find root cause?

Has the OP taken you up on this offer? Requesting the av-bay as configured for root cause analysis is about the best customer support you can ask for!

 

[WFWalby]

could it be an issue with the simple circuit?

Tony

I wonder the same thing. Anyone have insight to this possible failure mode?
William

 

[Adrian A]

Has the OP taken you up on this offer? Requesting the av-bay as configured for root cause analysis is about the best customer support you can ask for!

I haven’t heard from them yet. In the meantime I’m working on my own test setup to investigate the susceptibility to a ground bounce transient or inrush current when the screw switch makes an intermittent connection some time after the altimeter was powered off. The simple circuit could add some capacitance but I doubt it’s the main issue. My intuition says that the high voltage and capacity of the battery, is more likely to be a factor.

 

[Fireflash]

Thanks for the help Adrian, we'll be in touch via email.

And thanks all for the comments, we use 3s Lipos when we're launching 2-stage rockets because we use Aerotech FirstFire ignitors that need 12v. I understand it makes a lot more sense to use different ignitors that need less voltage but that's tricky over here in the UK. Commercial vendors only stock these Aerotech ignitors and thinking about making your own ignitor is a big no no from RSO's.

We have recently been moving towards Cesaroni motors for our sustainers as they come with ignitors that can ignite with a 1s, but this limits us to certain motor configs so we are trying to find alternative solutions to our ignitor problems. Any tips/recommendations would be appreciated!

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