High-current battery recommendations

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AlexBruccoleri

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Hi, Does anyone have any recommendations for a high-current battery as the second battery for staging flight-computer? I am looking to ignite a standard igniter such as an Aerotech fire fire junior. Thanks, Alex
 

cautery

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One of the folks with REAL HPR experience will likely chime in here soon, but my research/experience says that LiPo chemistry will yield most energy for volume/weight. Look up the igniter specs and verify what voltage and current requirements are.

What motor are you thinking about lightin' up in-flite?

In my case, both my flight computers will run off 3.7vdc nominal LiPo batts, but also have the option for a separate pyro battery... Check your computer specs...

Apogee has this on their listing:

The First Fire Jr. Starters are Aerotech's 2-wire starter that are designed for easy insertion into most medium-size composite propellant motors. Works in most E-G composite motors motors. Requires a 12V launch controller to set them off. NOTE: Will not work with 18mm D-10/D-21, 24mm E6/E15/E30 nor F10 motors due to the narrow nozzle.
So, you need 12vdc per that text, and the current is not specified.... I'd DEFINITELY test for sure IF I were to use these (or any other lighter/match).

Might be better choices... Like I said, the "real" HPR guys will likely chime in soon.
 

AlexBruccoleri

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I am thinking of a 29 or 38 mm Aerotech. I have not decided which yet. I would prefer to light it with a regular igniter for safety reasons though happy to hear other views on that.
 

BEC

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A small two or three cell LiPoly will fire the igniter easily. Now whether your desired flight computer can handle one as an input power source is a question I can't answer as I'm not a real HPR guy either :).
 

heada

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A 2S 30C 1000mAh LiPo will fire pretty much anything BUT you'll be limited by the electronics. Lots have a 10A limit so check what your electronics can support. That said, get an ematch and pyrogen dip. All electronics can fire an ematch and modern pyrogens will start nearly all motors. If you're still worried, a pyrodex pellet or some blue APCP shavings can be used for 100% ignition.
 
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It depends on the electronics, but you can light a FirstFire igniter with less than 12V. I've done it before with a 7.4V 2S Lipo. They usually pull a few amps, so make sure your battery can handle it. IIRC, mine was rated to 450mah and 30C.

If not using a FirstFire, then I second heada's approach.
 

manixFan

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You will need to make absolutely sure you won't fry your altimeter/timer outputs with a high current battery. The current Featherweight altimeter product page says:
  • Four 25-Amp outputs compatible with batteries from a single Li-Poly cell to a 16V pack.
As far as I know, those are the highest rated outputs of any of the regular altimeters. Plus it has very sophisticated programming that you can apply to your staging output to help ensure it fires at the right time. Note that if you add a RockeTiltometer 3, it is limited to "Max 12.5 volts DC @ 12 amps for <2 seconds, non-inductive load". A 3 cell LiPo should work for the vast majority of ignitors, if the combo of C rating and amp hours gets you to what your ignitor needs.

For your usage, a 3S, 45C, 450mAh battery will output a max current of about 20 amps, (unless I messed up my math). So that would prevent you from overloading the outputs and should still fire most ignitors. From some testing I did several years ago, I recall the ignitors I was using needed about 8 amps to fire, but that was using a 4C pack.

The real take home message is you need to know your electronics, your ignitors, and your battery.

Good luck,


Tony

PS: The way C ratings work for LiPo batteries is you can take the rated mAh of the battery and 1C = output amperage. So a 1000mAh battery rated for 1C will output up to 1 amp of current. That same battery rated at 40C can output up to 40 amps of current. Some batteries have two numbers, one for sustained draw and one for surge current. LiPos with low C ratings will often have a small circuit board that limits the current to specified rating. The ability to dump huge current is one of the things that makes LiPos dangerous to work with if you have unprotected connections.
 

jderimig

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PS: The way C ratings work for LiPo batteries is you can take the rated mAh of the battery and 1C = output amperage. So a 1000mAh battery rated for 1C will output up to 1 amp of current. That same battery rated at 40C can output up to 40 amps of current. Some batteries have two numbers, one for sustained draw and one for surge current. LiPos with low C ratings will often have a small circuit board that limits the current to specified rating. The ability to dump huge current is one of the things that makes LiPos dangerous to work with if you have unprotected connections.
Tony, I am pretty sure the C rating is not how much current it will deliver but how much load current your load must not exceed. Individual batteries can deliver much higher currents into a dead short than their C rating, then they will burst into flames and or melt the insulation on their leads.
 

manixFan

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Tony, I am pretty sure the C rating is not how much current it will deliver but how much load current your load must not exceed. Individual batteries can deliver much higher currents into a dead short than their C rating, then they will burst into flames and or melt the insulation on their leads.
Whew, thanks for pointing that out! That is exactly what I should have said - the C rating is the highest rated load the cells can deliver in usage without damaging the battery. You of course are correct that in a dead short they will dump an insane amount of current. So while a 25C should not dump more than that, it can, unless it has a current limiting board. So thanks for the clarification - pretty important distinction between what I said and the actuality of the what the batteries can do.

So the real issue then become how much current does the ignitor draw when fired. I have a bunch of old First Fire ignitors I'll try and test, as well as several other types. IIRC the ones I tested that drew 8 amps were ones we made ourselves.

To protect the board, one would need to add a current limiting board into the pyro circuit. I suppose something like the below would work:



For a board like the Raven 4, 15 amps is well under the limit and should still fire most ignitors. Would be interesting if someone who has used something similar could chime in with their experience.


Tony
 
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jderimig

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Alex, measure the resistance of the First Fire Jr igniter. I suspect from searches on web that the resistance is is probably in the 3ohm range which should draw ~4A to fire. Any fully charged 3S lipo of reasonable size (~300mah) should do the trick. Most altimeters should have no problem conducting 4-5A.
 

jderimig

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Another issue you may have with an igniter is how long current needs to be flowing. For ground launch, the LCO will usually keep the button depressed until the igniter fires. Altimeters don't work that way, they are on for a limited amount of time, usually less than 1 sec. So you need to test with your altimeter to make sure they light in time. I would test several, not just one.
 
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Just make sure whichever battery you choose has a current limiting circuit that is above the "all fire" current for your igniter. Otherwise, the battery will current limit itself and may not start your igniter.
 

jderimig

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Just make sure whichever battery you choose has a current limiting circuit that is above the "all fire" current for your igniter. Otherwise, the battery will current limit itself and may not start your igniter.
The all fire current is NOT the maximum current the igniter will draw. Do not use any battery protection circuits in your deployment computer battery unless you are ok with occasional recovery failures.
 

AlexBruccoleri

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Hi All, Thank you for the input! I ordered a 1000 mAh 2S LiPo, 20C. It seemed like a good place to start from this thread and Additive Aerospace sells convenient holders for this battery too :)

Cheers, Alex
 

Jmhepworth

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I’m not sure why you’re trying to light the sustainer with a standard igniter. In my high power two stage rockets I’ve been 100% successful in lighting the sustainer with an ematch (at least when the ematch has fired). Using an ematch lets you use the battery that works for the altimeter. There are tested ways to get an ematch to light the sustainer. On the other hand, if you’re using an eggtimer product, like the Quantum or Proton, you can use a separate battery for the deployment side, including the 1000 MHz 2S LiPo you ordered. That battery would also work for the Proton or Quantum in a single battery configuration.
 
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Steve Shannon

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I am thinking of a 29 or 38 mm Aerotech. I have not decided which yet. I would prefer to light it with a regular igniter for safety reasons though happy to hear other views on that.
What are the safety reasons that prompt you to use a high current igniter rather than a low current electric match?
 

AlexBruccoleri

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What are the safety reasons that prompt you to use a high current igniter rather than a low current electric match?
One of my biggest concerns in hobby rocketry is having a low-current device inadvertently firing on the ground. While its rare, electric matches do go off accidentally and I strongly prefer to keep low-current devices away from motors when possible. My current plan is to have the high-current igniter battery separately armed with a robust screw-switch.

Cheers, Alex
 

BigMacDaddy

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I have not done anything in HPR or any remote ignitions or anything so forgive any ignorance but I figured I would comment just in case I have something of value to add.

I have found that there are some great high C-rated LiPo batteries for drones that are really light (I have used these in Nerf Blasters as well as hand-held rocket launch controllers). Do you need something as large as the 1000 mAh? I assume it is pretty heavy and the only benefit I can imagine over a higher C-rated but smaller battery would be that you do not need to charge it as often. For example, this 2s LiPo is a great battery and fits in the space of 2x AA batteries and will put out more current than a 20c 1000mAh battery: https://www.amazon.com/Tattu-650mAh-7-4V-Battery-Torrent/dp/B0727XZFDW

I was also struck by the discussion of the amp draw, altimeter rating, etc... Do folks in this hobby use Mosfets for ignition controls? These are another thing that is used in re-wiring Nerf blasters to avoid putting all the amps through the trigger switch. Mosfets act as a digital switch and allows the main current to flow from battery directly to your load (in this case your igniter but in Nerf blasters it is the flywheel motors).
 

StreuB1

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I have shot literally hundreds of electric matches over 20 years; from oxral and jtek to the cheapy-chinese ones. I have never in my life ever had one fire accidentally. They measure 1.1-1.4 ohms always (I check them before wiring and before firing) and they are always dead on. They take more current to fire than can be had from any type of leakage or even static. Bare in mind, an electric match still uses a hot wire (or burst-wire) for initiating the pyrogen/pyrotechnic material in the head. I have used them for solid motors, hybrids, liquid propellant, pyrotechnics and explosives and have never once had an issue.

That being said, (2) 9v batteries in parallel (or series) will fire an Aerotech ignitor no problems. Even one 9v will. Though, I would prefer parallel e-matches and single 9v battery for initiation. It is dead reliable. Never once have had a failure. I am absolutely not an advocate for firing any short circuit resistive device with LiPo chemistry. I know people do it, but I always prefer alkaline or nicad chemistry. Aerospace agrees with me. :)
 

StreuB1

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I would not use mosfets unless you have a properly designed circuit. Mosfets being a voltage controlled device can be triggered by static electricity where as a tranny actually takes current and can be a lot safer.
 

AlexBruccoleri

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I’d be very curious about the circumstances of an electric match firing accidentally. Can you share the details?
I do not know the exact circumstances of how to fire an electric match accidently. Back when I was more active in the hobby in the late 90s, there was caution related to static firing an electric match. I used to use flashbulbs instead for ejection. I suspect if one of the altimeter/flight computers is faulty or damaged it could easily fire an electric match from a capacitor in its circuit.

For what its worth, I have never had an electric match or any low-current device accidently go off. It is still something to be vigilant about.

Cheers, Alex
 

Charles_McG

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I've done tests with an Eggtimer Quantum (iirc) and various igniters and batteries. 2S, 350mAh, 20C and 45-90C.

The C rating did have an effect - the 45-90C was faster all the way across. The 20C wouldn't light an Estes Pro Series igniter - it got warm and smoldered, but didn't actually light.

The first fire mini was the most impressive. Very sparky.
 

manixFan

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I've done tests with an Eggtimer Quantum (iirc) and various igniters and batteries. 2S, 350mAh, 20C and 45-90C.

The C rating did have an effect - the 45-90C was faster all the way across. The 20C wouldn't light an Estes Pro Series igniter - it got warm and smoldered, but didn't actually light.

The first fire mini was the most impressive. Very sparky.
For a 350mAh battery, 20C is about 7amps, which is below the 8 amps that the igniters I tested required. I have not seen the FFminis so it would be interesting to see how they are made.

I am just starting to work on a two stage rocket, so this is useful information to me. One thing that I’ve learned from working with others who have flown staged rockets is to test, test, and then test again.

John’s comment about not using battery protection circuits is at odds with what I’ve seen others do, so more elaboration on that subject would be useful. As a circuit designer, that would certainly provide a lot more insight into the pitfalls an average user might not consider.


Tony
 

heada

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BigMacDaddy

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I would not use mosfets unless you have a properly designed circuit. Mosfets being a voltage controlled device can be triggered by static electricity where as a tranny actually takes current and can be a lot safer.
Interesting -- agree about using proper circuits. As I researched this I came across information about Mosfets being damaged by static discharges but not accidentally going off. The circuits I used for Nerf blasters in the past had resistors and diodes to protect against back-emf that could be created by the motors but I probably did not worry sufficiently about static electricity (accidental firing of my Nerf Blaster was not a big worry).

Good discussion about how to use a Mosfet as a switch here in case this is interesting to anyone:
www. reddit. com/r/Nerf/comments/6ufmm8/the_complete_nerf_blaster_mosfet_wiring_tutorial/

EDIT: Sorry, not sure why that was posting the whole thread instead of just the link... Tried to fix now (had to hack up link a bit but you can figure it out if you want to read it)...
 
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StreuB1

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I can trigger a mosfet my simply touching it if the gate pin is floating or not properly terminated. The thing is that they take nearly zero current, in the order of nanoamps, or even femtoamps depending. So if you have 10kV of static on your body but very low charge count, the gate of the mosfet can act as a sufficient load to drop the 10kV to just a few volts of suitable current to latch the mosfet if it is in circuit and the source and drain being terminated.

I would post a link to that subreddit post and not post the entire thread as it kills this thread due to its length.
 

BigMacDaddy

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I would post a link to that subreddit post and not post the entire thread as it kills this thread due to its length.
Sorry, I just tried to post the link but for some reason it defaulted to a full preview... I tried again but had to hack up the link a bit to avoid the preview being posted...
 

jderimig

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I can trigger a mosfet my simply touching it if the gate pin is floating or not properly terminated. The thing is that they take nearly zero current, in the order of nanoamps, or even femtoamps depending. So if you have 10kV of static on your body but very low charge count, the gate of the mosfet can act as a sufficient load to drop the 10kV to just a few volts of suitable current to latch the mosfet if it is in circuit and the source and drain being terminated.

I would post a link to that subreddit post and not post the entire thread as it kills this thread due to its length.
Standard best practice is to have a strong pull-down (or pull-up for a P-fet) and a series resistance on the gate drive.
 

StreuB1

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Tony, I am pretty sure the C rating is not how much current it will deliver but how much load current your load must not exceed. Individual batteries can deliver much higher currents into a dead short than their C rating, then they will burst into flames and or melt the insulation on their leads.
Exactly; and exactly why I am not an advocate of using LiPo chemistry for dead-short resistive element devices. LiPo's can deliver staggering amounts of current into a dead short. The one thing you are not supposed to do to LiPo chemistry, expose them to dead shorts. Repeatedly whacking them with dead shorts is a good way to possibly cause a runaway event or damage them enough to where they catch fire upon charging. Dead shorts cause microscopic hot spots in the battery laminations. Over time, these areas go low resistance and upon charging (taking current) the hot spot gets sufficiently hot over time to go thermonuclear.

Aerospace uses NiCads almost exclusively because they are arguably the most bullet proof chemistry that exists. Sometimes they use SLA's as well but we'll ignore that..... NiCads always work, they are hard to kill, work across a wide temperature range and vibration range, they can deliver large amounts of energy quickly, they're cheap, they're easy to charge, etc. Though, NiCads make less sense for HPR, but some use them. I have used them in several applications over the years; these are custom made small cell packs though.

Alkaline is available off the shelf, everywhere, 24/7, its foolproof, its cheap, its safe, etc. I buy Rayovac's and use them for two flights and then retire them. Cheap insurance.
 
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