High-current battery recommendations

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jderimig

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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
This comment and my opinions applies mainly if you are using the battery to also power your electronics.
  • If your battery protection circuit activates it will result in a brown-out or reset of your flight computer.
  • You should not prioritize the protection of your battery over the protection of your rocket.
  • A well implemented overload protection circuit should only be used if your electronics actively controls the current to the load. Thus the overload protection will kick in only if a failure of your primary method of current control occurs. Your electronics and power supply is a system.
  • Most altimeters do not control the current to the load. The instantaneous load current is unknowable.
  • The battery protection circuit introduces an addition point of failure in your power chain. (I have recently bought a new 18650 battery pack with a defective protection circuit.)
  • Rocket ignition conduction time is usually very short, often less than 1s latch time. Most Lipo batteries can safely deliver current well in excess of the protection circuit rating for such a short time. The protection circuit is not needed and can only do harm.
The above opinions are wholly my own and do not represent the position of TRF.
 

teepot

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How do you know which batteries have current protection? I looked at LiPos on Amazon and couldn't tell if they had it or not.
 

jderimig

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How do you know which batteries have current protection? I looked at LiPos on Amazon and couldn't tell if they had it or not.
No high c rc batteries that I know of have protection circuits.

Most all 18650 Li-ion battery packs have them.

Most low discharge , 2-3c rated lipos likely have them, you can usually see the protection pcb on the battery
 

AlexBruccoleri

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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.
Hi Brian, Do you have any specific recommendations for NiCads? Thanks, Alex
 

manixFan

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I think we've way over thought this and maybe just a simple current limiting resistor inline with the ignitor is the way to go. I think the main concern is saving the flight electronics, not the battery. I already use resistors with some of the Perfectflite altimeters, so using it with an ignitor should be no different.

And really, dipped e-matches are probably the best way to go anyway, basically using the altimeter the way it was intended.


Tony
 
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