Ejection Canisters

iter said:

I use 10uF, 35V caps. The trick is reverse polarity. 12 volts the wrong way and they explode every time.

I encourage you to experiment with just the cap first, without any powder. One word of warning: you may want to do the experiment outside. The burn produces a nasty smell that can linger in your workshop for hours.

Also, in my experience, axial caps are immune to explosion. There may be something about their construction that contains the heat more evenly. Radial caps like the one in my picture explode reliably for me (haven't had a failure yet).

Ari.

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So, are these tantalum capacitors a type of electrolytic capacitor? I had the understanding that any electrolytic capacitor would explode if reverse biased, axial or not.

That is correct. iter , Who do you buy yours from?

GaryT said:

For use in "Rocketry" 4F BP is superior to pyrodex, Burns quicker, Provides much more energy and requires much less attention to containment, Dirtier yes but when I have 2000.00 dollars invested into a rocket I'm not about to use anything but 4F BP.

Now I'm NOT saying pyrodex dosen't work as well all know people do use it succesfully but not me.

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Fair enough, I'm using pyrodex for the moment, (I went to Fleet Farm and asked for black powder, I was given a container of FFg pyrodex). I have succsessfully made it go bang. In my pipe nipple canister, containment seems easy enough, you just stuff it with dog barf and cover the end with tape before threading it into the bulkhead.
Do you know how BP compares to pyrodex in terms of weight? Also, I have read that BP will have trouble burning at higher altitudes, I assume pyrodex would have similar problems. Do you know at what altitude pyrodex would have difficulty burning?

stealth6 said:

One of them - Graf & Sons - sells in quantities of 2 pounds. They also seem to be "good folk" and they offer a lot of choices. So, I purchased from them and have been so far entirely happy with my purchase. Yes, it was pretty expensive in the short term.

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That's $65.43 by the time you add the HAZMAT fee, but before you factor in shipping. By then you're probably pushing $100!

Ari.

graf - $114 for 5 lbs

Powder inc - $115 for 5 lbs

Pretty close.

cwbullet said:

iter , Who do you buy yours from?

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I buy my capacitors from a local surplus house, https://www.halted.com/

RadManCF said:

Fair enough, I'm using pyrodex for the moment, (I went to Fleet Farm and asked for black powder, I was given a container of FFg pyrodex).

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This is my experience too :=)

Ari.

cwbullet said:

I have seen people use plastic wrap, but that make me worry of static charge. Is that me overthinking or is it a possible problem?

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I've been using plastic wrap for about 4 years now. No static problems
even during Florida dry winters.

Here's how to make the plastic wrap charge holders - https://www.info-central.org/?article=302
(scroll down near the bottom).

brianc said:

I've been using plastic wrap for about 4 years now. No static problems
even during Florida dry winters.

Here's how to make the plastic wrap charge holders - https://www.info-central.org/?article=302
(scroll down near the bottom).

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Thanks. I will try it out.

iter said:

This is my experience too :=)

Ari.

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I was actually surprised at how easily the FFg pyrodex ignited. I've done two tests thus far, both using Q2G2s for ignition. The first charge ignited more slowly, but the second charge, which was more tightly packed, ignited immediately. Just remember to use a non sparking implement for packing the charge.

RadManCF said:

I was actually surprised at how easily the FFg pyrodex ignited. I've done two tests thus far, both using Q2G2s for ignition. The first charge ignited more slowly, but the second charge, which was more tightly packed, ignited immediately. Just remember to use a non sparking implement for packing the charge.

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You are correct. The key is tightly packing it. Flexible containers lead to failure.

iter said:

I buy my capacitors from a local surplus house, https://www.halted.com/

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They don't have any tantalum caps listed currently. I looked at Digi-Key and caps with the given specs were about the same price as e-matches or Q2G2 igniters.

I found a couple sites cheaper. I will try them out off education purposes.

They are probably too cheap for Halted to ship out profitably. I think they sell them for $.30 or so in quantities of 1. You might call Halted and ask if they'd ship you some.

The spec aren't terribly important. The lower the voltage rating, the less voltage it takes to burn them.

Ari.

so how many volts and mF are the maximum?

Any of you guys want to experiment with capacitors, send me a SASE and I'll throw some caps in it for you.

I don't know the limit values. I know the kind that work for me. My understanding of the theory is that the actual capacitance has very little effect on their explosiveness.

Ari.

Try the search feature on their site. I just purchased a variety for testing. They ship in quantities of (10), which makes them between $.18 and $.42 each, depending on spec, before shipping.

Rocketjunkie said:

They don't have any tantalum caps listed currently. I looked at Digi-Key and caps with the given specs were about the same price as e-matches or Q2G2 igniters.

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I could not find any capacitors.

iter said:

Any of you guys want to experiment with capacitors, send me a SASE and I'll throw some caps in it for you.

I don't know the limit values. I know the kind that work for me. My understanding of the theory is that the actual capacitance has very little effect on their explosiveness.

Ari.

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Sounds right to me, the way I understand it, an electrolytic capacitor, in addition to having separated charged surfaces, uses chemical tricks to increase the capacitance. If I remeber right, the electric field produced causes the polar molecules in the electrolyte to all align themselves with the field, and that this raises the capacitance. I would also guess that the electrolyte is somewhat standardized between capacitors, and that different capacitances are produced by varying the distance between surfaces. I don't have a guess as to why the thing blows if the molecules make a simultaneous about face. Maybe Adrian A. would know for sure...

iter said:

Any of you guys want to experiment with capacitors, send me a SASE and I'll throw some caps in it for you.

I don't know the limit values. I know the kind that work for me. My understanding of the theory is that the actual capacitance has very little effect on their explosiveness.

Ari.

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I am game.

From wiki...
Tantalum capacitors are, under some conditions, prone to self-destruction by thermal runaway. The tantalum oxide layer may have weak spots that undergo dielectric breakdown during a voltage spike. The tantalum anode then comes to direct contact with the manganese dioxide cathode, and the leakage current causes localized heating; a chemical reaction then produces manganese(III) oxide and regenerates (self-heals) the tantalum oxide layer.
However, if the energy dissipated at the failure point is high enough, a new self-sustaining exothermic reaction may initiate, similar to the thermite reaction, with tantalum as fuel and manganese dioxide as oxidizer. This can destroy the capacitor, and occasionally produces smoke and possibly flame.[1] To prevent catastrophic thermal runaway failure, auxiliary protective devices (e.g. thermal fuses, circuit breakers, or current limiters) may be used to limit fault currents.

Worsaer said:

Try the search feature on their site. I just purchased a variety for testing. They ship in quantities of (10), which makes them between $.18 and $.42 each, depending on spec, before shipping.

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Search came up empty.

Rocketjunkie said:

Search came up empty.

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Same here. I have tried all categories.

Are you using these for ejection charges? I saw a post about reversing polarity and using 12 volts. How do you reverse polarity?

I went by the local HSC and got some 10uF 35V caps. $.55 each. I also picked up some cheaper ones 6 cents each..not sure what their rating/specs are though.

I'll play with them tonight.

Tony

"Reverse polarity" means finding the terminal on the capacitor that has a + and plugging it into the - on your battery and vice versa.

Ari.

tfish said:

Are you using these for ejection charges? I saw a post about reversing polarity and using 12 volts. How do you reverse polarity?

I went by the local HSC and got some 10uF 35V caps. $.55 each. I also picked up some cheaper ones 6 cents each..not sure what their rating/specs are though.

I'll play with them tonight.

Tony

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If you look at your capacitors, they are marked with a + and a - to identify polarity. Co if you take 12 volts, from a battery or power supply, with one side + and one side -, identified on the battery for polarity, then to reverse this polarity, you attach the +(positive) of the capacitor to the - (negative) pole of the battery and the - (negative) of the capacitor to the + positive of your battery or power supply. It is very very simple. If you have a light emitting diode, they will have polarity marked on them and they will only work in one direction. Same principle on polarity. If you hook up 9V batteries, you can plug two or more together, in what is called series, + to -, and - to + on down line, and build batteries that will give you 18v or with three, 27V; with 4, 36V;and so on. In the same manner, if you have a cordless 18V drill, it is 12 - 1 1/2V batteries attached in series that gives you 18V, and they do this a number of times but in parallel, (+ to +, - to -) to give the battery endurance and you have a cordless drill battery.

I copy all that..So, to use these in an ejection charge. I'll need to make sure I reverse the polarity when I hook them up to my flight computer?...as where with an ematch it does not matter.. Will a flight computer using a single 9 volt battery still work..or do they need 12v?

Tony

Ground test and see. Do it a number of times to check for consistency. A lot of it depends on the capacitors that you test with. What are there values? You know, if you put enough juice/power into it, all kinds of things can happen. I made a 3 ohm 1 watt resistor blow up and burn real good when I took 4 - 9V batteries and hooked them up in series to get 36V. I was using them in a form of electrolysis to make colloidal silver water using a generator. I should have had about a 5W resistor for the amps I was running through it and that resistor blew up in a ball of fire. So in theory, if you have enough Volts and Amps, you can make just about anything blow up. I ended up taking 5 of those resistors in parallel to make my generator work and not overheat.

BEAR said:

Ground test and see. Do it a number of times to check for consistency.

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I do not think you find many disagreements here.

tfish said:

I'll need to make sure I reverse the polarity when I hook them up to my flight computer?...as where with an ematch it does not matter..

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Tony, you need to figure out which terminal in your flight computer is + and which is -. As you're saying, with an e-match, you can plug it either way and it works, like a light bulb. Tantalum capacitors are like LEDs, the only work one way, so you need to make sure where the positive and the negative terminals are.

Ari.