Christmas tree bulbs for testing

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jhornsby3

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When testing your electronics, what kind of bulbs work? I wanted to make up some test bulbs but everything we have is LED. So, will LED bulbs work the same as incandescent for testing? Or will the resistance not be enough?
 
No, LED lights will not work the same. They are basically a diode, a near-zero resistance load in the forward direction, with some kind of much higher resistance to keep them from frying when you put current through them. Get the incandescent miniature Christmas light bulbs... you can get a string of like 100 of them for $6 on Amazon.
 
cerving said:
No, LED lights will not work the same. They are basically a diode, a near-zero resistance load in the forward direction, with some kind of much higher resistance to keep them from frying when you put current through them. Get the incandescent miniature Christmas light bulbs... you can get a string of like 100 of them for $6 on Amazon.
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I tried those, never worked for me, I think I was busting the thin wire when I broke the glass but it’s so thin I couldn’t tell for sure.
 
NTP2 said:
I tried those, never worked for me, I think I was busting the thin wire when I broke the glass but it’s so thin I couldn’t tell for sure.
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Why are you breaking the glass?
 
NTP2 said:
To get the BP in. How else could I?
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The thread is about "testing" the electronics. When testing, we just use the incandescent miniature Christmas light bulbs intact.

Why you would even use them on a rocket is another matter.
 
cerving said:
No, LED lights will not work the same. They are basically a diode, a near-zero resistance load in the forward direction, with some kind of much higher resistance to keep them from frying when you put current through them. Get the incandescent miniature Christmas light bulbs... you can get a string of like 100 of them for $6 on Amazon.
Click to expand...

Thanks Cris. That is what I thought. But better to ask and be sure before I start cutting the wife's decorations.


I remember the old Christmas tree light ejection charges. Always a pain in the butt to not break the wire.

My father being an old civilian contractor/ electrical engineer for the Navy, finds this "new" rockets electronics fascinating. He worked out of Port Hueneme, CA for Naval Ship Weapons Systems Engineering Station, back when it was started. He worked on the Tartar, Terrier, Harpoon and Tomahawk missiles and the launch systems back in the 70's through the early 90's. So having all kinds of components laying around is common in dad's house. But, he has nothing labeled and tells me to just figure it all out. It's a little overwhelming.
 
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rcktnut said:
I hear you, I thought Christmas tree light bulbs and flash bulbs have gone by the wayside long ago, even before NTP2 was born.
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I remember seeing instructions for DIY e-match alternatives using christmas tree lights 9 or 10 years ago. With Firewire Ignitors on the market, I wouldn't want to make my own for ejection charges or just lighting BP. Save the dipping and nichrome for things that need more energy to light and use something proven to be reliable for ejection charges.
 
rcktnut said:
I hear you, I thought Christmas tree light bulbs and flash bulbs have gone by the wayside long ago, even before NTP2 was born.
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They did (I did see a sign saying no flash photography once, I had to ask my dad what that was) I was doing it because I didn’t want to pay hasmat on Emachs and it was in the manual.
Not too toot my own horn but I think I ended up with better options than that in the end.
 
jhornsby3 said:
Thanks Cris. That is what I thought. But better to ask and be sure before I start cutting the wife's decorations.


I remember the old Christmas tree light ejection charges. Always a pain in the butt to not break the wire.

My father being an old civilian contractor/ electrical engineer for the Navy, finds this "new" rockets electronics fascinating. He worked out of Port Hueneme, CA for Naval Ship Weapons Systems Engineering Station, back when it was started. He worked on the Tartar, Terrier, Harpoon and Tomahawk missiles and the launch systems back in the 70's through the early 90's. So having all kinds of components laying around is common in dad's house. But, he has nothing labeled and tells me to just figure it all out. It's a little overwhelming.
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Yeah, that was in the days of flashbulbs too, before ematches came along. Best to move on and use a modern reliable method of lighting charges. The nice thing about the miniature Christmas tree bulbs is that they're about the same resistance as an ematch, so if the light bulb lights you can be assured that your charges are going to fire too.
 
If you don't want to do the Amazon thing for a new set... goodwill stores usually have some strings of incandescent holiday lights. (I think the last set I cut up is orange from Halloween.)
 
Tractionengines said:
If you don't want to do the Amazon thing for a new set... goodwill stores usually have some strings of incandescent holiday lights. (I think the last set I cut up is orange from Halloween.)
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Ours doesn't have them. That was my first stop.

I asked a friend at our local Lowes. He said that I might have to wait until garage sale season gets started. He was saying that retailers cant sell them due to the gooberment shut down on the incandescent bulbs.

A new journey in life.
 
LED's will work fine for testing if in series with a resistor appropriate for the voltage.

As long as we're talking about testing, what voltage and current are usual for continuity tests at rocket launches? I have made some igniters which drive my voltmeter nuts but still work. Was thinking of including a tiny wire.

Speaking of igniters, I coated one in RNX the other day. When tested, it produced a persistent little fireball. RNX, when used as fuel, is actually hard to light. Probably works best when there's a generous amount of current in the igniter, so maybe not suitable for an ejection charge to be set off by a 9V alkaline battery. My guess is that you could find a lipo adequate for the task that was lighter. But I haven't actually explored how much current is necessary.
 
Up until this thread, I’ve only seen posts by people talking about how their mini Christmas light ejection charges work great. Is this a thing where some people figure it out and get consistent results and other people not so much, and that gives the impression that the technology is suspect? Or is there an inherent problem that causes failures for everyone, regardless of techniques?

I can definitely see how there are enough ways to not get it right that the simple incandescent glow could allow failures, while ematches are far more robust due to generating a larger ignition source. But on the other hand, it seems that if a person's designs and techniques were good, reliable results ought to be achievable, just like turning on an electric light.

I am kind of attracted to the $3.50/100 at Walmart price tag.
 
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If you want to know how to make igniters with Christmas tree bulbs, poke around at nakka-rocketry.com
He even has an igniter design with "grain" bulbs which are even smaller. (Maybe not cheaper.) He claims 1.2 volts and 20 milliamps are enough to get one to fire. Tested, apparently, with a nearly dead 9V battery that had been in the refrigerator. I don't know if you can still get "grain of wheat" bulbs for current and voltage that low, but the model train guys still use them and they show up on eBay.

I have no doubt that this type of igniter can be reliable for people who are careful. Of course, when they're this sensitive it's probably best to wrap the leads together when not in use so that they don't get set off by accident.
 
rcktnut said:
I hear you, I thought Christmas tree light bulbs and flash bulbs have gone by the wayside long ago, even before NTP2 was born.
Click to expand...
I think they went out in the Aughts. I make them up and used them with 100% reliability in '08 & '09, then went to commercial ematches.

The unreliability of the xmas bulbs was something I tried to get around and think I did pretty well. I broke the glass and used a tweezers to remove the shorting wire that kept the string lit if the filament broke. I then tested every bulb and throw out the 10 - 20 % where the filament broke while removing the shorting wire. I then took the remaining bulbs and twisted two in parallel and soldered on about 10" of wire extensions to the small wire on the bulbs. I then throw away the 10% that didn't test right after that. Then use hot glue to glue and seal the two bulbs into the bottom of a paper tube rolled around them. They were very similar to an ematch in the bottom of a centrifuge tube you see people use today. I always tested them again at the field before pouring in BP, folding over the paper and loading them in the rocket. The final test was the continuity beeps from the altimeter. Never had one fail, but boy, were they time consuming and a PIA to build.
 
LEDs are fine (got mine from BDale) they light dimly for continuity and then bright when deployment charge is triggered.
Used set for testing EggTimer, RRC3 and Altus Altimeters with no issues
 

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