Bench testing - anyone know how many amps the 2.5V mini Christmas light bulbs draw

[kjkcolorado]

I'm bench testing altimeter and battery combinations in a vacuum chamber. Does anyone know how many amps the 2.5V mini Christmas light bulbs draw individually (think directly hooked up to altimeter drogue and main channels)?

 

[ksaves2]

I'm bench testing altimeter and battery combinations in a vacuum chamber. Does anyone know how many amps the 2.5V mini Christmas light bulbs draw individually (think directly hooked up to altimeter drogue and main channels)?

Get a 10 amp VOM and connect one up in a series. I suspect the draw is low. An alternative would be LEDs. I got a canister full from Electronics Goldmine when they had a sale on them a few years ago for $3.99.
They're a little more pricey now. https://www.goldmine-elec-products.com/prodinfo.asp?number=G7436 and https://www.goldmine-elec-products.com/prodinfo.asp?number=G8063

If your altimeter fries one, no big deal. Kurt

 

[djs]

I use a LED in series with a 100 ohm resistor, as I don't think LEDs have enough of a load to "trick" the altimeter into thinking it's hooked up to an ematch.

 

[kjkcolorado]

Good suggestions. Thank you. I just remembered I have a stash of 'bad' e-matches that were replaced by MJG. I won't use those for actual flights, so I'll start by blowing through those before trying to replicate e-matches with a Christmas light bulbs.

 

[Titan II]

I do not know the answer to your question regarding the current, but I use Christmas tree light bulbs to test all my altimeters. This is also from the RRC3 manual:

The Output Diagnostics allow you to verify the firing circuitry on your RRC3, as well as verify that the matches you’ve
chosen can be fired by the RRC3’s firing circuitry. If your goal is to simply test the altimeter’s output circuitry, a single
miniature Christmas tree bulb works well ‐‐ it provides sufficient resistance for the continuity circuitry to detect it as a
charge, and will light up when the altimeter fires the output.

 

[kjkcolorado]

I do not know the answer to your question regarding the current, but I use Christmas tree light bulbs to test all my altimeters. This is also from the RRC3 manual:

The Output Diagnostics allow you to verify the firing circuitry on your RRC3, as well as verify that the matches you’ve
chosen can be fired by the RRC3’s firing circuitry. If your goal is to simply test the altimeter’s output circuitry, a single
miniature Christmas tree bulb works well ‐‐ it provides sufficient resistance for the continuity circuitry to detect it as a
charge, and will light up when the altimeter fires the output.

That is helpful. The altimeter I'm testing is an RRC2+. I'm assuming this portion of the RRC3's manual would apply to the RRC2+.

 

[cerving]

LED's aren't really good for testing deployments because they draw so little current that the continuity check circuitry is liable to light them up, at least a little bit. The incandescent Christmas lights are much better, they run about 2 ohms so with a 7.4V LiPo they'll draw 3 amps or so, and they won't pop when you fire them (although I have to admit that it IS fun to watch a LED go off like a flashbulb...)

 

[ksaves2]

LED's aren't really good for testing deployments because they draw so little current that the continuity check circuitry is liable to light them up, at least a little bit. The incandescent Christmas lights are much better, they run about 2 ohms so with a 7.4V LiPo they'll draw 3 amps or so, and they won't pop when you fire them (although I have to admit that it IS fun to watch a LED go off like a flashbulb...)

I haven't had a problem with them except I burned out an LED one time. The TRS, Quantum, EggTimers and Qwarks all worked with them well for testing and had no continuity problems. Kurt

 

[UhClem]

Based on some guesses about the bulbs (50 per string and 20W per string) I get a resistance of 15 Ohms. If you know the voltage applied you can calculate the current.

 

[SolarYellow]

LED's aren't really good for testing deployments because they draw so little current that the continuity check circuitry is liable to light them up, at least a little bit. The incandescent Christmas lights are much better, they run about 2 ohms so with a 7.4V LiPo they'll draw 3 amps or so, and they won't pop when you fire them (although I have to admit that it IS fun to watch a LED go off like a flashbulb...)

https://people.howstuffworks.com/culture-traditions/holidays-christmas/christmas-lights1.htm

If you look closely at a bulb, you can see the shunt wire wrapped around the two posts inside the bulb. The shunt wire contains a coating that gives it fairly high resistance until the filament fails. At that point, heat caused by current flowing through the shunt burns off the coating and reduces the shunt's resistance. (A typical bulb has a resistance of 7 to 8 ohms through the filament and 2 to 3 ohms through the shunt once the coating burns off.)

If that "How Stuff Works" article is correct, it looks like a Christmas mini light driven by a 1S Li-Po should draw about half an amp until burned out, then around 1.2-1.9 amps after it's burned out.

Ima need to test this when I can get to the shop instead of being chained to a desk.

 

[Handeman]

I never bothered to find out the current draw on incandescent xmas lights. I just use them to test pyro channels. Haven't had one damage an altimeter or fail to light or burn out when the channel was turned on. Been doing this for 15 years.

Just hook them up and use them. Red for apogee, green for main works well.

 

[Adrian A]

Incandescent bulbs do work well for testing because they start out with a much lower resistance and sink a lot of current until they heat up to start glowing. Then when they are glowing white-hot, the resistance goes up enough that they are safe to stay lit until you turn it off or your battery runs out.