How do you measure PR Bulb voltage?

lctorana

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Hi experts,

Purely a mechanical question.

How do you measure voltage at the bulb in PR-based bulb torches?

I have been building quite a few entry-level hotwires lately, and would like to measure their actual performance.
 

MikeSalt

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I should imagine you need a VERY thin wire that you can temporarily solder to the base of the bulb, and then install the bulb if there is enough room for the wire to dangle out. You have to be very careful not to short it though. Then you can measure the voltage between the wire and the bulb collar.

If you are using unprotected Li-ion batteries, you can forget doing this though. The chance of shorting, and causing massive catastrophic failure is not worth it.
 

lctorana

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Thanks for the quick answer. This does give me an idea - very fine insulated wire, such as used for wire-wrap. I'll give it a try.

But still interested in other answers - after all, I'm sure there are hotwire (e.g. RoP) builders who have done this routinely. How have you people done this?
 

Icebreak

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I do it without soldering.

One end of the wire has 2 to 3 mm exposed and that goes under the lamp. See that V cut on the flange of the PR base? Fish it through there and through the loose and free retaining ring then tighten the retaining ring back down. Wrap the other end around your positive probe. Loosen the tailcap so that the negative probe can get in there but the cap is still connected by the threads.

MAKE SURE YOUR EYE PROTECTION IS ON.

Turn the switch on and probe with the negative lead in between the cap and the body. When the light comes on you are getting a true reading. It won't be an absolute scientific read because of the little probe extension wire but close enough.

I would think that a temporary soldering of the small wire would a be better approach. Also, I've thought that I'd like to get some teflon coated wire to avoid shorts from abrading the coating. Wouldn't want to turn the little lead wire into a filament.
 
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Icebreak

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For current:

to measure amps.. you need to put the meter in series with the lamp..

1) meter must have a 10A or 20A scale.. this usually means it also has a separate jack for measuring amps typically on the left.

2) turn the switch to 'on'.

3) put the black lead on the neg. of the battery pack and the red lead on the edge of the flashlight body.

-awr
 

fivemega

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Remove and disassemble the switch slug, run some wire through center of focusing spring and solder it to upper cup where bulb positive terminal has direct contact.
Put everything back together and instal switch but not the flashlight head. Make sure not to touch this wire to body.
Measure positive voltage at this wire and negative at bulb collar while bulb is on.
Precaution necessary.
 
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