Question about Resistance

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Old-Lumens
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Question about Resistance

I was going to make some resistance mods in my P7 3AAA light, but I figured I would check if there was any voltage drop with the current stock parts. I checked my 3AAA batteries laid out together first and they read 3.9VDC. I then put them back in the battery holder and they read 3.9VDC. I then put the holder in the tail cap and turned the switch on and they read 3.9VDC measured from the top terminal to the body of the light. (Meter set at the 20V setting, next lowest setting is 2V - too low). If the resistance is low enough that it doesn't even draw a 10th of a volt, why bother to mod it for less resistance?

I decided to check resistance where I could. I took the meter set at 200 ohm (lowest setting) and measured from the tailcap bare metal to the switch spring and got 00.5 ohm with the switch on. I also measured different parts of the battery housing and got 00.4 to 00.3 ohm. I then checked a piece of 16ga bare copper wire to use as a reference and got 00.2 ohm.

If I have that little resistance in the stock parts, where there "seems" to be no voltage drop, then why would I even worry about any resistance mods? It's not worth bothering right?

I don't know, that's why I'm asking. It's not an expensive meter (Sperry), but I have checked it against someone elses expensive meter and it seems consistent for what it does. Maybe the only way to really know is with expensive testing equipment, if so, then I still shouldn't bother with modding, since I can't even tell the difference anyhow right?

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gcbryan
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It's not something I'd worry about.
peteybaby
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voltage = resistance x current, so even if there is a lot of resistance in your battery holder and tailcap switch, you wouldn't be able to measure it when there is almost zero current flowing.  That is, when you use your meter on the voltage-measurement scale, the current passing through the circuit is tiny.  Therefore, the voltage dropped on any resistance in your battery holder and tailcap is also tiny.  As an experiment, you could probably put a 1 kilohm resistor in series with the batteries and still measure 3.9 V with your meter.

Also, trying to measure the resistance of the battery holder and tailcap switch directly with your meter on the ohms setting will be inaccurate.  You could buy a meter that's made for measuring small resistances, but really what you need to do is take measurements when there is more current passing through the circuit.  e.g. measure voltages when the light is on in high mode (you'd still measure fractions of a volt across the battery holder and tailcap switch), or better, measure currents.

If you use a set of batteries fresh off the charger, turn on the light in high mode, and measure the current, and then do your resistance mods and repeat the measurement, you'd probably find that you get higher current after your mod (if your mod was successful at decreasing the resistance).

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Resistance is Futile! BLF

 

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Leelou
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What peteybaby said.

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Old-Lumens
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peteybaby wrote:

voltage = resistance x current, so even if there is a lot of resistance in your battery holder and tailcap switch, you wouldn't be able to measure it when there is almost zero current flowing.  That is, when you use your meter on the voltage-measurement scale, the current passing through the circuit is tiny.  Therefore, the voltage dropped on any resistance in your battery holder and tailcap is also tiny.  As an experiment, you could probably put a 1 kilohm resistor in series with the batteries and still measure 3.9 V with your meter.

Also, trying to measure the resistance of the battery holder and tailcap switch directly with your meter on the ohms setting will be inaccurate.  You could buy a meter that's made for measuring small resistances, but really what you need to do is take measurements when there is more current passing through the circuit.  e.g. measure voltages when the light is on in high mode (you'd still measure fractions of a volt across the battery holder and tailcap switch), or better, measure currents.

If you use a set of batteries fresh off the charger, turn on the light in high mode, and measure the current, and then do your resistance mods and repeat the measurement, you'd probably find that you get higher current after your mod (if your mod was successful at decreasing the resistance).

See I never learmed anything about electrical well nothing other than when you stick your mom's keychain keys in the 110V outlet, the key chain blows up in your hands (yes I did that at age 4). Duh, without current flow there's no resistance. (Oh Mr. Wizard of OZ, I'd like a brain please - When Dr. Frankenstein made me, he had run out of brains, so he used oatmeal for a filler).

 

gcbryan wrote:
It's not something I'd worry about.

That's the best answer, since I don't have the setup and the equipment and especially the knowledge, I don't need to to be F***in with it.

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