How to measure and reduce Parasitic Resistance in a flashlight?

Hi H) ,

I am modding one of my flashlights right now [ Trustfire df-007 ].
I plan to change the pill + building a new driver to it which will be based on AMC7135 chips.

I would like to reduce the parasitic resistance as much as possible, what is the best way to do it?
What cables should I use? what springs are the best?

Also, how do I measure that resistance?

Thanks :slight_smile:
Jan.

By parasitic resistance I’m assuming you mean voltage drop due to resistance because you mentioned wires and springs.

Use the thickest possible wires that you’re comfortable working with. Often thick wires will get stuck in pills or get squished under reflectors, causing problems.

For springs, you can use any spring as long as you solder some copper braid across the ends to minimize resistance.

You can’t really measure the flashlight’s resistance because the LED is in the way, although you can compare the currents before and after you use thicker wires and copper braid springs.

However, since you’re using a linear regulator (AMC7135), minimizing resistance won’t be as important as in a direct drive setup. What current are you planning to drive your LED with? (How many AMC chips?)

Use the largest gauge wire that will fit, and there are some beryllium-copper springs that I know have low resistance. Or you could use regular springs, with some copper braid soldered to them.

As for measuring it, you’ll need a multimeter with a resistance mode. The issue with this is that there is some resistance between the leads and what they are touching.

I’ll let someone with a little more experience than me fill in the rest.

It would just be called resistance. People don’t usually call it parasitic resistance. There is a thing called parasitic drain but that only applies to drivers using a small momentary button, usually side button lights.

I usually us my HP3458A multimeter or ESI VideoBridge to measure low resistances… they use four-wire Kelvin connections. For really low resistance measurements I have a custom made device that can resolve below a micro-ohm.

Certainly helpful to the OP there TP. :zipper_mouth_face:

It is fairly easy to measure low ohmic values with a power supply and a DMM, especially if the power supply has a constant current mode.

If have showed how to do it here (Without a constant current mode): http://www.lygte-info.dk/info/Measurement%20UK.html

A cheap 3½ DMM with a 200mV range and a power supply that can deliver 1A gives 0.1mOhm resolution

Excellent article - highly valuable for our forum where most of the people would not have access to precision measurement equipment.