ROP Voltage Drop

I have been reading about people getting about a .5 voltage drop when using the ROP. I am using Energizer 2500 in mine and only get a .01 voltage drop with the high bulb, is this normal?

how are you measuring the loaded voltage at the bulb?

I am using the DMM to complete the circut at the tailcap.

they give off a fairly strong initial boost but then settle in, does the current remain stable at that reading or is it dropping?

I might be completely off here but as far as I know that's not voltage you're measuring. You use the DMM to complete the circuit when measuring current, not voltage. To measure voltage you should hook it up like this picture:
http://www.8886.co.uk/ref/img/bulb_circuit.gif
(random image from google image search, credit goes to whoever made it)

If I'm wrong here please correct me.

you can figure out the voltage by the current

That reading is after about 10 seconds and settles down after about 2-3 seconds.

wow - pretty good for consumer type NIMH I guess, what's that actual voltage you're getting?

I get about 8.3 volts on a full charge and under load is only about .01-.02 under that.

something is wrong here.. like Robban says.. if you are completing the ckt at the tailcap you are not measuring voltage under load... If you have the meter set to 'volts'.. and measure with the light on across the tailcap you will get vBat.. but not under load (notice the light is not lit)..

to measure the voltage under load you need to measure at the lamp while on.. something very tricky to do with a PR lamp.

If you know the baseline current of an ROP at a specific voltage (something the likes of me can measure).. you can measure the current under load at the tailcap and calculate the voltage at the lamp.. that's by far the easiest way.. but the baseline measurement has to be done.

The voltage drop is easy to calculate if you are using a MagD..

The PR mechanism of the maglight has some pretty serious resistance.. typically between 150 and 180mohm (0.150 and 0.180 ohm)..

if you measure the current at the tailcap.. multiply by about 170mohm and you'll get the voltage drop.. say it's 3.5A.. multiply by .170 and the results: .595V.. in-line with the expected voltage drop mentioned above.

fix your PR with my prfix: http://prfix.rouse.com and you will go down to about 40mohm or less.. then that 3.5A x 0.040 ohms = 0.14V drop.. pretty big difference.. typically it'll add 10% to the brightness of the light.

hotdriver halves or thirds even that resistance.. there is only about 10-15 mohm resistance on the hotdriver circuit.. i use 20mohm for my calculations to be conservative.. 20mohm x 3.5A = 0.07V. that's a huge improvement from .6V!

-awr