DMM testing standby/parasitic drain of Zebralight H52Fw question

[scs]

I attempted to measure the standby drain of my H52Fw on a fully charged Eneloop and got alternating results of 1926 micro A and 2.6 micro A. My DMM is a Mastech MS 8268.

I've figured out the respective action sequences that cause my DMM to generate each figure.

• 1926 micro A reading:

• Turn on the DMM and turn the dial to select the micro amp range.
• Place one lead on the negative end of battery and the other on the unanodized end of the tail. The DMM registers 1926 micro A.

• 2.6 micro A reading:

• Follow steps 1-2 above then...
• Remove the leads from the tail and battery.
• Turn the dial to select the mA range.
• Test the light. A reading shows on the display but quickly returns to zero.
• Remove the leads from the tail and battery.
• Turn the dial to select the micro amp range again.
• Test the light. The DMM now registers 2.6 micro A.

If after completing Step 3 above, I skip to Step 6, and then test the light, the DMM still registers 1926 micro A. Therefore, there's something about testing the light with the DMM dialed to the mA range that causes the reading the change.

The light does NOT turn on when the DMM reads 1926 micro A.

What might be going on between the DMM and the light that's causing this behavior?

Thanks.

 

[RetroTechie]

A regular (?) DMM doesn't have high enough input impedance, or enough significant digits to produce an accurate reading for such a small current. On the most sensitive current ranges, voltage across the DMM is non-negligible and may influence the flashlight's behavior. On a higher current range, you lose significant digits.

So you'll probably get the most accurate reading on a higher range, where the result is in just the last 1 or 2 digits. If you want better than that, you're looking at 6+ digit bench meters, or a low value / high-accuracy series resistor with instrumentation uV opamps, a Wien bridge, or things like that attached. Not to mention a thorough review of such a measurement setup... :green:

Note that with eg. a 2000 mAh battery, a 10 uA standby current translates to 200,000 hrs standby time which is ~23 years. So anything in that range or below it, translates to "negligible for all intents and purposes". Self-discharge of even a low self discharge battery will be a much bigger factor.

 

[scs]

A regular (?) DMM doesn't have high enough input impedance, or enough significant digits to produce an accurate reading for such a small current. On the most sensitive current ranges, voltage across the DMM is non-negligible and may influence the flashlight's behavior. On a higher current range, you lose significant digits.

So you'll probably get the most accurate reading on a higher range, where the result is in just the last 1 or 2 digits. If you want better than that, you're looking at 6+ digit bench meters, or a low value / high-accuracy series resistor with instrumentation uV opamps, a Wien bridge, or things like that attached. Not to mention a thorough review of such a measurement setup... :green:

Note that with eg. a 2000 mAh battery, a 10 uA standby current translates to 200,000 hrs standby time which is ~23 years. So anything in that range or below it, translates to "negligible for all intents and purposes". Self-discharge of even a low self discharge battery will be a much bigger factor.

Thanks RetroTechie. I'm not looking for accuracy as much as I'm curious which measurement more closely approximates the actual standby drain, when the tailcap is tightened. If the 1.9mA is closer, then my sample is defective, and that's a cause for concern.