Measuring current at the tailcap

[sygyzy]

Hi,

I am trying to measure the current of my p7 Mag at the tail cap. I touch the black probe to the bottom of the battery pack. I touch the red probe to the tail cap threads on the body and I turn on the light. Nothing. No light. No reading on the DMM. What am I doing wrong?

Oh yeah, a few times I got sparks from the end of the battery. Sometimes I hear a "poof" sound and sometimes the battery gets really really hot. All this and no reading.

 

[old4570]

Eeeeeer ! Wow ok , where to start ..

Does your Multi Meter have a 10Amp setting ? if your going to read Amps this is what you want to set it to .

What sort of flashlight do you have ? Tail Clicky or on off switch in body ?


To read Amps : Voltage ... Voltage = if your set to reading voltage the light will not come on - OK .

AMP's = set MM to 10A setting ... If its a body switch , leave it on and remove tail cap . Black to the neg tail of the batt , and red to the threads , this should give you an Amp reading .

The snap crackle and pop ? :thinking: Dont short the leeds !

 

[MWClint]

Dave, if after you make sure you have the DMM set up right as per the above post..
then it definitly sounds like you have a short, i'd take it apart and double
check the connections... there should be no sparks and no hot batteries from
performing a quick amp check on 6AA's.

are you able to take pics?

 

[Justin Case]

Aren't the Mag threads anodized? Try touching your positive DMM probe to the rim of the Mag tube at the tailcap where you see bare metal.

 

[sygyzy]

Yeah the threads are annodized. I will try to pit it on the bare metal but it's very difficult to position sometimes.

I set my DMM to the 20A setting and it works fine reading the current of the system in series (with driver). It doesn't give any readings from the tailcap though.

Clint - I can take pictures and I will tonight. I wonder if this short is what's affecting my flashlight. What's strange though is if I remove the probes and screw on the tailcap, the light works fine. In other words, the light has no problem functioning with the tailcap in place.

Question - if I am able to measure the current at the tailcap properly, will the LED be lit?

BTW I am using 6xAA NiMH in a Fivemega 2D adapter if that matters.

 

[sn0wBLiND]

Yes, the led should light up when you measure the current. The meter is in series with the circuit.

 

[Al Combs]

FiveMega battery holders have a charging jack in the rear. Your black lead is not sitting on the minus end of the battery, it's shorting it out.:sick2: Yes the LED should be lit, albeit slightly dimmer because of your meter's shunt. Try it again but don't stick the probe in the little hole in the center.

 

[sygyzy]

Al Combs - That was the problem! I was able to measure it just now and it's 2.95 A. I am not sure what it should be. It's 2.5 in series with the LED.

 

[Fallingwater]

A word of warning: when you're done measuring current, ALWAYS switch the meter back to voltage mode. Failure to do so will, sooner or later, cause you to forget its setting and short out cells.