Testing Ampere draw with a multimeter

member 6142

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Feel like a dumb yet I do need a hint so....I've a SF L6 and I would like to test Ampere draw with a multimeter (I already own).
How?

Thanks
 

MrAl

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Hi there daberti,

Using a 0.1 ohm resistor to measure current sometimes
works out better than the meter itself. The 0.1
ohm resistor is connected in series with the battery
and the voltage across the resistor is measured with
a digital voltmeter. The voltage measure reflects the
current, and is ten times higher than measured.

For example, if you measure 0.1 volts then the
actual current is 10 times that, or 1 amp.

If you still want to use the meter, connect it in
series with the battery.

Take care,
Al
 

mrme

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If your multimeter has a current setting, you have to use it in series and never parallel.

Most meters will let you measure up to 200 ma through the regular test leads plug. If you have a 10 or 20 amp setting, that usually requires use of a different plug for your positive test lead.

If you tried using it in parallel like you would to measure voltage, you probably blew the fuse. It is a common mistake. Good luck finding a replacement fuse.
 

member 6142

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@MrMe
That's the problem: fuse has not been blown, yet how to measure in series? I'm really a beginner /ubbthreads/images/graemlins/icon23.gif

@MrAl
Thanks for your advice too /ubbthreads/images/graemlins/smile.gif
 

andrewwynn

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The simple basics of measuring current is that you must interrupt the circuit and put the meter in series with the power source.. i.e. typically with a flashlight like a maglight that has a tail cap.. you can turn the light 'on'.. take off the tail cap.. set the meter to 'amps' and put the leads in the right holes.. at that point touch the 'negative' lead to the bottom of the battery and the 'positive' lead to the shell of the flashlight.. the meter acts as the tail cap and completes the current loop.. if you hook up the leads backwards most meters don't care they just display negative values.

The higher end meters have an alarm if you have the leads in the 'amp' connections and the meter set to anything but amps.. easy way to melt things is to hook a meter into a circuit thinking it's set to volts but it's still in the 'amps' mode.. to a circuit, an ammeter looks like a 'short'.. a voltmeter looks like an 'open'.

It will become 'second nature' if you do it enough... just remember.. amps you have to disconnect.. volts you don't.

-awr
 

member 6142

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Never say thanks enough /ubbthreads/images/graemlins/grin.gif
 

jayflash

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I can't remember if I welcomed you in a different thread. I think I did but, so what, so there, welcome to here. /ubbthreads/images/graemlins/grin.gif
 

member 6142

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Yes you did /ubbthreads/images/graemlins/smile.gif
Thanks for welcoming me, again. /ubbthreads/images/graemlins/smile.gif
 

member 6142

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Ok.
Picked up DMM and MAG 3D torch.
Turned mag on then tailcap off, turned on DMM using first 10A setting then 200ma.
In both cases A reading is 0 and torch does not light on.
 

MrAl

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Hi there daberti,

You need to touch one meter lead to the minus side
of the battery inside the light while applying a little
pressure to keep the batteries in good electrical contact,
and the other meter lead to the INSIDE of the light where
the threads are. Note the outside is covered with a non
conducting paint so you cant touch the meter lead there.

Have you used the meter for other current measurements yet
to prove it works ok?

Take care,
Al
 

member 6142

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Ok. Was only a matter of threads.
Now: I guess that Resistance is something different if between - of batteries and threads than with tailcap. Am I right?
 

gadget_lover

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[ QUOTE ]
I guess that Resistance is something different if between - of batteries and threads than with tailcap. Am I right?

[/ QUOTE ]

Resistance is never checked with a power source attached. Resistance is the measurement of how well something blocks electricity. The DMM has a small battery inside that it uses to check the resistance at a known voltage.

To practice, Take the lamp from your mag lite. Set the DMM to the 200 ohm scale, and touch one lead to the silver case and the other to the metal blob at the tip of the lamp. Your meter will then tell you the resistance of the bulb.

Daniel
 

member 6142

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You're right and I spoke not so clearly: I meant to say that the spring in the tailcap is more conductive than the threads, but I had a second though....as both are used when closing my torch. uuuhh feel like a moron /ubbthreads/images/graemlins/icon23.gif
 

CNC Dan

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Thats OK daberti, we all had to learn.

You need to have both test leads in good electrical contact.
The edge of the maglight should be bare metal. The threads may be coated.

Your meter should be on the 10A (or 20A) range, AND the RED lead should go into the jack marked 10A (or 20A).

If it still doesn't light up, check the fuse in your meter. It should be someware near the battery area.

Dan
 

wintermute

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I am using 2 x MicroPuck 2009-HI drivers wired in parallel, and my MM is reading 980mA at the batteries, what kind of power am I getting at the LuxIII??
 

member 6142

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Problems solved: it was dealing with some coating over mag's threads.
Thanks
 

member 6142

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How many batteries have you got?
Lets make an example:
assumed that ya're running at 6V
W=V*A (note: I'm simplifying, it should be something like V*A*0.8 instead)
W=6*0.980 thus ....?(Waiting for yor calculation /ubbthreads/images/graemlins/smile.gif )

In any case given that LuxIII should run at 3W in any case you're overdriving it, as you're running at 5W levels (if I recall well 0.980 is the current of SF L5 which runs @6V).
 

wintermute

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2 alkaline AA batteries. When I put in fresh batteries and tested, I had 3.06v and 1000mA at the batteries.
 

member 6142

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How did you measure Ampere? As you measure volts? Or as stated here above by andrewwynn ?
 

member 6142

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Anyway assumed that you got 3.06V you should be slightly below 3W, thus in safe zone...but also correct thermal dissipation must be assumed /ubbthreads/images/graemlins/wink.gif
 
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