# How to check mA draw of led?



## shortstack (Aug 22, 2009)

i was wondering how to check the mA draw of a led with a multimeter??





this is the one i have


----------



## Light Sabre (Aug 22, 2009)

Just put your test leads in the amp jacks, turn the dial to amps, and place in series with the LED, on/off switch, and batteries. The easiest place to do this is take the tailcap off and touch one lead to the flashlight body and one lead to the negative end of the battery. If the flashlights switch is in the tailcap (pushbutton or twisty), then you don't need to do anything else. If you're trying to test a minimag for example, then you need to twist the head so that the flashlight would be on. If a 2D type mag light then you need to push the switch so that the flashlight would be on. Then take your measurement. Don't forget to move your amp lead back to the voltage jack when you're done, or the next time you use your meter for voltage it can go  If you want to test just the LEDs current in a regulated flashlight, then that gets much more complicated. I usually just wanna know what the total current is and not just the LED. Hope this helps.


----------



## shortstack (Aug 23, 2009)

well theres a few ones im trying to check is one a utility vehicle i want to install a led strobe controller and it has a certain max mA. i wanted to see what the that led draws so i know how many i can make strobe. 

i also have a 12v driver that has 3 led in series and i wanted to double check the mA of what the driver is pushing out.

thanks


----------



## Justin Case (Aug 23, 2009)

If you want to measure the drive current from the driver being sent to the LED, then Light Sabre's method won't give you that. His method gives you current draw from the batteries.

Try doing a search on CPF. This link might give you a start.


----------



## Capo_au (Aug 26, 2009)

The way i have been checking mine is just simply inline with the output from the driver and the led.

So that is Driver+ --> multimeter --> Led --- Driver-.

Just be sure to turn your DMM to the highest AMP setting and make sure you have the lead in the right spot. Some DMM's have a different spot for the positive lead for hight current applications like the one in the picture you linked.


----------



## Dadholly (Nov 7, 2013)

Light Sabre said:


> Just put your test leads in the amp jacks, turn the dial to amps, and place in series with the LED, on/off switch, and batteries. The easiest place to do this is take the tailcap off and touch one lead to the flashlight body and one lead to the negative end of the battery. If the flashlights switch is in the tailcap (pushbutton or twisty), then you don't need to do anything else. If you're trying to test a minimag for example, then you need to twist the head so that the flashlight would be on. If a 2D type mag light then you need to push the switch so that the flashlight would be on. Then take your measurement. Don't forget to move your amp lead back to the voltage jack when you're done, or the next time you use your meter for voltage it can go  If you want to test just the LEDs current in a regulated flashlight, then that gets much more complicated. I usually just wanna know what the total current is and not just the LED. Hope this helps.



Sounds like my project...My question is, I want to tap off of a existing LED on a circuit board in parallel, but feel I need to match up the MA ?


----------



## bshanahan14rulz (Nov 7, 2013)

Your results may vary depending on the circuitry that powers the LEDs. If it is a constant current circuit, which is usually the best way to run LEDs, and the LED you put in parallel to the existing LED is exactly the same, with the same Vf, the current will be split in half. 

If you want some more help and can provide more details, post up your project in a new thread and the folks here will give you some suggestions or advice on how to achieve what you want your end results to be.

Oh, and welcome to CPF!


----------



## DIWdiver (Nov 7, 2013)

shortstack said:


> well theres a few ones im trying to check is one a utility vehicle i want to install a led strobe controller and it has a certain max mA. i wanted to see what the that led draws so i know how many i can make strobe.
> 
> i also have a 12v driver that has 3 led in series and i wanted to double check the mA of what the driver is pushing out.
> 
> thanks


 
The second one is easy - set up the meter as LightSabre suggests, break the connection between the driver and the LED string, and insert the meter. The LEDs should light up as normal. If so you will have the accurate reading. 

The first one is more difficult, because it requires a deeper understanding of what's going on. 

LEDs don't 'draw' a particular amount of current. They'll pretty much take what you give them. And if you give them too much, you damage them. The LED has a max current rating, but that's not the max it will take. It's the max you should give it. The actual current that flows is determined by the rest of the circuit, not the LED. 

Something similar may be happening in your strobe controller. It may give as much current as the load will take, but if the load takes too much, it will damage the controller. So what determines the current? That's where the LED driver comes in. This can be anything from a simple resistor to a complex electronic circuit. Your strobe controller could have this circuit built in, but if it has a max current spec, it probably doesn't. So you'll need to understand resistors, voltage, and current, or LED drivers, or get advice from someone who does. If you post some more information, like what LEDs you plan on using, and what controller you have, we can give you better advice here.


----------



## bshanahan14rulz (Nov 8, 2013)

Sorry DIWdiver, I was replying to Dadholly, he's new here. ShortStack hasn't been here for a few months :-/


----------



## DIWdiver (Nov 8, 2013)

Oops. Guess I should pay more attention to dates!


----------

