Checking Li-Ion battery voltage under load?

34 posts / 0 new
Last post
sbslider
sbslider's picture
Offline
Last seen: 15 min 25 sec ago
Joined: 01/22/2017 - 13:41
Posts: 721
Location: United States

Pete7874 wrote:
Thanks. One question about this: when measuring voltage under load in a flashlight, I do not see the LED light up, so where is all the energy going? What is absorbing it if there is no dedicated resistor?

I don’t know what your test setup is so I can not provide helpful advice except this – if your intent was the flashlight be the load for your battery, and the LED is not producing light, it is not loading the battery, and you are not measuring the battery voltage under load.

In my test, the battery voltage is accessible via the contacts. this review shows the tailcap about 2/3 of the way down the page.

PocketSammich wrote: I don’t need this, but I want it. Please sign me up.

Pete7874
Pete7874's picture
Offline
Last seen: 21 hours 42 min ago
Joined: 11/23/2011 - 16:47
Posts: 1915
Location: USA

sbslider wrote:
Pete7874 wrote:
Thanks. One question about this: when measuring voltage under load in a flashlight, I do not see the LED light up, so where is all the energy going? What is absorbing it if there is no dedicated resistor?

I don’t know what your test setup is so I can not provide helpful advice except this – if your intent was the flashlight be the load for your battery, and the LED is not producing light, it is not loading the battery, and you are not measuring the battery voltage under load.

I am using a Convoy S2+ with the tail cap removed. I press one DMM probe against the back of the battery and the other DMM probe against unpainted surface of the flashlight tube. I get 3.67 Volt this way.

When I measure voltage of the battery at rest (outside of flashlight), I get 3.74V.

My guess is what I’m doing is not the correct way to measure voltage under load in a flashlight, and that’s why the LED does not come on, but why am I seeing some voltage drop then?

sbslider
sbslider's picture
Offline
Last seen: 15 min 25 sec ago
Joined: 01/22/2017 - 13:41
Posts: 721
Location: United States

Your meter connected in series with the battery is not an appropriate way to measure the battery voltage. I can not counsel you how to go about measuring the battery voltage under load with that flashlight.

I suspect you are seeing the voltage drop due to a small current flowing through the light and your meter.

PocketSammich wrote: I don’t need this, but I want it. Please sign me up.

Pages