[Q] How to measure the current consumption of a bicycle torch...

I have several flashlights that I use for my mountain bike hobby, some of good quality as the Serfas True 1500 [/ b], and with a questionable quality I got in from DX (Deal Extreme), They have different LEDs, (P7 LED, T6, U2) , each giving a different amount of light. (two are mine and two of my wife)

Some of the batteries I have are good, but getting old, and the ones that come from DX, are not trust-able...

Now, I am planning to buy several LiPo batteries, and my question is capacity.

• Battery with low capacity will leave me without light halfway ..
• Battery with large capacity weigh much more and maybe are "over kill".

To do this, I want to measure that consumption of each lantern and then choose the correct battery capacity ..

Therefore, how can I measure the consumption of each torch, using the original batteries 7.4V.

Dump question that expects an correct clever answer

Thanks in advance

--- Ricky Marek ..

the simplest method would be to simply put batteries of known capacity in the torches and see how long they run. If a 2000mAH battery lasts 1 hour, for example, then a 4000mAH battery would last 2 hours. It does require having new-ish batteries that you can trust to have the advertised capacity, though.

If you want to get more complicated, then you'll need to hook up a meter than can measure current, and there's not a simple way to do that.

Steve K said:

the simplest method would be to simply put batteries of known capacity in the torches and see how long they run. If a 2000mAH battery lasts 1 hour, for example, then a 4000mAH battery would last 2 hours. It does require having new-ish batteries that you can trust to have the advertised capacity, though.

If you want to get more complicated, then you'll need to hook up a meter than can measure current, and there's not a simple way to do that.

Click to expand...

Hi,

I just made a measurement table with my three lights, the fourth is in its way in the mail...

Here are my results that I have uploaded to a "spanish" forum.. (with some spelling mistakes as usual)
(Linterna = Light, Potencia = Power, Amperage = Current, Tiempo con 6000mAh = Time to consume a 6000mAh battery, Capacidad para 3:30 = Required capacity for 3h 30min)



Now, how do I test the capacity of my current batteries?

Thanks in advance..

Steve K said:

the simplest method would be to simply put batteries of known capacity in the torches and see how long they run.

Click to expand...

Most batteries have rate dependent capacities, ie the faster you drain them, the less you get in A-h.

But why wouldn't you just get a cheap multimeter (assuming you don't already have an expensive one), put it on the 10A range and directly measure the current? You could put the batteries into a standard battery holder so you don't have to juggle too many things in your hands...

Or am I missing something obvious?

I'd keep this simple too. My preferred method is to use a power resistor to discharge the battery, and measure the voltage across the resistor (and then calculate the current).

It would be a good idea to measure the value of the resistor when it is warm (during battery discharge) for the best accuracy. The resistor's value does change with its temperature.