Can't understand the battery current reading LSH-P

Can\'t understand the battery current reading LSH-P

I can't keep myself from the excitement of having a new LSH-P and I believe all senior CPFers will understand why I keep measuring the voltage and current and so on... /ubbthreads/images/graemlins/grin.gif

I have trouble understanding this current meter reading of my LSH-P and hope someone can enlighten me. /ubbthreads/images/graemlins/help.gif (I admit my DMM is a cheapo and the result may be quite erratic.)

The 123 battery which came with the LSH had 2.93V (a little used during QC test?) and draws 1.05A current.

A new replacement battery had 3.27V and reduced to 2.93V soon, it draws 1.02A.

Freshily charged GP NiMh 1300maH had 2.60V and draws 0.8A.

The brightness of all 3 battery sets look alike (I don't have a meter) but the total wattage consumed is about 3W for CR123 batteries while 2W for NiMh.

Assuming 80% of efficiency for the regulator, it is still 2.4W and 1.6W respectively.

I understand the standard current driving of LS1W is 350mA at Vf=3.5V, it comes to about 1.2W.

1) Why is the wattage from CR123 and NiMh are so different if the current to LED is regulated to be the same? (Or am I missing a point somewhere else in other CPF threads?)

2) Does LSH overdrive the LS1W? (My LSH-P is really nice bright.)

Whatever outcome, I know the functionality of the light is never affected, but just can't keep the curious mind bugging. /ubbthreads/images/graemlins/wink.gif

DJP

Re: Can\'t understand the battery current reading LSH-P

The LS is driven at 333mA. As far as power effiency, you need to measure the voltage at the terminal of the battery while under load. The open circuit voltage will mistakenly give you a higher power input level since the battery voltage sags under load. Also, some DMM's insert so much resistance into the circuit it affects the measurement. The Arc is constant current regulated and inserting resistance into the battery path will cause the regulator to draw a higher current which will mislead you. 1A does seem quite high even considering it could be due to higher LED forward voltage. Mine draws about 600mA from new 123's. I use a Fluke 77 for my current measurement.

CM

Re: Can\'t understand the battery current reading LSH-P

Your meter becomes part of the circuit and thus changes affects the readings.

The voltage that is critical is the Voltage directly at the converter board input.

Since you stuck a current meter in series, the internal sense resistor drops some voltage. A single 123 is considered a low voltage application and a few tenths drop here and there make a huge difference.

That said. The voltage dropped across the meter refects as a lower voltage to the input of the regulator. In order for the regulator to boost or maintain the output power it will draw more current. This is the same as if the battery voltage was lower and you did not have the meter in series.

In any case, inserting a meter to measure current from the battery invalidates all testing and is not considered accurate so it's highly possible to get the meter readings you are posting. Who knows what is happening when you do this. Also, you could be introducing a series inductance in the long DMM leads and this could make the converter board unhappy. You may not notice the brightness change, but if the converter board is not in the steady state condition it could draw double the normal current. Again, this is all speculation and like I said before, inserting a meter in series can cause all kinds of havoc with the circuit.

There are more accurate measurement setups that don't disturb the actual circuit and battery performance and the equipment will like be more $$ than a regular DMM.

Wayne

Re: Can\'t understand the battery current reading LSH-P

CM & Wayne, thanks for the clear explanation.

I do have all the condition to lead higher current -- a cheap DMM & long (possibly thin) probe cable. I didn't expect it to affect this great.

Then, what is the better way to measure the current without affecting much of the original circuit performance? I always wanted to learn this!

Re: Can\'t understand the battery current reading LSH-P

It's hard to do that on the Arc as Wayne pointed out the parasitics involved. What exacerbates the problem is that the Arc does not have an input capacitor, unlike other circuits such as used in the Surefires and Wayne's BB and DB circuits. This capacitor acts as a "local" battery to the circuit and in its absence, parasitics such as lead inductance will lead to erroneous results. It might be easier to just do a runtime test and infer the current draw from that. Probably more useful and possibly more accurate in the case of the Arc.

CM

Re: Can\'t understand the battery current reading LSH-P

Perhaps you could hook up an oscilloscope probe to the contacts?
I suppose this might help.

Re: Can\'t understand the battery current reading LSH-P

My LSHP draws 550 mA circa from 3V batt. 1 Amp drawing is really too much, you can do a run-time test using the NiMH.
Take note of how much time do you need before moon mode !
So you can know if your LSHP is ok.

Re: Can\'t understand the battery current reading LSH-P

I thought the LS uses a switching power supply, and I thought the switcher draws current in pulses. I don't see how a DMM can give a valid current reading here.

Where have I gone wrong?