Learning how to take light measurements with a DMM

Hello all you wonderful folks. I see posts where people are measuring draw, tailcap measurements, figuring out runtimes, etc. I want to learn to do this stuff on my own lights. I have a meter and want to learn what to test and how to test to get the measurements that you talk about on this forum. Thank you for the help with this. :)

This article is very good. Like I've often said, the Other Place is full of useful information, pity about the attitude.

That should cover most things. Any problems, let us know and we'll be able to add to it as required.

Thank you very much for the help. I am off to CPF to read and play. This will be fun. I am going to use the light that Foy sent to me for learning.

This is interesting reading, thanks again. I will play and then post what I find and see what you think....that way I can learn from the results of my own light.

Best way to do it. It is always cheaper to learn from the mistakes of others than to make your own. Believe me on this. I learned the expensive way.....

I am using this article to teach me: http://www.candlepowerforums.com/vb/showthread.php?236906-Simple-guide-to-using-a-DMM-for-measurements

Light:

Solarforce L2P host

5 mode XM-L T6 drop-in (not sure which model it is)

Trustfire 18650 flame cell 2400Mah @ 4.04Volts

Now doing a current consumption test I get these results (the first test in the article):

I get nothing at all, the meter reads 0.00, what is going on? My test leads are in the 10A unfused and com slots. I am using the scale for A and tried 20m and 200m in the A scale.

TailCap:

0.3 ohms meter set to 200ohm scale (lowest it has)

Make sure the DMM is switched to the 10A range. With the tailcap off of the light, touch the black lead to the negative end of the battery and the red lead to the bare threads of the light (anodizing doesn't conduct electricity, so you have to touch bare metal). The DMM will complete the circuit instead of the switch. The positive end of the battery should still be in the light touching the spring in the head, just like it usually does.

Also to note, you will be needing to cycle the modes by taking the DMM lead off of contact for a moment, then back on.

One of the things I've noticed with my fairly expensive meter, is that if you accidentally select the lower current bracket on the DMM, then it will do some current limiting to the driver. Hence, the "set it to 10 A" is good advice if you want real readings.

OK my leads are red in the 10A unfused slot, black in the Com slot, DMM is set to the 10A scale. Black lead is at back of battery in the light and I have plenty shiny metal on the treads for red lead, still get nothing. :) Could the meter be fried? It has a funny smell to it yet it will read battery voltage and to the tailcap test. It is a $12 autoparts store meter.

If your meter is kinda crappy, the funny smell might be from the lack of a fuse, but I'd be more worried about the battery if you put it in backwards.

The battery in the flashlight is in the right way, the meter was taken apart and it is powered by a 9v which goes in one way and it does have a fuse in it. The fuse is good, but guess what, the three ports where you put the leads in from the inside are burnt looking, smell bad, and have a corrosion white look to them. I think I fried the DMM. :( I did not use the 10A setting at first, so it was my fault. I used what they said in the article not knowing any better. Who makes a good DMM on a budget? LOL

You can't fry a meter if you only put it on the wrong setting with the leads in the right holes, only if you tried to put too much current through the ports.

Just get the cheapass one from harbor freight.

Another reason to start off with cheap equipment and move up to more expensive stuff later. Sounds like it may well be fried. You have to use the 10A port and the COM port and switch the DMM to 10A.

I bought this one at Amazon for about $7. The price varies. There are a lot of very similar ones all over. There is also one on eBay for pretty cheap but it is from overseas, so it will take a while.

This one on eBay is $4. I ordered one, got it, and my puppy chewed it up before I could even try it out. Someone else here liked it though:

http://cgi.ebay.com/LCD-Digital-Multimeter-Voltmeter-Ammeter-Meter-OHM-DVM-/330578539400?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item4cf8043388

Well looks like I need a new DMM. LOL :) Now I know. I will have to order the Amazon model, for the price no need to wait for post from China.

Depends on how much you value your own safety. But hey whatever, I use recycled unprotected 18650's.

Those are the same design (ic inside) as the cheap hb ones.



Another reason to start off with cheap equipment and move up to more expensive stuff later. Sounds like it may well be fried. You have to use the 10A port and the COM port and switch the DMM to 10A.

That's not how he burned his, though. He probably tried to measure tail current across a shorted batter or w/ the 400ma port.

What about this model here? Good idea or overkill?

http://www.amazon.com/Equus-3320-Auto-Ranging-Digital-Multimeter/dp/B000EVYGZA/ref=sr_1_17?ie=UTF8&qid=1308712950&sr=8-17

I had that in my cart before I found the almost-free HF ones work adequate enough to bother clicking buy on it. I didn't get the other cheapos because they didn't have backlight (and equus doesn't either but it's got the big lcd). Go for it.

Now when I get me another meter to replace the one I broke I will keep learning and go from there. Oh well glad it was a cheap meter and not a $200 Fluke.

I think you didn't set the dmm to 10AA. I did that myself once ( a long time ago)

Not that a Fluke can't be smoked, but you do have to try pretty hard.

I'm amazed at the blunders I've done and my Fluke has survived. (Like leaving it on continuity while I'm checking the output of a power supply.)

For some fun check out www.eevblog.com/2010/05/05/eevblog-84-high-energy-multimeter-destruction/ its about 12 minutes long and is quite entertaining.

I just got this guy in the mail today:

http://www.amazon.com/Equus-3320-Auto-Ranging-Digital-Multimeter/dp/B000EVYGZA/ref=sr_1_17?ie=UTF8&qid=1308712950&sr=8-17

I now know what I did wrong before so now I can learn by playing with my Solarforce L2p. :)