Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

Buy Site Supporter Role (remove some ads) | LPF Donations

Links below open in new window

FrozenGate by Avery

Craftsman Multimeter Issue

C

chido

0
Joined
Dec 4, 2007
Messages
1,918
Points
0
Ok, I need help, this is my first multimeter and I thought I had covered all the basics on how to use one. But I just tryed to measure the amperage of a NIMH 7.2v 900mA battery and for some reason, the meter won't measure it. It looks like the measurement gets it out of range. Like if you place two AA batteries in series and you try to measure the voltage when the knob is set to the 2v scale instead of the 20v, it won't measure and all that shows up is a one. Well that's the same deal when I tried to measure this battery pack, I also tried out other battery packs. A NiCd battery pack rated at 1500mA got a reading of .20 whick I think is 200mA, a 270mA pack got a .02 which I assume is 20mA, and finally a 650mA pack got a reading of .01 which I think is 10mA. Yes I am setting the knob to the 10A scale, and yes I am putting my positive probe on the 10A jack, this is the multimeter: Any help on what's going on? :-/
http://www.sears.com/shc/s/p_10153_12605_03482345000P?keyword=craftsman+multimeter
 





As many times as you have told other members how to properly test their driver, I am surprised you are hooking your probes directly up to a battery to measure current. Big no no and you may have damaged your meter.
 
Then how are you supposed to measure the current of a battery? Damn I feel stupid, I did a lot of research on how to use one, and even watched videos of people connecting it directly to the batteries to measure for current.
 
chido said:
Then how are you supposed to measure the current of a battery? Damn I feel stupid, I did a lot of research on how to use one, and even watched videos of people connecting it directly to the batteries to measure for current.
Click to expand...

You would need a battery charger capable of doing it. The advanced chargers have a capacity mode that will let you test the capacity of the batteries.

Another way you could do it is to connect the batteries to a known load and let the batteries run down until they reach 1 volt per cell. This is how manufacturers test them. For example let's assume you have 2000mah nicd batteries. You hook them up to something that draws 250ma's consistently...like a laser using the 317, and using 6 nimh batteries. You would measure the time it takes for the batteries to reach 1 volt per cell, which would be 6 volts. In this case the batteries should last for appx. 8 hours. 2000mah's divided by 250ma's = 8 hours.
 
Never mind, I can't believe how stupid I am, I just did more reading and figured out how to test for current. I only knew how to test DDL's driver, but I didn't really understand why it was done that way, now I know, for all of those who are reading this, it doesn't matter the # of posts you have or the time you've been on the forum, there is always something that you will not know, and there will always be something you'll mess up. I bet I still have thousands of things I'm gonna mess up. ;D
And Gazoo, how do I know if I damaged the meter? I just tested the the current of the 900mA battery (the right way, and the battery was fully charged) and I got 1.2 amps, also I tested the 1500mA battery and I got a reading of 400mA at first, then it went down to 300mA because the battery was really weak, then motor I was powering stopped spinning and it stayed at 180mA, is this normal, or did I mess up the meter? :-?

EDIT: I just read your post. But I still want to know if the info above is enough to determine if it's broken or not, how can you tell? It seems to still work properly when measuring for voltage, testing continuity, testing diodes, taking temperature measurements, and resistance testing, does the whole multimeter stop working properly if you damage it, or just the function for measuring current?
 
It would most likely only damage the current function. The only way to tell if you damaged your meter is to test it with a known load. Make sure your meter is in series with the load.
 
So, what could I use for a load? All I have is one silicon diode and some 10ohm resistors.
Man, I'm going to need some help with this. :-[

Oh, and then how do I know what current I'm supposed to get? :-[ :-[ :-[
 
Flashlight bulbs come spec'd for a specific volt and amp and I use them to test circuits before using my diodes.

Even radio shack has a 2.47v 400mA bulb thats decent for many diode simulations.

Tho maybe you just blew the meters fuse.

Open the meter and see if the little glass fuse is spent.

SN
 
I can't recall a DMM that was not fused on the current measurement side.

99% chance you need a fuse

SN
 
So if the multimeter has a fuse I should be safe, right? And all I could find for a load were 12v bulbs, but the box doesn't say anything about the current needed, so I can't use a resistor or anything like that for a load? :-? :-[
 
Replace the fuse if blown and if it reads a current for a load, its ok,,, Ok means accurate to what it was designed for, It may or may not be super accurate, but if the fuse was blown then replaced, it should be as accurate as it was. The bulb will draw a consistent load, It may increase a bit as it heats up. It should be ~ as accurate as it was before.

SN
 
Yeah I know about the fuse, but I thought it only protected the multimeter when you went over the 10A of current, I didn't know it protected the DMM if you stupidly tried to measure current like I did. Anyway, I checked the fuse and it looks ok, the only thing I was worried about was that I damaged the current setting and that it wasn't going to take the measurements right. Thanks for your help guys. :)
 
LOL thats like when i first got a multimeter. I hooked it up to 2 car batteries in parallel trying to measure the current, and wondered why i got big sparks and the wires got hot ;D ;D
 
The 10 amp section of my meter is not fused. The ma section is fused.
 
i had a meter that was rated at 20 amps unfused. i was measuring how much current an electrolysis cell when it shorted out. the cell was pulling 15 amps from a 100 amp DC welder. . . lets just say the meter never worked again. ;D :) ;D
 
I put the multimeter inline with the highest amp load i can find, not directly shorting out the cell.
 
You must log in or register to reply here.





Back
Top