Technical HOW TO USE A MULTI METER/VOLT METER

A bit pricey, and many of the functions will be of little use on a Hamb-friendly vehicle. I don't care for the lack of a DC amps function. If you're working on late-model computer-controlled vehicles, this would be the hot ticket as long as you know what/how to check things.

 

You can pick up this combo set on eBay for $196.
http://pages.ebay.com/link/?nav=item.view&alt=web&id=251445543504
It has many different leads and a short finder. You can plug the short finder into a circuit and use the hand held device to locate a break in a wire or short.

What makes this really nice is that a LED will light up green when the probe is touched to ground and red when touched to power. So you can check for more than just 12v. There is a momentary switch that enables you to either power up the tip with 12v or make it ground. This makes it nice to test non working circuits. Lets say you have a tail light out, you can check for power and ground. If both are good you can also supply power to see if the bulb may be bad. I'm sure there are many other uses I have not even found yet.

 

I use a headlamp bulb for heavy circuits like power windows. just because it lights the test lamp does not mean there is enough current to operate a motor. The headlamp bulb puts enough load to prove the circuit.

 

voltage (E) is checked in parallel and amps (I) is checked in series . make sure the is no voltage (E) when checking ohms (R).

 

resistance in a circuit dictates current draw . voltage is the "pressure" that moves current

 

Yep, that's how I learned it. R= E/I

 

So back to our regularly scheduled programming, how to use a meter or test light for figuring out why something is not working, like tracing wires, finding out if they have voltage, solving problems. Since the HAMB is not Back to the Future, How about Back to Basics. How would you teach someone to find electrical problems? There are plenty of threads about that every week.

 

good thread.....

 

This is a good thread....hopefully someone can post a detailed step-by-step on how to find a parasitic drain.
My old man's '61 galaxy has had one for the last five years.... I only found out about it last week.
I've been searching the internet for instructions, videos, etc, on how to find the drain, but they all seem to vary in terms of method and which types of meters to use. Plus, most deal with modern cars with multiple fuse boxes.
I'm a noob when it comes to this electrical stuff, but I'd really like to help him figure this out.

 

Ruben, Here is a start. Super basic. Remove all fuses. Take a reading of battery voltage. Let it sit for a while and take another reading. If the reading is not lower, put in one fuse. Let it sit for a while. repeat til you see the voltage drop. Trouble shoot the circuit that fuse feeds until you can put that fuse in and not get a voltage drop. Put in another fuse. Wait. Test.

 

for a drain on your battery turn everything off as you would normally but also make sure that radio , heater and every device possible is in off position .remove your + batt . terminal and hook your ammeter inline (series). black to the battery , red to the clamp. be sure your meter is in the proper range (start high). if there is any amps flowing you have a drain. pull fuses till it stops to isolate the circuit. repair circuit.

 

you can do the same with your test light . hook it in series off of your removed positive terminal . if the test light glows you have a big problem. the trouble with this test is that the stray current drain and the test light bulb are splitting the voltage so the light may be dim or not even glow at all.

example of a series circuit below, R1 and R2 are resistors (pretend they are lights) , V1 is your battery. notice in a series circuit voltage splits ? because the resistors are equal (1000 ohms), it splits even.

 

http://lmgtfy.com/?q=Parasitic drain test
This should get you a bunch

http://m.wikihow.com/Find-a-Parasitic-Battery-Drain
This is very basic.

The meter is the best way.
If it's drawing power it will be warm too.
Once I know I'm hunting a draw, Usually I remove all fuses first then start looking for the draw - adding them back in.

 

here is a parallel circuit vast majority of auto cicuits are parallel so everything gets 12 v

 

Once you have learned Ohm's Law and the difference between an open and closed circute then you'll be ready for a battery/bell and test light. The Power Probe is the ticket but unless you have a good understanding of what it's telling you, you'll still be scratching your head.

 

WOW Rfraze .I didn't know there where others out there that didn't know that much about meters like me.GOOD SUBJECT! Bruce.

 

Bruce,just listen to fraze,he is trying to tell you in laymans terms so you can understand eaiser..,,forget all the hi-tech talk as some have added..

 

or maybe.....it is there and the analog meter isn't sensitive enough to detect it.

 

Thanks bct , To be measuring amps, the meter should be set to the proper ohm range or volts range?

 

an ammeter test amps . if you are using a multi meter then set to the amps in DC . start in the highest range and work down. until you are in a range that's about double the reading you are getting. you don't want to peg the meter in an analog meter or replace the fuse in a digital.

a tip I learned recently is that the end of a probe will hold rock solid to a wire with a marrette or wire nut. helps to leave one hand free for other tasks.

I also keep a short piece of 14g wire with a female or male spade crimp on it and a stripped end . marrette it to a probe and you can get into all kinds of things with the spade ends .

a frustrating thing when using a meter esp. under a dash or at the rear bumper is finding a solid ground point to test for voltage. make sure to take the time to clean to bare metal or you may be chasing your tail

 

also dielectric grease. I slather that shit all over myself . you can't use it enough.

 

I crimp an alligator clip onto a probe for a slip fit, which allows it to be used or not depending on circumstances.

 

You can also put a light bulb scoket with a bulb in series with ether the + or - and if you have any load the light will light. Pull fuses untill the light goes out and you have located the load.

 

Another reason I like Fluke digital meters is the hold function. When you get in a position where you can't read the dial and watch the probes it will read and hold that reading on the screen then you hit the reset button. Fluke meters are the world standard and are expensive but you only pay for quality once. Most troubleshooting on cars can be done with a simple test light and a $5 OHM meter.

 

Test light tells you there is enough current to light the bulb. $5 ohm meter tells you what?

 

Hopefully some basics on circuitry will help everyone understand as well. This is a pretty useful forum. V=IR; Voltage= Current x Resistance (or in an audio circuit frequency based resistance AKA impedance). A little bit more about basic circuitry.
When it comes to calculating resistance, if the resistors are in series, resistances add. For example, two 1k resistors in series in a circuit with a 12V battery and the circuit's total resistance will be 2k. If you then use the formula above, you will see the current is .006 amps or 6mA.

If the resistances are in parallel you would need to use 1 divided by ( 1/R1 +1/R2 + 1/Retc.) Its always easy if resistors in parallel are of equal values, as you will only need to divide. Using the same resistor values, again with a 12V battery, your circuit would now read as 500 ohms. This would then provide you with .024 amps or 24mA of current.

From this you can see if the voltage stays the same, rising current means less resistance and vice versa.

Capacitors, which store a charge, can also be added in series or parallel, although they use the same formulas for opposite configurations (caps in parallel actually add, caps in series use the PITA formula listed above). When probing around, be careful with capacitors as they do store a charge! Caps can be discharged by shorting them with a low resistance resistor.
This is why when you see the guy riding down the road in his civic, with his headlights flashing every time his two 12" subs in the back hit, you know he needs a cap in his system. The cap will charge and when the system requires the extra power discharge.

Also note, high voltage isn't the killer - high current is.

 

To measure amps, you will want to set the meter to amps written as A, not ohms or volts. You may also see mA (milliamps) or μA for microamps. If you are not sure what the reading should be always start with A and work your way down to milli and then micro. You will want to make sure you are reading the amperage in DC on most car applications. You may want to google the symbol for DC, the best I can describe it is a hard line with a dotted line underneath it.

 

Lots of good ideas and information here and we are just getting started. Thanks for answering all questions.

 

If someone is trying to find the other end of a wire with a meter, what dial setting would they use and what do they look for on the screen or dial?