## Step 12: Reading Amps. (current Draw)

Although often used interchangeably in this Instructable, and wrongly so, "current" and "voltage" are actually different from one another. Voltage concerns the pressure at which electrons flow, like water pressure in a pipe.  Current (amps. or amperes) deals with the volume of electrons flowing at the operating voltage. A device may appear to work, but makes an unusual noise or quickly overheats. A check of the amps. drawn by the circuit can tell you if there is a problem, even though it will not identify the exact problem.

First, check the device specifications.  Look for a plate or label on the back or bottom of the device. It may tell you the device is designed to draw (for example) 2.3 amps. at 120 volts. Or, it may tell you the device uses 276 Watts at 120 volts. (Watts equals volts multiplied by amps., so divide Watts by volts to determine the proper amps.) If this device were found to draw (for example) 4.5 amps., you would know immediately something is wrong.

Reading amps. is different from reading voltages. Voltage readings are the drop in electrical "pressure" across two points in a circuit, or a whole circuit. The meter is not part of the circuit, but reads what happens across or between two points in the circuit.  When reading amps, the meter must become a link in the circuit, just like a link in a chain. See the graphic showing how you can make a sandwich with two conductors and a piece of plastic between them. This sandwich can be placed between two batteries in your device to see what the current draw is. The alternative is to break the circuit by cutting a conductor and connecting the meter to the ends of the cut conductor. You would need to reconnect the cut connector when you are finished. Set the selector for DC amps in the desired range.

You may need to change the holes into which the probes connect on the meter. See the second photo.
<p>Helpful tip! I have my own multimeter which I am very satisfied with just don't know how to use, this is a good read. I bought the unit at www.gainexpress.com and used the code 10SPECIAL to avail 10% off.</p>
Thank you for your comment. I am glad it is useful to you. A multimeter can save the owner a lot of money quickly. Also, you can use a multimeter with benefit for things where you feel safe and comfortable. When you get to something that makes you nervous, call in someone with more knowledge and experience.
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<p>Thank you. </p>
You are right,and as far as carrying one in the purse, ladies who may not be so bold as to carry the larger meters in the pocket book may be interested to know that Radio shack makes a nice little meter that is small around 4x3x1/2.It folds in half, it is kinda expensive,I paid about 30.00 for one a few years back as I needed it often for work,and it was small enough to carry in my shirt pocket.Very good advice,for all ,good thinking.
Thanks. The photo of the meter sticking out of a woman's purse with her cosmetics nearby was a little tongue in cheek joke. I ran it past a lady preschool teacher I know and she thought it was pretty funny. <br><br>I have seen some pocket meters like you describe. They would be great for what you describe. My brother gave me a basic Radio Shack meter that does not fold, but is about 3/4&quot; x 1&quot; x 6&quot; with an insulated fixed probe on the front end and a wire lead near the front end. It is small enough to carry in a pocket case for eyeglasses. I have often taken it with me when I travel.
Sorry I didnt catch on,the reason I took it serious is because my mothers purse had a small screw driver set,keychain type multi tool,a credit card tool with many uses,well you get the just of it.She didnt however have a meter as she was scared of electric;its just my Pops and myself now,and we ran a small plumbing/drain cleaning company from 1987-2010.We are some do it ourselves kinda people.It is kinda funny now that Ive thought about it,but I think man and woman alike should at the very least carry a pocket knife,and I like your instruct.I hope ladies read it and take it to heart.
There are probably a few ladies adventurous enough to use a meter, even if for a few basic things. Imagine a woman in a group including a few men. The TV remote does not work. She removes the batteries, pulls a VTVM from her purse and tests the batteries. In a few minutes the remote is working again. Some will admire and respect her. Others will feel outclassed and hate her.
I would be of those who respect her for sure,I respect anyone who will at least take a wack at it,and those who dont know how,but ask get my respect as well.
My wife was the first woman I ever met who knows what a wood lathe is. Her grandfather had one. I had bought one by saving my allowance in junior high. I still have it almost 55 years later.
My mother knew what a forge was,and when I was making mine out of an old wheel hub,she told me that a wheelbarrow made a much better one,course I didnt know she even knew what a forge was,but her grandmother who raised her was a Hatfield,and up in west Virginia they had to make do.Ill tell you Phil,woman folks will surprise you sometimes,wont they?
Well, it did save you money in a way because you didn't have to pay a mechanic \$60-\$100+ an hour to find that problem.
You are quite correct. I am so accustomed to doing whatever work I can on my car that I do not even think about what I would have paid at a garage, not to mention towing the car to the garage. Thank you for looking and for your comment.
I've got one of these meters from harbor freight i'm glad you wrote this Ible now i can use it where i didn't have a clue before how to start now i know <br> <br>Thanks for a great Ible
Those are not bad little meters for home use. I think I have one,too; but, I got mine at Home Depot and paid a lot more for it. I did this Instructable for people in your situation.
Before i read this i really didn't have much of a clue how to use it on much thanks for this ible now i understand a-lot more about it and how to use it now if i could just get a handle on basic electronics i''ve got a-lot of ideas for LED's and and some cool steam-punk stuff I've fallen into this steam Victorian era kick and can't seem to throw it off i find some of these things very fascinating to build and goof around with and of course my nieces love the stuff ...
There are some good basic books on electronics for the person who wants to learn on his own. There are also some good tutorial sites on-line. Here is a <a href="http://www.falstad.com/circuit/" rel="nofollow">link</a> to a pretty good circuit simulator that allows you to test circuits without the expense of buying real parts. If you go to this <a href="http://www.phy.davidson.edu/instrumentation/NEETS.htm" rel="nofollow">link</a>, you can download an older version of the US Navy Electronics Course for free. I apologize for taking so long to respond to your comment. I wish you well.
Hey np problem and thanks for the links i'll be checking them out !
When I was much younger I was very interested in radio circuits and wanted to learn all about them. Years later I met someone who had studied electronics by means of a famous (at the time) mail correspondence course. He said he did not use most of what he learned, but found what he had learned about power supplies gave him all he used and needed. Many things these days run on 5 volts, which is the exact output of a USB port and also an old phone charger. Once plug-in power supplies contained transformers with real copper wire. Now most are switched mode power supplies. The older style allowed adding a variable voltage regulator chip configured to the exact voltage you needed. The new style does not work with the regulator chips (as best I can determine). I wish you well. You will have fun with your electronics learning. Be aware some published circuits have bugs in them and when they do not work, it is not your fault.
lol np = no
i was subscribed to a magazine that had free DMM coupons for harbor freight, i think i have 3 freebies now, one for my tool box, one for my car, one i gave to my dad. i have a more expensive DMM for my electronics tool box. i find a reason to use one all the time
i was subscribed to a magazine that had free DMM coupons for harbor freight, i think i have 3 freebies now, one for my tool box, one for my car, one i gave to my dad. i have a more expensive DMM for my electronics tool box. i find a reason to use one all the time
i brough a multimeter to school, because you never know ehn you might need it and people kept asking waht it was, i was famouse for a little bit
One day they will wish they had been more like you and learned to use a meter. Thank you for looking.
I can't tell you how many times I have pulled my meter out only to have someone ask &quot;what's that?&quot;. I have saved time and money for sure. Awesome and informative instructable sir.
Thank you for looking and for commenting. This Instructable attempts to explain uses for a meter I have found in everyday needs. I expect my experiences are close to those of others. Have you used your meter for some common needs I missed? Thank you again.
I have several TV monitors around the house linked with coax cable. Sometimes in order to troubleshoot them I use the continuity setting, I have someone short out one side using metal to touch the center pin to the outer connector. I then use the two probes to check my various cables to identify them. <br><br>This also allows me to identify which cable connects to which device at friends homes when helping them connect TV, satellite or other antenna. <br><br>Jeff
I have a spool of bell wire I use to connect to a wire at a wall box a couple of rooms away. The continuity tester or the Ohms scale lets me check for a break in the wire inside the wall. I once found a broken wire inside a ceiling box this way, even though there was no visual hint of the break. Thank you for the information on how you use your meter.
Just the title made me proud to own one :)
I am glad you already have a multi-meter. You will find a lot of uses for it throughout your life.
thanks for the overview. I've read this and the sparktronics tutorial and it all makes a lot of sense - though I didn't read anything about the different sockets in yours (10A?) for mains voltages? <br> <br>Either which way, I'm off to do some soldering today and play with the multimeter to make an RFID arduino door lock!
Generally, you can do most of your work with the COM and + sockets. But, when measuring the current flow in a circuit you need to match the current type, AC or DC, on the dial with the current type in your circuit. You also need to use the socket appropriate to the current level expected. Recently, I wanted to check the parasitic current draw my automobile makes from its battery when everything is supposed to be &quot;off.&quot; If the door has been opened recently and the interior dome light is &quot;on,&quot; the current draw rose to 2.99 amperes. That meant I needed the dial set to the 10 A DC range. It also meant I needed to use the 10 A socket and the COM socket. If I had been measuring current in an AC circuit and it was expected to be more than milliamperes, I would have needed to use the same sockets, but change the dial to the 10 A AC setting. Which socket to use more concerns the type and level of current expected than the voltage.
You can add this use to your list of common uses for a VOM (common for me anyway). <br> <br>https://www.instructables.com/id/Attack-of-the-Killer-Strobes/ <br> <br>I use my VOM to repair cameras all the time. Luckily, I'm dealing with pretty low voltages and amperages to make it absolutly safe. The only risks are when dealing with photo flash capacitors.
I have a vague memory when on holiday with friends of breaking open a disposable camera and taking the AA battery out for my walkman. Saw what I thought was a 2nd AA battery and broke the camera open further to get it out. <br> <br>Que burst of light from flash and large electric shock. It was the biggest capacitor I'd seen at 11 years old, same size as an AA battery. <br> <br>Most people might have stopped playing with it at this point, but I recharged it and said to my mate 'go-on, touch those two wires' <br> <br>He didn't die and he learnt a life long lesson on what not to touch in electronics.
Thank you for your comment. I read your Instructable on checking trigger voltages of electronic flash units. I have two digital cameras, neither of which has a hot shoe. In the days of film cameras I did have a couple of Vivitar 283 units and used them with slave triggers for multiple flash. What I had really been looking to find was a way to use my 283s with a slave trigger that would get around the pre-flashes on most built-in flash units used on cameras like mine. I once found a schematic for a home built delaying trigger and built it, but it did not work. <br> <br>When I did this Instructable on using an electrical meter, I hoped people would take the basic things I showed and expand their usage to special purposes like yours.
i've seen a few old-timer mechanics turning on the wiper to check the battery strength when a car is having trouble starting.. i guess the wiper cranks more amps then the headlights.. once a car gone dead on me, even the instrument panel was blacked-out, it turned out the alternator had failed completely.. <br>
I am sure that would work. I used to buy repair manuals by Motor's. They always had excellent general diagnostic and repair material in the front section of the volume. Another technique was to turn on the headlights and have someone attempt to crank the engine. The engine should turn over with the lights dimming only slightly.
Another example of how a multimeter (and troubleshooting skills) can save a few hundred bucks.
It is not true that corrosion could be a problem if it is not visible. For there to be enough corrosion to cause a problem it is progressed to the point it is very plainly visible and there is no need to check it with a multimeter as it is obviously in need of cleaning.
I am sure I remember reading that not all corrosion is visible. Before responding I did a search and found someone had problems with corrosion he could not see without removing the battery connectors. I have found the newer side post terminals can be quite corroded, but the corrosion remains covered and not visible from a quick glance under the hood.
This is true, corrosion can &quot;hide&quot; in the contact areas between the terminal and post. What your doing is called a &quot;voltage drop test&quot;. It's a quick and easy way to locate where a bad connection is raising havoc. There are several good videos showing how to use a voltage drop to solve real world problems, including cars that won't start with battery terminals that look clean!
Thank you. I assume the videos are at YouTube. Is that correct?
Yes, and they scattered about the web as well. Several auto manufactures are teaching their factory techs how to use voltage drops to more effectively repair cars and especially computer circuits in cars.
I first became aware of the voltage drop test for auto battery connections testing from an old Motor's Auto Manual. That particular manual was published in 1969. Thanks.
I once replaced my car battery that seemed to have expired, with very poor response from the starter motor.&nbsp; But the new battery made no difference.&nbsp;&nbsp;<br> <br> After carefully tracing volt drops, I discovered substantial corrosion on the engine block where the battery ground cable terminal bolted to it.&nbsp;&nbsp;<br> <br> Just cleaned and greased, and no more problem.&nbsp;&nbsp; Thinking about it, two different metals, plus a bit of moisture and a current, is a beautiful recipe for corrosion.&nbsp;<br> <br> I always grease or oil nuts and bolts and electrical connectors when reassembling things, particularly on my car, both for preventing corrosion and ease of extraction the next time.
Your information is very good. I knew a man back in the 1970s who had spent over \$100 to have a bad ground discovered and fixed. To complicate things, grounding terminals are often hidden under layers of other things. Thank you for the important reminder.
You are right. I have watched my husband working on a small circuit board that would not work he took out the battery and used very fine sand paper on the contacts, suddenly the thing just stared working right again. This always amazes me. I have to say my first experience helping to fix something was my grandmothers toaster would not work. My dad took out his meter, tested good, then tried another plug and looked inside and scratched his head. The two copper leaf contacts were only very slightly brown like a dull penny. I offered maybe an eraser on the contacts. So he chuckled and let me try it. Then when we plugged it back in and it lit up, he was amazed...My dad was an electrical engineer...only time I ever got over on him as he was sure it was a broken internal element...lol
Apples and oranges, brass and copper especially degrade much more resistively and faster than lead, which is why lead is chosen, BUT we were speaking about visible corrosion too - brown like a dull penny is considered visible corrosion on copper.
If you are familiar with electrolytic capacitors, those are made by allowing an oxide to form on one side of the aluminum foil. It serves as an insulator and has the advantage of being thinner than paper or mylar film. It is a powerful reminder that oxides look like conductive metal, but actually insulate. Your father's experience with the toaster shows we look for what we expect to find, and sometimes that blinds us to what is.