Electricity 101 Part 3: Using Multimeters


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Electricity 101 Part 3: Using Multimeters

Postby WingAdmin » Sat Nov 30, 2013 5:56 pm



Part 2: Using Multimeters

Having amperage and voltage is great, but how much do you have? How much should you have? To know this, you need to be able to measure it, and to do this you need a meter of some sort.

Meters come in various shapes and sizes, but virtually everyone uses digital multimeters nowadays, and with good reason. It is much more difficult to physically damage a digital multimeter by utilizing it incorrectly, and they tend to be a bit more accurate than old analog meters.

I'll show a couple of them here. This first one is a very cheap, simple meter that Harbor Freight gives out for free (or just a few dollars). It will do the job, although it's not very accurate - but in a pinch (i.e. emergency) it will definitely work, especially this one which has a backlight in it. I carry one of these in my bike with me - I don't care if it gets wrecked or damaged, I'll just get another one. When the batteries in these die, I just throw them away and get another free one.

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The second is my bench meter. This one is extremely accurate, calibrated, and the numbers are much bigger and easier to read.

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Another main difference between the two is that my big meter is autoranging where the Harbor Freight cheapie is not. What this means is that on the non-autoranging meter, you must select the range of voltage or amperage that you are expecting to measure. It has a setting for 0-200mv (200 millivolts, or 0.2 volts), 0-2000mv (0-2 volts), 0-20 volts, 0-200 volts, and 0-1000 volts. When working on motorcycles, you're fairly safe setting it to 0-20 volts, as you shouldn't ever see voltages higher than that. However, if you don't know what voltage you are measuring, start at the highest setting and move downwards as needed. Measuring 200 volts with the meter set to the 0-200mv scale will quickly let the smoke out of the meter, and you'll be off to Harbor Freight for a replacement.

An autoranging meter dispenses with all of this. It automatically starts at the highest range, and works its way downward as it sees fit, without you having to switch a dial. You can safely put 0.2 volts or 200 volts into it, it will figure out how to deal with it.

Also note we are talking exclusively about DC voltage in this article - AC is a topic for another day.

Some meters require you to switch the test leads depending on what you are measuring. The black is almost universally always plugged into the "common" plug. In this meter, to measure voltage of any kind, the red test lead is plugged into the plug on the far right.

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To measure amperage (up to 400 mA), resistance (in ohms), or continuity, the red lead goes in the second plug from the end.

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Lastly, to measure high amperage up to 10 amps, the red lead goes in the leftmost plug.

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The Harbor Freight cheapie has one less plug - one red plug for volts, ohms and current up to 200mA:

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And one plug exclusively for 10 amps (DC only, as this meter does not have the capability of measuring AC current):

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I've spent a fair amount of time on these plugs, because it is very easy to make a mistake - i.e. leaving a test lead plugged into the amperage socket when trying to test voltage, which will provide a direct short and at best blow a fuse inside the meter, and at worst blow up the meter. Whenever you use your meter, double check your test lead plugs! I say this because after over 35 years of working with electronics, I STILL make this mistake from time to time - in fact, I blew the 10 amp fuse in this Harbor Freight meter while taking these pictures. Yes, I still make mistakes! :)

So how do we hook these things up to measure voltage and amperage? Let's start with voltage. Remember, voltage is electrical POTENTIAL to do work - we can have voltage without any work being done. A motorcycle battery can provide 12 volts when it is not even connected to anything - that potential is there. So we can hook up a meter to a motorcycle battery - red on positive terminal, black on negative terminal, and we will see the voltage that battery is capable of putting out at that moment:

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Note that these two meters are hooked up to the same motorcycle battery. Notice the difference? The Harbor Freight cheapie meter is showing 0.32 volts higher than my "good" meter. You get what you pay for. :)

What happens if you hook the meter up backwards, with the red wire on negative and black wire on positive? Not much. The meter will show the same amount, only it will show it with a negative sign in front of it - which is technically correct. It is measuring negative voltage.

Don't try this on an old analog meter! You can and will damage an analog meter by hooking it up backward.

Here's an old analog meter, also hooked up to the same battery. Note that it is showing 14.25 volts, even higher than the other two meters. This meter needs to be calibrated.

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So what does this tell us? Well we can utilize this information in a couple of ways. First off, we can measure the condition of the battery under load. We do this by setting the meter to measure voltage, and hooking it up to the battery, in PARALLEL with the motorcycle. This means the motorcycle is hooked up to the battery, and so is the meter, as in the diagram below:

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Now we watch the voltage on the meter when starting the motorcycle. When the starter is cranking, we really shouldn't see the voltage on the battery drop below 9 volts at the very least. Any less than that, and the battery is either discharged to begin with, or is near the end of its usable life.

The second thing we watch is after the cranking is done. Without actually starting the bike, after cranking it, how quickly does the meter return to (or near) the original value? We want to see just over 12 volts - repeated or extended cranking will deplete the battery so that we see less than 12.

We can also check the condition of the bike's charging system. Once the bike is running, rev the engine up to 3,000 RPM, and have a look at the voltage. Ideally, you should see 13.8 volts. It may take a few minutes to get up to 13.8, depending on how much cranking was required, and how long since the battery was last charged.

What about identifying poor connections or failing wires? This is a fairly simple task with a voltmeter. Let's say we have a light bulb on our motorcycle that is dim. We need to find out what is causing the problem. For the sake of our example, we'll assume there are two sets of connectors in between the battery and the light bulb.

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Setting our meter to volts, we connect the black test lead to the negative terminal on the battery. For test #1, we put the red test lead on the positive terminal of the battery. This is our baseline test - it tells us what the voltage SHOULD be at the light bulb.

Next we test the red wire at of the connector at test #2. If the voltage is much lower, we know there is a problem with the wire somewhere between the battery and the first connector. If test #2 shows OK, we test the other side of the connector, at test #3. If the voltage is low here, we know there is a problem with that connector. We keep going all the way out to the light bulb, until we find the point in the circuit at which the voltage drops. When we do find that part, we know now where to look and what to fix.

The same thing goes for a circuit that just stops working altogether. If we get to test point 4 and still have +12 volts, but at test point 5 we have 0 volts, we know that the connector has failed.

Or if we have +12 volts at test point 5, but 0 volts at the light bulb, we know that the wire in between the connector and the light bulb has been cut.


Next, there's current. We can measure current, in amps. Unfortunately, with a limit of 10 amps on the average meter, just about every item on a motorcycle draws more current than we can safely measure. Attempting to measure more than 10 amps will damage the meter or blow the fuse inside the meter. However, there is one thing that the current measuring capability of a motorcycle is good for: Measuring parasitic draw.

Parasitic draw is the electricity used up by the motorcycle when it is sitting turned off. Thinks like the clock and radio memory require power to keep running, so they are always connected to the battery regardless of whether or not the ignition is turned on. If your battery is dying quickly when the bike is not in use, it's possible the parasitic draw is too high. Different models have different draws, but for an example, the maximum spec for the GL1500 is 5 mA. To measure parasitic draw, we hook our meter in SERIES with the motorcycle - this means it goes in between the battery and the motorcycle.

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It is of critical importance that when you have your meter hooked up this way, that you do not turn the ignition on! The bike will instantly draw many amps of current, far beyond the capability of the meter, damaging it or blowing its fuse.

A better (and safer) way of measuring current draw is by using a shunt meter. This is an example of a cheap Harbor Freight shunt meter that will measure up to 30 amps - and it is more than capable of measuring any one circuit in your motorcycle. The way it works is by temporarily displacing a fuse in the fuse block. Keep note that this meter has a limitation for measuring high amounts of current - 10 seconds for 30 amps before you need to allow it to cool down. It will be safe to measure less current for longer periods of time.

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First, you identify the circuit you want to measure. Let's say you want to know how much power the radio is drawing. You remove the fuse that powers the radio:

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In its place, you plug the shunt. The original fuse that you removed is plugged into the side of the shunt:

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The motorcycle ignition is then turned on, and the meter will display the amount of current being consumed by the circuit you have displaced:

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Lastly, we have resistance. Our meters can measure resistance in ohms. The meters work a little bit differently when measuring resistance: Instead of measuring voltage or current being supplied by the vehicle being tested, instead the meter provides the power, and measures how much of that power it gets back. For this reason, it is of CRITICAL importance that there be NO POWER in the circuitry being tested when the meter is set to measure resistance. Having power in a circuit when you are attempting to measure resistance is a very good way to quickly destroy a meter!

Why would we want to measure resistance? Well, for vehicle diagnostics, for the most part, we don't. But what we DO want to test for is open or short circuits, failed switches and sensors.

Autoranging meters just have an "Ohm" setting:

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Where non-autoranging meters have a setting where you must set the resistance range you wish to measure. For measuring open and short circuits, we want to pick the lowest range as shown:

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Digital meters show an open circuit (no connection between the test leads) in different ways. This meater shows an "L" for "out of range":

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Whereas this meter just shows a "1" which is its way of saying "more resistance than I can measure":

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When the test leads are connected to one another, you should see a reading of zero, or close to it:

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For measuring open and short circuits, this meter has a buzzer setting: When you connect the leads together, the meter buzzes. When you open the leads, the buzzer stops. This makes it very easy to test things hands-free:

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Using the meter this way is quite simple: Put one test lead on one end of a wire, and one test lead on the other end. Does the meter show 0 ohms (or something close to it), or buzz (if it has that feature)? If so, then the wire is good. If not, the wire is bad.

Same thing goes for testing switches, like a neutral switch, thermostat switch or oil pressure switch. These switches have a single wire that runs to them, and when the switch is closed, it connects that wire to ground (the engine case, which in turn is connected to the negative terminal of the battery). Put one test lead against the engine case, frame, or any other bare piece of metal on the bike. Put the other test lead on the wire leading to the switch. If you see ~0 ohms, then you know the switch is closed. If you see the meter's indication for "out of range" then you know the switch is open.

Short circuits can happen when wires are damaged, most often when an incorrectly assembled component or a misrouted wire causes a wire to get pinched against something. The insulation on the pinched wire is breached, and the wire inside touches a metal piece of the motorcycle, which connects it to ground. When you turn the power on, this direct short to ground draws a tremendous amount of current, blowing a fuse.

Putting one test lead on the wire and the other against ground, start to manipulate wires or components until you see that the wire is no longer shorted.

Keep in mind that if the wire is feeding something like a light bulb, the low resistance of the light bulb itself can cause the meter to indicate a short circuit. In this case, remove the light bulb before testing the wire leading to it.



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Re: Electricity 101 Part 3: Using Multimeters

Postby dwight007fchr » Sun Dec 01, 2013 8:12 am

Great article! Regarding the fact that starters do get hot and many people are clueless about not cranking and cranking and cranking without giving cool-down periods.........has any starter makers thought of adding cooling fins on the outside to absorb the intense heat? But then again, I would guess that the windings would still burn/melt way before the cooling fins could save them.

Another interesting electrical fact is that for up to a minute AFTER an electrical motor stops spinning, it takes less amps to start it up again.....I think the electromagnetic fields are still "spinning", and thus it takes less power to get the motor turning again. So, theoretically, it should take a bit less power to crank the Wing starter after she fails to start the first time, and you waite say 10-15 seconds before trying again. Theoretically, that is......but factor in those 3 corroded yellow wire connections, then anything could be happening.

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Re: Electricity 101 Part 3: Using Multimeters

Postby redial » Sun Dec 01, 2013 7:09 pm

Thanks for the Part 2. Your efforts are well appreciated.
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Re: Electricity 101 Part 3: Using Multimeters

Postby minimac » Sun Dec 01, 2013 8:19 pm

Good job explaining this. It has to be good because it made me finally get my watts and ohms straight!

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Re: Electricity 101 Part 3: Using Multimeters

Postby bohdan » Tue Dec 03, 2013 8:51 am

Thanks for this!!! Using those DVM is much more understandable now.

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Re: Electricity 101 Part 3: Using Multimeters

Postby tandem54 » Fri Dec 06, 2013 12:19 pm

Thanks for a great article! Well written and great pictures!
I (we) sometimes take things for granted when I (we) understand them, It is hard to think of people who just don't.
My wife tells me I'm amazing sometimes when I fix something and I tell her it was no big deal (simple to me) and she tells me
"A lot of people couldn't do that"
I thank god for giving me the knowledge to understand stuff.
Keep up the great educational articles!
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Than sitting in church thinking about my Motorcycle

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Re: Electricity 101 Part 3: Using Multimeters

Postby WingAdmin » Fri Dec 06, 2013 10:07 pm

tandem54 wrote:Thanks for a great article! Well written and great pictures!
I (we) sometimes take things for granted when I (we) understand them, It is hard to think of people who just don't.
My wife tells me I'm amazing sometimes when I fix something and I tell her it was no big deal (simple to me) and she tells me
"A lot of people couldn't do that"
I thank god for giving me the knowledge to understand stuff.
Keep up the great educational articles!


That's funny, my wife tells me the exact same thing all the time! :)

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Re: Electricity 101 Part 3: Using Multimeters

Postby nsjoe » Mon Dec 16, 2013 1:37 am

Well done WingAdmin. I particularly enjoyed the statement, "Measuring 200 volts with the meter set to the 0-200mv scale will quickly let the smoke out of the meter, and you'll be off to Harbor Freight for a replacement." I've done that.
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Re: Electricity 101 Part 3: Using Multimeters

Postby JDMAG » Sun Jan 12, 2014 10:48 am

Very good article. explained just the way I was taught. :)

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Re: Electricity 101 Part 3: Using Multimeters

Postby bustedwing » Sun Jan 26, 2014 6:24 pm

Nice article Wing. The pictures with different volt meters was a nice touch considering the differences. You have done it again! In perfect layman's terms, anybody should be able to understand this and put it into use. I hope you are putting these articles in storage so anybody can go back and review them. Very good.
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Re: Electricity 101 Part 3: Using Multimeters

Postby NKYWinger » Mon Jan 27, 2014 8:32 pm

Great article, Admin! Makes feel feel REALLY old thinking of the Simpson 269 we used in the Navy and thought t was 'state of the art' ...well, I guess in the 60's and 70's it was....and then there is the Tektronix 545B o-scope...
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Re: Electricity 101 Part 3: Using Multimeters

Postby bellboy40 » Mon Feb 03, 2014 9:09 am

The picture of that old analog meter reminded me of the multimeter we used to use in the Air Force in the early 60s. It was officially called a PSM6 but most everybody called it "Pissum 6". It was in a metal case and was very durable. No telling how many times those things were dropped on the floor or the concrete out on the flight line and they just kept working. I've seen them hooked up backwards and the needle would be bent when it hit the peg going the wrong direction!
Ah, those were the good old days of my youth! :lol:

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Re: Electricity 101 Part 3: Using Multimeters

Postby seelyark1 » Wed Feb 12, 2014 9:58 am

I'm going to set my daughter down in front of the computer and let her read this set of articles. Wery well done and in simple terms. Would be great reading for anyone that doesn't understand electricity. I once helped her change a circuit breaker in her house via the phone. Just before she started, she sat down and had "her last cigarette", and then did just fine. Simple fact that electricity flows just like water. The easiest route.
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Re: Electricity 101 Part 3: Using Multimeters

Postby flogger » Fri Jan 29, 2016 9:29 am

Just got a new high quality multimeter... So if I understand all the electrical postings, if I just use the connectors to touch the battery terminals as it sits in the cycle still connected, then I will be in parallel? Use that method or proceedure to test the battery starting under load and to test the charging while running? Why while running am I seeing the charging state versus seeing the actual battery charge?
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Re: Electricity 101 Part 3: Using Multimeters

Postby WingAdmin » Fri Jan 29, 2016 9:49 am

flogger wrote:Just got a new high quality multimeter... So if I understand all the electrical postings, if I just use the connectors to touch the battery terminals as it sits in the cycle still connected, then I will be in parallel? Use that method or proceedure to test the battery starting under load and to test the charging while running? Why while running am I seeing the charging state versus seeing the actual battery charge?


Yes, connecting your test wires to the battery terminals will be a parallel connection. And that is exactly how you would check the battery voltage under load, and to see the charging voltage.

If the alternator is active, it is putting out 13.8 VDC, which when applied to the battery terminals, will cause the battery to absorb power (i.e. charge). If the voltage being put out by the alternator is lower (say 13 VDC) the battery will still charge, but much slower. If the alternator has failed, the battery will be running the bike, and because of the draw, the voltage will be less than 12 VDC. If the regulator inside the alternator is not working correctly, it can put out too much voltage - you could see 15 VDC, in which case the battery will be damaged.

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Re: Electricity 101 Part 3: Using Multimeters

Postby sunprowl@1 » Thu Jun 16, 2016 6:51 am

Thank you for the instruction will have to read a time or two.
Should be able to put it to good use with a brake light problem




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