Troubleshooting A Heavy Duty Alternator
John: Now these big rigs are full of accessories and not to mention the massive draw that it takes to start one of these. That's why the charging system has to be in tip-top shape.
Chase: And, John, before we dive into that charging system we need to turn our attention to the battery. Because it has to be in excellent shape before we go any further. Let's go ahead and start with a visual inspection. And what you want to do is come down to your battery. Look at your terminals here, look at your cables, make sure there's no corrosion. And also look at the batteries and make sure they're not leaking. You can also check the dates, make sure they're all the same. Also, super important, make sure they're all the same battery. Next thing you want to do is you can take your terminal cleaners here, you can clean your terminals up before you put it back together. Make sure you do that, it's super important. Also, you got some battery cleaner here. Put that down on the batteries and clean them up, make sure you get good connections. And once you get them clean, it's always a good idea to come back with some dialectic grease so the connections are good.
John: Yeah, no matter how good the charging system is the battery is the heart of the system. The hold downs, make sure they got all the same cold cranking amps. And make sure they're in good shape. And one test you want to do is a test called OCV, open-circuit voltage. It's simply just taking a DVOM, a digital volt meter, and going across the battery and measuring the voltage of the battery. Because we have to have 12.6 or more to run any of these tests. So let's see what we got.
Chase: Let's go ahead and do that. What you see, John?
John: 12.8, yeah, around 12-eight. That's good because we've driven it in here, it's got a surface charge, it's been on the road a lot. But we'll take that surface charge off with the machine. But you know what's really amazing? Take a look at this graphic right here. And on this graphic, you know Chase, I would think 12 volts is a good battery. Let's go ahead and test it, you know? I would expect 10, eight, seven to be dead. But actually 12 volts is 50% charge. 12.4 is 8% charge, that's crazy. So you really need that 12.6 before we go any further. And we got that with our 12.8.
Chase: We sure do.
John: So the next thing we want to do is we actually want to do a load test. Now to do a load test we're going to use a carbon pile tester. And I have one right here, we're going to go ahead and hook it up.
Chase: We're going to take our positive lead and go right across the positive terminal here. So remember to always separate these batteries. Do not do this test with all the batteries connected.
John: Yeah, that's a good idea. This rig actually has four. And that's an amp clamp, show them the amp clamp. Now that amp clamp, that's going to read the amperage as the machine starts to draw it out of the batteries with the load test. It's going to draw the amps out into a carbon pile. It's like a big accessory is what it is. It's going to go ahead and draw it. That's going to count them. So that needs to go in the negative cable going to the machine. And that's going to count them as we load it up. So you can see our machine right here. This is a carbon pile tester. Now carbon pile tester, you can use an electronic tester that looks like this. This is a conductance tester, same difference. A little electronic tester, just make sure you're using a tester that's capable of drawing these massive amps. Because, like Chase said, there's four batteries here. We separate them, but I'm assuming these batteries probably have some big cold cranking amps.
Chase: You know, John, it's very important that you separate these batteries because you need to test them individually. Because you could have one bad battery drawing the whole system down.
John: That's true. Now let's take a look at our machine, you're seeing right here. Just follow the prompts, it's very, very simple. It says, "A battery test?" I'm going to hit yes. I'm just going to answer the questions. It wants to use the battery right now. We're going to do it right there in the vehicle. And then it wants the cold cranking amps. So, Chase, we're going to have to recognize that. Where do we find that?
Chase: Right here on top of the battery on this label here. You can see this one CCA, 950.
John: 950, that's a lot of cold cranking amps. Now if you're not using an automatic, perhaps you have an old VAT-40? You have to take the cold cranking amps and divide it in half. You want to cut it in half and you want to load test it for 15 seconds. That'll give your battery a proper load test. You don't want it to drop below 9.6 volts. Now, with temperature, that will vary a little bit. If it's really cold out it may get a little bit lower. But 9.6 is our threshold we want to kind of stick to. Our machine is going to do it all for us. If I just come over here now, I go ahead and dial it in, you can see the 950. I can go up to 960. I'm just going to leave it at 950, because that's what our cold cranking amps are. Hit the yes. It says, "Do you want to test now?" I'm going to go ahead and start it.
Well it just clicked. It says it's putting load one on. We mentioned that surface charge earlier, that 12.8. Very important because you think you've got a good battery at that 12.8, but remember that alternator was working really hard charging it up. You may have 12.8, you may have 12.9, you may have 12.7. It's not a good battery. We really need to get that off. It went ahead and did that. It's testing a second time now. Now what's happening is it's actually drawing the amps out of the battery into the machine. The carbon pile is eating up all that amperage and it's seeing how tough that battery really is and how thick those plates are and how much it can actually hold a charge. And it gets done with the second charge, it's doing it right now. You can see it dropping on this side over here, our volts are dropping a little bit, 11.32, I'm suspecting it's a pretty good battery.
Chase: Me too.
John: But we'll see, yeah.
Chase: Yeah, John, we could have that 12.6 on a surface charge but you may not be getting the amperage you need.
John: Exactly. And now it's going through it's [inaudible]. And it tells you right there, battery is good. Pretty good. And it's even recovering to 12.5, 12.6. So this battery is in good shape. But that test we have to perform before we do anything. You know, we're going to dive into the charging system. We're going to show you a charging system output test. We're going to inspect the belts. But before we do that, I want to show you a term called voltage drop and how you can do it right on the bench. I got a demo set up. We want to do voltage drop before we actually start testing the alternator output to check for any resistance.
Now voltage drop testing is an awesome way to test for resistance. And I want to show you how we're going to do it but, before we get started with all these cool tools, let's look at the set up. It's the same thing that's on the semi. I actually have a battery here, of course a fully-charged battery 12.6 volts or higher. I'm feeding it to the negatives coming over and it's grounding on the alternator. Just like it does on the truck. Over here, on the positive, I'm coming over to the back terminal. So we're actually feeding voltage to it. What I'm going to do is I'm going to use a carbon pile and I'm going to run that voltage through it by using this carbon pile so we can measure voltage drop. Okay? That's different than resistance. Now how to do it? Well, it's pretty cool. I want to take the carbon pile tester and I want to go to the positive and then I'm going to go to the negative.
So what we're doing is we're getting the voltage, we're getting it into the system. We have it right there. We can see that we have a good functioning battery. And then I'm going to take the volt meter and I'm going to put the volt meter over here on volts, DC voltage, okay? Now here's the interesting part. To do voltage drops we're going to measure from the actual positive to the positive. Why? Because when I actually put some pressure in there and I get the amps to start running through, that's when we're going to measure the drop. So I want to come here on the positive terminal, with the positive lead, or the negative lead it doesn't make any difference. And I'm going over to the positive. So positive to positive. We're not going to show any voltage right now. And you can see our meter is showing zero. That's because we're positive to positive. But, when I load it up, the amps are going to run through there. And if there's any voltage drop we'll count them on the meter.
Let me go ahead. I'm going to run the dial, put about 100 amps into the system. That wire can handle it. Once I put about 100 amps through there you can see our meter is about one, point one, one-two. It's going to fluctuate a little
bit. But point one is fine, that's a tenth of a volt. And three-tenths on the positive side which equals up to about a half a volt. You start getting more than a half a volt you start to have some problems with your system. Now just as important as the positive side is the negative side voltage drop. And a lot of people forget that because the electrons have to run home and they're going home through the case so negative is just as important as positive. And to do that one what I'm going to do is I'm going to take it and I'm going to go to the negative.
So I'm coming over to the wire here on the negative side. And then what I'm going to do, once I get it on the wire on the negative side, I'm going to come to the negative post of the battery. Well, once again, negative to negative. So when I put some load here with the carbon pile it's going to pull the amps through that wire. We can make sure the connections are good. We can make sure that we don't have any voltage drop getting from the alternator to the battery. Now let's check the negative side. So, once again, I'm going to dial it up. Start drawing about 100 amps through there and you can see about the same voltage drop. About one point or point one-32. No problem there. One and one equals about two, point two, that's no problem. No more than point five.
Now what is resistance and what causes resistance? Well, I got a cool little demo here for you. Resistance comes in many shapes and forms. I mean resistance is heat. You see this wire right here that's toasted? Well, if you run your wires near a heat source, it's going to introduce resistance into that. It's going to have to overcome it, the alternator is going to have to work a lot harder. You can have premature failure. So make sure you run your wires right. Wire connections, so important. This one right here all crimped up and butchered up? It's not going to do the job. Now it may do it with not much amperage, but once you start pumping that amps through like this system does? It's not going to be able to get through there. It turns into a ginormous fusible link.
Now these two wires, this is pretty cool. So if I take my meter and I switch it over to resistance I want to show you something. Because if I go across this wire here, which is a brand new battery cable, and I click it to it. Now when I click it to it we're seeing point one, a tenth of a volt, or a tenth of resistance excuse me. Point one, so that's really no resistance whatsoever. Well, what would you think this wire would be. You would think it would be a lot of resistance if we go across it. But actually, if I come across that wire, and I go the same way we just did, it's showing point one which is the same resistance as that brand new wire. Well what does all that mean? Well, it's resistance. It's good through the strands, but guess what? You start pumping amps through there, it's not going to work. That's why it's so important to do voltage drop. Voltage drop you have to the system operating and that's going to measure the current flow going through there and the voltage as well. That's the way to check for resistance. Now we need to get over to our semi and do the output test on the alternator.
Well, we know our batteries are in good shape. And we know we don't have any resistance because we know how to do voltage drops. Let's turn our attention to the alternator here on the semi. And the first thing we have to do is actually locate the alternator. And it's located right here on the bottom of this big old engine right here. Now, before we do an output test, which we're going to check the output of the alternator to make sure it's putting out the amperage we need along with the voltage. You want to make sure the belt is in good condition. And just come over and check your belt. Make sure it's not too tight or too loose. Now if your belt is too tight on there? It's going to pull up in that bearing. It's going to introduce heat into the alternator and that's going to do damage as well. If it's too lose, it may be slipping and you'll have an undercharge condition. And you don't want that. You want to make sure you're getting the full potential of the alternator back over here to the battery.
Now we're going to go ahead and do an output test. Now in order to do an output test we changed up a little bit. We used the VAT-45 for the battery test, I'm going to use the VAT-40. And the only reason why I'm doing that is because I want to show you the actual amps as it starts to charge. And remember, a battery really, an alternator only puts out what a battery needs. So we may see it actually charge a lot and then drop back. Now you can use the VAT-45 or you can use the conductance tester. They work great, there's no problem with them. But I want to show it to you where you can actually see it work. What I'm going to do is I'm going to take the VAT-40, just like we did in the battery video. I'm going to put the positive on the positive, I'm going to put the negative on the negative terminal. Now, once I've got it hooked up, we know our voltage is good. I want to go ahead and I want to take this amp probe.
Now I'm going to take the amp probe and I'm going to go around the alternator output wire going back to the battery. So just like we did the batteries, we were counting it to the machine. This time we're counting the output of the alternator that's returning back to the batteries. Now what's going to happen? Well, eventually, here I'm going to get Chase. Let me pull this back off for a second because it's so important. See I missed a step. I want to go back here and I want go and zero that. That's the most important thing, all right? And you can see if you don't put it on there zeroed, it actually was reading 40. Not a good thing. You want to make sure it's zeroes right here. And then I'm going to come back, put it on once again, to make sure you zero your amp probe. Now once I did that, we're on zero.
So what's going to happen is Chase is going to go ahead and crank the semi. When he cranks up the semi we should see this needle here start to come over. It should start to charge. Now once it starts to charge it may drop off a bit as the batteries start to get charged up. But we should see it charging. Then we know it's putting out the amperage. Then what I'm going to do is I'm going to come over and I'm going to switch to diodes. And when I switch to diodes we're going to watch it go in that little blue circle right there and make sure the diodes are in good condition. Those are two checks that we can make on it. So, Chase, why don't you go ahead and crank it up? Let's see if this thing is charging.
All right. Well, it took it a minute. And I had to make sure the clamp was in good shape. But, once we did, what you saw is you saw it actually come down here. It was putting out about 80 amps. That's good. And you see it slowly start to come back because the batteries are starting to get fully charged. Then when I switch to the diodes we watch that bottom down there and we're in the blue. We knew we were okay. So with that we know our alternator is in good shape. Now you take these visual inspections with all these tests and you can test any alternator and trouble shoot any problem that's going on with a charging system.