Can I test the amps from my alternator like this?

[ThomasH]

I think there is a bit of confusion in some of the postings on this subject. Current is determined by the amount of resistive load in the circuit. If there are item(s) with partial short circuits, such as a battery with a shorted cell, it will increase the amperage draw on the alternator. No amount of bad connections, etc., will *increase* amperage in the circuit, they will in fact cause it to decrease. And typically overheat a well and probably fail at some point if they are bad enough.

With that said, you have already diagnosed a heavy drain on the circuit, which includes accessories (lights, etc), glow plugs, and the battery. How you diagnosed it was to note that the wire going from the alternator to the battery (or B+ junction) was getting hot and there was a significant voltage drop across the wire. A normal voltage drop on across that wire would be .1 to .2 volts. This high a drop indicates that either the wire is defective (possible, but can be easily looked at for corrosion or an obvious physical defect), or that the load on that circuit is causing the problem.

It's possible that the battery has a shorted cell, the glow plugs are staying on, or some other abnormal thing. Batteries are not hard to check, and having a shorted cell is not terribly uncommon so I would start there. You can also check the glow plug circuit to see if there is voltage at any of the glow plugs while it is running.

Good luck!

 

[jinman]

It's possible that the battery has a shorted cell, the glow plugs are staying on, or some other abnormal thing. Batteries are not hard to check, and having a shorted cell is not terribly uncommon so I would start there. You can also check the glow plug circuit to see if there is voltage at any of the glow plugs while it is running.

Good luck!

Thomas, your comments about current draw are right on. Your list of things that could be wrong is also almost complete. What I fear may be wrong is this. We can't rule out that the starter solenoid (high current portion) may have a partial short that is drawing current through the starter without it being enough to spin the motor. Since the alternator is putting out voltage higher than the battery voltage, it would try to supply all this current which constitutes an overload. Now, when the low current portion of the solenoid is engaged, it operates the electromagnetic coil and everything works normally.
What I want to do is to be able to suggest to Smitty some way of starting his tractor and then eliminate one thing at a time to see when the overcurrent stops. We'll try the battery first, then the starter, then go on to glowplugs, etc. if he wants to follow my lead. What do you think?

 

[rsmith02184]

I am willing to try anything at this point. I didn't think to try things like solenoid to the starter and glow plugs. I have only checked the charging system.

i will do the positive battery disconnect if you think that will help me figure stuff out. I can also just take the battery to a auto parts store and have them check it.

I would prefer to do the test on my tractor rather than take it out, but I don't have a battery tester.

 

[jinman]

If you disconnect the battery while the tractor is running and the wire from the VR stays hot, you know your battery is not the problem. With the battery disconnected, it should read around 12.8 to 13.2 volts if it is fully charged. If it reads that voltage level and starts your tractor without a problem, then I think you can rule out the battery being bad since it is also new.

Here is what I found out about your tractor. The alternator puts out 28 to 35 VAC (yes, AC voltage) to the regulator with the engine at moderate RPM. I'm told that it can go as high as 50 VAC with the engine revved up. This is all normal and probably accounts for the 29 VAC reading you got there before. Inside the regulator, there is a rectifier pack and the voltage regulator to supply 13.2 to 15 VDC to the battery for charging. I believe your alternator is capable of putting out 35 amps, but your regulator is a 20 amp regulator. There is a special alternator that can put out 55 amps, but I believe that one is mostly available in the European configuration for the 4100. I wanted you to read the AC voltage coming into the regulator from the alternator and also to read the DC out of the regulator on the AC scale to get some idea if there is AC ripple on the DC side that would indicate bad rectifiers inside the regulator. There will be some ripple, but there should not be a lot of it. My guess is less than 5 VAC.

Also, I think the diodes you searched for at one time are not the rectifiers for the regulator. Those are most likely isolation diodes and/or diodes that are across relays to conduct the inductive spike when the relay coil opens. They don't have anything to do with producing the power from the alternator and regulator. They are more or less "traffic cops" for controlling the flow of electricity and ensuring proper relay operation.

If you find the wire still heats up after you have removed the battery connection, the next thing is to get the starter solenoid off the circuit to see if that cools down the regulator. Do you have a good set of battery jumper cables? If so, I will probably tell you how to use those to isolate the starter. Let's not get too far ahead right now. I'd like to know the voltages I discussed before and what happens when you disconnect from the battery. After that, we'll go on. I know this is a tedious approach, but it's the only way I know how to proceed since I'm not there with your tractor.

 

[Soundguy]

If I might add, connect a lamp across the battery cables before you disconnect them with the machine running.

unloading the output of the charge system can allow te syse voltage o ikequihigh and take out the vreg .. the lamp will provide some load so that the system won't spike.. but you should still be able to do the voltage test..

soundguy

 

[rsmith02184]

I appreciate all your help...I am at my wits end. I actually said to myself "I give up" and I was going to call the local shop and have them come get my tractor and fix it. But pride and the fact that I have already invested $400 in voltage regulators keeps me hanging on. Your offers of help also give me courage.

I tried to disconnect the positive battery cable and the system just died. By disconnecting it, I am breaking the circuit...aren't I?

My biggest question at this point is:

the technical manual says I should have battery voltage at the starting motor, key switch, main fuse and VR. I do have good voltage there.

Then it ask me to test the system with the switch on and it should also be battery voltage. This is where it gets screwy. I immediately notice a drop in voltage with the key on which I assume is due to some relays activating as well as some dashboard idiot lights being on. The first place that I check (with the key on)is the VR and it has about 11.9V . I then test the wires going to the alternator and there is a big drop down to about 10.7. Which makes me think the wires are shorted or something but when I do a continuity test, they are good.

Does this sound strange to you yet?

One other answer to ginman: I was testing the red wire that goes from the VR to the battery. I disconnected it at the first fusible link after the VR and it put my meter on it. It was reading like 30 volts DC and it was also reading the normal range for AC (30-50). It was registering both readings at the same time. That seemed real strange to me.

One other thing (if you are still reading): I wanted to make sure the red wire leaving the VR was truly connected back to the battery so I did a continuity test and I found that it somehow was connected to 3 other wires (2 at the key switch and I can't remember where the other one was but I suspect it might be to the starter).

What do you think?

 

[rsmith02184]

sorry, I forgot to add that the red wire was reading 30VDC and 30-50VAC but when I connect it at the fusible link, it is showing 13-14VDC (I didn't check whether it is also showing VAC)

 

[jinman]

Smitty, this is getting really complicated really fast. In another thread where you first posted about your burned up regulator, Mitch Becton said that the JD4100 has a permanent magnet alternator (essentially a dynamo). A dynamo requires no battery for output. As a matter of fact, you check it for operation by disconnecting the output and measuring to ground with a voltmeter. However, if you have a traditional alternator, you may need to have it spinning at a minimum rpm and have battery voltage to excite the field windings.

You also mentioned that when you turn on the key, the battery voltage drops. I think this is due to an automatic glow plug cycle that puts a load on the system and pulls the voltage down. I'm just not sure.

I'm afraid to give you anymore advice without the system schematic. I really think my best advice would be for you to "bite the bullet" and put your tractor in the shop with experienced technicians. Your problem could be something simple that they have seen. Wouldn't you hate to "throw good money after bad" and just keep having problems? You've given this a good go and haven't found the problem. I think it's time to turn it over to the professionals. We all mean well, but nobody here seems to be an expert with your system. That goes especially for me without some documentation and manufacturer's references. We all want to help you, but we're a bit like the blind leading the blind without all the details.

BTW: I put together the following schematic that basically illustrates how most of our tractors are wired. Notice that the voltage regulator red wire goes to the starter terminal and attaches to the battery. It also branches and goes to the ignition switch. The switch then powers the various circuits of your tractor through individual fuses (blue line). When you turn the ignition to Start, the green wire is powered to pull in the coil of the starter solenoid and close the high current switch to the starter motor. This simple diagram should look something like your tractor's schematic in a very simplified form.

 

[rsmith02184]

thanks again for the info.

this problem has definitely gone way past my knowledge base, which I am sad to say is not that deep.

i am ready to hand it over to the pro's.

i am curious though about your point about the dynamo. i don't know if it is called a dynamo but I do know that it is a small 20amp alternator.

I don't know why it won't run without the battery...I just thought I was breaking some sort of circuit and that is why it stopped.

 

[jinman]

i am curious though about your point about the dynamo. i don't know if it is called a dynamo but I do know that it is a small 20amp alternator.

I don't know why it won't run without the battery...I just thought I was breaking some sort of circuit and that is why it stopped.

I've attached a photo of a JD dynamo and regulator. Does this look similar to yours?

Did you disconnect the positive battery terminal at the battery? If that's what you did, you did not disconnect anything but the battery. Everything should have kept working. Your fuel solenoid alone pulls enough current to keep the alternator/dynamo from operating into an open circuit. When you said everything quit, that's when I decided to suggest turning this over to your JD shop.