How do I find which is bad, alternator or voltage regulator?

[maple flats]

I have an issue with my tractor, the battery seems to be good, because when I connect a charger to it and the battery gets fully charged, the tractor starts well for a few days but then it begins to crank slower and finally won't start.
The tractor is a 2012 Mahindra, 36 eng HP diesel. How can I test the alternator output and the voltage regulator? I figure one must be bad. Any mechanics out there? I'm certainly not one, but I do fix most issues on my tractor when needed.
The battery was new this past spring and it's higher cold cranking amps than the original was.

[TroyC]

I'd suspect the battery if it is more than about 4 yrs old. Take it to a parts shop and have it load tested if you do not have a load tester. Load testers can be had cheaply at HF for about 20 bucks or so. From what I read it appears the battery is taking a charge but not holding it which is an indication of a cell deteriorating.

If the battery is strong, you can check the alternator and voltage regulator easily with the tractor running. Get a simple volt meter, hook it up to the battery post, you should read close to 14.2 volts DC. Also, check all of the battery terminal connections and make sure they are clean, corrosion free, and tight.

[Wlmedley]

I would check the battery out first especially if it is 5 years old or older.Tractor should have a charge indicator light or a ammeter.If light goes out after starting alternator is probably charging.If you have a voltmeter you can probe between negative and positive at the battery and should read 13.5 to 14 volts with engine running high idle.Might take a minute or two after starting.If it has a small permanent magnet alternator like most small tractors they hardly ever go bad unless bearings fail.

[Ljohnsaw]

Based on your initial post, I don't think your battery is bad since you get a "few days" of starting out of it. Check the alternator output with a meter and I think you will see it is around 12v, what you are actually reading the battery voltage.  I know that AutoZone has an alternator tester that will at least tell if the whole unit is bad (do you have a separate voltage regulator or is it internal?).

I thought my pair of Interstate batteries were going bad on my SkyTrac.  I know they are at least 10 years old.  Turns out the One-Wire (GM) alternator that was installed long before I got it had a stranded wire that only had a couple strands left at the alternator - so it couldn't get enough amps to the batteries.  I lucked out on both sides - batteries and alternator. 

[Erik A]

Check your voltage at the battery with it not running. Then start it and check the voltage at the battery. If the voltage goes up, check the battery, if not check the alternator.

[Hilltop366]

Don't forget to check the alternator belt/tension if you haven't done so yet.

[Tom King]

Without typing out a long explanation here, there are plenty of youtube videos.  I didn't watch this one, but if you don't like this one, google "checking charging starting auto system youtube"  and you will find all you want.

DIY Car Alternator Test (Voltage & Amperes) | Multimeter Edition - YouTube

[scsmith42]

Most modern equipment has the voltage regulator built into the alternator.

The easiest solution that I know is to remove the alternator and take it to a local alternator repair shop for testing.  

[maple flats]

The battery is only 4 months old and when I put the charger on it, the tractor starts good for 4-5 days before it shows signs of cranking the engine slower. The battery is higher cold cranking amps than the original.

[maple flats]

We used to have a couple of alternator repair shops, there doesn't see to be any left anymore.

[red]

Back in the day , 40 years ago we would remove the negative battery cable with the vehicle running
If the vehicle continues to run your alternator is charging if the vehicle dies it is not charging 

[rusticretreater]

Given the age of the alternator, it is likely to have gone bad.  It is possible for an alternator to put out the required voltage, but not high enough amperage(regulator gone bad).  This can cause the issues you are experiencing.  So checking the voltage delivered to the battery is not a complete test.

However you could also have a parasitic drain.  This causes the same symptoms as the bad alternator regulator. To check for a parasitic drain, you simply disconnect the positive cable and hook up your voltmeter in between.  Any reading on the voltmeter shows the electrical drain.  To try and isolate the problem, pull your fuses for circuits one by one to see if that circuit is causing the drain.  A likely culprit is the fuel sending unit.  Rusty ground connections, wires rubbing are also common causes.

[TroyC]

Back in the day , 40 years ago we would remove the negative battery cable with the vehicle running If the vehicle continues to run your alternator is charging if the vehicle dies it is not charging

Do NOT do that with an alternator. On a relative newer vehicle you will unleash a bunch of demons. That was a shade tree test with a generator (think VW Beetle) but you will kill your alternator if you disconnect the battery with it running. Generators have permanent magnets, alternators do not. The alternator has to 'see' voltage in order to work. Another thought- I've seen bad diodes in an alternator drain the battery over time.

[TroyC]

The battery is only 4 months old and when I put the charger on it, the tractor starts good for 4-5 days before it shows signs of cranking the engine slower.

OK, without testing the battery, let's assume it is good and working properly. The problem now looks like a drain (parasitic as mentioned above) on the battery or the alternator is not charging. You really need to test voltage on the battery terminals with the engine running.

[maple flats]

I won't get back there until Monday at the earliest, if raining it will be after that. The tractor stalled in what seemed like a fuel outage, but the gauge shows over half. The tank holds 7 gal total and I topped it off about 2 hrs before it quit, I was brush hogging an overgrown field, that uses just under 1 gal/hr. For that I suspect the fuel filter, and I have a new one to put in, I always keep every filter spare ahead of needing it. This tractor has never been fueled using a fuel can, I have 2 tanks of fuel one at each of 2 locations, my blueberry fields and my sugarhouse. They are .7 miles apart. I had fueled from the tank where the tractor quit, I wonder if it might have gotten some condensation in it. I'll test using water finding paste to verify. I never had an issue on that at either tank in the past. I also have a water filter on the tank I used, (just in case), and a half micron fuel filter too.
When I get back to the tractor Monday or beyond, I'll have my multi meter and will test as suggested, after I change the fuel filter. The bowl showed no signs of water on Friday when the tractor stalled.

[rusticretreater]

Ah, I have too many days like that.  You might also want to test for a bad fuel pump.

[jcbrotz]

quick and dirty test if the back of the alternator is magnet then its charging. Simply put a screwdriver to the center of it and if it sticks then the alt is OK then time for a multi-meter or load tester.

[maple flats]

The forecast for tomorrow looks good, I'll try following the above suggestions, except I won't pull the negative cable off. 
I have a new fuel filter ready, then after I change that I'll try to start the tractor, if it starts I'll follow the suggestions, if it won't start I'll try to drive a F350 diesel 4x4 in to where the tractor stalled and jump it. If that fails my brother has a large skid steer track loader, he can pull me out. If we hadn't had so much rain lately, I'd be able to drive in without issue.
I'll post what happens tomorrow.

[maple flats]

It's not typical of me, but I took a picture of every reply in this thread so I'd recall exactly what each suggestion was when I get to the tractor. 8) 8) 8)

[rusticretreater]

Good idea.  I have printed out various forum threads in the past to have handy.  Lots of ones from auto forums.

[Nebraska]

A battery cut off switch may be an easy solution  to the slow drain issue if  chasing the alternator issue doesn't bear fruit. It at least kicks the can down the road a little bit.

[doc henderson]

or get a maintainer charger if you got juice to the area.

[maple flats]

The stalling turned out to be the fuel filtr, but the old filter told me a story. I have an "algae" issue. Now I need to treat my storage tanks (2) , the tractor fuel tank to kill the "algae" and then another chemical to clean the fuel, then change the filters frequently as the then dead and broken up "algae" flows thru and gets trapped in the filters.
I still need to test the alternator output to determine if it is actually charging. From what I read about the "algae" (really not an algae but rather a bacteria and fungal growth) I should not continue to operate the tractor until the fuel has been treated with the bactericide and the fuel cleaner, in the tractor and also in the fuel tanks I use to fuel the tractor. I ordered what I need including 3 filters to change as needed. The chemicals should be here by 10/4 at the latest. I won't run the tractor until then. At that time I'll test the alternator to find out if it's charging or if I have another issue, like a phantom draw.  

[maple flats]

Doc, if the alternator proves to be the issue, I will run a maintainer charge for a while, until I get a new alternator. In the meantime, while I await the chems I ordered I'll wire in an outside receptacle on the side of my shop. It just happens I just bought whaqt I need to do that just 3-4 days ago. Even before I knew what the issue was  (devine suggestion?).
I'll wire it tomorrow or the next day, conveniently I just bought a large pack of new blades for my oscillating saw about a week ago. I tried to start the cut today but the sawzall blade I had was too long and danced around rather than making a plunge cut on the line I had drawn. I'll just need to take my oscillating saw and blades down to the shop (at my sugarhouse, about 3mi. from my home)

[maple flats]

My new filters, the biocide and the fuel cleaner arrived over the last 2 days. I'm now heading down to add the chemicals as directed to each tank and I'll make the first fuel filter change on the tank I suspect. On the other tank I've had no issues and I use it often, on the second tank, the one I suspect, it only gets used on rare occasions, and while bush mowing the open fields I  have pumped from it twice  recently. I still have a set of new filters when needed, and I ordered 3 for the tractor. Once I get this all done, I'll test the alternator, I don't have an amp meter, but I do have a high quality multimeter.
If I do have a parasitic draw I will likely need to jump start the tractor, it has been setting since it stalled since I started this thread. 

[maple flats]

Concerning the battery, it is almost new, and I bought a gel battery, which should handle vibration better than a lead acid battery, I'll see. This battery was bought from my local farm supply and it had a mfgr date that was only 2 months old when I bought it. If it's bad, it is still in warranty.

[rusticretreater]

You probably should check if your tank has an internal screen at its outlet.  I have seen a number of vids of guys siphoning their tanks to get the crud out after the screen clogged.  Depending on your tank, it may be difficult, it may be hard or maybe you can remove it and drain it well.

[maple flats]

I got the chem in both the bulk tank and the tractor tank. looking in, the tractor tank only shows 1 spot of black "algae", and when I put a piece of EMT in the big tank it showed I only have about 3" in the bottom. This is a 150 gal round tank that sets on a flat end, thus very little fuel in it. Once it runs out I'll wait to see if I ever want to get in filled again, since it's at my blueberry fields and I put those fields up for sale last week. Too much trying to keep up with tending them. If they don't sell, I'll clean the tank before it gets filled again. It has the biocide and fuel cleaner in it now, and I pumped enough fuel back thru to get it mixed well.
I didn't get to run the tractor yet, likely tomorrow because the 3 spare fuel filters arrived today so if the filter gets plugged, I can swap it out.
I can't see very well into my tractor tank, the filler has a 90 bend in a short way from the cap, looking in required a mirror on an extension and then it was extremely hard to see anything in there. Worse come to worse, I may need to remove the tank, but with the cab and configuration  of the whole thing, it may need way too much to make it worth it. My tractor is a Mahindra 3616 with a full cab and the front windshield fits around the fuel tank and they are sealed together with a black adhesive sealant.

[moodnacreek]

Assuming the tractor has headlamps, turn them on at slow engine speed and when you rev it up they should get brighter meaning it is charging.

[maple flats]

Great idea, but the headlights don't work anymore.

[scsmith42]

My "biocide" story...

For 20 plus years I've run diesel equipment here on the farm with no issues.  This included heavy equipment that sat for 3-4 years w/o being used.

In 2020 I purchased a Sterling Semi with 900K+ miles on it.  Turns out that the tanks had black slime inside them, so I treated them with a Biocide.

I've had a 500 gallon storage tank on the farm for over 20 years, but a few years ago I picked up a used portable 500 gallon double wall tank that I mounted to an old military trailer.  I use this rig to pick up fuel at the local jobber / gas station and transfer it to my farm tanks.

Being the genius that I am (NOT), I decided to treat my 500 gallon storage tank too.  Rather than put the biocide in the storage tank, I added it to my trailer mounted 500 gallon transfer tank so it would mix up well before going into my storage tank.  Turns out this was one of those things that was "better in theory than practice...."

Life happened; I left the treated fuel sitting in my transfer tank for a week or so before I got around to transferring it to my storage tank.  Because it take 30 minutes or so to fill up my elevated storage tank, I usually start the pump and then do other chores for a half an hour.  Unbeknownst to me, while sitting for a week in my transfer tank the biocide cleaned up the inside of the tank and once I started pumping fuel into my elevated storage tank it promptly clogged up the gears on the fuel pump and smoked the pump!  Of course, the fuel filter is downstream of the pump so once I replaced the pump I had to keep cleaning out the inlet screen. i finally gave up - used a separate pump to empty the tank and then took a pressure washer to it's inside in order to clean the residual gunk out of the tank. The biocide had cleaned it off of the tank walls, but turned it into some type of black grit that kept clogging up the strainer.

If I would have just left things alone, it would have save me a couple of day's of aggravation and a few hundred bucks for a new pump!

[SawyerTed]

In the marine industry, "fuel polishing" is a real thing.   It's a fancy name for pumping the fuel out of the tank, externally filtering it, then returning the "polished" fuel to the tank.  

There's lots of DIY fuel polishing information on the web.  The process gets the algae and gunk out of the tank before it gets to the engine filters.

I've done it a couple of times, the setup cost about $50 to filter 500 gallons.  

[rusticretreater]

I have siphoned my fuel out of the tank into a large funnel that has a filter screen in it.  I have also blown air through the fuel line into the tank, to stir things up and then reached into the tank with a net used in fish aquariums.  You can get a surprising amount of stuff out of there.

[Ianab]

Great idea, but the headlights don't work anymore.

You said you have a multimeter, so you can do the same test. A 12V battery will read 12.? when it's not being charged. Maybe 12.8 at full charge, down to 12.1 when it's effectively flat. When it's being charged, the voltage across the battery should be close to 14V. That's why you can see the change in the headlight brightness, 12V vs 14V is noticeable.
So either test will give you a clue, If you aren't getting ~14V at the battery with the engine at fast idle, then you look at the alternator / regulator / wiring. If you are getting the charging voltage, that suggests the alternator etc is working, and you need to look at the battery itself (not accepting charge or self discharging) or a parasitic load drawing it down. 
I guess the only trap would be if the parasitic load was actually the alternator? Someone mentioned a faulty diode in the alternator, so keep that in mind when looking for a parasitic load. 

[maple flats]

Sorry for the delay, first I had a minor case of Covid, then my wife got it too. I'm mostly better now and finally yesterday she was a little improved.
Back to the tractor issue. I got the tractor running, with a new fuel filter and a biocide + a fuel cleaner in the tank. I got the rest of the mowing done without issue. The tractor then sat for 6 days while my wife and I had covid, and the tractor started ok, this time it didn't hesitate, but fired up as it should. I did test the output of the alternator when running at about 1600 rpm (pto speed is just north of 2400 rpm). The meter read slightly over 14V. Thus I must have a phantom draw. I'll eventually add a battery disconnect, but until then I'll put it on the charger every few days. I can charge it using my plug in charger or I just got an PWM CC (charge controller) for my 50 watt panel. I'll hook that up after I pack more syrup. Right now I'm low on dark syrup and I have 4 full SS barrels, all dark. That is my job before the solar charger.
Previously I had a MPPT CC for to 50 watt panel, but it failed. I then learned that a MPPT CC  draws some power all of the time and if the solar panel doesn't get enough sun the MPPT CC can actually draw the battery down, thus I ordered the PWM CC.

[maple flats]

After several unscheduled delays, I will get to wire the  shop to run a 120v receptacle thru the wall to power a maintainer in the next day or 2. 
Tomorrow I need to load up lots of syrup and restock the outlet where I sell my syrup, sales have been thru the roof the past month, and it's not looking like Christmas type buying, that is still on the horizon. 
Once I get the syrup stocked, I'll run the power to plug in the maintainer to keep my tractor battery fully charged, a week or 2 later I should have time to try to figure what the phantom draw is on the battery. If that fails, I may just keep running the maintainer. 
I also have one more sawing job, I need to replank the bed on the 16' gooseneck trailer I jointly own with my brother. I have the logs waiting, the first one is started, flat on 2 sides. I just need to find a helper, After my yearlong layup from 3 major surgeries, I still have not built up my strength enough to handle 16' 2x8's alone without a major struggle, and 1 major struggle caused to 3rd surgery last year, a huge hernia. I now try not to over do it!

[barbender]

I am always looking for smarter ways to handle 16' oak decking. It's a killer!

[doc henderson]

 

 

shop built in 2005, and just got my plug on the south end of the shop, by the splitter.