JD 2640

My friend has a 2640, and his batteries recently became run down, and he was unsure about charging them. At first we thought it was a 24 volt start system, but after close inspection it's 12 volt. There is a big warning by the batteries to disconnect the positive cables before charging. Why do they recommend doing this? Why can't you just charge it awhile and then put the charger on boost and start it? That's what I do normally and have never had a problem. Thanks in advance!

The electrical system is nothing anymore special than any other alternator system. The warning label is just another "CYA" for the manufacturer.

The warning is there because some of the alternators Deere used would sometimes get diode damage when a boost charger was used. I have only seen it happen myself on the Delco alternators. We had many diode failures with them on Deere tractors from using chargers on high amp rates.

Typically there wouldn't be any problem. Their engineers and/or legal eagles just worry about excess voltage or spikes possibly causing damage thus the "warning" to cover the bases.

John T One of those engineer attorneys who ponders such questions lol

Like I already stated, it is not just a mindless legalistic warning. We fixed several Deere tractors with failed alternator diodes caused by using boost starters. I was working at a Deere dealership when Deere started using AC Delco SI alternators and we had many failures. It was the diode-trio that often failed. Not something you find in the Denso or Motorola alternators. As I recall, the Delcos were used primarily in yellow industrial/forestry Deere machines mid-80s. I think some of the green machines had them too but do not recall off-hand.

The issue was discussed many times at John Deere service schools when I went in Syracuse. It is a simple concept. Machine won't turn over fast enough to start, especially a diesel in cold weather. You stick a boost-starter/charger on it with connectors clamped over the existing battery-cable ends (not directly on the battery posts). If there is a bad cable-end or bad connection between either the NEG or POS tractor cable where it goes on battery post? What happens? No battery in the system to buffer the power from the boost charger. When this happens, especially with old tech boost chargers - power is sent right to the alternator at sometimes over 30 volts. Thus the problem and this is why boost charging by hooking on battery-post connectors (cable-ends) can result in diode failure in the alternator. It was taught ever year in Deere service school and I have seen it happen several times. Some alternators have rectifiers/diodes rated at 50 volts and some only at 30 volts. The little diode-trio used in Delco SI alternators was very vunerable.

As far as just hooking a small charger to the battery-cable ends while still hooked to the battery? I cannot see how it can hurt anything as long as there is no way to spike the entire electric system up over 30 volts.

Again - the issue is when a battery-cable end has bad contact with a battery post while trying to boost or charge at a high rate.

I don't blame Deere for putting on the warning. It makes enough sense to be worth printing a warning label. More sense then some other stupid warnings I see on machines. Besides - if you want to fast charge a battery with high amps, it not all that difficult to unhook at least one cable end and hook the charger/booster directly to a post.

As far as boost charging by saying the heck with it because all that counts is getting the machine running? We had stuff with two boosters hooked up, and have burnt up starters and alternators. Stuff happens. That said, Deere would rather not pay for these sorts of failures under warranty. Same reason why they warn to use the starter for only X amount of seconds and then let the starter cool down before cranking again.

Seemed to make sense 'til I confirmed my memory and checked on the DEERE parts site, the 2640 used Motorola alternators throughout it's production run.

So much for the "weak diode trio in 2640 Delco alternators" theory, I guess!

Back in the 70's- late 80's I jumped off/charged many JD utility tractors without disconnecting the batteries with no alternator failures that I remember. i was employed at an ""AG only dealership"" no new industrial units were sold there.

EXACTLY like I also indicated, the engineers and/or legal eagles have reason to issue such a warning just in case a voltage problem when jumping damaged something. Being an Electrical Engineer plus an Attorney I just think about those kind of things, I cant help myself lol

I agree its "not just a mindless legalistic warning" there were reasons for doing so !!!!!!!!!!

Best wishes nice chatting with you

John T

I never posted any "theory" about a 2640 using a Delco Remy alternator. I made that pretty clear. I said my experience was mostly on yellow Deere foresty and industrial machines that did indeed come with Delco SI alternators.

That said, we also had the isolation diodes failing on Motorolas that came on new green farm tractors.

Can I say exactly why every alternator ever failed that I have worked on? No.

Do I know that John Deere explained their reason for the warning in service schools? Yes. It appears to me that was the basis of the original question here.

Just for the nitpickers here - let me clarify I never attended a John Deere service school class that was specific for a 2640 either. 2940, yes - since we had a LOT of cold weather starting and smoking problems with them.

Are you claiming your personal anecdotal experience proves that John Deere simply made up the basis for their warnings?

Kind of hard to "prove a negative." Your experience of something not happening does not prove things occurred differently elsewhere.

I CAN attest to one "positive." John Deere officially discussed the possible problems of "boost starting" as already discussed.

A basic knowledge of electronics should give understanding of the benefit of a battery's ability to act as a spike-buffer and its ability
to smooth out crude ripple currents. If a battery accidentally is taken out of the circuit when boost starting - like with a corroded
battery post connection? You can get some very high voltage spikes that are hooked directly to the alternator with heavy gauge wire. Makes
sense to me. Made sense to John Deere to.

I am not arguing whether someone, somewhere, will or will not have problems boost starting.

The question as I understood it - was the reason behind John Deere's warning.

I will note many AC to DC power supplies in older RVs carried similar warnings. I.e., never to try to power DC appliances in an RV with
just the converter and no battery hooked into the system as a buffer.

Now adays - many converters and high-amp chargers are more sophisticated then they were 30-40 years ago and are safer to use (less ripple
and spike risk).

Also, many new diodes for 12 volt alternators are rated for 400 volts which is pretty high. I do not know what the original ones were
rated in the 70s and 80s. I do know that several people here have complained about them failing in brand new alternators - supposedly from
China.

Going by Bob's reply to me, it seems he thinks the Deere warning only applies to the 2640? Not the case.

Regardless - to be specific to the 40 series green ag tractors. The ones I worked on new came with 35 amp or 55 amp Motorola alternators. Oddball in a way because they used external isolation diode assemblies. Same as many American Motors cars had in the 60s-70s. When I was a Deere mechanic, I carried new isolation diodes with me and had to replace many. Very easy to replace since they simply bolt to the outside of the alternator. 35 amp alternator used a single diode, and the 55 amp used a dual. When they got damaged, the batteries would get a constant drain on them when parked unless a battery cable got unhooked.

Like I said, I had to replace many. Why? I did not always know for sure. Many however were from boost-starting in cold weather.

As to my mention of the 10SI Delco alternators Deere used? Most I saw were on yellow forestry and industrial. That said, we put many Delco alternators on green tractors that needed more amp output since the OEM Motorolas were only 55 amp. Some of the Deere Delco alternators were rated 82 amps. When the diode-trio got fried, the alternator would only have partial output and if a no-charge light was used - it would glow dimly all the time.

Jim, I have been both a farmer and used tractor dealer and had to jump tractors literally hundreds of time way more then any average Joe, grrrrrrrrrr. I never had any problems jumping and NOT disconnecting the batteries. HOWEVER being an electrical engineer as well as an attorney, I fully understand why the manufacturer would place such a warning just to cover themselves in the event of a yes RARE problem.

I wont be back in your great state until next fall so you're in charge and take care

Best wishes

John T