And I think it is a strange one.
Sorry about the double picture post.
Not followng….what’s up ?
This machine hit my yard a couple of weeks ago for me to work on boom pin bushings and replace the boom side cab window that broke because of the play in the boom. Ever since it hit the yard if it sits for more than a day it will not start without jumping. Alternator is charging just fine. I had to replace the battery box floor because it was all rusted out and the battery hold down brackets had broken off, so I took the batteries home to charge them and then tested them, one was okay and one was junk, so I replaced the pair. On Monday or Tuesday I was told they had to jump it again. I was stuck up the mountain (almost literally, what a mud pit) working on an articulated rock truck all day yesterday (probably going to post a question about that one right after this one). This morning after looking at turbo problem on a c15 (another thing I have a question about). I went down to the yard to start trying to figure out why. I was thinking maybe a pretty nasty parasitic draw or a blown diode in the alternator. Iirc A bad diode will allow the alternator to charge when running but suck a battery dry when not running. In all honesty, I do not know how I know that or if I am mistaking a diode for a capacitor. But I do remember that you test for that with a dmm Set to read ac voltage. If anybody wants to help me with that, great. Because I am pretty sure that I have that same problem on a cat 246b. That one doesn't just have low voltage, the battery is dead flat. Anyway, lets get back to this machine. when I got there I started it and it fired right up. Not surprised, they are using it daily to load out a rockpile. So I checked the batteries to see how it was charging just in case it stopped charging since the last time I looked at it. It was charging at 28.3 volts in series which seems okay to me. Now to the thing that I think is strange. When I checked the individual batteries, one was charging at 16 volts and the other at 12 volts. I cannot ever remember seeing that before, even with a known failing battery. The low voltage battery is (in my mind, anyway) the first in series. Being the positive terminal that is fed by the alternator via the starter. So I think that rules out connections in battery cables (I am pretty meticulous about battery connections any way) and ground. So, I decided that the low voltage battery was probably defective. I know new parts don't necessarily mean good parts, especially from auto parts chains. A wise man once told me, and I know it is a crass way of saying this, "new babies die, too". I mean it made sense to me. The computer wants to see 28+v so it ramps up the alternator to get to that number. So, went and swapped out the low voltage battery with another one from napa. Same situation (maybe a .5v difference between batteries) second in series battery is still at 15.5, first at 12.5. Just to check if the " crossover " cable is bad, I decided to swap the two in series. And... No. Now the first in series is overcharging and the second is still at 12.5. Did I get another bad battery from Napa? Is the battery that is charging at 15.5 bad? I don't ever remember a defective battery overcharging in series.
It is strange because it follows that crossover cable?
The machine requires 27-28 volts charging voltage at the main cable. Most dual battery systems will receive the same amount of charge during operation, but cable, terminal, and connection issues may change that. Power will travel through the least resistance first and foremost. You have an issue with one of those above issues I mentioned.
All of the connections are as clean and tight as possible. And wouldn't swapping the battery positions rule out a bad crossover cable?
Post number 2 has a Red battery charger clip on a battery terminal. That terminal looks junk to me. All the others don't look that clean either. How is the ground strap. If the jumper cable is burn't internally one battery will charge more than the other. You have to test these cables with lights and fan on and engine revved up. Helps if the batteries are discharged a little as it will cause the alternator to put out more current. Cables cannot be tested without current flowing through them. #1 Try this,... with engine revved up and lights and fan on stab the one end of jumper cable at battery post and other end of same cable at battery post, what does the meter read. #2 To test the diode trio for too much AC leakage just put meter on AC volts with engine revved up and lights on and fan on. The hotter the engine the better, Put Red test Lead on alternator output terminal, and black lead on the negative post of the battery that the cable goes to frame ground. What does the meter read? #3 Also with engine revved up and loads on try stabbing the Alternator output terminal with the Red test lead and meter on DC Volts and the black test lead on the the battery 24Volt terminal. What is the meter reading. I have seen too many what someone said was good cables. Some failed badly. These would be what I would start with. Take a picture of this and I doubt after you test something won't be wrong. Simon
All of the Battery terminals and clamps were cleaned with my battery reamer. Very clean, shiny metal and copper. All the cable ends and the surfaces that they bolt to as well as the ground were gone over with a grinding disk on my die grinder. I didn't bother cleaning the outsides. Hey, thanks for test details. It was driving me crazy that I couldn't remember.
I found one with cable skin still on and almost complete disconnect inside of it. My meters don't ever lie or mislead me, at least not on battery cables. Simon C
By the way, clean and shinny means nothing if the cable is badly compromised inside and you can't see. That why I do 3 tests in 5 minutes to know what is what. Simon C
The ground cable is new, the old one got damaged by the batteries sliding around in the box. I will admit that the crossover cable is pretty suspicious and I am going to change it next. I still can't get my head around the uneven charging not depending on the battery position in series.
Will do, be a few days. I have a rock truck that suddenly is front wheel drive. Or always has been and they never knew until it got stuck in the same mud pit I did on Wednesday. I made them move it down the mountain and now I am wondering how I will know if I can get the rear wheels under power without the front spinning in the mud. And an engine swap on a ctl ahead of the excavator.