Cat 325BL Battery wiring schematics

I keep getting hard starting on my newly acquired Cat 325BL from discharged batteries. It's currently set up with 4 Cat 31's that looks to be 2 parallel sets of 2 batts in series for a 24v system. If the machine sits for a week or so, even with the battery disconnect switch turned off, I'll get 18-19v across each set of 2 connected in series. That's even after I measure each set of 2 batts at 27v fully charged after being charged by the alternator after a few hours of use.

I pulled all four batts and have them charging at the house tonight before I get them load tested tomorrow. I'm sure I'll find a bad batt or two (they're 5 years old per the date code) but I also want to make sure the previous owner didn't 'optimize' the wiring. I see some random wires disconnected near the batts so I want to verify the right cabling/wiring layout with a schematic. Anyone got a pic of the battery cabling schematics? Can I go with 2 batts or do I need all four for Central Texas cranking?

Apparently that's a 3116 engine, I don't know about the extra load on an excavator engine from hydraulic pumps, in a truck it will start down near zero with one good battery on a 12V system.

This doesn't sound like a load test issue, more like a slow drain issue. Are the four batteries hooked up in two parallel strings of two each? that is, one terminal on each side of your disconnect switch, the two series strings are connected even with the switch off so that one bad battery will drag the other string down. That's the advantage of only two for a 24V system, batteries don't like to be parallel, they age differently and drag each other down.

I'm lazy and cheap, so I'd charge up all four, leave them a week with at least one terminal disconnected from each battery, then check the voltage, anything less than 12.5v gets removed, if you have two at 12.5 or more, then hook those two back up, and run it till they die. If you have three good ones, keep the spare in case one of the others dies. If you go with new, it's all or nothing, don't mix new and old. (if you only have one good battery out of the four in there now, and you happen to find a spare in the same size, I won't tell anybody if you run with two mixed used ones)

It is the Cat 3116 engine with a 24v setup of 4ea 12v batteries. So yes, it's two parallel strings of two batteries in series. When I jump the batteries with my truck, the engine purrs to life within a second of cranking. It's a very smooth engine with almost no initial smoke and a fast crank so I'm pretty sure I just have bad batteries. What I don't know is how the two strings are connected to the overall electrical system so I wanted to ensure my system is wired correctly. There are two circuit breaker(?) reset buttons near the battery cut-off switch which leads me to believe it's just not two parallel strings simply connected together but I need to dig around a bit to figure it out. The previous owner did some 'optimization' and I can see where he spliced off some power lines (pretty heavy splices)- just don't know how far he fiddled with it. I think he tried to pull 12v off one battery to run something for the cab but can't be sure. Since this system appears to have a 24v charging system, it's disastrous to pull off just one of the batteries- will definitely cause an imbalanced set and early death.

And yes, I completely concur about not mixing new batteries with old ones. I've been driving diesel pickups for a while and learned the hard ways many years ago about replacing just one of the two batteries to save a few bucks. I also like your advice about finding the two batteries that maintain above 12.5v after the surface charge goes away and just using them until they die.

Your machine has a factory cold start system. I’ve seen lots of those with one set of batteries removed within no problems.

John- Thanks for the info- I searched the forum before posting and saw your posts about this issue. Does it matter which set of 2 batteries I remove? I doubt it matters which pair I remove but I haven’t traced the cabling to verify.

Two pair of batteries.
Each pair has short cable from a (+) to a (-)
Each pair has a red 24v positive going to the starter motor.
Each pair has negative going to the kill switch (ground disconnect).
That's it.
The breakers that you see are on the 24v to the system that are feed from the starter 24v stud (that has both 24v red from each battery).
There are no small wires of any type to be connected to the batteries.

like heymccall says, the little cables and breakers shouldn't be hooked to the batteries. But even if they are, if the disconnect is on the ground, then it shouldn't matter what's on the positive side.

With the battery strings tied together even when disconnected, they function as one battery, and drag down/drain down the other one. your wiring issues aren't affecting the starting if the disconnect is functioning. And it sounds like it's charging fine.

Be careful with hooking and unhooking these, the cables don't become dead once they're unhooked if the other batteries are still hooked up. Much easier to vaporize your tools with this setup.

[QUOTE=" And yes, I completely concur about not mixing new batteries with old ones. I've been driving diesel pickups for a while and learned the hard ways many years ago about replacing just one of the two batteries to save a few bucks. [/QUOTE

If you want to know the condition of the batteries as well as the cranking/charging, for less than $50 you can get an analyzer. It will tell you the CA/CCA available in the battery as well as other things. Below is just one brand you can find on Amazon. It saves a lot of time and guesswork.
ANCEL BST200 Battery Digital Analyzer & Load Tester 12V 1100 CCA

Thanks for all the info so far. It looks like the 4 battery 24v set up for cold weather operation then just doubles the power of the regular 2 battery 24v set up. I wasn't sure if the extra two batteries for the cold weather set up were just energized during the starting cycle and then isolated from the standard electronic drain during running time (but still being charged). This would ensure at least one fully charged pair during cold weather ops.

CatKC- It's funny you mention about buying an analyzer as I spent most of last night researching these while I was charging my four batteries. From what I read online, the latest (and best) method to analyze a battery is using conductance as opposed to short term amp draw, voltage, or specific gravity measurements. I've been dubious of the new testers that don't draw a good current across a heater coil (like the old school ones) as i figured high amp draw best mimics starting conditions. According the internet experts, conductance is much more linearly related to battery capacity/condition and thus more accurate. Looks I'll be getting a conductance based analyzer...

I have a 10 year ESI 720 tester that has never, ever, lied to me.
I mix and match batteries all year long, simply by keeping their tested ratings all within 50CCA's.
But, I only have 200 batteries in service at any one time.

If you have small diameter disconnected wires in the vicinity of the batteries I suggest first to try to establish if they are OEM or not.
OEM wires will have reference numbers on them. Their function will be easy to identifyfrom the Electrical Schematic.
Customer-installed accessories (e.g. fire suppression systems, comms radios, etc.) can often be connected direct to the batteries although in truth only a fire suppression system should ever be wired direct IMO.

[QUOTE="LCA078, post: 853470, member: 81531 " I've been dubious of the new testers that don't draw a good current across a heater coil (like the old school ones) as i figured high amp draw best mimics starting conditions. ................. According the internet experts, .[/QUOTE]

Not trying to sell anything, but the electronic analyzers measure the internal battery. As a battery gets 'used' the internal resistance changes and it will not 'take a charge' as well as not provide the 'rated' output. The electronic testers 'do not draw any amps' but they measure 'amps drawn' and they measure the battery's capacity.
You can't be any 'older school' than I or you'd be dead. As 'the internet experts'. . . . . . don't get me started on that.
For me the proof is in the pudding, and they've proved their worth to me.
FYIW- I also have carbon pile LOAD TESTERS but I rely on the other. The amps drawn when starting, the real time load, is measured by the electronic tester.

No worries. I have enough experience and background with electrons and circuits to weed out most of the fake-tech on the interwebs too. It’s not always easy to extrapolate one thing (battery life) based on another (conductance) but as long as the science is right, it’s all good.

Final bits of the story:

Two of the batteries were bad as they wouldn’t hold 10.5v even after long charge. The other two held 12.6v but are about 70% capacity. Not wanting to deal with more starting issues from sub-par batteries in the near future, I picked up two new Cat 31’s from the local dealer and installed them by themselves. Machine fired right up like it did when I first inspected it.

I’ll see how the two ‘good’ batteries crank my 5-ton military truck.

I forgot to add I took Delmer's advice to heart and solidly insulated and secured the second set of battery cables to keep them from giving me a future insurance claim. I also removed an extra set of capped-off power cables the previous owner installed. It was a good quality cable (probably welding cable because it was so flexible) with good crimped fittings. The negative section was hooked to the disconnect switch and the positive section was tied into the original starter cable so he was expecting to pull off some decent power when used. Who knows how long the original cables were before they were cut back and capped-off. Maybe he used these as a remote jump starting system? Fuel transfer?

I still need to decipher the few smaller loose wires hanging around the battery compartment. Good advice to look for numbering on the wires (there is none on them) so I'm sure they were for radios, operator fan (it is Texas), extra flood lights, etc. Also, I need to inspect the cold weather ether system and ensure it's not another future failure point (thank you Nige for recommending this in another post). Seriously doubt I need ether here so decommissioning it might be the right option.

I'll finish up this post with a short story from yesterday when I replaced the batteries:
My in-laws are staying with us for the holidays so I took my father-in-law out to the hoe to let him play with it (boys with toys, right!). Unfortunately, the hoe didn't start that day so I decided to pull the batteries which prompted me to start this thread. After I came back from the Cat dealer with only two new batteries instead of four, my FIL asked why I only bought two. I said I didn't need all four since the set up of four is for cold weather. We went back out to the hoe, installed the batteries, took some videos of both of us ripping cedars on the ranch, then retreated to a local brewery for bevvies. It was here he asked me again why I installed only two batteries instead of four? I started to explain again the extra two were for cold weather operations but he stopped me and asked if I was being safe by only installing half of them. And he mentioned he saw me removing random cables, etc. and questioned why I did that. I had that puzzled look on my face so he bluntly said "How do you know what you're doing won't damage your excavator?" My FIL is not mechanically savvy so a technical explanation was not what he was looking for. Instead, I pulled out my phone, pulled up this thread and explained to him I'm following the advice of experts. He glanced through the thread while I explained I used this forum to learn about excavators and how to inspect them before confidently buying this one as a 'semi-informed' buyer. I showed him other posts where folks like me post questions and get amazing solid information for repairs, operation, maintenance, etc. At that point he handed my phone back to me and said "Well, I'm impressed and apologize for questioning your repairs. It's obvious you're in good hands."

Thanks for all the help, both with my hoe and FIL! LOL!

From my experience, its not the Fil you need to please. Its his daughter!!!!

LCA078 said:

... Also, I need to inspect the cold weather ether system and ensure it's not another future failure point (thank you Nige for recommending this in another post). Seriously doubt I need ether here so decommissioning it might be the right option...

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Are you talking about the D5 heater grid thread? If you have a heater grid, it will help start on cold mornings and run smoother. As long as it's working (by the light lighting up, and it drawing amps) it isn't in much danger of falling apart. If it's not working, you might want to fix it, or inspect it for cracks, or remove it.

According to the As Shipped Consist the engine is equipped with an ether injection system, probably because it was also equipped with the Attachment cold start package of 4 batteries and a bigger than standard starter motor. In warmer climates I always try to remove an ether system so that there’s no chance of one of the small tubes cracking (for some reason people seem to stand on them) and potentially letting dust into the engine.

Thanks, I missed that.

Following up on the cold start ether kit inspection:

So Nige has apparently seen one or two of these as he called it right- folks have been stepping on the thin line and caused a crack to develop near the engine fitting. Very minor issue but glad I know about it.