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Old 05-27-2022, 06:44 AM   #1
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Caterpillar C12 starting batteries?

Had a fair bit of electrical 'rearranging' done this past winter to sort out decades of past owner 'attempts'. It would seem that an oddball cross-connecting of starting banks and house bank was due to the C12's needing more CCA than than the one-each 8D was providing. They're tired anyway so it's time to replace them. It's all new wire and connections so we're good on that front. Just not enough capacity in the battery to crank it over, even with a full charge.

I'm wondering about the possibility that the starters might be likewise tired and drawing more current than they should. I can't recall the specific number but both engines are just past 1200 hours. I don't have the model# for the starters on there.

Anyone run into cranking issues with the C12 engine and have actual experience to share?
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Old 05-27-2022, 06:57 AM   #2
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What does the Cat manual say about the starting battery size? After 5 years starting batteries are throw away IMHO. But if severely drawn down due to tie in to house bank, the 8D may well be toast now.

Standard check issues:
- 1. Shorten the cables from the 8D as much as possible,
- 2. cables may be too small
- 3. cable ends may be internally corroded.

Unless damaged, a starter should last for well more than 1,200 hours. If in doubt replace or rebuild but I'd start with 3 items above.
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Old 05-27-2022, 06:58 AM   #3
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Shouldn't need starter info, I think. If you have the C12 manual/specsheet ?? it should specify minimum CCA. Or even the Eastbay manual might speak to that.

Does the 12 mean it's a 12L engine? "One each 8D" suggests 12V?

Our boat manual specifies a minimum of 1400 CCA, and that's for our V8-900 MANs, ~15L each I think. So far, the lame 8D pair the PO installed for our starboard engine -- 1150 CCA when new, and they're not, now -- are working sufficiently, and I'm taking that as suggesting there's some significant leeway in cranking requirements.

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Old 05-27-2022, 07:15 AM   #4
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Originally Posted by sunchaser View Post
What does the Cat manual say about the starting battery size? After 5 years starting batteries are throw away IMHO. But if severely drawn down due to tie in to house bank, the 8D may well be toast now.

Standard check issues:
- 1. Shorten the cables from the 8D as much as possible,
- 2. cables may be too small
- 3. cable ends may be internally corroded.

Unless damaged, a starter should last for well more than 1,200 hours. If in doubt replace or rebuild but I'd start with 3 items above.
As I mentioned, the cabling is new and connections are not the issue. I didn't mention the specifics, because I wasn't asking about cabling.

I figured a starter wouldn't be a problem as most tend to work until they don't, or there's solenoid issues.

I can't speak to the specifics of how the battery 'arrangement' did or didn't contribute to their lifespan. In the three years we've owned the boat we've never run any of the banks below safe voltages. Given it's mostly weekend recreational use actual cranking of the engines was likely a lot less one might find in a lot of other situations. I'm fine with having them replaced.

The question here is for folks that have actually HAD the C12 engines what if any battery/starting specifics come to mind.
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Old 05-27-2022, 07:27 AM   #5
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Shouldn't need starter info, I think. If you have the C12 manual/specsheet ?? it should specify minimum CCA. Or even the Eastbay manual might speak to that.

Does the 12 mean it's a 12L engine? "One each 8D" suggests 12V?

Our boat manual specifies a minimum of 1400 CCA, and that's for our V8-900 MANs, ~15L each I think. So far, the lame 8D pair the PO installed for our starboard engine -- 1150 CCA when new, and they're not, now -- are working sufficiently, and I'm taking that as suggesting there's some significant leeway in cranking requirements.
Yes, these are the 12L C12 Caterpillar engines, two of them. I have not yet looked into the specifics of what the C12 manual indicates.

Apparently, when clamped it exceeding the reading of the 1000A meter used. Which, from some brief searching elsewhere online says is not unexpected, as these beasts draw more than that.

Yes, the boat is all 12vdc. And was previously set up with one 8D for each engine and some hodge-podge of additional connections "with the house bank". I don't have specifics on how that was set up. This was a winter project done by MTS for me, but coordinated through our boat manager. Long story there, but the tech doing the actual work has had a good handle on the job. Now we have new wiring and other hardware to put things back on a sensible track. Batteries closer, wire gauges increased, etc. The number of "why the eff did they DO THAT?" questions that came up legion.
My checkbook weeps.

We're now at the last stage of the project and the unexpected discovery of the 8D's being unable to start each engine on their own. Because apparently part of the previous mess was to keep them paralleled all the time.

So now it's a question of what are we going to use to replace those individual 8D's such that they'll start the C12's. I bring up the question here, not because I can't easily go look up the factory stated requirements, but to see if anyone else has had to deal with the C12's and starting woes.
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Old 05-27-2022, 07:39 AM   #6
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How long are the cable runs from the 8D to the starter? Relays and corroded fuses in the starting circuitry can affect starting as well. On my Cat 3056s (6 liter) too long a cable length and slightly corroded spade fuses affected the starting.

I have two 8Ds that I just replaced. Overkill - of course. Security, yes. Based upon dirt moving experience a single 8D will suffice for the C12. Boat wiring can be vastly different than a small loader though.

PS
My 8Ds are in Parallel which may be the best for your 12s
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Old 05-27-2022, 07:45 AM   #7
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How long are the cable runs from the 8D to the starter? Relays and corroded fuses in the starting circuitry can affect starting as well. On my Cat 3056s (6 liter) too long a cable length and slightly corroded spade fuses affected the starting.

I have two 8Ds that I just replaced. Overkill - of course. Security, yes. Based upon dirt moving experience a single 8D will suffice for the C12. Boat wiring can vastly different than a small loader though
Yep, previous gauge and distance was less than ideal. Which has, supposedly, be rectified. I wouldn't imagine the starting experience to be much different between boat/road grader both using the same C12 engine.
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Old 05-27-2022, 07:57 AM   #8
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The C12 and 3196 are quite similar if not near identical for starting needs. Maybe somebody with the more common 3196 could chime in, I'll check same with a dock mate when he wakes up.
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Old 05-27-2022, 09:42 AM   #9
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I have C-12 Cats in my boat. The only difference is I am 24V. I replaced my 8D batteries and went with 4- Group 31 batteries. I also replaced the MT 50 starters since they were 14 years old and had 1600 hours on them. Mine turn over fast. I would think about going with two group 31's instead of the 1- 8D. Just a suggestion. Good luck
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Old 05-27-2022, 10:51 AM   #10
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I dont have Cats but do have 8Ds for both starting and house.
Doing research & planning for eventual replacement mynfibdings are a pair of GP31s are roughly equal or exceed one 8D.
I shorted my start run (about half what is was) and increased cable size when I moved my start to my thruster bank. I'm just monitoring health of my 8Ds awaiting the need to replace w GP31s.
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Old 05-27-2022, 11:07 AM   #11
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They only splashed the boat a few days ago and I haven't had time to crawl over all the details. Part of the winter work also included repositioning the bow thruster battery bank from the engine room to the bow, and replacing a single battery with two. Don't recall which size. So the idea of using two 31s (or whatever) in replacement of the 8Ds is not a foreign one.
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Old 05-27-2022, 11:11 AM   #12
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As far as physical fit goes, an 8D battery box should hold 3 group 31s if I remember correctly. The 3x G31 will be somewhat more powerful than a single 8D in most cases.
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Old 05-27-2022, 11:59 AM   #13
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I have 2 Group 31 for each of my 6CTA Cummins that are 8.3 liters. It seems to do the job well. Yours is a larger engine so I donít know if they would be enough or not.
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Old 06-06-2022, 01:15 AM   #14
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I have 2 Group 31 for each of my 6CTA Cummins that are 8.3 liters. It seems to do the job well. Yours is a larger engine so I donít know if they would be enough or not.


I have a Cat 3406 (15 liter). 2 group 31s in series (24V) crank it over plenty fast enough. Group 31s in parallel for a 12V system would be fine for a 12 liter engine.
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