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Old 01-03-2020, 01:10 PM   #21
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We have two large 8D's for cranking our Lehman 135's (overkill, I know) and four 6V golf cart bat's(new) for house/Inverter. With two switches (in saloon) we can combine cranking bats, and or combine crank/house bats. While on shore power (bat charger) or when underway (160 and 40 alt's on the two 135's) we combine all for charging. When on the hook, we 'un-combine' house and crank, unless we are running the generator - which we do when too hot or too cold. Works well so far.
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Old 01-03-2020, 02:20 PM   #22
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AGMs tend to be better at delivering large bursts of current than good deep cycle wet cells, so an AGM bank may mitigate the voltage drop issue to some extent.
I think I wouldn't count on that. Even our Odyssey G31s -- huge cranking amps compared to Lifeline AGMs (both the deep cycle and starter G31s) -- drop enough voltage so our electronics usually crap out when starting that engine.

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Old 01-03-2020, 02:26 PM   #23
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I think I wouldn't count on that. Even our Odyssey G31s -- huge cranking amps compared to Lifeline AGMs (both the deep cycle and starter G31s) -- drop enough voltage so our electronics usually crap out when starting that engine.

-Chris

Then your batteries are nearing the end.... I am a HUGE Odyssey fan by the way. My batteries in my boat were from Sears "Die Hard Premium Marine" or something like that. Same as the Odyssey 2150s...and confirmed by Odyssey as such. Scored them fro $250!!! I sure wish I could get that deal again. It is difficult to find 2150s for under $400.
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Old 01-03-2020, 02:39 PM   #24
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Then your batteries are nearing the end.... I am a HUGE Odyssey fan by the way. My batteries in my boat were from Sears "Die Hard Premium Marine" or something like that. Same as the Odyssey 2150s...and confirmed by Odyssey as such. Scored them fro $250!!! I sure wish I could get that deal again. It is difficult to find 2150s for under $400.
It may also depend on the specific starters used on the engines in question. Some have a spectacularly large power draw when you first hit the key. Mine are bad about that, being old school (big) direct drive starters, not modern reduction drive units.
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Old 01-03-2020, 02:53 PM   #25
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All my batteries are used as one bank. I watch the voltmeter and run the genset (separate battery) when I need to.
Never had an issue.
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Old 01-03-2020, 02:55 PM   #26
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It may also depend on the specific starters used on the engines in question. Some have a spectacularly large power draw when you first hit the key. Mine are bad about that, being old school (big) direct drive starters, not modern reduction drive units.



Excellent point. A smaller motor at screaming high revs with gear reduction can move the engine using lower current draw, amps.

Many of us, me included, have older starters which demand a huge burst of current to get the engine to roll over. I have measured mine at over 1,000A to get the engine rolling settling back to 750A to 800A once the engine actually starts to roll. Technically a couple G31 may do it but without the lasting power, maybe not often needed , if the engine decides to be a bit difficult you may be in trouble.

With the newer, NOT new, starters that are supplanting the older starters I think you have a much better bet with the G31 pair including another couple rounds of cranking if needed.

So be aware of the type of starter your engine uses.
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Old 01-03-2020, 03:21 PM   #27
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All my batteries are used as one bank. I watch the voltmeter and run the genset (separate battery) when I need to.
Never had an issue.
I think this is an important point as it relates to the "overly redundant" crowd that usually is the majority on this subject. I am very in touch with what is going on with my batteries when I am relying on them solely. A good battery monitor(I use Magnum products so the Magnum Battery Monitoring Kit) go a long way to preventing battery disasters. Please realize I am not saying you should do it like I do. We all have different risk tolerances. For me, when it comes to limited space for huge battery banks, this is my solution. My new-to-me boat will offer some other options as it actually has an engine ROOM!!!!
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Old 01-03-2020, 04:59 PM   #28
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4mo, if you have decided to go with 6 V Golf car batts and have not yet purchased consider going direct to Dyno. If they will fit get the D145, a bit longer and taller but 145 min reserve capacity as opposed to the Dyno GC2b at 125 min reserve.

Dyno will let you choose the terminal type and orientation you want to make your cable runs cleaner.
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Old 01-03-2020, 09:20 PM   #29
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Just remember, a battery setup for cranking your 125 hp Leman is not going to be the same as the setup to crank a DD6v92.
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Old 01-03-2020, 10:16 PM   #30
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If you are going to have one big bank, give yourself some way of isolating a bad battery or the rest might be useless to you. For example, have two peer banks (12V units, not 6V units) each of which can be independently connected and disconnected from the common bus, e.g. two on-off switch, one per peer bank. So, if one battery rolls over, you can isolate, at the least, that half easily, leaving the other half useful.
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Old 01-04-2020, 10:06 AM   #31
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Then your batteries are nearing the end.... I am a HUGE Odyssey fan by the way.
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It may also depend on the specific starters used on the engines in question. Some have a spectacularly large power draw when you first hit the key. Mine are bad about that, being old school (big) direct drive starters, not modern reduction drive units.
Might be approaching end of life, but... the voltage drop thing has been that way since day 1 of installation. Well, at least since the first time I started that engine with electronics already turned on, probably after several hours of trolling on the other engine only.

Could be something else about our system, of course...

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Old 01-04-2020, 10:58 AM   #32
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Another thought on separation: engine rooms aren't an ideal place for batteries due to heat. So if you've got a suitable location that stays cooler, it makes sense to put the big, pricey house batteries there and just keep what you need for starting within a short cable run of the engines.

In my case, the start batteries are in the engine room, the house bank is under the forward stateroom against the forward engine room bulkhead (where it stays much cooler).
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Old 01-05-2020, 09:51 AM   #33
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Might be approaching end of life, but... the voltage drop thing has been that way since day 1 of installation. Well, at least since the first time I started that engine with electronics already turned on, probably after several hours of trolling on the other engine only.

Could be something else about our system, of course...

And I committed a semi-brainphart, too. When I mentioned the Odyssey bank that if getting a bit long in the tooth, I linked that with voltage drop to our electronics suite when we start an engine.

Actually, all our electronics run from the OTHER engine bank. The rest of what I described was semi-accurate, though; many of the electronic components drop out when starting that engine... and it's mostly always been that way. The earlier bank of Odysseys on that engine have since been replace by a bank of 6V Lifelines, not quite a couple years old now, same results (just retested, a few minutes ago). Plotter, radar, autopilot, and at least one VHF radio drop out... That's while connected to shorepower/charger, too.

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Old 01-05-2020, 10:21 AM   #34
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That matches my experience with a lot of setups that power electronics and engine start from the same batteries.
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Old 01-05-2020, 11:02 AM   #35
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As a fellow Navigator owner, I will give you a few bits of advice. First is that you should totally reconfigure the DC system. If it is anything like our 2000 model, it is a really bad design that was one of the first things I changed. The switch config is silly and ineffective. Second is that the 8Ds are junk. Replace them.

Two banks is ideal. You need the ability to use both banks for both jobs, and what will start a Leman or Perkins will not work as well for our big six-liter Volvos. The rotating mass is huge and compression is high. However, there is no need for separate starter batteries for each. I opted for eight GC2s for a nice large house bank and three Group 27 dual purpose batteries combined in parallel as a single start bank and backup house bank. You will need to make new battery boxes, but that's easy enough.

If you want to see my config, I would be happy to share it with you. I would also say to join our Facebook group. We share a lot of ideas over there.
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Old 01-06-2020, 02:34 PM   #36
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Hey Tom,

Thanks! I would love to see your config, I'll DM you.

I am part of the facebook group, I joined a year ago when we decided on the Nav 53, since then have flown from Cordova, AK to San Diego looking for the right one. Finally found ours in Newport Beach.
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Old 01-06-2020, 08:33 PM   #37
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One of the topics I'm not seeing on this thread is the relative design difference between start batts and deep cycle batts. I'm talking FLA batts. They really are different animals and not necessarily well suited to the other task.

I've got 6 golf cart batts for house bank and one 8D to start two 3208s. I can tie them all together but I'm not at all sure it's a good idea.
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Old 01-10-2020, 08:59 AM   #38
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I have twin engines. Each engine has a start battery. My generator battery is entirely independent. One of the engine start batteries is actually a house bank of 2x 4Ds. My 12 volt power panel has a selector switch and I can select either the start/house bank or the other start battery. I can also temporarily combine the batteries and start either engine. My engine alternators are on a combiner and charge both sets of batteries. My generator has its own alternator. My 40 amp three bank battery charger is separately connected to each engine bank and the alternator battery.
This arrangement has served me well and my batteries are lasting about 7 years. I'm 3 years into my third set.
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Old 01-11-2020, 07:18 PM   #39
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If you replacing everything why not do it the correct way and use dedicated batteries for start and genset and separate for house bank, put a switch in a place so you don't have to crawl down in engine room or lift hatches to jump banks, Also get a larger charger 40amps is too small for your house bank, you want 10% min.
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Old 01-13-2020, 01:26 AM   #40
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I redid my DC systems this year, and opted to keep a start bank for the main engines, and a start battery for the generator, mainly for redundancy, but also because I chose to move to LiFePO4 for my house bank, and didn't want to mix chemistries.



I ended up combining the two start batteries into one bank instead of two separate individual batteries, each dedicated to one engine.

Even on a 42' boat, I would prefer to have this setup than one big house bank, unless you only do day cruises and plug in every night, which it does not sound like the OP was doing.
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