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10-14-2019, 09:20 PM
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#1
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Guru
City: San Francisco
Join Date: Apr 2018
Posts: 3,089
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Any reason not to share engine and gen start batteries?
Other than the obvious reduction in redundancy. I'd like to recover the space. Most of the objections to two alternators on one battery seem to center around overworking one while the other idles. Since a rarely run both at once, and the engine alternator has higher set points, seems like a non issue in this case.
Something I haven't thought of?
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10-14-2019, 11:07 PM
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#2
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Guru
City: Bayview
Vessel Name: Puffin
Vessel Model: Willard Vega 30
Join Date: Aug 2013
Posts: 1,443
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Is this also your house bank? Our setup is one 12v bank for electronics, one 24v bank for house/start and one 12v bank for the genset. We keep the genny battery completely isolated. It is the emergency backup, if the genset starts we can get everything else to function via chargers.
__________________
What kind of boat is that?
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10-15-2019, 12:08 AM
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#3
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Moderator Emeritus
City: Au Gres, MI
Vessel Name: Black Dog
Vessel Model: Formula 41PC
Join Date: Jul 2015
Posts: 21,131
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We have 2 start batteries and a house bank. The genset starts off the house bank. I can get the genset off one of the start batteries. I also carry a jumper pack along just in case.
__________________
Boat Nut:
If you are one there is no explanation necessary.
If you aren’t one, there is no explanation possible.
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10-15-2019, 12:56 AM
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#4
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Guru
City: San Francisco
Join Date: Apr 2018
Posts: 3,089
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There's also a house bank, and a paralleling switch so if the start battery went dead I could still start the engine or genset from the house bank. I'm planning on re-battery-ing, leaning towards two G24 for engine and genset start, three L16 Firefly for house. That would take a much smaller footprint than the existing setup, more capacity, less complication.
Currently the bow thruster is powered from the 4D engine start battery, but two good G24 have more CCA and lower internal resistance than a 4D.
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10-15-2019, 05:59 AM
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#5
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Guru
City: Beaufort, NC USA
Vessel Name: Sylphide
Vessel Model: Kingston Aluminum Yacht 44' Custom
Join Date: Aug 2014
Posts: 2,228
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My engine and generator use the same start battery. I don't know enough to be able to say if you should do that or not, but it seems to work well enough for me so far.
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10-15-2019, 06:38 AM
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#6
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Guru
City: Fort Myers, FL... Summers in the Great Lakes
Vessel Name: Slow Hand
Vessel Model: Cherubini Independence 45
Join Date: Dec 2010
Posts: 12,818
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IMO, it depends on your cruising style. I have read on TF about people who have one house bank and start everything off of it. If you're a local cruiser within easy reach of Seatow or Tow Boatus, I guess that's fine. As you venture to more remote locations, I think separate and redundant is more prudent. Don't know how big your generator is, but a properly sized battery is pretty small in the scheme of things. Maybe you could find a better mounting location. My engine, house, generator, and bow thruster batteries are all separate, although I can jump the engine battery off of the house bank with the flip of a switch. That same switch also allows me to charge the house bank off the engine alternator when the house bank alternator regulator failed (have 2 alternators on the engine for engine battery and house battery).
Ted
__________________
Blog: mvslowhand.com
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
"Slow Hand" by The Pointer Sisters
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10-15-2019, 07:19 AM
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#7
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Guru
City: Rochester, NY
Vessel Name: Hour Glass
Vessel Model: Chris Craft 381 Catalina
Join Date: Aug 2019
Posts: 7,539
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I have 2 start batteries. Each engine and the generator has a 1-2-both-off switch, so any of the above can be started from either battery. Normally the port engine starts from battery 1, stbd and generator from battery 2. I've had no issues with this sharing arrangement. In my case, the house bank is separate and nothing can start from it without jumper cables (it only ties to the engine batteries via ignition-interlocked ACRs for charging with engines running).
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10-15-2019, 08:16 AM
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#8
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Guru
City: Cape May, NJ
Vessel Name: Irish Lady
Vessel Model: Monk 36
Join Date: Dec 2007
Posts: 4,947
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You need a backup of some kind. There is at least a hundred ways to wire them up. Learn what works for you in the simplest and safe arrangement.
__________________
Archie
Irish Lady
1984 Monk 36 Hull #46
Currently in Cape May, NJ
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10-15-2019, 08:47 AM
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#9
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Guru
City: Bethesda, MD
Vessel Name: Solstice
Vessel Model: Grand Banks 47 Eastbay FB
Join Date: Feb 2018
Posts: 2,164
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With proper battery management and maintenance all sorts of setups are possible. The trouble is most folks aren't going to put in enough of the gear AND monitor it effectively. Batteries are more tedious than you might think. Temp, types of cells, dis/charging rates, float, etc.
So, can you do it, sure. Should you? Only if you're really going to set it up right and monitor it.
Just how much 'space' is it you think you'll be recovering? And what is it you anticipating putting there?
__________________
-- Bill Kearney
2005 Eastbay 47 FB - Solstice, w/Highfield CL360 tender
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10-15-2019, 09:05 AM
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#10
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Guru
City: gulf coast
Join Date: Jun 2014
Posts: 3,440
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No problem sharing batteries. However you will have to run cables to the gen that will probably cost as much as a small battery. I like having the genny on a separate battery because I can use it to charge dead start batteries if necessary. If you have separate house bank then you can use that if youcan connect them.
I always kept jumper cables so I could jump anything in an emergency.
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10-15-2019, 09:17 AM
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#11
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Guru
City: Alexandria, VA
Vessel Model: 2000 Wellcraft
Join Date: Sep 2013
Posts: 1,467
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Our genny has its own separate battery (with a pair switch to the other batteries). It's a nice bit of redundancy, but our Xantrex controller has an adjustable setting that will shut off our inverter if we go below a certain voltage to keep from running our batteries too flat, so I don't see us ever having to use it (unless our twelve volt systems ran them down).
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10-15-2019, 10:38 AM
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#12
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Guru
City: Bellingham WA
Vessel Name: Hatt Trick
Vessel Model: 45' Hatteras Convertible
Join Date: Nov 2016
Posts: 1,971
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I have separate gen, start and house batteries, and house can be paralleled for start. I see no reason why the start batteries couldn't also be used for the genset, 2 group 31's in parallel in my case. I also carry jumper cables for any unplanned cabling permutation that might pop up.
__________________
Ken on Hatt Trick
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10-15-2019, 08:58 PM
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#13
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Guru
City: Gig Harbor
Vessel Name: Kinship
Vessel Model: North Pacific 43
Join Date: May 2015
Posts: 9,046
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My boat comes with a separate genset battery. When my genset battery died a couple days after I bought the boat, I didn’t know any better so I just replaced it. In retrospect, I probably should have simply gotten rid of the genset start battery and used the engine start batter to start the genset as well. I have the ability to start the genset from the house bank with a cross connect switch.
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10-15-2019, 09:39 PM
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#14
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Guru
City: Sydney
Vessel Name: Sojourn
Vessel Model: Integrity 386
Join Date: Oct 2011
Posts: 13,293
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Our start and house is one combined bank of 2 8Ds. Sub-optimal but IG tradition. Genset has separate N150(?6D) battery,so it and genset are backup if the dual use bank gets messed up(which it hasn`t).
Genset batt has its own regulated solar panel so it is good backup, otherwise it only gets charged when genset runs. I like the self contained stand alone backup.
__________________
BruceK
2005 Integrity 386 "Sojourn"
Sydney Australia
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10-15-2019, 10:09 PM
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#15
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Guru
City: SF Bay Area
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 12,569
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House bank is as the name implies... 4 deep cycle bats hooked in parallel. Runs all our 12 V general needs. Charges from charger activated by gen set or shore power. Also charges from starboard engine alternator
Both engines start off the house bank
Gen set has independent starter batt. Charges from solar panel in front of fly bridge. Also charges from 2 amp float charger that runs whenever 120 V AC is on during gen set or shore power activating.
Have isolated starter batt in its own batt box - for emergency if all else fails. Float charger same as the one on gen set batt is also activated whenever 120 V AC is activated.
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10-15-2019, 10:16 PM
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#16
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Senior Member
City: FL
Vessel Model: Benneteau Swift 42
Join Date: Jun 2019
Posts: 469
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I have 3 groups
house 6 6volts also wired to Solar
two grp 31 one for each engine
Gen 1 grp 27
The charger onshore power has 3 legs
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10-15-2019, 10:21 PM
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#17
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Guru
City: Adelaide
Vessel Name: Kokanee
Vessel Model: Cuddles 30 Pilot House Motor Sailer
Join Date: Jul 2012
Posts: 3,218
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I run everything off the 4 x 220Ah house bank and have one separate 220 Ah backup battery (charged by an ACR) that can be switched for house or start.
So far I haven't had to use it.
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11-01-2019, 12:47 PM
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#18
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Guru
City: Seattle
Vessel Name: Aruna
Vessel Model: Kristen Yachts 50 Pilot House
Join Date: Sep 2018
Posts: 540
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As others have said, it really depends on your cruising style, location, redundancy requirements, technical knowledge, etc. etc.
My boat had two separate main engine starting batteries that couldn't be combined and a single generator starting battery when I bought her. I combined the two main engine starting batteries in a way that allows me to use them individually or together, and replaced all of the batteries with more modern and smaller AGM batteries.
I usually leave the two main engine batteries combined all the time and start both engines from that. I have not seen any issues with that setup. I like having the generator battery completely separate as it is my "last resort" if for some reason I drain my house bank, and somehow mess up my main engine start bank, I can at least start the generator and have power to start figuring out what mess I got myself into, and charge other banks back up.
Current diagram below
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11-01-2019, 12:58 PM
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#19
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Dauntless Award
City: Wrangell, Alaska
Vessel Name: Dauntless
Vessel Model: Kadey Krogen 42 - 148
Join Date: Jan 2013
Posts: 2,820
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Wow, I wish that I'd thought of that. Last summer i had to replace my gen battery, in part because it was used so little.
With my setup it would have worked fine with one start. I can always stsrt engine with house bank of needed.
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11-01-2019, 01:03 PM
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#20
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Guru
City: Ingleside-On-The-Bay, Texas
Vessel Name: Papillon
Vessel Model: 1978 Mainship 34 Trawler #95
Join Date: Jan 2018
Posts: 643
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I can think of one reason for two separate batteries. It has just happened to me.
The engine battery failed and I could not styart the engine. I am at a bulkhead with no power and use solar to charge both batteries. The GenSet started and I was able to recharge the main engine battery enough to start the engine.
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