Any reason not to share engine and gen start batteries?

[DDW]

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?

 

[Bob Cofer]

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.

 

[Comodave]

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.

 

[DDW]

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.

 

[Wayfarer]

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.

 

[O C Diver]

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

 

[rslifkin]

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).

 

[High Wire]

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.

 

[wkearney99]

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?

 

[bayview]

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.

 

[Group9]

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).

 

[Ken E.]

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.

 

[dhays]

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.

 

[BruceK]

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.

 

[Art]

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.

 

[lipets]

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

 

[AusCan]

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.

 

[stevemitchell]

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

 

[Wxx3]

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.

 

[jimisbell]

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.

 

[The Other Gary]

My port engine battery is stand alone as is my generator battery. The starboard engine start battery also charges the house bank through a combiner that cuts off so that start battery will not be drawn down. The Starboard engine has the bigger alternator.

I also carry a 20 foot pair of heavy duty jumper cables that I can use in the event a battery goes weak and needs a boost or to combine both alternators to the house bank if I have been anchored out a long time without using the genny. I have also used them to jump another boat that allowed their banks to discharge.

 

[jimisbell]

I have also thought about a spring wound starter that would make the engine startable even with NO BATTERY. They are not too expensive but still an extra expense.

 

[obthomas]

Me and my trawler follow a simple rule. Keep things separate except when they need to be combined. My fuel supplies, batteries, and charging are by engine. I can cross them over if need be. My House is connected either starboard or port. My port set is twice the amp hours as starboard. My main engine alternators can be combined. My generator battery and alternator are on thier own. My battery charger charges each bank independently.

 

[DDW]

2 separate batteries might be justified for reliability, but as I said I have three: House, engine start, gen start. I am reducing it to two, house and engine/gen start. Can be cross connected for unusual situations.

 

[Pete Meisinger]

You don't say what type of boat you have, I would be interested in knowing that. If you are really, really interested in saving every available square inch of room one single house battery could be enough to start both engines and run your house lights for a few minutes in the evening. If you have a windless that battery might be on the foredeck and serve as a back up with a set of cables.

Why not invest in a couple of the "gel" type batteries. You could mount them upside down on the ceiling of your engine room not taking any floor space. Just giving you a head ache when you crawl around the bilge and bang your head.

I am in totally the other camp from you. I just pulled all my batteries for the winter. (Single engine 36 foot trawler) :
2 house batteries with a spare stored on the opposite side for balance making 3 house batts
1 Engine starting battery (F.L. 120)
1 Genny Starting battery
1 Windlass battery
2 batteries wired to my inverter
1 fully charged jump pack

That's a total of 9 batteries. The only time I regret having them all is in the fall when I have to move them for storage and again in the spring when I re commission.

One more thing, I never let any of them get over 3 years old. When they get that old I relegate them to inverter duty since I rarely use the inverter.

But then, I am Anal and love redundancy!

pete

 

[FF]

"The only time I regret having them all is in the fall when I have to move them for storage and again in the spring when I re commission."


There is also the replacement expense and perhaps a watering drill.

 

[OldDan1943]

Just my preference.... separate start battery, separate gen start battery finally, the house batteries. (hello combiner, to the ME battery)
The gen battery is totally separate from the rest of the batteries and charger.
If you have solar panels, they charge only the house batteries.
AND that big red parallel switch is for when the main engine battery goes flat and you need to start the main engine off the house batteries.
IMO, it is totally foolish to routinely use the start battery as part of the house battery.

The jump packs are fairly inexpensive and fantastic 'insurance' against a total screw up on the part of the operator and failed batteries.
I guess, one should consider getting a jump pack large enough to start the ME but if not, get one large enough to start the gen.

 

[Art]

Did Noah have a get home-engine? - Yeah, his wife!

My preference for batt layout: I use good ol', fairly high quality Flooded LA batts, manufactured by East Penn. IMO... Can't beat the economy and service life in relation to the price.

1. Four - 31M deep cycle batts hooked in parallel for house bank and start batts for both engines - > Consistently held at charge when starboard engine runs. - or - Charged by on board Professional Mariner 60 amp straight line charger that operates from shore power or genset by flipping "charger" breaker to on. - or - Charged by NOCO 12 V, 40 amp Genius 4 Bank charger that runs off shore power or gen set my flipping "120V" breaker on and flipping its own seperate switch on.

2. One - 24M starter batt for gen set - > Charged by solar panel on face of fly bridge. - or - by its own smart trickle charger that runs whenever 120V breaker is on; getting power from shore power or gen set.

3. One - 24M starter batt; that is isolated in its own batt box for "any" emergency - Charged by its own smart trickle charger that runs whenever 120V breaker is on; getting power from shore power or gen set.

4. One - 24M starter batt that is in Crestliner tow behind runabout w/50 hp Johnson o/b - Charged by the o/b.

Stats:

a. Regarding # "1" - Four deep cycle batt house bank lasts for nearly a decade before replacement. Cost for all four at Battery Plus [considering discounts etc] was $450 +/- beginning of 2019. The four replaced were put in at beginning of 2010.

b. Regarding # "2" - Gen set starter batt lasts for many years [not sure exactly hoe many]. When that went bad a few years ago I simply moved the isolated emergency batt [#3] into place.

c. Regarding # "3" - Isolated emergency batt's name says it all... it is for either replacing gen set batt, or replacing Crestliner's o/b batt [see #4]. It is also for starting main engines if for some reason that becomes necessary [never has yet!]. Each time the emergency batt gets used for replacement into the genset or Crestliner o/b the emergency batt get replaced with a brand new batt.

Pretty simple and near fool proof batt layout. Darn well affordable too!

PS: The inexpensive, always kept 100% charged, emergency batt [#3] means no need for expensive jump-pack... that eventually looses much of its power anyway...

 

[overgill]

Interesting that there are as many configurations as there are boats. I guess its whatever works for you.

I didn't notice anyone mentioning a battery isolator. I my case I have a single engine with a start battery and two house batteries. The engine alternator is wired to a three bank isolator that charges all three batteryies when the engine is running.
The generator shares the engine start battery. In the rare event that the engine and geny are running at the same time the alternators are electrically separated via the isolator. If the engine battery ever fails then I can switch in the the house bank via a battery switch.
My bow thruster is wired to the engine start battery, the only time the thruster is used is when the engine is running. See no need of redundant batteries.

This set up has served me well for a long time.

 

[DDW]

You don't say what type of boat you have, I would be interested in knowing that.

.....

But then, I am Anal and love redundancy!

pete

It is an AT 34.

My original question was would there be charging issues with the genset and engine running together, the consensus seems to be no problem. How many batteries you are willing to deal with for other reasons might have a number of right answers depending on owner and use.

I've even thought of simply having a house bank and nothing more, start the engines from it. Properly maintained and managed, this is more reliable than any other scheme (i.e., fewer failures/year). In 35 years of (large) boat ownership I've used the combiner switch to start the engine exactly once, and that was after winter layup when the boat watcher set the charging switches wrong. So 2 banks (house and engine/genset start) is plenty redundant enough for me.

If you are replacing batteries every 3 years, you are either murdering them, or throwing away perfectly good batteries. The Lifeline AGMs on my sailboat are going on 13 years now, still serviceable, if down a bit on capacity.