Third / starting battery?

[gfatula]

I have managed to securely locate three identical group 27 batteries in our I-28. That gives us 345 AH@20A which has been all we need with a comfortable margin. At the same time I have made access to the aft end of the engine difficult. I am considering replacing one of the group 27 batteries with a group 26 that will fit under the floorboards in the bilge. That would give me the access room I need in the lazarette. The group 26 would have 525 CCA and would be dedicated as the starting battery.

What are the consequences of this change I need to anticipate?

[roadnsky]

...I am considering replacing one of the group 27 batteries with a group 26 that will fit under the floorboards in the bilge...
What are the consequences of this change I need to anticipate?

• Lots of nasty, sealed up moisture down there?
• Potential long cable runs?
• Fumes sometimes end up in the bilge. Fire hazard?

I have to ask? Do you really need 3 batteries?
If it were my vessel, I'd prefer the batteries were grouped together.
YMMV...

[gfatula]

• Lots of nasty, sealed up moisture down there?
• Potential long cable runs?
• Fumes sometimes end up in the bilge. Fire hazard?

I have to ask? Do you really need 3 batteries?
If it were my vessel, I'd prefer the batteries were grouped together.
YMMV...

That may just be my conclusion, too. Two is enough. Thanks,

G

[joe_db]

I would do without the third battery or move it when it was in the way before I would go stuffing a battery in the bilge.

[Al Schober]

FWIW, I have 3 batteries. Two of Gp 31 for a house bank and a Gp 24 for starting the A4. Boat originally had two Gp 27 and an A/B/Both switch.
You're going to need a 'combiner' or voltage sensitive relay to connect the batteries for charging. My alternator (upgraded from 35A to 55A) currently feeds the house bank, then overflows to the start battery.
You haven't mentioned your alternator capacity or regulator, so I'm not going to try answering questions you haven't asked.

[tomsailmaker]

I am watching the reply's very carefully on this because battery replacement is one of my on going projects.
I have the same problem we all have (no space) but I want as much capacity as I can get and want to keep the weight down and centered in the boat. Reading Nigel Calder's book mechanical,and electric manual I just bought 3 Trojan 27 AGM/VLRA deep cycle's for my house bank and a Trojan TM deep cycle flooded cell for my second bank to run stuff like a SSB, new bilge switch with counter,high water alarm CNG sniffer,and a watch alarm and low battery alarm. These are low draw alarms but they are almost always on.I bought a OPTIMA RED TOP for starting.
Nigel says a larger bank is faster to charge and easy to monitor. Iam still cutting and drilling to fit this all in but think this is the way to go. I just wish the flooded was AGM but I screwed up.

[ndutton]

Tom,

Did Calder recommend AGM's? If he did, was there any mention of optimal charging voltage? Any mention of different battery chemistries charged together? How about electronic ignition? Pending your responses I will likely have many more questions/considerations.

[tomsailmaker]

Neil I only read the same few pages about batteries about 20 times so it is still a little vague to me.Regarding the AGM he called them jell and he was impressed with the cycling ability but they would be better if they were all the same. Regarding the charging Trojan says the flooded and jell use the same voltage but Nigel said the jell will charge faster. I have been reading so much stuff about batteries the last few weeks that I am totally confused and my eyes hurt from watching the Oakland game, just kidding. I will get the book out tomorrow and check through it and get some real answers for you

[ndutton]

Looking forward to it Tom. The big thing here is charging voltage and if you meet the AGM's voltage needs, the effect it has on everything else at the higher voltage (I've heard as high as 15 volts in the past), particularly the effect on the narrow volts-amps-resistance balance with our electronic ignition.

Regarding mixing battery types, imagine designing for a higher voltage to please the AGM's then charging a wet cell at the same voltage. My AGM experience was not positive. I now have 4 deep cycle GR29 wet cells and one GR24 no maintenance, isolated engine starter.

Also George, I vote for no battery in the bilge. No good can come from that.

[tomsailmaker]

Neil I feel like the guy asking the doctor for a free operation. Looked at Nigel's recommendations again last night, I cant tell if he recommends AGM or WET CELL, it is one of those (if you do this then you get this). Regarding the ideal charging voltage I would think the battery mfg would be rule but I haven't found out what that is yet.Nigel's recommendation of a larger bank being easier and faster to charge led me to go with a 3 battery house bank and 1 battery backup (battery 2 bank 2). For charging I am using the standard small alternator (35 amps ??). What I would like to know is what amps at what RPM, may take it to LUCO and have them check it out.Iam curious about your thoughts about battery composition because I need to buy 1 more to make my house bank. I have 2 new AGM and 2 new WET CELL, the odd battery goes to the power boat to run the bait pump etc.I have gone with a separate OPTIMA AGM start battery all the battery's are isolated from each other from the switch and controls who gets charged,no automatic switching etc. This electrical stuff just drives me nuts,its kinda like buying stock. You do your homework place your bet and hope for the best.

[BunnyPlanet169]

Hi Tom -

I think you need to be a bit careful. It's not stock picking but engineering, and you should be able to design a system that works for your needs.

I have managed to securely locate three identical group 27 batteries in our I-28. That gives us 345 AH@20A which has been all we need with a comfortable margin.

A single, deep cycle, group 27 from Trojan has 110 AH @ the 20 hour rate at which point the battery is dead. DON'T do this.

With 3 group 27s, what you really have is about 100 AH to play with. Maybe a little less if your current draw is high (refrigeration, autopilot?) See below for where the 30% comes from.

I re-read some of Calder last night also as a refresher... His advice (as I read it) was that for the money, a well maintained, wet-cell lead acid battery is the best value. The caveat being 'well maintained', which he defined as regularly charged, watered and occasionally de-sulfated with a controlled over charge.

The AGMs don't self discharge as quickly, and are 'maintenance free' (which also means you can't maintain them.) AGMs were originally intended for automotive, with thinner plates and glass mat between the plates to deal with vibration, shock, and freezing conditions. They charge faster, but they are also twice as expensive.

Most, if not all of Calder's big cruising boat examples have conventional wet cell, lead acid technology.

He recommends a big single house bank, and a smaller, dedicated starting battery. The reason for a single big house bank is to have the capacity for intended use without deep discharge (defined as >50%) which will definitely shorten battery life.

His design goal was to assume the average cruiser will typically have undercharged batteries, and to only count on using the power between 50% and 80% of charge. That means you have a useful 30% of the total AH capacity of the bank before you need to recharge. The 50% assumes you never want to deep discharge, the 80% assumes you don't run the engine enough to make up the last 20% to full charge (this last 20% takes the most time). It's a very realistic and conservative approach.

If you haven't already, I'd suggest you follow the book and develop a listing of all electrical loads and duty cycles. This will really clarify your needs, and provide the sound basis for any further decisions. I did this several years ago, and it quickly clarified for me what I needed VS what I wanted, and how much money, time, and space made up the difference. I got what I need, which has actually been more than adequate for my use. YMWV, and you should do the exercise.

[BunnyPlanet169]

Tom,

Did Calder recommend AGM's? If he did, was there any mention of optimal charging voltage? Any mention of different battery chemistries charged together? How about electronic ignition? Pending your responses I will likely have many more questions/considerations.

As to E.I. all the blue water boats are diesel - not an Atomic 4 in whole book.

AGM and wet lead acid are the same chemistry so charging voltage is the same, but charge acceptance is very different.

Most of Calders examples presume the use of a multi-step smart regulator to deal with the requirement for a bulk charge, float, and occasional de-sulfation. The electrical portion of the book is primarily large power budget blue water cruising - although you can gather a lot of great ideas for coastal cruising / day sailing.

[tomsailmaker]

Jeff All good points for sure,thanks. My plan for the single WET CELL is to use it for the windless and the SSB the engine SHOULD be running when there used.The other time it will be used would be to power my alarms and bilge pump if I figure out how to set this up right.Per Neil I don't want to HARD WIRE them but I want to keep that battery off the grid unless its charging.Regarding setting up a power consumption plan that is a great idea except things keep changing,LED;S, new gotta have's.Every time someone post a site that has something cool I seem to buy it. I sort of got behind the 8 ball and had 2 boats that both needed batteries so 750.00$ latter I still need 1 more battery,so do I get another AGM @250.00 to make 3, or do I go to 3 wet cell's @159.00each-just bought 2 and cant return.The odd battery goes to a 15.5ft power/fish boat I re-did a few years ago and thought I should use it and or sell it. ITS all so dam confusing.

[Al Schober]

Been thinking about this...
Read somewhere some time ago that the AGM batteries become cost effective when you have high charge current capability (big alternator) and can use this capability to cut down your engine run (and maintenance) hours.
Other than that, they're not cost effective and flooded is the way to go.

[sastanley]

gfatula,
I have three batteries. I have two Gr29's wired in parallel as my house, and a Gr24 as my start. House = #1 and start= #2 on my switch. I have yet to 'need' my start as a start. My two Gr29's house have 230 Ah.
Mine are all Wal-Mart lead-acid flooded batteries. I can't see the added complexity of other mixtures being an advantage at this point (AGM or gel).

YMMV as Jerry says.