Adding another 2 house batteries....Need suggestions

kevin babineau · Post by **kevin babineau** » Sun May 10, 2009 7:02 pm

ur something else mikey....i can suggest whatever i like to whomever i like....and u can do the same.....oh my free boat is looking pretty good huh?

kevin babineau · Post by **kevin babineau** » Sun May 10, 2009 7:18 pm

as for the orginal question ur layout would work and connect one set of wires to one bank and the other to the other bank..do u have starting batteries for the engines?...and yes having a soleniod to combine batteries would work if u had the set up..the soleniod isolates one battery from the other so if u have a drain it will only drain one and by the click of the soleniod u have two batteries combined if need be...but if u had good running engines with the right switches u could just use one starting battery..either way without the solenoid u have two alternators put juice into one set of batteries...i have never heard of that being a issue.....if it was mine i would have switch so i can charge the start batteries with the genset and also be able to use the house batteries to start with. i would also have a way to completely shut off all power to house except for an auto bilge pump with alarm...this is what id do.... not what im telling u do ...ok mike?

ready123 · Post by **ready123** » Mon May 11, 2009 8:01 am

jwrape wrote:I do have an emergency switch that I have had to use on occation but I think that's all I really need.

I agree.
So you should remove those wires that combine the two starting batteries. You should do the same with house and genny batteries... the genny should be standalone as the Onan charges it and should you run the onboard battery charger while the genny is running the battery charger should not be feeding the genny battery also.
You don't show on your diagram if all the negative terminals of the batteries connect to a common ground bus connection for the 12V system?
Are my suggestions clear or do you need a diagram?

In my setup I use a three bank charger for port, starboard, house. The Onan battery is charged by the genny when it runs. This system I have described runs well for me.... my batteries are three years old and each winter I just disconnect them fully charged and leave them in the boat all winter.... in spring they all measured around 12.8V which is still 100% charge. I try to not run them below 12.2V (50%) before recharging.

I prefer to size my house battery so that one can do all the work, rather than use multiple batteries. This is my house Lifeline:
http://www.lifelinebatteries.com/marineflyer.php?id=6
It handles 15A for well over twelve hours.

guglielmo6160 · Post by **guglielmo6160** » Mon May 11, 2009 11:40 pm

I always carry two addtional batteries on board, NOT hooked up to anything, and always on charge mode, with a maintainer, JUST IN CASE
ya never know,
nothings worse than dead batteries in the middle of west bumblef--k knowwhere

jav · Post by **jav** » Tue May 12, 2009 8:51 am

my .02c on a pretty in depth topic.

If your adding 2 batteries- it does make a difference how you implement them. My opinion, and how I run my boat- which has no gennie but instead uses a large inverter for on the hook AC, is make the house bank as large as possible. Keep your starting batteries isolated, and I use battery switches both for isolation and combining as needed.

The reason for a single large house bank relates to overall battery life. The larger the bank, the slower the discharge/recharge rates per battery, and as long as the bank is maintained in the 50-100% range, a very long service life should be expected.

I do have one concern on your effort though. A bank of batteries should be well matched in order to reap it's benefits. Adding 2 new batteries to a bank of 2 old batteries is not the best idea. In fact- combining 4 new batteries of different sizes or types is not the best of ideas. You really want all the batteries in the same bank to be the identical in every way including age. In a house bank, I beleive it's better to employ a true deep cycle battery versus a starting or hybrid type of battery. A great low cost option for house banks is good 6 volt golf cart batteries (which is what I use). They are true deep cycle batteries designed to frequent discharge/recharge cycles and they are very economicaly per amp hour compared to just about anything else.

Good luck.

kevin babineau · Post by **kevin babineau** » Tue May 12, 2009 9:17 am

i agree with jav...two good and identical batteries are better than a bank with 3 good batteries and one bad one....the bad battery will kill the bank.... two 6's series (thanks for the correction) makes 12v...some one said first u must detetrmine how much power consumption u'll need....u said u need to run a frig u need to find out how much juice for how long with out the engine running.....someone here should know

jav · Post by **jav** » Tue May 12, 2009 10:00 am

quick correction Kevin- 2 - 6 volt batteries paralleled adds the amp hours of each battery together (for twice the amp hour rating) but is still 6 volts. 2 -6 volt batteries in series provides twice the voltage (12 volts) at the amp hour rating of each single battery.

kevin babineau · Post by **kevin babineau** » Tue May 12, 2009 11:34 am

opps wrong word sorry i meant series....positive to negative...... one wire from neg of the boat goes to neg on first batt a jumper from that batt positive to the next batt neg terminal then the positive to the boat 6+6=12 ....like a flashlight

jwrape · Post by **jwrape** » Wed May 13, 2009 7:11 am

Ok, i looked at my setup again on Monday a little closer.... I have two isolated starting batteries for the engines and two batteries wired in Parallel but connected seperately for the house and generator.
My plan is the build a slightly larger box to house 4, no maintenance Marine batteries wired in Parallel for the house/Generator. This should give me the capacity I need. The batteries that are there now are only a year old and have one season on them. They should be fine to add the other two to. I beleive my on board charger to be ok to charge them as it sits and adding the capacity will keep the house batteries from dieing while on hook without starting the Generator.

Below is what I have for house currently and on the bottom is what I plan on making.

What do you think? Will that be good? Simple and effective right?

jav · Post by **jav** » Wed May 13, 2009 9:58 am

Will it work for what you want to do? Yes.
Is it the cheapest way to get additional capacity? Probably.
Is it technically the correct way to set it up? No.

I know this is hard to understand so allow me to try and simplify why this is so important in a way most folks can visualize.

Adding new batteries in parralel to even 1 year old marine batteries adds capacity but can create some problems. When you wire them in parrallel like your doing, all 4 smaller batteries become 1 large battery . This means that when drawing power from the one large bank, each individual battery will release or take up energy based on it's own internal resistance. The large banks perfromance will be limited by it's weakest batteries performance.

To understand how this works, think of a battery like a bucket full of water you hang up on a tree limb and connect a 5/8" hose to. When using that hose off the 1 bucket (or 2 in your case but, it will be easier to understand if talk about 1 versus multiple for the moment), 1 bucket can provide enough water to run the hose for 45 second before running dry. You can also re-fill that bucket through that hose in 10 seconds using a pressurized spigot. Pretty simple.

You've decided that the 45 seconds isn't enough run time so you want to add more buckets. You add 3 more (4 total) to make the hose run 4 times longer. BUT- in order to get that 5/8" hose to flow 4 times longer , the amount AND pressure of water coming out of the hose has to stay the same as it was with just the one bucket... SO, the hole in each of the 4 buckets now has to be 1/4 of the size as just the single bucket so you get the 1/4 of the water out of each of the 4 buckets - and so the hose flows 4 times longer.

If the hole in each of the buckets is not identical, the bucktes will empty and fill at different rates. A bucket with a larger hole will empty before the others and you'll lose pressure AND volume at the hose. Likewise, when you go to refill using the spigot- that bucket with the larger hole will be over flowing while a bucket with a smaller hole may still be half empty.

No 2 batteries have identical internal resistance (which is akin to the hole in the bucket). That resistance changes with design, capacity, age, even temperature. This is why it's so important to use identical batteries in any single battery bank. If you don't, when your using and CHARGING that bank, you may be cooking the one battery with the largest "hole" and barely using the one with the smallest.

The same is true for individual cells in a single battery. If anyones ever heard of a failry new battery dieing becuase of a bad cell- this is why. If the cells aren't matched- a single cell can kill the whole battery.

ready123 · Post by **ready123** » Wed May 13, 2009 10:04 am

Well said jav....
I restate my earlier point... this is not an area to scrimp on $$, it is the key to a happy time on the boat. I say again "Go with one big house battery"... cheaper and more effective than starting with 4 new identical batteries now, and as jav said no guarantee that all four are in fact equal.

jwrape · Post by **jwrape** » Wed May 13, 2009 10:04 am

That makes sense.... Good analogy

jwrape · Post by **jwrape** » Wed May 13, 2009 10:06 am

ready123 wrote:Well said jav....
I restate my earlier point... this is not an area to scrimp on $$, it is the key to a happy time on the boat. I say again "Go with one big house battery"... cheaper and more effective than starting with 4 new identical batteries now, and as jav said no guarantee that all four are in fact equal.

What do you mean one large battery? What type do you recommend? Would I need a different charger? Is it something I can find local or have to order?

randyp · Post by **randyp** » Wed May 13, 2009 10:21 am

Just to add to the discussion. I agree about spending the money to ensure that your batteries are new and not using an older one in the group. I also am a big fan of the Blue Seas ACR (Auto Charging Relay) which allows you to FORGET about which battery or battery bank is doing what while on the hook. That being said, I have a new 1-2-All-Off battery switch because I trusted the original one, only to find that it had a bad/old/corroded contact that "automatically" defaulted to "off" (obviously, since the contact was bad) while I was undeway, thereby frying my alternator not once, but TWICE until I figured out the problem.

Now, back to the ACR. It monitors and senses what's going on with the house bank (2 125 AH deep cycles in parallel for 250 nominal AH) and the engine "bank" (only have one engine, so I use 1 battery - cranking/starting marine battery), I have a 20 Amp Charles Charger runninng off the AC when I'm back at the dock or can plug in. This is a dual bank charger that I have wired both banks to the two house batteries. I do not charge the engine battery as the ACR monitors the charges of all batteries and does not allow the engine battery to drain. The battery switch is always on "2" (House Bank). When underway the alternator charges whatever battery bank needs charging. The ACR has an LED arrary that lets me know what's going on. Plugged in to AC the charger pumps in the amps to the house bank and any excess goes to the start battery if needed, then it "idles" at a trickle charge.

I don't have to worry about the battery switch or the batteries draining off my start battery.

For a little over a hundred dollars I have peace of mind. The Blue Seas people were very helpful on sizing and installation tips.

jav · Post by **jav** » Wed May 13, 2009 11:35 am

On the one large battery thing, I think what READY123 was suggesting was something like a singe 8D marine battery. But that has it's limitations too.

1)They are large and HEAVY- a real pain to transport, mount and replace (about 160 pounds)
2) A single battery doesn't have enough capacity to run much while adhereing to the 50% rule- (expect about 100-110 amp hours of use).
3) Good ones aren't cheap
4) They are still made of smaller cells in series so their is still the risk (albeit lower) that a mismatched cell could occur.

There's nothing to be afraid of when considering mutliple battery banks. You just have to understand that for it to perform well as a "bank" each component in the bank should be as close to identical as posssibly. Preferably, the exact same battery of the same exact age.

There's also one other thing I didn't bring up (and others but this would become a novel) but you need to be aware of it. When working with larger capacity banks- you need to consider your charging methods. Hooking up the genny start circuit and ALTERNATOR to a 400+ amp hour bank is going to stress the hell out of it's alternator. That alternator was was likely designed to replenish a starting battery, which is very light duty charging since it only needs to replenish 1 or a couple of start cycles. Now it's going to be asked to charge this large battery bank that, at only 10% discharged, is going to put about 400% more load on the alternator. Smaller amperage wall chargers will also be stressed. Ideally, you want a decent 3 stage charger with a built in equilizer to get the most out of a marine battery or bank of batteries.