Connecting batteries in parallel

[Roc]

I was thinking about increasing my amp hours by connecting additional batteries to my already new 4D's.  What I want to do is keep the set up as it stands, and connect another battery to each of the existing 4D's, making each bank larger.  I like the way the system is set up now (to me it's very simple), as what I do is flip-flop between banks on any given day.  I don't want to get into a whole project of adding starting batteries and major rewiring, etc.  I'll have to take some measurements, but figured I could fit a Group 27 (or something that would fit in the space) on the starboard side, outboard of the water heater, and put another one in the storage lazarette under the center seat at the dinette table.  I could use the largest wires (2AWG) and I wouldn't think the runs would be longer than 2 or 3 feet.  I figure the largest wire wouldn't give me any appreciable voltage drop.

But I was reading Jim Moe's write up on electrical upgrades, and he says you must combine same type batteries (I understand that), must be of same manufacturer and relative age (I get that too), but what I don't understand is that he suggests they need to be the same size??  For example, I couldn't parallel a Group 24, 27, or 31 with a 4D??  Only (2) 4D's can be mated together??  My thought is I could beef up each current bank by putting another battery (similar type, make, but different size to fit location) in parallel with each 4D, thus increasing the amp hours....???

Thanks!!

[Mark Elkin]

Roc,
The issue with parallelling batteries is the different charge/discharge voltages and rates.  If you don't match all of these, then as you use them, one (or more) will discharge quicker than the other(s) and then the less discharged battery(s) expends energy charging the other(s).

You match the voltages by using batteries of the same type (flooded, gel, AGM, deep cycle) and age -- older batteries discharge quicker and recharging takes longer than new batteries of the same type.  And a less charged battery has a lower voltage.  Humans may not think 1/10 or even 1/40 of a volt means much, but the batteries notice and will cross charge until all are matched.  That's wasted energy.

The size (24, 27,31, 4D) also affects how quickly the battery will discharge or recharge.  Smaller batteries discharge quicker (but also charge quicker).  So if you use different size batteries, you'll end up with different voltages at each battery as you use and charge the batteries.

Sorry, but Jim Moe's advice is correct.  Only use the same type, age, and size battery in a given battery bank.  To get the extra capacity you want, you're better off finding somewhere to put another single 4D than to "split that capacity" between several smaller batteries.

[Footloose]

Roc

I am in the middle of rewiring my charging circuit and would like some feedback from you.  I have changed the wiring harness, and alternator/regulator as well as installed new batteries.  Things are much more reliable.  Just spent a week and started every time.  Like you I like the simplicity af the dual battery banks.  

My question is do you feel the number 2 wire is large enough?  I have been considering using number 1 or 0.  I know there is probally no harm in using larger wire excet to my wallet.

[Roc]

Dave,
Being that you have hull #608, I would look at your wires from a condition perspective first.  Based on the age, you may need to change your wiring after a complete inspection.  Whether to go with a larger wire, I'll let someone else comment, since I'm not familiar with your set up.

[Ron Hill]

Dave : #2 wire is large enough unless you changed you 23hp to a 230hp engine!!  I still have the original #4 factory wiring, but all of my wiring connections are crimped & SOLDERED!!.  I have 4500hrs on the engine (that's a lot of starts) and have NEVER had a hesitation in starting!!  I touch the starter and BOOM the engine starts.

Roc : I switched battery banks according to the even/odd days of the week - just like you do until I read an article in Sailing World in 1994/5.  They ran a test over a period of time of using all of the house together or splitting them as you do.  
The results were that it's better to use all of the house batteries together.  It lowered the amount of discharge each time and therefore you got additional cycles out of the batteries that were all tied together.  
Since at article, I arrive at the boat and turn the battery selector to "All".  Turn on the starting battery to start the engine and turn the starting battery off after 20-30 minutes.  When we come back to the dock and tie up the boat, just before I leave I turn the battery selector to "Off".  The only time I select "1" or "2" is when I want to look at that particular battery bank with the Link 10 battery monitor.  

[Stu Jackson]

roc

I know you're a frequent contributor and reader here, so I am not quite sure about your approach given all that we've discussed here, and Jim's Project article.  Ron's right about the advantages of larger combined battery banks, and I've posted Calder's statement about that a few times (here's one thread: http://www.c34.org/phpbb/viewtopic.php?t=973&highlight=calder).  A larger battery bank will provide longer battery life.  Swtiching bteween two house banks daily reduces the life of the bazatteires.  You're better off with a larger house bank and a smaller start battery.  BTW, it'll cost less, too.  

Why put in two new batteries when all you need to do is put in one new start battery?  Complicating things by adding two batteries to each bank seems to make no sense.  There is no major rewiring involved, and it would be about the same to do it this way than would have been the case of adding two batteries.

What I recommend you do is to simply combine your existing 2 4Ds and buy a small separate start battery.  Heck, if you can fit two new batteries in your boat, why not only have to add one?  Then you don't raise ANY of the issues that have been discussed above.  Simpler seems better to me.

[Mark Elkin]

Roc,
Stu's and Ron's suggestions are very well taken.  Since you've already identified several locations for adding a battery, make one of those as your starter battery.  A single Group 27 or 31 would be fine.

Then minimal rewiring would be required.  First combine your 4D's into a single big house bank.  Connect that to one side of the 1-2-Both selector switch.  Connect the new starter battery to the other side of the switch.

If you're disciplined enough to make Ron proud, then just switch to "both" batteries for 20 minutes or so after starting the engine to recharge the starter battery and switch to "house" after that.  Or, if you would rather, install either an Echo Charge or a battery combiner.   (In fact, I will sell you my old WM combiner for dirt cheap now that it's been replaced during my latest project.)

One caution, pay attention to the alternator output.  Does it lead directly back to the batteries?  Or does it lead to the "common" lug of the battery selector switch?  The best route is a direct wire to the house batteries, with just a heavy duty fuse just before connecting to the house batteries.  

But if the alternator does go back to the selector switch, then make absolutely sure that the switch has "make-before-break" contacts when switching from "1" to "both" to "2".  All the name brand switch manufacturers (Blue Seas, Perko, WM, etc) make their selector switches this way.  The danger in this wiring arrangement is that a "break-before-make" switch can disconnect a working alternator from the batteries.  Even milliseconds of disconnection from a battery when under load can blow out the diodes in the alternator.

Roc, I'm not trying to talk you out of this.  Stu and Ron have excellent advice.  And making the change I suggest above is actually quite simple, so it meets your requirements of minimal modifications and low cost.  And it give you the extra capacity and longer life in the house bank.

[Roc]

Mark,
Thanks for your suggestion (Stu and Ron too).  As I think about it, making the (2) 4D's the house bank with an added starting battery seems to make sense.  Also, I'm pretty sure my alternator goes back through the selector switch, because when I'm running the engine, the battery that's selected is shown to be charging according to the volt meter on the panel.  I've never attempted to move the selector switch when the engine is running, because even though my switch may be the make or break type, I never wanted to try it incase of switch failure.

About combining the 4D's.  Will the wires leading to or from the batteries need to be upgraded/thicker gauge??  Or can I re-arrange the existing wiring to combine the two, and add a third starter battery with the appropriate wiring to that?  

About my 4D's....this past weekend my original (factory installed) batteries were dead (after 5-1/2 seasons).  Not due to user neglect for not checking the electrolyte (I check them every couple/few weeks).  It was because one negative wire was loose, thus the connection wasn't secure.  A dockmate told me that Sam's Club sells 4D wet cell batteries dirt cheap.  I bought two at $90 each.  The specs stamped on the batteries are 1000 CCA, 1200 CA, with  320 Reserve Capacity.  They are Champion batteries (made by Exide).  I called Exide to find out what the Amp hours are and they told me 205.  The Customer Service guy on the phone told me these are 'starting' batteries and not Deep Cycle.  I asked if they were really Dual Purpose, and he said, no, really just a starting battery that won't have the same longevity as a Deep Cycle in repeated use.  He said Deep Cycle batteries have thicker plates, like in Marine batteries....and so on..

Now, for that price, was it wise to get these batteries??  I wonder if they are really no different than a marked 'Marine battery', and the Cust. Service guy just didn't want to say that to me.  I looked at WM and B/US and their Dual Purpose 4D's only have 250 Reserve capacity minutes at around 1300 CA (amp hours are not shown on the sticker) and are twice the price of the Sam's Club batteries!

This leads to the reason of my original posting.  First, I've always thought of boosting up my battery capacity for when no shore power is available for a day or two.  And second, with the possibility of the Sam's Club batteries maybe not being as 'robust' as a true marine battery leads me to believe maybe this is another reason to do something with my overall battery capacity.

Thanks everyone..

[Stu Jackson]

Roc

Mark Elkin wrote:  ''One caution, pay attention to the alternator output. Does it lead directly back to the batteries? Or does it lead to the "common" lug of the battery selector switch? The best route is a direct wire to the house batteries, with just a heavy duty fuse just before connecting to the house batteries. ''

Based on your description, and the original wiring diagram on our boat from the factory, it appears that Catalina still runs their alternator output to the C lug of the switch.  You need to check your manual on that, or trace the wiring physically to assure yourself that that is the case.

What I did was simply move the alternator output to my house bank lug on the switch.  YOU CAN'T DO THIS IF YOU HAVE NO COMBINER, SINCE YOU'LL HAVE NO WAY TO CHARGE YOUR START BANK. I still have the OEM alternator on our boat.  If you install(ed) a higher output alternator, then the right way to go is to run the alternator output to a PDP (positive distribution post - like in Jim's project article) and NOT to the switch UNLESS you've increased the wiring from the switch to the battery bank, since the new alternator will put out more juice and then the existing wiring is too small.  

With my max 30 amp output from the 55 amp alternator, the original No. 4 wire size still works.  Also note that I also had installed a WMP combiner, so my charger output goes to the PDP and then charges the start battery through the combiner.  

So I have TWO charging routes: alternator - to switch lug 2 to house bank and via combiner to no. 1 start battery  AND shorepower charger - to the PDP to the house bank and via the combiner to the start bank.

By switching the alternator output to the No. 2 switch lug (our house bank) on the switch, it's electricly JUST like connecting it to the PDP.  Just think of it as the wiring between the battery and the switch allowing  current to flow both ways: alternator to switch to bank when engine is running and alternator is charging; battery bank to switch and 12 V distribution panel when running stuff.  This CAN happen AT THE SAME TIME.

When I do get around to installing my upgraded alternator and the new external regulator, I will move the alternator output directly to the PDP with bigger wiring.  This is essentially what John Gardner did in his electrical Projects, also published in Mainsheet.

If you still have the OEM alternator there's no reason to question the wire sizing.  Think of it this way:  the wires take the juice from the alternator and send it to the batteries when motoring.  The existing wiring is reasonably sized (some will argue with this based on the 3 percent wire sizing table, but see Ron's post above; plus, mine have been working OK for 19 years!!!).  

Next, think of the battery OUTPUT from the batteries TO the switch and, hence, the 12 volt distribution panel:  either when you are running things on board when the engine is OFF or ON regardless of whether there's a charger connected, you are usually running much less than 30 amps FROM the battery banks TO the load(s) - just add up the draw from the fridge (5 amps) and lights, (1 1/2 amps each), electronics (small) and you'll see that the wires FROM the battery bank TO the panel through the switch is extremely low.

Once you think of the wires AND the way the power is BOTH coming and going, you'll be able to check their lengths against the wire sizing table and see you don't have to change the wires regardless of how big a battery bank you install.  

In fact, you could put in a 1,500 Amp Hour battery bank, but unless you put in 4,000 neon lights and a freezer, you're NOT taking OUT any more that you already are.  Reread John Gardner's material, he is doing pretty much what you and many others are planning.

As far as your new batteries are concerned, I would be concerned that the manufacturer's rep told you they were NOT deep cycle batteries, so if that's true, you should expect their demise pretty early if you employ them in deep cuycle use, since as you know, starting battery technology is different that deep cycle.  In this case, the CCAs and all that are meaningless to us here.  It's simply how the insides of the batteries are built, which only you can find out and decide.