26X Battery bank questions

[bartmac]

Yes I've done the same...purchased 2 identical batteries and that's my start 1 & 2 and then a completely seperate deep cycle AGM bank for refrigeration mainly and all other 12v demand.Switching fitted to allow all or any to start the motor should it be necessary.A dc-dc charger from my start bank to charge the aux bank set to optimum voltage to complete the system.......ha cold beer at any time....not the most important thing but nice.Ho and yes 180 watt of solar panels to charge things when sailing as we don't tend to motor much.And yes the reference to gel batteries was just what I'm playing with now in our camper.....same scenerio.....motor alternator charging start battery,240 v -12v programmable charger for aux (when at home),and 12-12v charger from start to aux.Again the refrigeration is the main draw.

[Retcoastie]

Bartmac,

I also went AGM some years ago. I have a small one and a large one. I set the Battery Selector to BOTH during the day and to the large one at night. I try to save the small one for morning starts is case I go crazy with the power consumption at night. I have also just purchased an Edgestar in the quest for the perfect cold beer. I went with solar but cannot find a good place to mount the panels. Where did you find space to fit 180 W of panels? Right now I have two 15 W panels mounted on rods that go between the cabin top lifeline stanchions. They can be tilted out to match the sun angle or raised up so that they fit below the lifelines when docking, etc. I have them plugged into the mast light plug and they feed the system back through the Mast Light switch and fuse.

Ken

[bartmac]

I modified a "rocket launcher"? or possibly a radar dome mount of a Bertram 27 ...1" SS pipe frame 2 post angled back.Cut the middle of of it to get the reduced width and mounted 6 x 20 watt panels on the curved topside which over the rear of the cockpit also doubles as a shade maker.I also had made in China a flexible solarpanel 60 w to the size of the sliding hatch....glued to it when slid forward it comes out of our dodger and voila makes 12v.I've been meaning to post some photos.So the whole lot is permanently mounted and given the curve of the frame at least some of the panels are exposed to the sun.

[Gypsy]

Perhaps Gypsy's unfortunate experiences thru all those years are from older chargers or generators. Modern alternators and two or three level chargers are capable of safely charging multiple batteries. His future plans should do fine with what is available today.

Ken

When I started 'messing about in boats' the only charger available was a mechanical type with no auto shutoff , guaranteed to destroy a battery that you forgot about .
The charger that I installed in my Bay Cabin Cruiser was a state-of-the art , built-in MinnKota charger , that I had connected directly to my house battery. Plugging up te charger was our shore power connection . Interestaling enough , if I forgot and left the Perko switch in the "BOTH" position , while the charger was plugged up , it was the house battery and not the start battery that got hot .

There are chargers out there like what the bass boats have ,built-in , that charge several batteries at once , but they have seperate leads going to each battery and sense/charge each battery seperately.

If you don't wish to learn from my experience , thats fine , go ahead and pee on the fence .

You will get away wth it a few times , but then you will notice that ' only a year old battery ' just doesn't have the stamina it once did.

[Hamin' X]

In a parallel circuit, you cannot overcharge a smaller battery, unless you are applying sufficient voltage to overcharge the larger battery: Period. If using an automatic charger and one, or the other of the batteries is in poor condition, it could be signaling the charger to remain in bulk charge mode for an extended period of time. This will boil down the smaller battery first, but it is because of the higher voltage being supplied and the smaller capacity of the small battery.

~Rich

[Gypsy]

I have argued untill I am as blue in the face as a hull !

It can and will happen . My training and experience says it will . But some people will take theory over reality every time .
In the labs in college , I noticed real fast , the results never exactly matched the book , and so it is in real life.

And thats all I got to say on the subject . Got other projects to work on , outfitting my
for our cruise.

[Hamin' X]

I don't think that we are arguing with your observations Gypsy; just your conclusion that the size difference of the batteries is the problem.

Have fun on your projects.

~Rich

[robbarnes1965]

Sounds like my first year...

The replies to your question are enough to solve the problem. If you are like me however and want to really understand what went wrong, buy this little book: http://www.amazon.com/Understanding-Boa ... 157409162X Since I read the book and changed my batteries I have never had a problem again.

My boat actually came with a 1,2, ALL, OFF - 2 battery system with deep and starter batteries but I charged them in the ALL position. ALL should NEVER be used except in emergency and should always be labeled EMERGENCY in my opinion.

I also bought 2 of these to keep the batteries in shape when left for extended periods. http://www.canadiantire.ca/AST/browse/4 ... ?locale=en Unlike your car that you use most days, the boat and it's batteries can get lonely -e specially when the lake is frozen...

Rob

[Catigale]

Two group 24s with 1-2 Both Off switch on my

50 HP Merc Bigfoot EFI. If it doesnt start in 2 cranks, Ive forgotten fuel or kill switch.

For backup, I carry a jump pack that lives in the car in the winter...nice dual use of boat bucks.

I can also hand start the Merc - Ill describe that as very easy.

**added benefit of jump pack - last time I was out on the Hudson, a guy had launched his fishing boat but could not get his engine to crank - instead of dealing with jumpers - I gave him my starter pack and all was well. I told him to keep it on the water and return to me end of day. He had a boat load of kids who got to have a fun day on the water, instead of watching dad fume...good kharma..he dropped it off that evening and I made a new friend..

[esc]

I have a VERY mismatched set of deep cycle batteries connected to a off-1-2-all switch on my .

1 has 2 Golf Cart batteries in series providing 220 AH @12V.
2 has an old, small, mostly used up, 12V 24AH trolling motor battery that I used to use in my dingy (I had to sell the dingy (Walker Bay 10 on a 20' catamaran trailer) to make room in my back yard for the ).

Because the 2 GC batteries are about 6' apart, I can not easily hook my 12V 2-10-50A charger directly to them. I use the 2A setting. I can easily connect it to the small 12V battery and place the switch in the ALL position. Using this setup it takes about 2 days for the small battery to start to get warm. The large batteries never get warm, but they do come up to 13+V.

I suspect that the small battery gets warm (indicating a mild overcharge) as a result of the resistance in the battery wires and the switch, resulting in a higher voltage at the small battery (that the charger is directly clamped to) than the larger ones. But that doesn't seem to be a problem until after the larger batteries have had their fill.

I can easily start my motor on the small battery after it has sat idle for 2 weeks.

I have been using this setup for a couple of months now with no ill effects.
I don't claim that this anecdotal evidence proves anything except that I have a very mismatched system.
Why did I choose to install such a mismatched system you ask? When I got my both batteries were long dead, so I used what I had laying around.

[c130king]

...
Two group 24s with 1-2 Both Off switch on my

50 HP Merc Bigfoot EFI. If it doesnt start in 2 cranks, Ive forgotten fuel or kill switch.

For backup, I carry a jump pack that lives in the car in the winter...nice dual use of boat bucks.

I can also hand start the Merc - Ill describe that as very easy.
...

Ahhhh, great minds think alike (there is a joke here...Stephen's mind/brain is large, smart, and clean while mine is small, not-so-smart, and not-so-clean ).

I have the same thing going on except 40HP Merc. However, I have only ever tried to start my motor by hand once...didn't need to just decided to try it...but I pulled that rope about 10 times with no start. One of these days I will try again.

Jim

[seahouse]

Hey you guys! Is thread going to go on forever? Let’s keep it going. My posting doesn’t go on forever. Really.*

I’m not so sure that we really have a difference of opinion in this thread at the profound level.

I think one camp is stating what CAN be done, and the other is simply stating what SHOULD be done. It’s usually pretty easy to figure out what CAN be done. What SHOULD be done can be more elusive and complicated to uncover.

What CAN be done is subject to the real-world conditions – exactly as you’ve illustrated, esc, using what is readily available. When it comes time to replace your batteries it’s useful to know what SHOULD be done, if it happens to be practicable under those new circumstances.

Now the technical bits. Here’s what we do know about flooded lead acid batteries:
-overcharging a battery will damage it (= shorten its service life)
-undercharging a battery (chronically) will damage it (= shorten its service life)
-batteries are charged in 3 stages, known as bulk, absorption, and float.
-the charger (assume a “smart” charger, one which is not designed for charging more than a single battery, looks like that’s what’s being discussed here) adjusts the voltage and amperage to appropriate levels for these three stages based on what it measures from the battery (resistance and voltage, sometimes temperature)
-based on these readings a determination is made of the stage and state of charge and the voltage output of the charger is varied over a range from around 10.5 to over 15 volts, depending on the stage required and multiple other factors, which, let’s call, the “fingerprint” of the battery being charged.

The fingerprint includes many variable characteristics such as the level of discharge; the physical and chemical makeup of the lead plates (spongy lead, high/low antimony, high/low calcium, level of sulphation, positive plate degradation, plate size, thickness, surface area; presence of dendrites etc.); temperature; age; electrolyte volume and purity (no tap water, no acid, no snake oil!) etc. There are many more, but these readily come to mind.

All agreed so far? Should be, I think these are pretty well accepted maxims.

If two batteries are connected to the charger in parallel, the charger only sees one voltage. If one of them is at a higher level of discharge than the other, a net flow of electrons will happen before the charger is even connected.

Let’s look at the extreme and say one of the two batteries is at 12.0 V, and the other is at 12.7V. Connect them together and there will be a net flow of current from the 12.7V battery to the 12.0V battery, the rate at which will depend on the internal resistances of the batteries at that particular point in time. (The internal resistance of a battery is not a constant).

One is being drained, the other charged. Wait long enough and they will eventually become equal, as measured open circuit of course.

Connect the charger and it will measure the net voltage and the net internal resistance of the two batteries connected together. If the two batteries have identical “fingerprints” what the charger deduces will be pretty close to the actual conditions of the two batteries, and charging will be optimized.

If the two batteries are not identically matched, they will be either undercharged or overcharged, sometimes grossly so if they require different stages (bulk, absorption, float, or a level of these) of charging.

This also can happen to a 2V “cell” within a 12V battery itself. A single 2V cell within a battery can go “dead” because it was in some way out of match with the other five and ultimately failed. If you more closely check a “bad” 12V battery you will often discover that it is really only a single cell that is the cause of the failure.

I have a solar/wind battery bank which consists of 4 deep cycle batteries which are of consecutive serial numbers. This is canon in the industry because it is recognized that there can be variations even within a battery product cycle that are significant enough that they can affect longevity when connected in banks. This arrangement is particularly sensitive because banks are connected in series/parallel and are all normally charged (solar/wind/charger) and discharged (inverter, usually) together as a single unit.

I know first-hand of a situation where the 4 deep-cycle batteries used in a solar/wind setup were not from a consecutive production run and his system (all four were replaced at once) required replacement in less than one year. (Under full warrantee, BTW, the vendor realized his $500+ mistake and ate it). This failure is not an isolated occurrence either, others on this board have reported it as well.

If you want to charge two different batteries (and I define “different” as any two or more batteries which are not consecutively manufactured, although you might be slightly less fussy) and want to maximize the probability of long-term reliability, you will want to use a charger designed specifically for such use.

Or, you can use a mechanical battery isolating switch, or use intervening circuitry that will allow the charger to “read” the condition of each battery individually and apply the correct charging voltage which will bring it up to its fully-charged condition.

Or, you can choose not to maximize the probability of long-term reliability and just charge them together!

Similarly, you can choose to smoke cigarettes, which will minimize YOUR probability of long-term reliability.

But just because you CAN, doesn’t mean you SHOULD!

Best regards! - B.

* OK, OK . Sorry if I hogged more than my share of server bandwidth on this one.