Re: battery isolator question.
Alright since i've already thrown in my 2c, and because I love to argue with Bruce
I'll add some more just for your consideration, because after all, this is your choice here.
Keep this in mind to, there are 3 ways to do everything,
your way,
my way, and
the correct way.
Jason said:
Yes it's true, unless you use an isolator. That's the isolators purpose, to isolate 1 battery from the other so the alternator can charge both batterys without over or undercharging each battery. It all keeps a dead battery from draining down a good battery.
That statement is not 100% accurate and here is why. In a perfect world, the alternator doesn't care.
The alternator doesn't care if you hook up 100 batterys to it in series or parrallel as long as the net result is still 12VDC. Silvertip is correct, the alternator will charge them all, albeit a bit slower. But unfortunately
nothing in life is a perfect world.
Frog water isn't so bad to boat in. Sure you get corrosion and all that, but it doesn't happen overnight. The salty drink is a different story though. Epecially if your moored or docked and jacked in to the shore power with 100+ other boats.
Here is your new best friend, and worst enemy, so you best get to know him.... Corrosion.
Like I said (and silvertip) you can have 100 batterys all hooked up to 1 alternator, no problem.
But when you add corrosion you add voltage drops across a line, it is a problem inherent with DC electricity. (which is BTW, why we have AC electricity in our homes) If Edison had his way we would all be on DC. But if we all had DC there would be electrical substations every couple of miles compesating for the voltage drops. That and AC is cheaper to make on a grand scale and high voltage AC is somewhat safer than high voltage DC. Now bow your head and say thank you Tesla.
Anyways... if you have 2 batteries in parallel you will have at a minimum of 5 to 6 cables of heavy gauge. If you use a battery switch you will have even more cables. But if over time because of corrosion (and it will happen) you have a .5VDC drop in 1 cable, and a .3VDC drop in another, and a 1.1VDC drop in another etc etc... the batteries will not charge correctly. The batteries with little to no voltage drops in its cable will charge properly, but the other batteries with multiple drops in its line will not charge. The voltage drop eats up all the current that is supposed to go to the battery. No big deal if you have 1 battery that's good to go while your boating, but when you shut her off and let her sit for a week. The high battery will slowly drain into the low until they equalize. But here is the kicker, the alternator sees a group of batteries as 1 load. Wether it's 1 battery, 2 batts, 200 batts, it's still 1 load to the alternator. But if you have exxecive voltage drops in the entire battery system, the alternator will overcharge the high batteries if the overal voltage appears low in the system because of the drops. It's that what the alternator thinks 1 particular battery voltage is that controlls the charge rate, it's the overall voltage of the system.
So if you had 2 batteries.. 1 that was 12.7 volts and fully charged, and the other that was sitting not so pretty like the ugly gal in the corner at prom at 9.5 volts because the line drops ate the current. After a week you have a 1 battery system that are sitting at 11.1 volts. 11.1 isn't awefull, if the batteries have some current still in them. It will still crank a motor..... but slowly. Slow cranking RPMS is the #1 reason for hard starting, period.
On top of that, if your motor is EFI, or something else that relies on electronics as part of it's operation. (for example, A yamaha YMIS microputer, J/Rude optical eyes on their older carbed but electronic ignition motors) the engine will not start. Most electronics have a minimum voltage requirement. Drop below the min, and it doesn't function any more. So you can crank until the batterys are dead and the starter is smoking, but the electronic parts of what the motor needs to run will simply not even turn on.
So in the end... To isolate or not. Sure it costs money, but here is the benefit.
1. 1 battery will not drain into the other.
2. If you have voltage drops, (and you will given enough time), the high battery will not be overcharged, and the low battery will still charge somewhat, but still somewhat better than if it was just parallel'd.
3. It's sortof better if your mixing starting with deep cycle batteries, and i'll touch on that more in the next paragraph.
Now... onto
starting vs
deep cycle vs
combination batteries.
bruceb58 said:
An alternator can charge any type of battery you put on there. The only difference between a start battery and a deep discharge battery is the thickness of the plates.
Didn't I say I loved to argue with you????
Well I won't argue, but I don't agree with that statement.
bruceb58 said:
An alternator can charge any type of battery you put on there.
True, very true, as long as the system as a whole is 12 volts. But it comes down to charging rates, and how much the battery likes being charged at a certain rate.
You have...
1. Load/Bulk charging, which is what an alternator does.
2. Absoprtion/high trickle charging, which is found in a home battery charger.
3. Float/trickle/maintence charging, which also is found in battery chargers, but the chargers that are specifically designed for deep cycle batteries do a better job of it.
starting battery
Charging type
1. Bulk I dig it, I give up juice fast and i like juice fast, makes me strong like arnold
2. Absorption It's not a big deal, but can you get on with it man, I dont have all day
3. Float Okay serious, this is like trying to get fat on lettuce, throw me a bone here
deep cycle
Charging type
1. Bulk Whoah, this is like current overload man, I don't like it, I'm gonna make some heat
2. Absorption Okay, I like to slow dance, but i like to realllllllly slow dance, wink wink
3. Float Now your singing my song baby, don't stop
In a perfect world you would have 2 alternator options, 1 for starting, 1 for charging. Look at battery chargers. In el cheapo charger you get a 30-50 amp absorption charge option only. In a good high quality battery charger you get options like
1. Multivoltage
2. Starting/deep cycle/maintence selector switches. (Bulk, absorption, or float charging rates)
3. battery start
4. quality components, no AC to the battery while charging.
5. Automatic modes
6. Gel and AGM modes (effects charging rates).
If your building things on the cheap, there is no 1 charger to charge all types of batteries.
Alternators are a once size fits 90% of our battery charging needs solution. And cheap...(okay... not a Mando)
Deep cycles will charge off an alternator, is it the best for the battery? No. Is it the best for the alternator... it doesn't care, it has 1 charging rate. The alternator is either on or off depending on the sensed voltage. If it's on, most alternators will give you 50-75% of their total rated amperage output until the voltage on the sense wire raises.
Ever go to a fishing tourny. At night all the boats are parked at a hotel. All the competetors have extension cords thrown out their windows plugging in their batterys. These guys are serious boaters with serious engines. The new Optimax's, the New 4 strokes, all have conventional high output alternators on them, but they still charge their trolling deep cycle batteries with a high quality deep cycle charger. Those guys know how to squeeze every Ah out of their batt's.
Now on to the last of my tirade... Using a deep cycle as a starting battery.
Can you do it... sure.
Is it ideal.... Nope.
Deep cycles are rated in amp hours, not cranking amps.
Starting batts are rated in cranking amps, with amp hours being a secondary rating.
So when starting an engine, you need a minimum amount of amps, and ideally your way over the minimum with power on tap, how do you even rate a deeps cycles cranking amps?
Some companies that make deep cycles will throw a number on there to sell more batteries. Reputable companies will not.
If you plan on using a deep cycle for a starting, buy the biggest battery you can fit, not afford but physically fit, or else you'll have issues. If you use any deep cycle battery you are likely to have slow cranking rpms, even with a big one.
bruceb58 said:
The only difference between a start battery and a deep discharge battery is the thickness of the plates.
That is not true. The difference between a marine battery and an automotive one is in the thickness and overall durability of the battery to abuse. The difference between the 2 is surface area.
If you took 2 batteries that had the same external dimensions and cut them open what you would find is that a deep cycle has little surface area on it's plates, but a starting battery has more surface area by corrugating its plates or having the lead have a spongy like surface.
Every battery has 2 different typs of plates, an anode and a cathode. A cathode gives up free electrons that want to travel to an anode. A starting battery has a bigger cathode plate in surface area for the batteries specific external size than its deep cycle counterpart does. More surface area means more electrons. More free electrons means more on demand (starting) power.
A starting battery has tons of electrons to give you when you need on demand current for short periods of time. A deep cycle still has those electrons, but because of reduced surface area of the cathode, it can not give up those electrons as quickly as a starting battery.
Anyways, i'm done typing to this thread tonight, I may add to it in the future if i'm up to it.
