26X Battery bank questions

[Gypsy]

Hey everybody! Points to consider…


If a so-called deep cycle battery has a “cranking amps” or “cold cranking amps” or “marine cranking amps” rating when you buy it, be suspicious that it is not a true deep cycle battery.



I’m just sayun…

- B.

I 100% agree with that statement ! A true deep cycle battery , will not last , if its expected to provide 100s of amps in a burst. Therefore somebody is selling a start battery as a deep cycle battery.
This is what I suspect with the socalled start/deep cycle batt sold as "Marine Battery "


" Cranking my 70hp on one battery isn't a problem, but I wondering about cranking and running in the "both" position with my blue seas system switch (1-2-both-off). I plan to power the cabin overnight on battery 1 and switch to "both" in the morning to crank and run. Will the difference in charge level shorten either battery life? "

I do not reccomend the " BOTH " position except as a temporary measure OR unless the batteries are identical . By combining different type batteries , one is overcharging and one is undercharging , resulting in shorter life and a good chance you will get stranded. If you switch to the house battery at night , next morning switch to BOTH you are coupling a mostly dead battery to a fresh battery which results in two 1/2 dead batteries . It is better to switch JUST to the fresh battery and crank , allow time for this battery to charge , then switch to the house battery for the rest of the run time and recharge it for the next night.

[Trouts Dream]

I concur that running only one battery is best. That said the addition of a combiner really helps to keep the "backup' battery ready to go by throwing any extra charge that the primary can't accept to the backup. This system keeps the batteries seperate but allows best flexibility when charging.

http://www.yandina.com/combInfo.htm

[csm]

Thanks for the link Trouts Dream, I'll read through it, but I think that's probably what I need. My battery switch warns not to switch to OFF when the motor is running, and that makes me very leary of switching from one battery to another while running. Seems to me I read somewhere that can ruin your alternator. thanks ALL

[Russ]

Thanks for the link Trouts Dream, I'll read through it, but I think that's probably what I need. My battery switch warns not to switch to OFF when the motor is running, and that makes me very leary of switching from one battery to another while running. Seems to me I read somewhere that can ruin your alternator. thanks ALL

If there is no load on the alternator/regulator it can blow the regulator out. Most A/B/Both switches work just fine as long as you avoid the "OFF" position.

I'm sill a fan of the combiner (above link) because it takes no brain power to use it.


--Russ

[csm]

"If there is no load on the alternator/regulator it can blow the regulator out."
that's why I'm leary about switching from one battery to the other while running; I'd think that during the switch from 2 to 1 the alternator will be in "no load".........the Yandina link states the following:
========================================================================================================================================================================
Q Will banks of different sizes get fully charged?
A Yes, since the combiner just places batteries in parallel, they are all at the same voltage. The charge level of each battery is a function of voltage, so they will all receive the same level of charge. The actual charge capacity is governed by their size, age, chemistry and condition.

Q Won't the smaller battery get overcharged if put in parallel with a large one?
A The whole process of charging batteries in parallel is naturally self regulating, naturally governed by terminal voltage and current flowing through the internal equivalent resistances. For simplification, each battery can be considered as a perfect battery that holds the charge combined with a series resistor representing the internal resistance, and a parallel resistance representing the self-discharge leakage current.
Lets say you have a charging source dumping out say 100 amps. If you have 4 batteries in parallel sharing this source the distribution of the charge current is governed by those internal voltages and internal resistances. From Ohm's law, the charging current that flows into each battery is the voltage divided by the resistance. In this case the voltage is the charging voltage arriving at the terminals minus the actual internal voltage divided by the series resistance of the battery. A discharged battery is going to put a larger voltage differential over the internal resistance so more current will flow to it. A charged battery is going to put less voltage drop across the internal resistance so it will take less or none of the available charging current. A large plate battery which has a correspondingly lower internal resistance will demand more current because of this lower resistance. A small motorbike battery in parallel will have a high internal resistance and demand very little current.

All these demands for current result in a common voltage on the parallel circuit which is what the alternator or charger sees. None of the batteries will ever be "overcharged" as a result because the charging voltage is controlled. Even the smallest battery will only be seeing the same voltage so it is like the other batteries are not there. If you suddenly removed all the big ones and left just the tiny bike battery on the 100 amp alternator, the voltage would immediately rise because the amps trying to flow into the tiny battery have to pass through its internal resistance which is high. But instead of the voltage or current going to an excessively high value, the regulator in the alternator cuts the current back to a level that limits charging to a safe level.
========================================================================================================================================================================
I guess I need to verify that my battery switch has batt 1 and batt 2 in parallel when switched to both. I still haven't convinced myself, so I'm open to comments. I'd hate to have to buy new batteries every season or worse yet, blow my alternator.

[Gypsy]

"If there is no load on the alternator/regulator it can blow the regulator out."
that's why I'm leary about switching from one battery to the other while running; I'd think that during the switch from 2 to 1 the alternator will be in "no load".........the Yandina link states the following:
========================================================================================================================================================================
Q Will banks of different sizes get fully charged?
A Yes, since the combiner just places batteries in parallel, they are all at the same voltage. The charge level of each battery is a function of voltage, so they will all receive the same level of charge. The actual charge capacity is governed by their size, age, chemistry and condition.

Q Won't the smaller battery get overcharged if put in parallel with a large one?
A The whole process of charging batteries in parallel is naturally self regulating, naturally governed by terminal voltage and current flowing through the internal equivalent resistances. For simplification, each battery can be considered as a perfect battery that holds the charge combined with a series resistor representing the internal resistance, and a parallel resistance representing the self-discharge leakage current.
Lets say you have a charging source dumping out say 100 amps. If you have 4 batteries in parallel sharing this source the distribution of the charge current is governed by those internal voltages and internal resistances. From Ohm's law, the charging current that flows into each battery is the voltage divided by the resistance. In this case the voltage is the charging voltage arriving at the terminals minus the actual internal voltage divided by the series resistance of the battery. A discharged battery is going to put a larger voltage differential over the internal resistance so more current will flow to it. A charged battery is going to put less voltage drop across the internal resistance so it will take less or none of the available charging current. A large plate battery which has a correspondingly lower internal resistance will demand more current because of this lower resistance. A small motorbike battery in parallel will have a high internal resistance and demand very little current.

All these demands for current result in a common voltage on the parallel circuit which is what the alternator or charger sees. None of the batteries will ever be "overcharged" as a result because the charging voltage is controlled. Even the smallest battery will only be seeing the same voltage so it is like the other batteries are not there. If you suddenly removed all the big ones and left just the tiny bike battery on the 100 amp alternator, the voltage would immediately rise because the amps trying to flow into the tiny battery have to pass through its internal resistance which is high. But instead of the voltage or current going to an excessively high value, the regulator in the alternator cuts the current back to a level that limits charging to a safe level.
========================================================================================================================================================================
I guess I need to verify that my battery switch has batt 1 and batt 2 in parallel when switched to both. I still haven't convinced myself, so I'm open to comments. I'd hate to have to buy new batteries every season or worse yet, blow my alternator.

I'm not sure if you are talking about using a solid state combiner or not . If thats the case , different type batteries will charge and all will recieve the right amount of charge ., thanks to the combiner, HOWEVER if you are talking about using a mechanical selector switch , then you will ruin the smallest battery, guaranteed ! The alternator circuits will be the determining factor and as long as the voltage is low in the large battery , the smaller battery will continue to recieve charge untill it either boils or opens.
As far as changing the selector switch with the motor running , modern switches are "make before break" this means for a short time both poles are connected before one poles connection is broken .
So as long as you don't go to OFF sonmething will always be connected to the alternator. Your alternator is safe .

[csm]

"Make before break"; that's assurance I've been looking for. Thanks Gypsy. Since the batteries identical new "marine" types I guess the trick, without a combiner, will be work the battery switch to try and keep them equally charged.
Thanks again to ALL and sorry for hijacking this thread.

[Retcoastie]

Gypsy wrote:
The alternator circuits will be the determining factor and as long as the voltage is low in the large battery , the smaller battery will continue to recieve charge untill it either boils or opens.

That is not the way they taught it at any of the schools I have attended.

Voltage is constant in all the legs of a parallel circuit. How can you achieve a “low voltage in the large battery” and a high enough voltage in the small battery to cook it if they are the same voltage?

Seems I remember that, on all my vehicles and on both meters on my boat, when the engine starts the voltage is low and increases as the battery charges until it comes up to whatever that regulator is set at. That regulated voltage, if properly set, will not cook your battery, large or small. Placing additional loads on the alternator does not make its output voltage increase, it makes the output current increase. Think what happens to your car at night with the A/C running. The greater load causes the system voltage to decrease.

Now say you happened to discharge your large house battery overnight and took it down to 11VDC. You start your outboard with a small (motorcycle) battery that was fully charged at 12.6VDC. When the alternator kicks in, it will provide enough current to replace what was drawn out of the small battery during starting and then stabilize at a preset float voltage of around 13.6VDC (probably not a lot). Now, you reach down and throw your dual battery switch to BOTH. You have added the large house battery at 11VDC to the circuit. The alternator loads up and starts putting out additional current (think headlights and A/C) to charge the house battery. The system voltage DROPS. Even though the alternator may be putting out maximum amps, the voltage on the small battery DROPS. The voltage on the small battery will remain reduced until the large house battery voltage comes up. Even then, the regulator will limit the voltage in the system to the preset value and if that preset value was not enough to cook the small battery when it was in the circuit by itself, it will not cook the small battery when the large battery is in the circuit.

Ken

[Gypsy]

By the time you get the larger battery up to 13.5 volts , the smaller is toast .
Is not parrallel the avg of the two ?
If one is 11 volts and the other is 13.5 that equals 12.25 volts enough to keep the alternator charging . Perhaps for a long time to come even if the smaller battery long since reached 13.5

I'm an Old Salt , I 've accidently proven this theory on a few occasions at great expense to myself.

I have mentioned the wheel chair battery , I use on my dinghy motor . Its a deep cycle , little bigger than a motor cycle size battery. I have to be very careful when I parrallel it to charge , a little to long and its a goner .

[Retcoastie]

No, it doesn't work that way. Voltage is not the average of the numbers.

Voltage is constant in all legs of a parallel circuit, current is not. Hooking the large 11VDC battery in parallel with the small 13.5 VDC (as selecting BOTH on your battery switch without the engine running) will produce a lower voltage than the average number. It has to do with capacities and internal resistance. Without another source, the little battery would try to charge the big battery and its voltage would decrease, probably quite a bit as the large battery would suck up all the available electrons from the little battery with little change in its charge.
Lets say, ten billion (10B) electrons jammed onto the plates of the small battery makes a charge increase of 1 VDC. When the large battery sucked those ten billion electrons out of the little battery, those 10B electrons spread out over the larger plates of the big battery might only change its charge 0.2 VDC. The little battery will discharge into the the larger. But, 10B electrons is not enough for the big battery. It will continue sucking until the voltages are equal. In our example, the big is now 11.2 VDC and the little 12.5 VDC. The next 10B movement will produce 11.4 VDC and 11.5 VDC. So the voltage of the of the two will be about 11.45 VDC.

Now, when the charger comes on the line, it will attempt to bring the circuit up to 13.6 VDC. Lets say the charger is a small charger, like on an outboard and not a monster like on a big ship. This little charger can put out 15B electrons per minute. 3B are used to run the engine, that leaves 12B for the batteries. 10B will go to the large battery and 2B to the small. This will raise each battery's charge by .2VDC equally because voltage must remain constant in a parallel circuit. The next minute, another 15B from the charger. 3B goes to the engine, 10B to the large battery and 2B to the small, raising the circuit constant voltage to 11.8VDC.
In our perfect example, this would continue and in nine more minutes both batteries would be at 13.6VDC and stop accepting more electrons from the charger. At no time did the small battery voltage ever exceed the large battery voltage. The difference is the amount of current each took from the charger.

In actual practice there are a lot more factors to consider, but the idea is the same. The small battery voltage cannot exceed the large battery voltage because voltage is constant in a parallel circuit.

Ken

[Gypsy]

Some people learn by listening
Some people learn by reading
Some people just got to pee on the electric fence and see for themselves .

Old chinese proverb

I had to pee on the fence , and see for myself .

I have been playing with boats , batteries , and electric motors , for as long as I can remember .
And we won't even discuss what I did for a living for 30 years.

BUT
I can tell you for a fact , if you combine/parrallel different batteries , leave them on thier own to charge , without some solid state device sensing individual voltages , One is going to fry .

Theory is what they teach , practice is the reality.

[Laika 26X]

I had to pee on the fence , and see for myself .

Back in the day, a man in my hometown of Yonkers NY was found dead along the tracks of the Metro North Hudson Line.
With ALL due respect to MythBusters, cause of death as listed in the Journal News was electrocution due to urination on the third rail. 700VDC oh yeah!
BAC I think was given at .2 something.

BTW, WHAT a great discussion for a simple request!

Can anyone out tell me if the electrons or the holes themselves are moving? Skin effect issues??

Anyway, to my fellow Americans…Happy Thanksgiving..

I’m thankful for my LAIKA, this Forum, and all you sailors here!!

Godbless!

"Sub" Ed Tordahl
S/V LAIKA
USCG Auxiliary
Qualified Crew
Qualified Aids (Nav) Verifier
Qualified Public Education Instructor
NYS Qualified Safe Boating Instructor

[bartmac]

So the big thing about all of this is....if you're charging 2 different type of batteries which have different charging charactistics ie float voltages...you can cook a gel battery to death if the voltage rises above 14.2 soooo if its on a circuit which is going to do this....it'll cost you.By the way Retcoastie explanation is really good

[Gypsy]

So the big thing about all of this is....if you're charging 2 different type of batteries which have different charging charactistics ie float voltages...you can cook a gel battery to death if the voltage rises above 14.2 soooo if its on a circuit which is going to do this....it'll cost you.By the way Retcoastie explanation is really good

Not JUST gel batteries . Two regular wet cells of different sizes shouldn't be combined , a deep cycle and a start . A large deep and a small deep shouldn't be combined , old batts and new batts .
Old batteries develop different charge characteristics , even if the are the same battery.

The exception is if the parralleling is a temporary thing , to put SOME charge in both batteries , to start a motor , things like that .

On my I plan to permanenetly parrallel two deep cycle batteries . They will be bought at the same time , same brand , same size . This is as close as you can get to identical batteries.

[Retcoastie]

A 20 amp charger doesn't force 20 amps into the batteries so that the unused current from one battery has to go to the other, it puts out a voltage and each battery takes what it needs depending on state of charge, overall size, overall condition etc.

The only thing that boils a battery dry is overcharging.  Batteries start to overcharge and "boil" when the charging voltage gets to 14.2 VDC and above.  So if the voltage is above 14.2 VDC you are starting this overcharge process.  But that voltage is coming from a charger and a modern charger will stop charging at 14.2, dropping back to a maintenance voltage of about 13.6VDC.

So if one of the batteries were to overcharge its voltage would have to be above 14.2.  If the voltage on one is above 14.2 then the voltage on the other is above 14.2 since they are joined together.  If the voltage on both is above 14.2 then the charger is faulty.
Most garage and consumer (automotive) type battery chargers are bulk charge only, and have little (if any) voltage regulation. They are fine for a quick boost to low batteries, but not to leave on for long periods.

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