Different ways to wire multiple batteries

[ksanders]

I agree Kevin. I emphatically agree that I don't understand batteries and charging!


My newish battery bank was nominally 780Ah when new. The manufacturer recommends a charge current of 20% of the C20 capacity during bulk charging. That would be 156amps. My charger will only put out 125amps. So I'm not hitting the max charge current that my battery bank could absorb and my bank isn't that large, and my batteries don't accept a charge as fast as other batteries.



Lifeline says they can be charged at 5C, or 5 times their 20 hour capacity during bulk charging. My charger can't hit that for just one Lifeline 8D battery.

So far I don’t see an issue with your system. You may not be able to maximize your charge current but you do have close to the largest charger available... Good to go there.

Now lets take your loads and cruising style. Do you anchor out very much? when you do what kind of discharge do you have say overnight?

Do you tend to pull anchor and cruise daily, or do you like to sit in the same spot for days at end?

This will all dictate your battery bank size.

 

[dhays]

What I can never understand is why a 110 volt battery charger is necessary for starting batteries. The starting batteries get charged by the alternator as soon as the engine or generator starts.

I have a single engine. My alternator charges the house bank. My genset doesn’t have an alternator. Every boat is different, but for me it doesn’t make sense to have an alternator that is spinning but not really doing anything.

My alternator does a pretty good job of throwing a lot of amps into my house bank. Works well after a night on the hook using the inverter to run my wife’s CPAP, make coffee, and power the very power hungry music system in the boat. Between the alternator and my solar panel, all it takes is a few hours of running during the long summer days and my house bank is usually at 100% by the time the sun is too low for the solar panel.

So I agree that a full time dedicated 110v charger for my start batteries would be kind of overkill. All I have to do is keep the house bank charged and the thruster, start, and genset batteries get taken care of.

 

[dhays]

So far I don’t see an issue with your system. You may not be able to maximize your charge current but you do have close to the largest charger available... Good to go there.



Now lets take your loads and cruising style. Do you anchor out very much? when you do what kind of discharge do you have say overnight?



Do you tend to pull anchor and cruise daily, or do you like to sit in the same spot for days at end?



This will all dictate your battery bank size.

So far, my bank size has worked out pretty well. Having invested some time and money into them, I like to keep the 4 AGM L16 batteries happy. I usually don’t ever go below 30% DOD (70% SOC). Partly this is because my SOC is kind of a WAG. I try to keep my SOC meter calibrated, but it is pretty much guesswork as to what my total capacity is now. My rule of thumb has been to figure 5% loss per year. If I get that wrong, my 70% SOC could be off by an increasing large number over time.

I normally cruise daily so as I mentioned above, the alternator and single solar panel do a pretty good job. If we are staying at anchor for a few days, I’ll end up running the genset an hour or two in the morning and then again an hour or two in the evening. I time this with heating water, making coffee, using the microwave, running the stereo, charging all the gizmos etc... so my genset does some real work during that time.

However, my genset only has 438 hours total on it (it is 9 years old). I’ve owned the boat 3 1/2 years and have only put 110 hrs on it.

 

[FF]

"I try to keep my SOC meter calibrated, but it is pretty much guesswork as to what my total capacity is now."


I thought many SOC would self calibrate , watching the time, amps drawn and the voltage decline , then watching the charge needed to get to 100% .

 

[mvweebles]

"I try to keep my SOC meter calibrated, but it is pretty much guesswork as to what my total capacity is now."


I thought many SOC would self calibrate , watching the time, amps drawn and the voltage decline , then watching the charge needed to get to 100% .

What a SoC meter does not know is the initial capacity AH of the battery bank, and does not know how to adjust for the decline in capacity over time. The SoC meter knows the numerator, but needs help on the denominator. Thus the guesswork.

 

[sdowney717]

Bingo!


It is sad that folks think and believe there is more smoke and mirrors going on than there really is.

Simplifying a bit here but....

There are very few true multi-output, multi power supply and multi-voltage regulation chargers in existence. The vast majority of smart charger are use FET or diode isolated outputs all fed from one voltage regulated source.

Exactly, I am repairing a 40 amp 3 bank Promariner 1240i plus right now that had a stepdown transformer that supplies power the switching circuit fail due to corrosion, went open circuit.

The single source is divided up by diodes that isolate banks from back feeding power to other banks. All connected batteries get the same charge profile.
If one bank is low, forcing the charger to output more, all the banks get that boost whether needed or not, unless some special circuitry is in play.

This one has 6 idolater diodes counted from the right side of the board, 2 for each bank.

 

[dhays]

What a SoC meter does not know is the initial capacity AH of the battery bank, and does not know how to adjust for the decline in capacity over time. The SoC meter knows the numerator, but needs help on the denominator. Thus the guesswork.

Yup. All most of them do is count the amps going in and going out of the bank. It is like counting pennies going into and out of a piggy bank. No matter how good you are at counting, you don’t know the % of pennies left in the bank unless you know how many were in it to begin with.

 

[BruceK]

Bingo!


It is sad that folks think and believe there is more smoke and mirrors going on than there really is......

There are very few true multi-output, multi power supply and multi-voltage regulation chargers in existence. The vast majority of smart charger are use FET or diode isolated outputs all fed from one voltage regulated source.

Feel able to share the "very few" that discriminate between multiple banks? Alternative seems to be multiple chargers, which is how I wired my solar. It`s a multi channel charger I`m interested in.