Battery charging

[Graham_Wright]

I have just replaced both domestic batteries with the same make - Hankook.
I suspect I may have cooked one of them by overcharging.
Advice from Battery Megastore was to charge at 14.4 volts and not to exceed 20% of capacity which equates to 20 amps.

Advice duly followed but at 14.4 volts the charge currents to both were over 30 A.

The battery terminal volts on collection, were 12.5,

My simple mind suggests that the charge current depends on the voltage difference between charger and battery and the internal resistance of the cells.

I have reduced the alternator output to lower the charge current to an acceptable level.
Comments please.

 

[pmagowan]

Why do you suspect that?

 

[Sandy]

Are they bog standard Lead Acid or AGMs, what was the charger?

What is the current at rest of each battery in the bank? You may need to disconnect them from each other and then do something less boring for an hour or two before going in with your multi-meter.

Batteries usually absorb as much current as they want. My AGMs will consume 30 amps from the shore power charger when needed.

 

[Refueler]

"charge current depends on the voltage difference between charger and battery and the internal resistance of the cells"

Correct - but subject to the regulated limit of the charge source.

"I have reduced the alternator output to lower the charge current to an acceptable level."

Interesting .... how did you lower the alternator output ? 20A is a lot lower than near all alternators .... even a small car will have an alternator capable of 40A or more ... but that ampage as you correctly consider reduces as battery charge comes up.

12.5V from shop is typical of a battery charged and stood idle and settled. Would be normal after install to have quite a high charge rate from any alternator until it reaches full state ..

 

[Graham_Wright]

Why do you suspect that?

The cooking?
I noticed a charge current of 40A from time to time and BM pointed out that the inspection window was cracked. They have known one to blow out due to overheating.,

 

[Graham_Wright]

Are they bog standard Lead Acid or AGMs, what was the charger?

Lead acid. Alternator.

What is the current at rest of each battery in the bank? You may need to disconnect them from each other and then do something less boring for an hour or two before going in with your multi-meter.

They are charged vIa a diode splitter.

Batteries usually absorb as much current as they want. My AGMs will consume 30 amps from the shore power charger when needed.

 

[Sandy]

The cooking?
I noticed a charge current of 40A from time to time and BM pointed out that the inspection window was cracked. They have known one to blow out due to overheating.,

You may want to call Battery Megastore and arrange for a replacement. Inspection windows should not crack on first charge.

 

[Refueler]

"They are charged vIa a diode splitter."

Do you have any compensator to cover the voltage drop across the Diode Splitter .. which can be up to 0,7V ?? You can never achieve full charge with Diode Splitter without Battery Sensed or tricking the Alternator ...

 

[Graham_Wright]

"charge current depends on the voltage difference between charger and battery and the internal resistance of the cells"

Correct - but subject to the regulated limit of the charge source.

"I have reduced the alternator output to lower the charge current to an acceptable level."

The alternator is rated at 130A and has a built in regulator adjustable with a screwdriver.

Interesting .... how did you lower the alternator output ? 20A is a lot lower than near all alternators .... even a small car will have an alternator capable of 40A or more ... but that ampage as you correctly consider reduces as battery charge comes up.

12.5V from shop is typical of a battery charged and stood idle and settled. Would be normal after install to have quite a high charge rate from any alternator until it reaches full state ..

That is reassuring.
I'll see how it goes.

 

[Graham_Wright]

You may want to call Battery Megastore and arrange for a replacement. Inspection windows should not crack on first charge.

No - that was the original - several years old.

 

[Refueler]

The alternator is rated at 130A and has a built in regulator adjustable with a screwdriver.

That is reassuring.
I'll see how it goes.

mmm ........... 130A is quite a high rated unit - but that also depends on the capacity of banks you are maintaining with it.

As others have indicated - high rates would only be seen when batterys are low charged condition ... and if the batterys are of mid size - they could increase in temperature if such rate is well over their designed ...

Many people do not appreciate that charge rate IN is significantly less than AMP rate out ... applying too high a rate IN can cause gassing of cells or even buckling of cell plates in extremis.

 

[Sandy]

No - that was the original - several years old.

You are mixing different aged batteries in the same bank? Not something I would do.

 

[Graham_Wright]

#1
"I have just replaced both domestic batteries with the same make - Hankook."

 

[B27]

Charging at C/3 for an extended time might get the battery hot.
C/5 is a guideline, not really a hard limit.

Most basic alternator setups will put less than 14.4V at the battery terminals at high current.
The alternator itself has output resistance

I suspect that for best battery life you should charge at C/5 or less, but in reality, everything you want to do shortens the life of your battery, so long as the life is acceptable, carry on.

I have seen 40A into a single 110Ah battery, which happens to be a Hankook, it's several years old so presumably not suffering too much.
The current tends to reduce after a while and the battery doesn't seem to get more than warm.

Bear in mind that the 14.4V figure is for some temperature like 15 or 20degC and should be reduced with warmer temperature.

 

[Sandy]

#1
"I have just replaced both domestic batteries with the same make - Hankook."

But they are not the same age.

Like humans batteries age, I can't leap out of bed like I used to do 20 years ago - it is more of a roll these days.

You have placed a fresh new battery into the bank, a bank should be able to react as one but different cells are responding at different rates.

 

[Tranona]

But they are not the same age.

Like humans batteries age, I can't leap out of bed like I used to do 20 years ago - it is more of a roll these days.

You have placed a fresh new battery into the bank, a bank should be able to react as one but different cells are responding at different rates.

Suspect you have not really read the quote - both batteries are new but one seems to overcharge.

 

[Sandy]

Suspect you have not really read the quote - both batteries are new but one seems to overcharge.

I am getting very mixed messages from @Graham_Wright first he say he has replaced the bank #1 then in post #10 states its an old battery that he suspects he's cooked.

Perhaps @Graham_Wright would kindly clarify.

 

[Graham_Wright]

Sigh!
There were two batteries fitted on the boat. Separately charged via a diode splitter.
Both batteries I deemed dead. I took them to BMS who commented that one of them had a cracked inspection window that might have been cased by overheating. I admitted I had witnessed charge rates of 40A.
I have replaced both batteries with the same make and type.
On running the engine and setting the alternator output to the recommended 14.4 volts, one battery was taking 36A.
The other was around 18.

Clear now?

 

[B27]

Suspect you have not really read the quote - both batteries are new but one seems to overcharge.

That's this bit?

Advice duly followed but at 14.4 volts the charge currents to both were over 30 A.

If he charged his old batteries at high rates and cooked one or more of them, that's how it goes.
You want optimum life, you need optimum charging.
People generally compromise between looking after their batteries and using them.

 

[B27]

Sigh!
There were two batteries fitted on the boat. Separately charged via a diode splitter.
Both batteries I deemed dead. I took them to BMS who commented that one of them had a cracked inspection window that might have been cased by overheating. I admitted I had witnessed charge rates of 40A.
I have replaced both batteries with the same make and type.
On running the engine and setting the alternator output to the recommended 14.4 volts, one battery was taking 36A.
The other was around 18.

Clear now?

If two identical batteries are at different temperatures, the hotter one will have a lower internal voltage, so will take more current at the same voltage, so will get hotter still.
Lead acid batteries do not naturally share very well.