Battery charging

[Chris H]

It was never explained to me how the battery charging works on my boat when we bought it, I would like to get my head around what should happen before I start investigating, what I think is a fault.

we have two battery bank, one engine, one service, they all charge ok on shore power.
When at sea the service batteries do not charge off the engine alternator.
We have a generator and when started the battery charger power light comes on but doesn’t seem to charge the service batteries, this is what I think is a fault and would like to investigate.

I could bridge both battery circuits, with the onboard switch to charge the service batteries from the alternator but I’m not sure this is the done thing.

 

[markc]

Each bank should be charged by each engine/alternator. Have you checked the output at the back of both alternators? A couple of years ago I had a bad regulator on one alternator and they're easy to change in situ. Also could be a loose battery sensor cable on that alternator

 

[MapisM]

Good suggestion from Mark, but doesn't explain why the charger doesn't work with the generator.
I mean, if AIUI the charger has two outputs and charges both the domestic and the starting bank, and it works fine on shore power, it doesn't make any sense that it doesn't when on genset power.
In fact, the genset/shore selector (and also the general RCD+breaker for AC power) is upstream of each and every AC equipment - not only the charger, but also the water heater, airco, sockets, cooktop... You name it.
And for all these components, it shouldn't make any difference whether AC comes from the shore cord or from the genset.
Is there any other AC equipment that doesn't work when on genset power?

 

[PaulRainbow]

Good suggestion from Mark, but doesn't explain why the charger doesn't work with the generator.
I mean, if AIUI the charger has two outputs and charges both the domestic and the starting bank, and it works fine on shore power, it doesn't make any sense that it doesn't when on genset power.
In fact, the genset/shore selector (and also the general RCD+breaker for AC power) is upstream of each and every AC equipment - not only the charger, but also the water heater, airco, sockets, cooktop... You name it.
And for all these components, it shouldn't make any difference whether AC comes from the shore cord or from the genset.
Is there any other AC equipment that doesn't work when on genset power?

I was thinking the same. It makes even less sense that the charger power light comes on, but no charging ???

 

[PaulRainbow]

It was never explained to me how the battery charging works on my boat when we bought it, I would like to get my head around what should happen before I start investigating, what I think is a fault.

we have two battery bank, one engine, one service, they all charge ok on shore power.
When at sea the service batteries do not charge off the engine alternator.
We have a generator and when started the battery charger power light comes on but doesn’t seem to charge the service batteries, this is what I think is a fault and would like to investigate.

I could bridge both battery circuits, with the onboard switch to charge the service batteries from the alternator but I’m not sure this is the done thing.

Given post #3, i'd double check the mains charger when running the generator, that just doesn't make sense.

Nor sure how your alternator setup is connected, but the first thing to do would be to check the output at each alternator. I would also run one engine at a time to see which engine charges the engine bank.

I would not routinely link all of the batteries for charging, but if you have to do it as a temporary measure just be sure to turn the link off when you stop the engines.

I would have thought that each of your engines should charge all of the batteries, if you do the checks above you'll know for sure. With just the two banks I would have wired each alternator to a split charge device, so each engine charged both banks. Seems a waste of a lot of charging capability not to do so.

 

[Chris H]

All the A/C equipment works on the generator, as said, it shouldn’t make a difference where the A/C is coming from, I will check the charger output when the geny is on and start from there.
Seems there is also an alternator problem if these should be charging both sets of batteries.

 

[MapisM]

Just another though:
I've seen some builders (no idea about Pershing, though) using tricks for automatically disconnecting the charger whenever the engines are running, and/or when the engine keys are on the "running" position.
This shouldn't happen if you're running the genset with the engines off and disconnected, of course.
But if by chance you tried the charger while the engines were running (or just with their keys on), it could be normal that the charger doesn't work...

 

[Hurricane]

Not being funny, but is this a perception thing.
How old are the batteries?
Could it be that on shore power, the charger is running all the time and has time to settle down.
Dead batteries give strange results - appear to charge quickly etc.
Maybe when the engines or generator is charging, they haven't had the same amount of time that shore power would have had.

 

[Chris H]

Not being funny, but is this a perception thing.
How old are the batteries?
Could it be that on shore power, the charger is running all the time and has time to settle down.
Dead batteries give strange results - appear to charge quickly etc.
Maybe when the engines or generator is charging, they haven't had the same amount of time that shore power would have had.

Service batteries were new July 22, the previous batteries fried !
Took two days to cool down before we could remove them.

 

[vas]

reason for frying? shorted cell, or other? anything fixed afterwards?
bit hard accepting that all's fine but alternator not working, and charger even with light on doesn't charge from generator.
maybe another failure somewhere behind?

 

[MapisM]

Chris, what Vas said is precisely what popped to my mind after reading your last post.
Defective chargers making batteries fry (and even explode!) are not totally unheard of, as I learned from an electrician who was personally injuried by one of these accidents!
BTW, new and more robust batteries might "hide" the defect (if any), at least for some time.
Bottom line, an accurate functionality check of charger and alternators is in order, unless already done...

 

[Chris H]

reason for frying? shorted cell, or other? anything fixed afterwards?
bit hard accepting that all's fine but alternator not working, and charger even with light on doesn't charge from generator.
maybe another failure somewhere behind?

Marine electrician looked at them and said it’s normal when the cells breakdown.

 

[PowerYachtBlog]

I would also check about the battery charger, Since this is a 2002 (and saying it fried the batteries) most probably it still has a mechanical battery charger not a smart one.
I know for a fact that up to 2006 they still used to fit mechanical battery chargers on Pershings.

 

[Portofino]

Need more info .
Basic stuff like a voltmeter across each batt with charger on / off and motors on / off , both independent and together.

eg motors off the batts could read 12.7 v for eg , then jump to 14.5-16 v with them running .
We need both banks info .

If you are really clever take a record every few hrs on shore power only to see if the domestic changes a lot .Thinking by morning ( period of boat inactivity due to sleeping ) it’s input should have dropped as the batts expected charged fully .
If the chargers still on max stuff say 16 v or higher then as others have said they are in the knackered zone , or entering thus .

Fortunately on my boats I have gauges on the saloon that indicate both banks V , and the rate of Ah charge .Also discharge.( useful @ anchor = time to turn the geny on etc ) So between watching the three values for each bank i can see exactly what’s happening.

The boats alternator (s) recharge a lot slower than the 220 v charger FWIW .
I know this by observing said gauges .
Engine starters get priority via the trad split diode thing then the doms get some charge when running .

 

[PaulRainbow]

Need more info .
Basic stuff like a voltmeter across each batt with charger on / off and motors on / off , both independent and together.

eg motors off the batts could read 12.7 v for eg , then jump to 14.5-16 v with them running .
We need both banks info .

If the mains charger is putting out 16v the batteries will already be knackered.

I wouldn't assume it's a 12v system either.

If you are really clever take a record every few hrs on shore power only to see if the domestic changes a lot .Thinking by morning ( period of boat inactivity due to sleeping ) it’s input should have dropped as the batts expected charged fully .
If the chargers still on max stuff say 16 v or higher then as others have said they are in the knackered zone , or entering thus .

Again, 16v will kill 12v batteries really quickly (or higher will boil them to death even quicker).

Fortunately on my boats I have gauges on the saloon that indicate both banks V , and the rate of Ah charge .Also discharge.( useful @ anchor = time to turn the geny on etc ) So between watching the three values for each bank i can see exactly what’s happening.

"Rate of charge" is measured in amps, not amp hours.

The boats alternator (s) recharge a lot slower than the 220 v charger FWIW .
I know this by observing said gauges .
Engine starters get priority via the trad split diode thing then the doms get some charge when running .

If your engines charge the batteries slower than the mains charger something is odd.

My alternator outputs are 4 times the output of the mains charger, which wouldn't be untypical. Besides, charge acceptance will be whatever it is, no matter how many amps your alternators or charger can put out.

Split charge diodes (unless part of some fancy setup) do not prioritise any battery.

 

[Portofino]

If the mains charger is putting out 16v the batteries will already be knackered.

I wouldn't assume it's a 12v system either.

Again, 16v will kill 12v batteries really quickly (or higher will boil them to death even quicker).

"Rate of charge" is measured in amps, not amp hours.


If your engines charge the batteries slower than the mains charger something is odd.

My alternator outputs are 4 times the output of the mains charger, which wouldn't be untypical. Besides, charge acceptance will be whatever it is, no matter how many amps your alternators or charger can put out.

Split charge diodes (unless part of some fancy setup) do not prioritise any battery.

Still needs to take records.
The voltage I quoted was indicative ….yet to be published.
Yes it’s 24 v like mine , but the batts are individual 12 s .

It’s a dual meter with Ah for the charge and I flick a switch to the A .Plus which ever bank i select to view .

The MAN like all modern ECU , electrotwackery engines gobble juice just to run , so a high proportion of the alternator output is used to run the things , what’s left of the 60 A s is used to top up the batts . You can and are welcome to knit pick the exact % .

Yes my chargers on shore power does stuff em up rapidly, significantly at 100 A , 3 outputs independent, than the 60 A running the engines and what’s left after the MAN s have taking there cut , is prioritised to the engine bank then the doms .

 

[PaulRainbow]

Still needs to take records.
The voltage I quoted was indicative ….yet to be published.
Yes it’s 24 v like mine , but the batts are individual 12 s .

It’s a dual meter with Ah for the charge and I flick a switch to the A .Plus which ever bank i select to view .

The MAN like all modern ECU , electrotwackery engines gobble juice just to run , so a high proportion of the alternator output is used to run the things , what’s left of the 60 A s is used to top up the batts . You can and are welcome to knit pick the exact % .

Yes my chargers on shore power does stuff em up rapidly, significantly at 100 A , 3 outputs independent, than the 60 A running the engines and what’s left after the MAN s have taking there cut , is prioritised to the engine bank then the doms .

Totally pointless trying to take a battery voltage reading with the mains charger on or the engines running. All you'll be measuring is the voltage from the charge source, which will be the same across the whole bank.

As i already told you, Ah is not "for the charge". Current is measured in Amps. Ah is a measure of capacity and will be meaningless with the charger on or the engine running.

As for your engines needing a "high proportion" of the 60a that the alternator can generate, that just isn't true. Sure, if it's common rail the ECU, injectors etc will need some power, but it isn't going to be anything remotely close to 60a @24v.

 

[Portofino]

Totally pointless trying to take a battery voltage reading with the mains charger on or the engines running. All you'll be measuring is the voltage from the charge source, which will be the same across the whole bank.

As i already told you, Ah is not "for the charge". Current is measured in Amps. Ah is a measure of capacity and will be meaningless with the charger on or the engine running.

As for your engines needing a "high proportion" of the 60a that the alternator can generate, that just isn't true. Sure, if it's common rail the ECU, injectors etc will need some power, but it isn't going to be anything remotely close to 60a @24v.

Tells you if the charger …
A is working the voltage rise ?
B how much of a rise …..your 16 v point frying them .

works with the engines as well .re Alternator output(s) .

Helps in the Dx saves stabs in the dark .
So with a car it’s 12.7 , with the engine off and rises to 14 . Something maybe 14.7 or what ever with a functioning alternator that’s excited .

 

[PaulRainbow]

Tells you if the charger …
A is working the voltage rise ?
B how much of a rise …..your 16 v point frying them .

works with the engines as well .re Alternator output(s) .

Helps in the Dx saves stabs in the dark .
So with a car it’s 12.7 , with the engine off and rises to 14 . Something maybe 14.7 or what ever with a functioning alternator that’s excited .

When in a hole, stop digging.......

 

[Portofino]

When in a hole, stop digging.......

Find the right place to dig before digging .

You know having a parts fest .Rule out as much as you can .