24volt charge problem

[nairda96]

My Dads boat has a John deere engine with a 24volt starter and alternator, It has 4 batterys devided up into two 24volt banks, One for starting and one for electronics and the 12volt convertor, The boat had been
starting and stopping fine all morning and showed charge on the gauge. After maybe 2hrs at anchor with very few electronics running it failed to start and gave a low battery alarm. Neither bank would then start the engine.
On later inspection with a meter we discovered that the battery on each bank which has the negative lead connected to it were dead, 10 volts. The other 2 then started the engine.
When charging, the positive in each bank is getting about 14.1 volts and the negative ones are only getting 13 to 13.1 which I assume is why they eventually died. Does anyone know WHY ?????
FYI : One bank are new batterys and the other ones are 2 years old.

 

[VicS]

I think it will be difficult to work out what might be the trouble without access to a wiring diagram.


However
If you have a heavily discharged battery in series with one that is fairly well charged its reasonable for the volts across the charged one to be higher than across the discharged one. On that basis Id not worry about the difference between the two.

You have to look for the reason why one battery in each bank was discharged. I'll guess it is because it is used to supply 12 volt equipment.

Its bad practice to use one battery in a 24 volt bank to supply 12 volts. It will slowly become discharged and being in series with a well charged battery it will be slow to recharge.

 

[William_H]

Batteries

The question is what happens when you recharge the batteries perhaps from a shore power charger.
You need to decide if the charging system is faulty. ie the alternator regulator or the battery wiring and switching. Do you get 27.5 volts up to 28 volts at the battery terminals with the engine running? If not then your charging system is faulty. If you get that charging voltage but batteries are still reluctant to start the engine then I think it possible the batteries have died.
Put the good batteries together as you have done and see how they go. Batteries do die and if one dies and they are in parallel banks then it could pull down the other bank.
I think it most likely coincidence that only the negative side batteries have died or discharged first. Assuming as you say you use a 12v converter and don't tap off 12v as Vic suggests. good luck olewill

 

[Deleted member 36384]

Nairda26 I cant help with diagnosis but my boat has a similar system and this is what I find in a working system: -

Domestic 4 x 6V Lead Acid
Starter 2 x 12V Lead Acid

Both banks are connected through 1 2 Both switch. Both banks have their negatives connected to a common bus bar.

When my engine is running around 28V will flow into each bank if I measure across the bank + and -. Each individual battery (6V or 12V) measures almost identical voltage around 6V or 12V depending on the bank. I dont know what the figures are when charging as I have only measured at rest. However, I would expect each to be a bit more than 6V and 12V per battery (as appropriate) when charging.

The 12V electric's are provided by a 24 x 12 transformer or whatever the modern equivalent is. The power to this transformer comes from the distribution (switch) panel at 24V. There is a second 12V distribution (switch) panel after the transformer.

The only additional connections to the batteries are a shore powered battery charger and a wind powered charger to the domestic bank both of which pump out 24V - 28V.

I have found that the electrolyte level of the cells nearest the + or - posts of the bank tend to need topped up more. There is a nagging feeling that the negative side is the worst, but I am not sure. Hence it is possible that these cells are damaged more than the rest which is why you are not getting a full 12V charge on the batteries at the negative side.

Last year I went through a steep learning curve to try and understand what I have, so you have my sympathy. I still have a long way to go!

 

[nairda96]

Thanks for all the suggestions,
There is no 12 volt tap, All 12volt comes from a convertor on its own 24 volt bank.
It is reading 27-28volts across the bank when running and although both batteries had over
12 volts the neg one still charged at 13 and the other at 14 volts. I don't have a great understanding when it comes to the technical side of batteries, I had just read somewhere
that 13volts will never fully charge a battery.
Blowingoldboots: I think that he will have the water levels in them well checked but its interesting that yours dropped like that.

 

[Andrew_Fanner]

Slightly off the topic, but not much. What 12v converter do you use? A "proper" 24-12V battery charger or a voltage dropper? I ask because I bought a decent(?) voltage dropper from Maplins, installed it and found that the wretched thing ran a cooling fan, a not especially quiet fan at that. Fine if the engine is running, but not so clever when moored up. A previous owner left a muddle of 24 and 12 volt gear, not so bad for navigation stuff I dont use when moored, but some cabin lights, water pump, shower drain pump etc are 12V too. As a result of this I've taken the dropper out for the time being and I'm rethinking.
Apart from spending on the proper 24-12v charger (can't afford it atm) suggestions welcome. I've wondered about an extra battery (I have a spare) in parallel with one of the 24V pair and a relay in the join linked to the ignition, but then I have effectively a 105Ah and a 210Ah series pair for 24V which I think will be a disaster. I could add another 12V in parallel the other side, plenty of space, but still not sure its a viable plan and the cost climbs.

13V wont charge a battery proeprly and, like you, I have has similar issues and a battery going dry.

 

[nairda96]

Slightly off the topic, but not much. What 12v converter do you use? A "proper" 24-12V battery charger or a voltage dropper? I ask because I bought a decent(?) voltage dropper from Maplins, installed it and found that the wretched thing ran a cooling fan, a not especially quiet fan at that. Fine if the engine is running, but not so clever when moored up. A previous owner left a muddle of 24 and 12 volt gear, not so bad for navigation stuff I dont use when moored, but some cabin lights, water pump, shower drain pump etc are 12V too. As a result of this I've taken the dropper out for the time being and I'm rethinking.
Apart from spending on the proper 24-12v charger (can't afford it atm) suggestions welcome. I've wondered about an extra battery (I have a spare) in parallel with one of the 24V pair and a relay in the join linked to the ignition, but then I have effectively a 105Ah and a 210Ah series pair for 24V which I think will be a disaster. I could add another 12V in parallel the other side, plenty of space, but still not sure its a viable plan and the cost climbs.

13V wont charge a battery proeprly and, like you, I have has similar issues and a battery going dry.

I don't know what dropper he has exactly but I know it has a cooling fan, Noise isn't an issue for him as it is a Charter Angling boat not a pleasure boat, Starting is a issue though
as its started and stopped a lot.
It seems now that the batteries have been charged at home that one has had it so he has 2 brand new ones to put in and see what happens

 

[NB Willawaw]

I presume you have a 1+2 bank battery isolator to divide/share the charge from your single alternator to both banks ??


It sounds like something is splitting the 24V charge disproportionately across the two batteries in each leg - are the lower batteries (nearest the -ve) a different type (make/composition) by any chance ??