Battery expert question

[Renegade_Master]

I had two banks of four batteries on my boat, each set being linked together to become a 24v system.

After several of the batteries went down, a friend who investigated said that the previous owner (I had just bought the boat at the time) had fitted a new 12v Autopilot, and had taken a supply direct from one of the batteries in one bank of four. He said that this was taboo and should not be done as this "upsets" the charging process? and effects the batteries?

He then set about installing a single battery on a dedecated charger just fro the autopilot.

I have to admit there is a switch on the main switch panels which says 24v to 12v converter, maybe he has a point.

Can anyone confirm he is correct? is it wrong to link a 12v item direct to a 24v bank?

 

[tico]

Its not ideal, but quite widely done. It'll have the effect that the 12v supply battery will have a shorter life than the rest of the bank.
It'll only fully charge when the chargers gets to the 'equalising' phase of the charge cycle.
There are 2 alternatives..
1. install a dedicated battery/ charger
OR
2. install a 24>12v DC/DC converter to run the autopilot

 

[BGW]

I would agree that you should not tap off one of the batteries, but would have opted for the simpler solution of a voltage dropper to provide the 12V supply.

 

[Bilgediver]

I would agree that you should not tap off one of the batteries, but would have opted for the simpler solution of a voltage dropper to provide the 12V supply.

These voltage reducers are easy to obtain as truckers use them to power CB radiios etc.

 

[carlton]

Like this?

 

[jfm]

Yup, it's the wrong thing to do. Tapping a 12v item off half the bank will cause half the bank to discharge at a different rate to the other half and upset the charging.

Of course if the 12v item has a tiny current draw then it wont matter. Yuo don't say if it is just the a/pilot control head or the whole a/pilot system including the motor. If the latter then it is very worng to tap off half a 24v bank

Fitting a single 12v battery seems nuts. Much better to us a proper marine 24/12 dropper as other have said. Victron etc make them

The one in Carlton's post is a bit mickey mouse (5 amps, and it helpfully dosn't say if that's the 12 or 24v side) and therefore not suitble for an a/pilot motor

 

[carlton]

The one in Carlton's post is a bit mickey mouse (5 amps, and it helpfully dosn't say if that's the 12 or 24v side) and therefore not suitble for an a/pilot motor

Oops - you're right. I'd got it in my head he wanted to power the gps, for some strange reason.

Must learn to read...