Duff Battery ??

[syd]

Would one duff battery out of a bank of four cause you to lose all DC power?
I went down to the boat Monday with the intention of turning it around. Engines turned over slow, lights were dim, so put charger on for twenty four hours. While charger is on all the lights and pumps worked as normal but not enough power for engine crank. Turn the charger off and all goes dark within ten minutes. Disconnected the batteries and tested them one by one. Three are showing 13 plus, one is showing 9 and dropping. Would this one battery cause these symptoms? I've checked all the earths and connections, all seem fine. The batteries are in two banks of two. There is no isolator switch that I can find that normally allows you to select one two or all. I've ordered a new battery to replace duff one which is due to arrive on Friday(tomorrow).
Your thoughts on this would be greatly appreciated.

Syd

 

[PaulGooch]

Would one duff battery out of a bank of four cause you to lose all DC power?
I went down to the boat Monday with the intention of turning it around. Engines turned over slow, lights were dim, so put charger on for twenty four hours. While charger is on all the lights and pumps worked as normal but not enough power for engine crank. Disconnected the batteries and tested them one by one. Three are showing 13 plus, one is showing 9 and dropping. Would this one battery cause these symptoms? I've checked all the earths and connections, all seem fine. The batteries are in two banks of two. There is no isolator switch that I can find that normally allows you to select one two or all. I've ordered a new battery to replace duff one which is due to arrive on Friday(tomorrow).
Your thoughts on this would be greatly appreciated.

Syd

Not really enough info. How do the batteries work ? Is it two banks of two batteries, one for starting and one for domestics ? Are they wired 12v or 24v ? Single engine or twin ? How do they charge from the engine/s ? What isolator switches do you have ?

IMO, you ought to investigate exactly how they are wired and take measures to rectify what is clearly an issue. A single battery failure that can stop you starting the boat is bad news. Sketch out where all the positive cables go and post it back here.

 

[sarabande]

Sys - just to check that you have ordered a new battery of the same size and characteristics as the duff one ? Otherwise there may be charging and discharging issues.

It sounds as if all the batteries are somehow paralleled. Is there a 1-2-Both-Off switch hiding somewhere ?

So it's two domestic, and two engine ?

 

[syd]

Two banks of two that are charged by the engines. All four batteries are 210ahr so can't tell which may be leisure or engine crank. No isolator switches that I can find, all the cables disappear into the bilges

 

[syd]

I'm still searching for an isolator switch, there must be one. I'll do my best to trace all cable roots and destinations. I've never come across a wiring set up like this before. Do the Americans do it differently to us?

 

[sarabande]

I am beginning to think those 2 banks may be physically separate for weight distribution purposes but electrically connected in some way.
e.g.

+ --- + --------- + --- +
_ --- _ ---------- _ --- _

The normal way to connect the above is for the Neg to be taken from bottom left, and the Pos feed from Top right. That's called "opposite ends".

However, that means that if you lose one cell in any of the batteries then you lose output power.

You need to identify the connections, to see where the current flows.

 

[PaulGooch]

I am beginning to think those 2 banks may be physically separate for weight distribution purposes but electrically connected in some way.
e.g.

+ --- + --------- + --- +
_ --- _ ---------- _ --- _

The normal way to connect the above is for the Neg to be taken from bottom left, and the Pos feed from Top right. That's called "opposite ends".

However, that means that if you lose one cell in any of the batteries then you lose output power.

You need to identify the connections, to see where the current flows.

Hard to say for sure with the current info, but it does sound like all four are wired in parallel. That's a pretty bad way of doing things and it needs changing.

 

[syd]

Yep, well spotted. Can confirm all positives are connected to each other as are the negs.
Sorry about the lack of detail but I'm not really sure what I'm looking at or for.
Electrics not my field

 

[sarabande]

Nothing really wrong with that. The power should be taken from / put into opposite ends, and not just one battery. Have you managed to check the routing ?


I think there must be a paralleling switch somewhere with two engines (each with an alternator ?)

Good to hear of progress

 

[Divemaster1]

Syd,

Those DD's probably have 24V starters ... and they need good cranking power ... the 9V one is a right killer for starting ...

If 24V, then you probably have two banks seperated somewhere and your engine is trying to turn around with the bank with the poor battery .... and less than 22V and dropping is pretty bad news for those nice DD's... they won't like that !!

If you are anything like we are, you will have a swich somewhere that enables you to run domestic off start batteries (should not be default which it sounds like in your case.......).

DD installations off that era had Port engine charging Start Bank and Starboard engine charging domestic batteries ... nothing more complex than that ... but both engines running off starter battery bank .... and you may have a paralell switch somewhere on the dash which enables you to boost the starting crank with the domestic bank if it is cold, or your starter bank is poor...

 

[PaulGooch]

Nothing really wrong with that. The power should be taken from / put into opposite ends, and not just one battery. Have you managed to check the routing ?


I think there must be a paralleling switch somewhere with two engines (each with an alternator ?)

Good to hear of progress

No need for a paralleling switch, they are already wired in parallel. I don't agree that there is "nothing wrong with that". There clearly is, he has four batteries, three of which are good and cannot start his engine.

IMO, there should be two separate banks. One for the engines, one for the domestics. Isolator switches for each bank and to parallel the banks for emergency starting, or a combined "On-Off-Combine" switch. Some form of split charging system could then be fitted so that each engine charges both banks, a simple diode should suffice.

I'm also a little sceptical that three fully charged batteries won't start the engines, even with one faulty one. I'd suggest to the OP that he bypass the faulty battery and see if the engines will start.