Battery troubles

[asteven221]

A few weeks ago the alternator charging light came on for the port engine. A few of days ago I noticed that both batteries were in need of a water top up and looked dry. There wasn't any water covering the plates. I topped them up. Nothing has changed in that the charging alarm still sounds when the engine is started, however by chance I noticed today that the same two batteries are really quite warm. The other battery on the other bank seems fine.

There is a rather old battery charger (probably original from Sealine in 1999) which is always left on.

I have not done any serious troubleshooting yet, because I not sure where best to start. Warm batteries don't seem a good thing! BTW they are warm from (I assume) the battery charger as the engines have not been on for at least 24 hours.

I suspect the batteries are stuffed, but I don't want to just buy new ones and find that the alternator or the battery charger is the source of the problem.

Is there any fire risk with batteries heating up? Should I disconnect them?

Any pointers on how best to troubleshoot would be most welcome. Thanks.

 

[A_8]

They should not get warm so you need to understand why that is and disconnect the charger until you do. If you have one battery that don't get warm then disconnect the others and use that one on the port engine and see if the light still comes on.

 

[halcyon]

A few weeks ago the alternator charging light came on for the port engine. A few of days ago I noticed that both batteries were in need of a water top up and looked dry.

Any pointers on how best to troubleshoot would be most welcome. Thanks.

The first thing is measure battery voltage, then battery voltage with engine running, both engines.

The probable fault is over voltage alternator due to regulator fault.

Brian

 

[rafiki_]

If your batteries have cooked their water, then they are stuffed. You are right, you need to find the root cause. Do you have a smart battery charger? If not, then you should not leave the charger on all the time as it will cook the batteries.

 

[asteven221]

Thanks. Good advice and appreciated. I will start troubleshooting today.

 

[asteven221]

This has got me a bit stumped. I have done some troubleshooting and can't find what the problem is. If anyone can offer any advice then that would be appreciated.

Regarding the batteries that cooked themselves. They are actually charged by the starboard engine which is seems to be charging as it's meant to. The port engine with the warning light charges the engine start battery, which according to the indicator light on the battery, is charged. I assume that it's charged from the battery charger which is always on. BTW the battery charger is a so called smart charger and is meant to be on all the time. It's made by Newmarc and looks as if it's a Sealine supplied charger.

I have done some tests with a DVM. With both engines running the reading directly on the back of the port alternator is 13.5v. However on the battery the reading is 12.7v. That's the side with the warning light flashing. By comparison the starboard side reads 13.32v at the battery.

I tried a brand new battery on the port side to see if that made any diference, but there was little difference. In fact the reading at the battery was less - 12v.

It looks to me that there is a problem between the back of the alternator and the battery, but I have checked as much of the wiring I can see and everything appears solid enough. From what I can tell the cables from the back of the alternator are heavy cables battery sized cables and I wouldn't expect to see a voltage drop from them. I can't easily trace the path of each cable as they disappear. Should I expect to see some device/component between the back of the alternator and the battery?

Am I barking up the wrong tree with this? Is my thinking correct that the problem is between the alternator and the battery indicated by the voltage drop reading?

Thanks.

 

[beltsandbraces]

i would personally turn of the charger if the batterys are getting hot, I have seen 2 go with a hell of a bang no fire but battery acid everywhere. I have a sealine and made the original charger redundant for a new up to date smart charger which has a separate cable attached to the batteries and if they get to a certain temperature it cuts the charger out.

 

[IDAMAY]

This may be a red herring but on our T47 (previous boat, also with Newmar smart charger) we had a problem with the split diode that handles the charge from the alternators to the different battery banks. It overheated to the extent of almost melting. On the T47 the diode was located on the forward engine room bulkhead. As I say could be a red herring.

 

[asteven221]

Thanks for your advice. It looks like one for the pro's.!