Domestic alternator / battery question

[GinJer]

2 weeks ago our domestic alternator broke apparently cased by a faulty solar panel regulator putting out 20 volt when it should have been 12 volts. We had a new domestic alternator and the solar panel regulator was sorted. This weekend we travelled 3 hours per day, every evening all was okay, the central heating was on for a short while in the evenings, 12 volt fridge and LED lights. By the morning the domestic batteries were almost flat again.

 

Our marina will be sorting but any ideas what the problem might be?

[Grace and Favour]

How big is your battery bank?

How old is your battery bank?

Do you know what State of Charge the batteries were in (after each day's travelling)

Do you know what the bank voltage is/was first thing in the morning?

 

Dependent upon your replies to the above - - my guess would be that your batteries are on the way out......diesel heater and 12v 'fridge can take a fair chunk out of batteries

[GinJer]

The boat is only 2 years ago, I think there are 3 domestic batteries. We only use it about every other weekend.

 

Everything was fine before the alternator died

[Phil Ambrose]

Also what is the output of your alternator? Depending on its size it may not be putting enough back into your domestic bank even with the help of a PV array, in fact what is the size (output) of your PV array.

Phil

[bottle]

The boat is only 2 years ago, I think there are 3 domestic batteries. We only use it about every other weekend.

 

Everything was fine before the alternator died

or so you thought.

 

Two months let alone two years of abuse is enough to kill batteries.

 

You think you have three domestic, you should know and if they are open wet lead acid been checking their fluid levels.

 

Are the batteries looked after when the boat is not being used, are they left discharged?

 

You say the batteries were flat by the morning, how did you monitor this?

Edited May 26, 2014 by bottle

[Paul C]

How long did it put 20V out for? That kind of voltage can damage batteries because they'd gas a lot, thus I bet that the electrolyte levels are low or non-existant.

 

I think you should add a voltmeter to the shopping list of new alternator, solar controller and possibly batteries, a simple (but built in) voltmeter is handy because once you're used to checking it occasionally you'd immediately see it was going into the 'red', an alternate is a more expensive battery monitor which would probably have a high voltage alarm (as well as alarm for other conditions eg low voltage, low state of charge, etc).

[MtB]

How did your supposed solar controller failure present itself? I mean what happened to make you realise something was wrong? Flat batteries perchance?

 

I'm wondering if the solar controller failure is a mis-diagnosis which masked another fault which has not actually been fixed.

 

MtB

[GinJer]

We have the engine serviced every year, up to now we havent let the batteries run flat, the solar panel kept them charged. On this occasion we were travelling up the canal when an alarm went off, we called the RCR who said it was a broken domestic alternator. This weekend each morning the lights and the fridge still worked but the central heating wouldnt I presume because it needs much more power that the lights and the fridge. After 3 hours travel everything worked again.

 

Why do you think we have been abusing the batteries, what should we have been doing or not be doing?

 

How would a voltmeter help?

[Paul C]

We have the engine serviced every year, up to now we havent let the batteries run flat, the solar panel kept them charged. On this occasion we were travelling up the canal when an alarm went off, we called the RCR who said it was a broken domestic alternator. This weekend each morning the lights and the fridge still worked but the central heating wouldnt I presume because it needs much more power that the lights and the fridge. After 3 hours travel everything worked again.

 

Why do you think we have been abusing the batteries, what should we have been doing or not be doing?

 

How would a voltmeter help?

 

Its not so much that you've been abusing the batteries; more that, because you don't know (except very roughly) what is going into or coming out of the batteries, you don't know if they're being abused or not. In theory the solar panels should help a lot, but in practice if you have high-power-consuming items such as central heating (its pump etc) and the batteries were already reduced capacity through simple age or some kind of previous poor charging regime, then it won't be enough (after all, solar can't do anything through the night!)

 

A voltmeter will give a basic idea of battery capacity (you'd need to know the loads or charging, and take this into account or arrange zero charge-discharge and a rest period) and also if they're suffering during a big discharge or being overcharged (generally speaking, anything over 14.6-14.8V isn't great - but it depends on the battery type and also listen to the battery manufacturer's guidelines on charging).