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Leisure batteries not charging


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I've been cruising a couple of days and it has become apparent the domestic batteries are only being charged by the solar (1x100w), which isn't enough to run the fridge and isn't enough full stop on cloudy days like this. Now, when the engine is running the dashboard gauge reads 14v so the alternator is working and presumably charging the starter battery. I can't find any issues with the wiring so I suspect the box that sends alternator charge to the leisure batteries (what do call one of them?) is knackered.

 

I was thinking I could simply connect the starter battery to the leisure batteries to make a single battery bank. Is this a good idea? What are the potential problems?

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Do you have just the one alternator? Presuming yes, then the box you are referring to is probably a split charge relay.

 

Yes you could connect both battery bank together whilst the engine is running, but be sure to disconnect them again when you stop, otherwise you may wake up to a flat engine battery and thus unable to start the engine.

 

Make sure any temporary connection can't come adrift and thus short circuit to -ve / hull.

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Ah, Cheers.

It had occurred to me that it might drain the starter battery in the evenings, but I'm not an early riser so at this time of the year the solar should get it well over 12v by the time I set off...

However, "well over 12v" whilst on charge is not the same as necessarily having enough oomph to start a Diesel engine. Especially if it's not sunny! As I said, I would disconnect once you stop the engine.

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I had this last year & did exactly as Nick suggests, in fact I put up an article on it called something along the lines of "A get you home fix" I think. Can't stress enough the importance of disconnecting the battery banks from each other at the end of the cruising day.

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I suspect the box that sends alternator charge to the leisure batteries (what do call one of them?) is knackered.

 

 

 

I hope you've been able to get going with the temporary fix already suggested. In the long term, there shouldn't be "a box that sends the alternator charge to the leisure batteries" if its a single alternator setup - the alternator, for best efficiency, is best connected directly to the LEISURE battery bank. Then by all means use a split charge relay to connect the leisure bank (thus the alternator) to the starter battery when the engine is running.

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I thought it was the other way ie it charges the engine batt first then switches over to the house bank,

 

Neil

 

I'm not sure what you mean by "charges first" - its not as simple as that, the split charge relay merely joins the two banks together and whatever battery "charges first" would relate to both its capacity, state of charge and the resistance of the wire from the charging source to the battery.

 

Also it doesn't "switch over" at any stage - it "switches" on or off, and the thing it switches connects the two banks together - the alternator is always permanently connected to one or other bank, not switched between them.

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I thought it was the other way ie it charges the engine batt first then switches over to the house bank,

 

Neil

The point is that typically, much more charge needs to go into the house bank (say 150AH), compared to the engine battery (maybe 1AH if it's a good starter). It is therefore sensible to have the short current path to the house bank, ie connect the alternator direct to the house bank and use the split charge relay to charge the engine battery, so that there will be less current flowing through the relay.

 

However, it's not quite as simple as that and it seems that boats are often wired the other way round, perhaps because the engine manufacturer sees the alternator's primary role as charging the engine battery, the house bank is an "extra". And also of course because in a case such as the OP's, if the alternator were wired to the house bank, the first he would know of a problem would be when the engine wouldn't start, which is probably worse than the cabin lights going dim.

Edited by nicknorman
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My understanding is that the cranking battery is treated as prime. The domestic is a secondary. If there is a very heavy draw prime takes charge priority.

Yes that's how it is usually connected, but is not how it should be connected.

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If there is a very heavy draw prime takes charge priority.

By what mechanism? If the batteries are paralleled then, as Paul suggests, the current will be divided between the two banks dependant on the relative states of charge of the banks, their size, and (primarily) the resistance in the two current paths.

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I've been cruising a couple of days and it has become apparent the domestic batteries are only being charged by the solar (1x100w), which isn't enough to run the fridge and isn't enough full stop on cloudy days like this. Now, when the engine is running the dashboard gauge reads 14v so the alternator is working and presumably charging the starter battery. I can't find any issues with the wiring so I suspect the box that sends alternator charge to the leisure batteries (what do call one of them?) is knackered.

 

I was thinking I could simply connect the starter battery to the leisure batteries to make a single battery bank. Is this a good idea? What are the potential problems?

 

Ideally you'd want to put a reasonably decent multimeter directly across the domestic batt terminals when engine is running, the voltage should steadily rise then settle at 14.4V

 

Without that info and more I'd hazard a guess that it may be failing batts, due to poor connections and/or insufficient charge voltage or charging time etc, and on sunny days the solar just masks it.

 

For 24/7 fridge use it sounds like some sort of batt monitoring would be useful, some feedback about available budget (£2? £200?) and typical boat use should get some good recommendations. Also 100W of solar alone may be a bit minimal for a 12V fridge, an extra 100W panel could help for mixed or lightly overcast days.

 

Meanwhile there's few tips on batt use and charging in this thread, but it needs a decent voltmeter and some sort of ammeter at least:

 

http://www.canalworld.net/forums/index.php?showtopic=76337#entry1576023

 

cheers, Pete.

~smpt~

Edited by smileypete
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I find my 100W solar panel is good for topping up the batteries when I leave the boat for 3 or 4 days a week, but not much use in terms of keeping up with daily useage. Looks like I use about 90Ah per day, with fridge, laptop and tablets, TV and lighting, the users.

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