Batteries knackered?

[jac]

We have 2x 85ah leisure batteries, charged by standard alternator and by dolphin battery charger when on shore power (boat usually left connected)

RCD on shore power has failed meaning we're down to alternator only for next few days, boat left for about 3 weeks before this trip so batteries shouldn't be too flat.

Circa 45 mins of engine running whilst leaving the hamble then tacking down the Solent yesterday - about 2 hours later the instruments failed - immediately rectified when the engine start battery was switched on and engine started.

Motor sailed for about an hour, moored up and ran engine for a while - total about 2 hours. This morning noticed low voltage. Ran for another hour , voltage according to the instruments showing at 12.5 after the engine stopped - 5 hours later and it's showing 11.1. Only load during that time has been the fridge.

To my mind that suggests junk them and replace (capacity is too small anyway) but could do without chucking out batteries if I'm overlooking something. Any thoughts?

 

[Rigger Mortice]

Switch the fridge off, leave it off, and try again. A battery at 12.5 volts is far from being fully charged. It's not surprising if, after 5 hours with the fridge on, it has gone down to 11.1 volts.

Can't explain why it went flat as you left the Hamble. The batteries may be on their way out. There may be another cause. It's worth at least a quick check to make sure that the battery terminals are not loose.

Unless you really want to spend £150 it's worth trying again.

 

[halcyon]

Circa 45 mins of engine running whilst leaving the hamble then tacking down the Solent yesterday - about 2 hours later the instruments failed - immediately rectified when the engine start battery was switched on and engine started.

Motor sailed for about an hour, moored up and ran engine for a while - total about 2 hours. This morning noticed low voltage. Ran for another hour , voltage according to the instruments showing at 12.5 after the engine stopped - 5 hours later and it's showing 11.1. Only load during that time has been the fridge.

Surface charge, start of sulphation problems. The batteries are low, so yo give them a short charge, you get a conversion of material on the plate surface, the voltage rises and you see a not bad voltage 12.5, but you only have maybe 20% charge capacity, so you rapidly drain the battery and you see 11.1 volt.

Depends on alternator, if it is running at 13.6 volt you need to mains charge, if the alternator runs at 14.4 volt you need to charge for say 5 hours.

Ensure you charge at 50% discharge, and charge until you reach max alternator ( 14.2 - 14.4 ) voltage and charge current at battery falls to a low level, what ever the capacity that's the max you can get. If the alternator is running at 13.6 volt think about a alternator booster, but you still will need adequate charge time.

Brian

 

[jac]

Think alternator booster might be good investment. We're heading from Yarmouth to Weymouth tomorrow and with maybe a f3 if we're lucky I feel that we may be motor sailing for about 6 hours which should do it.

 

[Tomahawk]

do a simple drop test...
If the batteries are light take them to a garage... otherwise borrow a tester or get someone to come out...
you have to turn off the charger for a god three hours before testing them...

 

[Paddingtonbear]

Your batteries may well be knackered but I get the distinct impression that your engine charging regime is not adequate. Get this sorted first as even with new batteries you will get the same problems.

 

[Paddingtonbear]

I suggest that the OP and anyone else interested should look at the Smart Gauge information here http://www.smartgauge.co.uk/technical1.html. Absolutely no connection, not even a satisfied user as I have a dynamo and one battery.

 

[jac]

Your batteries may well be knackered but I get the distinct impression that your engine charging regime is not adequate. Get this sorted first as even with new batteries you will get the same problems.

Think you may well be correct. Having lost the benefit of shore power until the RCD is replaced it has highlighted how much we depended on it.

Rough calculation suggests we use 40ah per day on domestic usage - predominantly the fridge which draws 5a when operating (in warmer weather have guessed at it being on 1/4 of the time)

Under way another 3amps per hour (or more if at night or if radar left on standby) so assume 6 hours of sailing and we're up to almost 60 ah for a day sail.

Charging at present is via a 60a alternator so thinking we really need to supplement that. As i know that an hour of motoring will not charge by 60ah. Would like to be able to run the domestic side at least by solar/wind which sounds like a lot of panels!

 

[halcyon]

Charging at present is via a 60a alternator so thinking we really need to supplement that. As i know that an hour of motoring will not charge by 60ah. Would like to be able to run the domestic side at least by solar/wind.

Did you do the 6 hour motor sail to-day ?

What you have not said is how your batteries are set divided up, plus what the charging system is from the engine and what charge voltage you have at the battery.

Brian

 

[Trundlebug]

With that usage I'd say you need at least 3x 110 Ah batteries to prevent further problems.

 

[Paddingtonbear]

No batteries give out 100% of their nominal capacity. The most that you should expect is 50% and you should only use this amount in extremis as it will take an age to charge the batteries again. The max. output from your alternator is likely to only be achieved at over 3500 rpm at the alternator. My guess is that the batteries are not ever fully charged and their voltage is gradually dropping as a result. Why don't you take them off or repair the RCD and give them a serious charge up. What is the output of the charger btw? It your power survey is correct and it sounds it although you have not included lights, any heating or pumps you are very near to the 50% figure mentioned above esp. if the batteries are less than new. Have a look at the Smart gauge site I noted above. Most of it is in everyday language that anyone can understand and it might save you plenty of money.

 

[Paddingtonbear]

Agree with Trundlebug but do a proper audit first.

 

[rob2]

Is your starter battery extra to the 2 x 85ah leisure batteries? If not, then a fridge will be too much for a single battery - just about acceptable with both in circuit. As others have already hinted, the voltage immediately after charging is misleading as they hold a "surface charge" for a couple of hours. With that in mind, dropping from 12.5 to 11.1 with a load on it isn't so bad. If the battery switch was left in "both" position, then the flat one will have drawn power from the good one.

In your position, I'd suggest you whip the batteries down to the garage and have them drop tested to see what the state of charge and capacity is, then use a multi-stage charger to get them right up to snuff if they're basically sound. When they are up for replacement, go up a size to make their life easier. Worth having a separate starter battery, too. Doesn't have to big so long as it's never used for domestic services - have you seen how small the batteries in a modern car are?

Rob.

 

[jac]

Thanks for all the replies.

To answer some quick questions.

No we didn't do the 6 hour motor sail. Started the engine in Yarmouth and had no electrics. Figured it was no power and that engine would fix so hung on buoy for a while then motored back to Boatyard.

The two 85 ah leisure batteries are in the domestic bank. In addition there is an 85ah engine start battery.

Interesting re the 50% max discharge. Are you sure? I have always believed that you should never discharge BELOW 50% and that the practical limit of charge was 80% to 85%.

As for the suggestions to take batteries - have bought another smart charger which is currently charging batteries / long story re the old one but will take tis home when this trip is finished. As for repairing RCD, easier said than done. Several locations have all confirmed that direct replacements are no longer available so may have to go for an alternative!

As for testing voltages, not my day for batteries. Multimeter battery also low, bought new battery and discovered that old battery has leaked.

Re the audit, the figures are from the user manuals f all the instruments and electronic equipment on board, excluding any nav lights but with young children tend not to night sail much and at this stage happy to use engine to supplement for night sailing Also excludes the use of webasto which I should add in.

Discussing with electrician who is looking at RCD. Simple truth is the charging regime is inadequate. Will stick with the work around battery charger and shore power until RCD is fixed but longer term solution is bigger battery bank. Probably 400ah ish together with 85ah for engine start but then with wind / solar to provide around 50ah a day.

 

[William_H]

.

Motor sailed for about an hour, moored up and ran engine for a while - total about 2 hours. This morning noticed low voltage. Ran for another hour , voltage according to the instruments showing at 12.5 after the engine stopped - 5 hours later and it's showing 11.1. Only load during that time has been the fridge.

To my mind that suggests junk them and replace (capacity is too small anyway) but could do without chucking out batteries if I'm overlooking something. Any thoughts?

That fridge will in fact be the biggest current drain for most people. Possibly 5 amps and if it is turned on from warm will be continuous for some time.
Batteries when they die will either exhibit less amp hour capacity or be unable to start the engine. Either way if they are fully charged then you find capacity is down then it is time to throw em away. However as said you need to esure the charging is fully charging them. good luck olewill