Is it a problem if batteries go flat?

Richard10002

Richard10002

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Disconnected shorepower when I came home on 25th April, (concern about galvanic corrosion). Turned batteries off at main switch, auto bilge pump works as connected directly to batteries.

Domestic batteries use 0.4A even when switched off, according to Sterling Battery monitor.

At 9.6Ah per day, 2 x 110Ah batteries will be flat by 18 May, or before - not planning to return till 22 May.

Do I need to get out there to switch on the charger/run the engine, or can I just charge them up when I get there? Could probably go on Sunday.

nobody has a key to get into the boat.
 
When I isolate our batteries,everying is turned off, our sterling battery monitor. This does mean that the amphours used counter on the monitor resets to zero, but I prefer to know that the only thing draining the batteries is themselves.

When the batteries are turned on the Sterling monitor persistently shows 100 mA or so discharge, even when I know by measuring with an AVO that the discharge is zero. I accept that as within the accuracy of the Sterling device.

Having said all that, 400 mA is a lot more! Is it possible for you to check the accuracy of this figure by disconnecting the battery and putting another meter in line with the lead?

If there really is this discharge going somewhere and you do leave the boat long enough to drain the batteries, then you will kill them. Very few lead acid arrangements of wet or gell type will survive being completely discharged. Furthermore, why arrive at the boat to 'flat batteries'?

My suggestion is, check whether the drain is real, and remove it, or isolate the batteries or you will destroy them very quickly.
 
Why not in the future add a couple of solar panels to make up for the natural discharge. I have a 5 watt solar panel directly wired to each of my batteries [I'm note electrically talented enough to do it any other way - although I do have one of those things that stop the batteries draining at night on each system]. I find this keeps them topped up even through the winter lay up.
 
As has already been said, nearly half an amp is too much for self-discharge: it's either not discharging at that rate (instrument problem) or something is still connected and taking current.

Once a battery is discharged it sulphates quickly. I would be reluctant to leave a battery completely discharged longer than overnight, and would accept that even this would have some effect on its capacity. If you left it discharged for a week it would be substantially degraded, but its hard to quantify the effect.
 
Running the battery flat once should not cause sulphation, it is repeated high discharge / low charge that causes it. But ensure that when the battery is recharged it goes upto around 14.6 volt.
When you get thare you will be able to check if it is draining .4 amp as indicated, or you wil find the batteies ok.

Brian
 
I agree with all the others too. 0.4A drain is either wrong info or wrong wiring! We had such a drain on our engine battery bank when we bought our boat and traced it to a strange lead connected to the ignition warning light presumably as an excitation feed, we disconnected it and it works fine. Also the gas alarm was taking 300mA if left on.

Personally we leave our boat on our home berth connected to shorepower and batteries on charge and we don't have a galvanic isolator. Some in our marina (and strangely all Moodys) have had corrosion problems and I heard discussion to the effect that Moody followed the EU rules as to on board wiring which contributed to the problem whereas older boats not so wired (earthed to anodes??) had no problem but might electrocute a swimmer nearby in the event of a seious earth leak - I will add that earth leak/bonding/galvanic isolators/anodes and such come into the category of alchemy and outside of my usually good understanding of electrics at 12v!
 
Richard, first thing to do is to locate the shunt (two heavy cables and two light wires) and disconnect one of the heavy cables - the one feeding the load, not the one going to the battery. This will let you check that your meter is zeroed correctly.

Assuming that you do have a genuine load of 400mA then it is possibly something like the radio/CD player or, as someone suggested, something on the engine wiring. If you are short of time you have two options (having pulled all the breakers and fuses first to see if you can isolate the load). Either you find a way to put the power into the battery or you disconnect the battery - pull the main fuse?

Now might be a good idea to fit some solar. We (and everyone we meet) find that solar is very valuable in the Med if you are anchoring. If you don't have time to install the panel(s) properly, just loop some steel cable through for security and leave them on the deck. You will need a regulator, of course, unless the panel is very small.
 
[ QUOTE ]
Running the battery flat once should not cause sulphation,

[/ QUOTE ]

Some suphation will occur as soon as it is discharged. Its a chemical reaction that occurs in discharged cells. The rate depends on a number of factors, including temperature and degree of discharge. The extent depends, in turn, on the rate and how long its left.

Discharging a cell once can and will result in suphation if it is left in that state for any length of time, particuarly if its warm.
 
0.4A is a lot when all switched off ?

As to disconnecting shore-power ... I understand that many do not want to leave connected all time - as this can ruin battery's as well if not a good "float" charge system.

My answer was to insert a timer in the mains power to the boat ... for less than a tenner - you get a means to physically control any possibility of over charging.

I know its too late for you now - but in reply to damage to battery if it goes flat - yes - generally the battery will suffer loss of charge capability. If not immediately apparent - it will be later when battery dies a premature death ...

My garden tractor battery is dead after 2 winters of neglect ... last year it was down on capacity ... but still sufficient for work. This year - no go ! The battery should have lasted 5 yrs or more ... serves me right not keeping a trickle charge on it through winter.

Now my boat on the other hand has had the timer and shore power connected ... 2 hrs charge per day .... 5 days a week ... and fed via a Maplin splitter ... so no "boost charging" - just straight short period charging at regular intervals ... Both battery's are in excellent charge state and ready to do biz ... One of them in fact is well past it's sell-by-date and still going strong.

If you must discon batterys - then it is well advised to either take home and put on charge at intervals ... or as others say - connect a solar cell or whatever to maintain ....

I'm not a Electrical expert either - just found own solution over time ...
 
I mis-read your dates, Richard. You are in the UK now? If I was in your position I would leave it alone and buy a Magpulse to take back with you - I think it is MailSpeed who are selling them for £45 and connect that on. At a discharge of only 400mA you won't have lost too much material and the only issue is sulphation which the Magpulse will deal with.

When you get back on board, just turn on the charger (I assume you'll have shore power) otherwise you will have to start the engine and charge that way. Easier and better to charge from mains, though, as it will not put all that load on your alternator belt, and will be much cheaper in diesel - kinder to the engine, too.
 
If you consistenetly run your batteries flat and leave them that way for a while, then you are gonna be in deep expensive poo poo, once in a while shouldnt do them much harm. A totally insulated small three stage battery charger with a direct connection to the shore power (isolated from boat) would keep your batteries fine and not cause galvanic corrosion.
Why are you worried about galvanic corrosion when you are away and not when you are there?
 
[ QUOTE ]
How does the Stirling monitor know about those 400mA? I don't see how it can measure "self discharge", as opposed to actual current going in/out of the batteries.

[/ QUOTE ]The "self discharge" was a misunderstanding by a previous poster. You are quite right - the Sterling monitor uses a large shunt and monitors ACTUAL current in and out of the battery. It reads out to the nearest 100mA, so when mine reads 100mA discharge, I don't worry, as I know its actually zero - its within the accuracy of the digital meter which is plus or minus one digit.

Batteries self discharge all the time, and you can't directly measure the rate. You can only infer the rate from the time it takes them to lose their charge...
 
Thanks to everyone for the input - I've booked to go back next Tuesday to Thursday, so they will probably be close to flat, (or fine if the monitor has a problem).

I'll have a closer look at the advice whilst there, and wont be leaving the shore power off again.

Why am I worried about Galvanic Corrosion when I'm away, and not when I'm there - I'm not anymore <g>

Might get the toilet and compass sorted whilst I'm there, so it wont be a waste of a trip.

Cheers

Richard
 
Arrived back at the boat to find the monitor says that 185 Amps have been used, (out of 2 x 110Ah batteries), and the voltage reading was 12.4V, which it still is after a couple of hours of charging... flickers to 12.5V occassionally. Started charging at about 12A and is now charging at 7A, (Load is probably about 2 or 3 Amps).

At this rate, should be fully charged by this time tomorrow... I guess that is the time to see what the voltage reads.

Discovered that the navtex ICS Nav6 is on 24/7. It doesnt have an on/off switch, and it isnt switched anywhere on the boat. According to the manual, it uses 300mA, which explains the drain. I'll have to add fitting a switch to my list of jobs.

All seems fine, but I'm wondering if I have actually done any lasting damage.
 
Your batteries should be fine. 12.4V is healthy. 12A? That sounds low. What size charger do you have? A pretty typical night time load in a marina, with lights, etc., is 20A to 25A and pumps add to that. Your charger ought to be able to comfortably supply the maximum load and give a good charge into the batteries, say C/10 which is, in your case, 220/10 = 22A. So by my estimation, given that our boats are of similar size, etc., your charger should be 45A minimum.

If your charger cannot supply the night time peak load then you will be giving the battery more work than necessary which will shorten battery life.
 
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