12v Sparks

[Guest]

Recently both my batteries went completely flat......it appears that the fan belt was a bit loose and hence a decent charge was not arriving at the batteries. After tightening the fan belt we got 14.4v at the batteries, however after about 6hours of charging (battery 1 only) it was still essentially flat.
Does anyone know, is it usual for batteries not to take a decent charge for a number of hours after being run completely flat? Both batteries are brand new.
I seem to remember seeing a graph that showed that the charging took ages from completely flat...maybe 6 hours of charging before any perceivable charge was accepted.
It all kinda worries me because I'm off in a few weeks time and will be at sea for a week, potentially without any means of starting the engine (it's a sailboat).

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[Guest]

if the batteries are new i suspect that you havent switched the flat battery into the charging circuit
stu

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[tony_brighton]

I suspect that from completely flat woul will need to give them a very long charge. Take them home and stick them in the garage on the car charger for 3 days.

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[LadyInBed]

That\'s what I would do as well - nm

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[andyball]

Re: That\'s what I would do as well - nm

definitely......I have often found that batterys which won't take a charge from a large charger or alternator system may yet recover much of their capacity if charged very slowly on a small home charger, say 4 Amps or less.

It could be worth trying paralleling the duff one with a good one when doing this, to keep the charge voltage quite low initially.

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[davel]

Get the batteries tested. 6 hours pumping energy from the alternator should leave them well charged and would certainly not warrant the description "essentially flat".

<hr width=100% size=1>Dave L.

 

[BrianMoffat]

Juliano,

I hate to say this but your fan belt was not just a bit loose. If it actually connected with anything, I would be amazed. You have subsequently suffered a loss of current from the batteries - so there is equipment connected to the batteries, or you have a severe electrical problem.
Your batteries are now completely flattened, will not accept charging current and you wish to go sailing.

1. Renew your membership to the RNLI
2. Go sailing - but do not expect your engine to work.
3. Buy new batteries - because you have managed to transform perfectly good new batteries into perfectly stuffed new batteries.

This hoary old story has been going on for at least 10 years that I know of.

If you completely flatten your batteries under laboratory conditions - then you have approximately 12 hours in which to connect them to a laboratory and calibrated charger and have them brought to a fully charged condition.

PS - You won't be able to do it twice

PPS - If you cannot find a local electrical engineer to test your batteries for discharge capability ( which means either a C20 test or a short duration 250A test) then you should isolate the engine starting system and proceed to connect each battery to the starter motor circuit in turn.

If you get a healthy 10 to 15 second spin on the starter - it is possible that your battery is OK .

If the starter coughs its way around - or if it groans out loud in agony - we can be fairly certain that your batteries have been well and truly ..................


regards


brian



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[BrendanS]

I've been told this story too, but my experience is different. My single battery is now 4 years old. Once last year, and twice this year it's been totally flattened, and I do mean totally. Tiny little cough from the starter, but not even turning over. (only my fault once)

Was told that alternators won't charge a flat battery unlike a dynamo, and would have to attach charger. Started it with a booster pack each time, and each time, a one or two hour run was enough to charge it sufficiently that it started the motor quite happily next day, though I wouldn't have wanted to have kept stopping and restarting until it had a good charge.

It's still starting my engine - even on those occassions when the engine needs a good turning over - and yet it still runs lights and other things overnight and starts the engine happily each time.

All this from a planing sportsboat that takes much more knocking than a yacht ever will - also supposed to be a battery killer?

A battery is only knackered when the battery decides it's knackered, and you can often abuse them much more than people believe. Maybe it's down to having a good battery in the first place.

On the other hand, I've had car batteries die on me 3 weeks after fitting from new, and replaced under warranty.

<hr width=100% size=1>Err, let me know if Depsol enters the forum, I'll go and hide

 

[andyball]

"A battery is only knackered when the battery decides it's knackered"

Too right: I don't make up stories & post them here.

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[Guest]

Dear Brian

I think you may have me mistaken for someone else......you say that this story has been going on for at least 10 years now.....this is the 1st time I've had this problem EVER.......

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[Alex_Blackwood]

Difficult to come to any conclusion without seeing your set up. However:
1. I am surprised both batteries went flat, assume you have one service and one engine start! Were you running with the switch in the "BOTH" position?
2. Did this problem arise immediately after you had installed the new batteries?
3. If so check that you have all your polarities correct:- Positives and Negatives in the correct place. Reversed polarity will destroy a battery!
4. You were getting 14.4 volts at the battery. This would be correct for a regulated voltage output from the Alternator and would seem to confirm that you don't have a short circuit. However did you have any means of measuring the charging current (AMPS). With a flat battery (Low internal resistance) this should have been quite high initially, dropping off as the battery charged and the internal resistance increased. The alternator should be capable of charging a flat battery fairly quickly!
5. You may be able to get the batteries up by charging in the garage (or with a battery charger from shore supply) for a couple of days. With completely flat batteries the charger meter (if fitted) should go almost full scale and then slowly drop back. Sometimes the charger will trip on overload with a flat battery. If you do get them to charge, check your system and make sure you don't have a fault somewhere that is drawing current when everything is switched off.
If you have a multi-meter connect it in series with the battery POSITIVE and see if any current is flowing. There may be a couple of milliamps but with everything off it should be virtually zero. Switch on your systems one at a time and see if anything is drawing more than expected. Make sure the meter is switched to the highest current reading, normally 10AMPS, and that you have the meter leads in the correct connections on the meter. DOUBLE CHECK before connecting. DO NOT LEAVE THE METER IN CIRCUIT WHEN STARTING THE ENGINE.
Tip for fault finding: - It is usually something simple. If you have touched or disconnected/reconnected something look there first.
Good luck and happy charging!

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