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grenchild
grenchild

Posted: Mon Sep 09, 2013 1:56pm

Post Subject: Battery Power

Hi Tony, I have just read your article about batteries, but I still have a question, You will probable think this is a stupid question but i do not understand battery power, I have a bank of 3 110AH batteries feeding my Boat with a charger connected from a shoreline whilst in the marina which keeps them fully charged, when away from the marine last week my batteries lasted for 14hrs before they dropped to 10V on the gauge, given in my opinion i was not using many Amps, this didnt seem correct, can you please tell me how the 110ah is calculated and at what voltage would your battery be at, when 50% discharged as recommended, they were at 13.8V when I shut the engine down for the day

Tony-B
Tony-B

Posted: Mon Sep 09, 2013 4:55pm

Post Subject: Battery Power

The first thing one has to accept when dealing with batteries is that the apparent maths and what seems obvious does not usually work. When your batteries were first made they could store enough electricity in each of them to deliver 5.5 amps for 20 hours. however they would then be so discharged that doing it regularly would wreck them. That 20 hours is an industry standard for testing the capacity of batteries. So 5.5 amps delivered over 20 hours = 5.5 x 20 = 110 Amp Hours. In theory one battery should be able to deliver 220 amps for half an hour, 100 amps for one hour, 55 amps for 2 hours and 1 amp for 110 hours. Note the IN THEORY! In reality that is not the case because a battery subject to long, low discharges will deliver more Amp hours (Ah) than theory says it should while high discharges cause it to deliver less but its the only thing we have to work on and unless you are into large inverters (high discharges) the it is near enough. So, when first made, your bank could supply 330 Ah in any combination of amps and hours as long as multiplying the time by the amps came to 330. Note the "when made" statement. From that time on they will gradually lose capacity because despite what the charger may be telling you it is almost certain they are not fully charged but only nearly fully charged. Things are worse when you go out cruising because despite what is claimed by some "add on" vendors you can only rely on your batteries being 80% fully charged buy the alternator. To get them fully charged would probably well over 12 hours - and thats with running every day. When a battery is left in anything other than 100% fully charged a chemical reaction in the cells produces an ever hardening form of lead sulphate and this gradually reduces the batteries capacity so over time the number of Ah a battery can store gradually diminishes. The other thing that is often overlooked is that batteries have a finite number of discharge- charge cycles and once exceeded other problems occur like internal cell short circuits. The cyclic life can be anything from maybe 200 cycles to over 15,000 depending upon the battery cost and type. Most boaters use batteries with a cyclic life in the low hundreds, hence the only discharge to 50% advice (it kind of doubles the cyclic life). Exceeding this a few times will not noticeably reduce the battery life, but doing it often will. The deeper the over-discharge the worse it is. My suspicion is that either you have lost a lot of capacity to sulphation or one or more cells are shorting out and discharging the rest. If when alternator charging the charging current drops much faster than it used to the problem is probably sulphation (the remaining capacity reaches fully charged faster because there is less chemical to convert in the batteries). If the charging current stays higher for longer it is probably a faulty cells. If your charger does Adaptive Charging it is probably best if you turn it off. In the past this has been shown to go to float charge long before it should, leaving the batteries only partially charged. You ask about voltage but again any values I give you are likely to confuse. This is because they apply to rested batteries that have been off charge and not used for several hours, preferably over night. However if you put a modest load of a few amps on them, for maybe 15 minutes and the take a reading with no load it will give you some idea. I bet your 13.8volts dropped very fas to about 12.7ish and the dropped far more slowly. On a rested battery 12.7 to 12.8 volts = fully charged. 12.5 consider half charged (actually its 3/4 charged but work to the 50% maximum discharge rule), 12.2 to 12.3 = fully discharged (actually 50% charged). If you have wet open cell batteries a hydrometer is a better instrument because no resting is involved if the batteries are cool. If you go onto my website (Tb-Training.co.uk and look in the maintenance notes you will find examples of how to carry out a power audit and charging calculations for your own boat, used in the way you use it. That should give you a better idea about what is going on. If this is not clear enough please come back. Tony Brooks

grenchild
grenchild

Posted: Mon Sep 09, 2013 8:16pm

Post Subject: Battery Power

Many thanks for your comprehnsive reply, I now understand a lot more, and as I thought I have got some faulty Batteries,as they are over 6 years old I will replace the bank and then get the old ones tested and if any are still good I will have a reserve. Many thanks

Tony-B
Tony-B

Posted: Tue Sep 10, 2013 8:08am

Post Subject: Battery Power

By all means get them tested but at six years old I very much doubt storing any as spares would be worthwhile. They will simply deteriorate further. My guess is that they all will have ends that have swollen outwards. This is an indication of bad sulphation. Unless the tester is a very expensive and sophisticated electronic tester it needs to be matched to your batteries and far too many are not so the reading is far from conclusive. Tony Brooks

Tina5271
Tina5271

Posted: Tue Sep 10, 2013 11:25am

Post Subject: Battery Power

Hi this is a question about batteries....I'm new to boating life and when I went away on holiday my boat was getting some work completed on it and when it was placed back into its mooring it was not hooked up to the electricity. This meant the batterys drained and I came back to a boat with no power! Not pleased!! When I moved the boat on starting the engine it had a continuous beeping noise for approximately 5mins. Also now the invertor is now beeping as if it is not enough charge but shows the batteries on float, can someone advise on what I need to do? Should I run the engine for a while to charge the system back up.

Tony-B
Tony-B

Posted: Tue Sep 10, 2013 11:57am

Post Subject: Battery Power

Ideally this should have been a new question to save confusing our readers. Also I can only see the original question while I write your replay making in much harder. First of all it is easy to be wise after the event but what you say about it being not hooked up suggest one of two things to me. Either you went away and left some electrical items running or you turned everything off (including the master switch(es) but your batteries are faulty. Read my reply above, I suspect a possible short circuit in a cell. There is not enough information in your question to formulate a reliable reply. For instance inverters are not chargers so can not indicate being in float mode. However a combi-inverter is both so it can. How long were you away from the boat? Please confirm what you are talking about. Next I need to know how long you ran the engine for. I suspect the beeping was a signal to show the alternator had not energised but it should have done so as soon as you gave the engine a fair rev. Did you wait 5 minutes before revving the engine? I also notice you give no indication on battery age, type, alternator charging voltage over time and alternator charging current (amps). The same applies to your battery charger. Is this a single alternator boat with charge splitting or a twin alternator one? If its the former then there is a charge splitter involved. Now I know these are technical questions that you may find hard to answer but the boat survey and its documentation should help. based on what you say I fear your batteries were failing long before this incident but that fact was hidden by always being on shore power. The incident was the last straw that made it obvious. An inverter beeping usually indicates that the voltage AT THE INVERTER'S 12V TERMINALS is too low. This should not be the case if the charger has gone into float mode so it may indicate a wiring or master switch fault. Did this work you have done include anything electrical? if so what was it? To save confusing this thread please email any reply to Tony@TB-Training.co.uk because this may require several emails to sort out. I will then post the result back here on the forum. Tony Brooks

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