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Monday, 3 January 2011
In 2010 our RCR engineers reported an increase in the number of battery related issues experienced by our members. A number of these resulted in the costly replacement of the full battery bank, and a small number in catastrophic explosions of the batteries resulting in acid contamination and expensive clean up operations, as well as battery replacements with the potential for severe injury to individuals extremely high.
Following one incident where it was identified that a new alternator was charging at a continuous steady rate of 14.8V (normally 14.4V). On checking with the manufacturer of the alternator they confirmed that this was the correct charging voltage, and that this was for two reasons 1) a higher charging voltage was more efficient way of charging batteries and 2) the new Calcium batteries (introduced in cars) can accept a higher charge voltage without damage. They also confirmed that the new charging voltage was likely to be the ‘norm’ for all future alternators. RCR decided to investigate this new charging voltage and look in to the issues this could cause
After discussions with ADVERC, who also reported coming across an increasing number of issues, and after speaking with a number of battery manufacturers and engine suppliers we believe that there should now be new guidelines issued on battery care. Although we strongly believe that the introduction of alternators which charge at the new higher voltage will increase the risk of battery issues, it may be that the best solution is to manage your battery life by following the advice provided in this article
Many people do not properly understand the way alternators work but the golden rule is to test maximum charging current (Amps) as soon as you start up and rev the engine in the morning. To check charging voltage you need well charged batteries so you should check the voltage after a day's cruise. So before you shut the engine down for the night; clip a multi-meter set typicalyto 20V dc for a 12v system or 200v dc for a 24 volt system (or to DC for auto ranging meters) across the batteries and rev the engine to about 1500rpm. You are looking for no more than about 14.4 to 14.5 on a 12v system or 28.8 to 29 volts on a 24 volt system.
If you have more than this you may have a problem; but first you need to check the alternator's data sheet to identify if the alternator has the new charging voltage, and also the datasheet for any external controllers fitted to the battery system.
Wet open cell batteries will stand charging at 14.8 as a maximum as long as you ensure they are kept topped up and accept you may shorten their life. The benefit of the new charging voltage is that it can push more amps through the battery, possibly giving you a faster recharge.
If you have an alternator or battery management system charging at the higher rate you MUST check your battery cells daily and top up as necessary. If you do not you will face a potentially very expensive exercise like some of our other members.
If you are worried about over charging your batteries it is worth noting that all the cells will bubble a little when on charge but if it is only one or two cells it may suggest faulty cells. However if all are bubbling and you also have a film of acid spots or white spots on the top of the batteries then this would definitely indicate that the battery is gassing excessively.
All of these subjects and more are covered on our practical hands on Boaters Electrical Course, running at locations around the country.
See our website www.rivercanalrescue.co.uk/courses
NB. Recent very cold weather has thrown up some instances of alternators with advanced controllers charging at 15 volts plus, extreme cold may cause some charging systems to apparently overcharge so simply keep a watching brief until the temperature rises to gauge if this is an issue or not.