I need some help to understand what I am doing with battery charging. I have a Nautilus Intelligent Battery charger from Canadian Tire which I understood should automatically stop charging when the battery is charged. It worked well the first time I used it. I select deep cycle battery at a rate of 2 amps. When I was charging once this summer it went up to over 15 volts when I un plugged the charger knowing something was wrong. Took it back to a diferent Canadian Tire store, because we were on the road and they said everything was alright. The charger does not seem to stop automaticaly but once it is in the 13 volt range. I stop it by unplugging, plug it in again and it shows fully charged and is off.
Should I be using a different rate of charging, 10 amps, 15 amps? I read somewhee where some one was trying to explain batch charging and I did not understand.
Any comments to help me get the full advantage of the charger with no harm to my battery.
It doesn't sound like there's anything wrong with your system. FWIW, The proper charging cycle should go like this.
1. Charging should begin before the battery is 50% discharged. For most 12v deep cycle wet cell batteries a reading of 12.2 volts is approximately 50% discharged. It's better to start recharging sooner rather than later in terms of battery life. A fully charged AND rested 12v battery should read 12.72 volts although I have seen some that read a bit higher. Rested means no activity (charge or discharge) for 24 hours or so.
2. The first stage is called bulk charging. The charger should put out voltage in the range of 14.1 to 14.3 volts. The amperage is not important since the battery will only absorb power at the rate which converts water and plate sulfation back into electrolyte. This rate, by the way, is called the absorption rate and it usually will be about 30% of the amp hour capacity of the battery. A 50% discharged 100 amp hour battery will, at least initially, absorb about 25 to 30 amps. This rate tapers off as the battery becomes charged. The more amps the charger can deliver (up to the battery's acceptance rate), the faster the bulk recovery stage.
3. The second stage is called absorption and the battery will be about 75% charged at this point. Typical 3 stage chargers reduce the voltage at this point to something like 13.5 to 13.7 volts. Smart chargers run this stage until the battery voltage stabilizes in this range.
4 The third stage is called float. At this point the battery is about 90 to 95% charged and the smart charger will further reduce charging voltage to something between 13.0 volts and 13.6 volts. This voltage can also be the maintenance voltage.
5. Overcharging results from voltages that boil away electrolyte. 14.3 volts (and higher) will boil away electrolyte which escapes the battery in the form of light
gasses. These gasses corrode battery terminals and often condense on cold terminals and wires. That's why grease coatings are used to prevent corrosion. It is also why batteries need to have electrolyte levels checked frequently and water added as needed. The higher the voltage the faster the fluid boils away.
Most chargers and alternator/regulator combos are designed for automotive applications. These applications are different from deep cycle applications. Deep cycle batteries are designed for long slow discharge where car batteries are designed to deliver lots of amps for a short duration. Likewise the automotive charging systems are designed to replace that power loss quickly. Most automotive regulators are set to charge at 14.3 volts for a short period of time and then switch to 13.6 volts or so for however long the engine is on. This replaces the 'surface' charge consumed in starting the engine and maintains the fully charged battery. This cycle is less than ideal for deep cycle batteries.
In theory you should follow the battery manufacturer's charging regimen. Unfortunately only the best batteries come with an owners manual. The best wet cell deep cycle batteries come from Rolls and Trojan and they cost more.. They are noticeably heavier than cheap deep cycle batteries.
You can buy three stage regulators and chargers but they tend to be expensive. The Xantrex charge regulator on my boat costs about $250. The 40 amp shore power battery charger I have now sells in the range of $200. However these appliances can be tuned to match the specs for most any battery.
Your charger may stop charging when the battery is fully charged but it may not turn off. Rather it will continue to provide a low voltage maintenance charge at 13.X volts. Check the charger's owner manual, it probably explains something like the above.
I would recommend that you buy a good digital volt meter (Radio Shack has some for as little as $15 and Harbor Freight sells one for $3 but I wouldn't vouch for it) and check the voltages periodically. The meter will come in handy for other things too.
Other types of batteries like gel cells or AGM types have different charging requirements and following the manufacturer's recommendations is even more critical with those types.
Hope this helps.