Being new to marine modeling , I am concerned about correctly charging my battery used in the model and the TX.
I have a 7.5 SLA 12v battery in my model which I am charging the night before I go to the Clubs Lake on Sunday am.
my charger states that it is a dual charger [6v/12v] and says the following:-sec:6v/12v 500mA6va[max]
Is this the correct thing to do as when I have charged it overnight it reads 14v on my multimeter at 7am ? ?
I have been told that the 12v rating on a battery is its bottom rate and the amount above this is the "Charge"
taken up by the battery during charging ....is this correct?
In my TX which is a DX6i I use a set of four 2900mAh rechargeable AA batteries which display a graphic charging rate and turn off when fully charged
So far I have had no problems .....but am I doing it correctly
14V is typical for a VRLA (aka SLA - though VRLA is the preferred term) as the terminal voltage off charge - typically it will relax back a bit (to maybe 13V) within an hour or so. Remember though that this is an off load voltage and the voltage output will be lower than that. 12V is the nominal battery output (in that typically the output is somewhere around 12V). The minimum output voltage is lower than that - you can typically run the things around the 10V mark if they are low.
At work we have batteries in a number of critical applications - we do not consider the battery to be critically low on charge until it hits the 9V mark under load. However the level of discharge that you can tolerate depends on the load - you can discharge further on high loads than light one - if the rating of the battery is 7AH and you only draw 0.7A average under load, you can only safely discharge to 11V
The recommendations from Yuasa for discharge are:
Discharge less than 0.1C or intermittent discharge - Min cell voltage = 1.75V
Discharge less than 0.17C - Min cell voltage = 1.7V
Discharge less than 0.26C - Min cell voltage = 1.67V
Discharge greater than 3C - Min cell voltage = 1.3V
Note C is the 1 hour current rating for the battery - a 7AH batter has a C value of 7A (easy innit). For a 6V battery multiply the cell voltage by 3 to get the on load battery terminal voltage, for a 12V battery multiply by 6. For most applications this give the minimum on-load safe terminal voltage for a 12V battery of 10.5V. Any lower than that and you risk damage to the battery.
For charging, you are spot on with the charging current. 500mA is the charging current - the figure of 6VA refers to the nominal power consumption of the charger. It is the nominal Watt power draw of the units (though expressed in VA for reasons too complicated to go into here). The safe constant current charge level for a battery is nominally 0.1C - so your charger is good for batteries down to 5AH. For batteries below that the charge rate is a little high and you should be looking at a smart charger that switches over from constant current to constant voltage charging) to prevent overcharging (I suspect all but the very cheapest are). The charge time depends on the capacity of the battery and the level of discharge. If the battery on-load voltage is 11V you can assume 100% discharge - you will need the full charge time. If it 12.3V then you will need a third of that time. However with the charger you have there is no problem leaving the battery on charge for longer.
Hope that has made it as clear as mud
To trickle charge