- Tue Apr 17, 2012 3:14 pm
#11636
There’s a couple of point to be made here. For a start the amperage as stated on a battery charger is its maximum rated current, and this is the current that the unit can supply in continuous use without tripping the fuse or thermal cut-out. It does not guarantee that when you connect it to a battery it will charge it at that stated current. Quite often a 4 amp charger will show only around 1-2 amps when charging a good condition battery that is only half discharged even if the battery is a decent size car battery.
Lead acid cells can take high charge rates which for car usage is a good thing as it means the alternator can pump back a high current after starting, possibly 30 amps or so, which quickly charges the battery back to 95% of it’s full charge and when the battery is nearly full, the voltage control regulator unit drops the charge rate off to a trickle charge to a few amps only.
Due to the lead acid battery having such a low internal resistance it can take a heavy fast charge and also a high current discharge with ease, which is why lead acid batteries have never really been superseded in the auto world (Always making sure the temperature is not allowed to rise more than a few degrees in either situation though). Sealed batteries and other modern types require much better control of the charge current that the Enfield electronics can't guarantee, but this is mostly to avoid overcharging and gassing rather than limit a heavy initial charge.
Personally, if your battery is a conventional wet lead acid battery I would not worry about using the 4 amp charger with it. However you must be prepared to monitor what is going on in real time and not walk away and leave it. As suggested above, the continuous safe charge rate is around 1/10 the batteries storage capacity, but that does not mean you cannot exceed 0.2 amps input to it. What does matter is that you don’t heat the battery up with the charge current as the plates easily expand and get damaged and either become open circuit or shorted.
If a battery has been very discharged and left for a while, you will often find that connecting up even an 8 amp charger will not push hardly any current through it at all as the plates have sulphated and block the flow of electricity. There are ways to overcome this though and bring the battery back to health. I won't mention these methods at this time.
On the bench or even if in the bike, continuous long term trickle charging has it’s drawbacks as if done too gently allows the acid electrolyte to stratify which is where it settles with a stronger acid (created during the charge) to lie mostly at the bottom and not mix thoroughly through out the electrolyte. To avoid this, it’s recommended to give the battery a good over charge every so often to really mix the electrolyte by the gassing off of the plates, it also helps breakdown some of the sulphation which can build up slowly over time.
In your situation, I would use the 4 amp charger but monitor the battery by looking closely at the plates through the filler holes or through the translucent shell. (don’t get acid in your eyes!). If the battery is not completely flat then 4 amps will charge a 2 amp capacity battery in less than half an hour, but it might not be completely flat or it might not charge at 4 amps either, but the likelihood is that within half an hour it will be at a point near to being fully charged. If you measure the voltage across the terminals after you remove the charging leads, a reading of nearly 14 volts will show you that it is charging nicely to its correct maximum. Once gas is seen to bubble off the electrolyte and you have a decent voltage, stop charging as it will be nearly fully charged and useable. Whatever the time, monitor the battery by feeling the case and stop charging if it begins to feel warm
So summing up, a conventional lead acid motorcycle battery can be used with a car battery charger as long as vigilance and care is also taken.
If I was buying a charger specifically for a motorcycle battery I would choose a modern “SMART†type with the more stages the better but they are proportionally more expensive the more stages they have. Some of the best have a desulphation phase which pulses a high frequency high voltage current which can break down the sulphation on the cells that often occurs.
