Tuesday, Jan 31, 2006 at 13:32
Lewjack
There is a lot of misunderstanding re
battery charging.
A
battery is charged by applying a voltage across it that is greater than it has already. The bigger the difference between the applied voltage and the original
battery voltage the greater the charge.
All basic
battery chargers (ie non-three-stage chargers) work by producing a more or less fixed voltage (typically 14.4 volts).
A 'flattish'
battery is likely to be at about 11.8 volts. Thus, when that
battery is initially connected across a fixed voltage charger, there is a difference of 14.4-11.8 volts. That is 2.6 volts - and more than enough for effective charging. In this condition, a '15-amp' charger will charge at 15 amps.
But as the
battery charges (and its voltage rises) the voltage difference decreases. By the time the
battery has reached 50% charge (which is about the lowest it should be anyway) it will have reached about 13.2 volts - and the voltage difference is now down to 14.4-13 volts = 1.2 volts. At this stage the '15-amp' charger is typically putting out about 6 amps.
By 60%, charger output is down to 4-5 amps, by 70% charging it is tapering off to an amp or two. From there on it will drop to about 1 amp. It will eventually charge the
battery and, if left connected will sooner or later boil it death.
With conventional chargers, the rated output is only realised with a close to flat
battery. Three-stage chargers work quite differently - such that a 5-amp unit may well outperform a 15-amp conventional unit (and almost always a 10 amp conventional unit).
The initial charge of a three-stage unit is at 'constant current' - that is, as the
battery charges the charging voltage automatically increases to maintain a constant voltage difference. So that whilst the charger is nominally (say) 5 amps, that 5 amps is maintained until about 80% charge.
If you routinely flatten batteries, then a 15 amp conventional charger will get them back up to 50% or so faster. But if you more typically wish to charge from (say) 50% to 95% then the 5-amp three-stage charger will beat that 15-amp unit hands down. Further it will charge that
battery more deeply and far more safely.
This is why virtually every
battery maker in the world recommends the use of high quality three-stage chargers.
I have both the
Redarc and a good brand 15-amp charger side by side and can demonstrate this effect any time.
Trust this helps
Collyn Rivers
AnswerID:
152061