AFAIUI the general battery charger is a power supply with both a current and a voltage limit. Ie. if the battery is low, there is a set maximum current that it will deliver, and then as the battery voltage rises it will reach a set voltage above which the charger won't let it go.
That's the basics of a lead acid charger, and there are variations on what they do when the charged voltage is reached, depending on what the application is. Some turn off and some stay there keeping it at the top voltage.
For NiCd and NiMH the current limit with a low battery can be replaced by sensing the temperature. The charger can then supply larger currents, sometimes in pulses, up to the point at which the cells get warm. This enables a faster charge. When the top voltaqe is reached, the battery stops taking current. The charger may just maintaining this voltage or it may switch to a different mode in which it puts in a low trickle charge, either as a continuous low current or as pulses.
There are variations that look at details of the voltage behaviour when the current is pulsed to decide how much current to deliver and when the battery is charged. There is also the simple and crude method of just suppling a lowish current for a long time and let the user disconnect it after some hours, but they are not applicable here.
For Lithium, I suspect the charger is back to the earlier principle of a current limit and a voltage limit and the management system that's built into the battery controls the current and decides when it is charged.
Can anyone confirm that rough summary, or correct me please? Secondly, what are the top voltages for NiMH and for Li-Ion?
Nick
That's the basics of a lead acid charger, and there are variations on what they do when the charged voltage is reached, depending on what the application is. Some turn off and some stay there keeping it at the top voltage.
For NiCd and NiMH the current limit with a low battery can be replaced by sensing the temperature. The charger can then supply larger currents, sometimes in pulses, up to the point at which the cells get warm. This enables a faster charge. When the top voltaqe is reached, the battery stops taking current. The charger may just maintaining this voltage or it may switch to a different mode in which it puts in a low trickle charge, either as a continuous low current or as pulses.
There are variations that look at details of the voltage behaviour when the current is pulsed to decide how much current to deliver and when the battery is charged. There is also the simple and crude method of just suppling a lowish current for a long time and let the user disconnect it after some hours, but they are not applicable here.
For Lithium, I suspect the charger is back to the earlier principle of a current limit and a voltage limit and the management system that's built into the battery controls the current and decides when it is charged.
Can anyone confirm that rough summary, or correct me please? Secondly, what are the top voltages for NiMH and for Li-Ion?
Nick