Usually, but only because a charger usually has a current limit built in. So with a cell at 3.0 V, you apply say a 20 A charger set to 4.0 V, and the charger immediately adjusts the voltage to say 3.02 V so that the current stays under 20 A. As the voltage of the cell rises, the output voltage of the charger rises, until it hits the limit you set of 4.0 V. At that point, the charger will be putting out little or no current, to maintain the cell at 4.0 V.for example if i have a lithium battery that i want to charge to 4v could i just pump 4v into the cell no matter what the voltage of the cell is. even if the cell is discharged to 3v.
It does, but the current limit on the charger does that for you automatically.or does the charge voltage need to be set at a slightly higher level then the battery voltage.
If these don't current limit, then they're not suitable for battery charging. All EV DC/DCs will have a current limit that reduces the voltage as needed to respect the current limit.Firstly I've seen a couple of people use dc/dc converters to charge cells individually and these can't adjust the voltage.
For that, you'll need some sort of current limit. Fortunately, it should be pretty easy to set up a circuit that adjusts the field voltage of the alternator to maintain about the right current into the batteries.Secondly i have been pondering the idea of putting in a permanent petrol generator, which I'll rectify to DC and then use that to charge the batteries on the go.
If you connect a power source with no current limit and there is a significant voltage difference, then uncontrolled current will flow. Lithium Iron cells do not like to be charged too fast (i.e. at too high a current), and will lose life if charged with too much current.So will a constant charge voltage damage the batteries?
The other issue is that no EV pack is a single cell; there are always cells (or groups of paralleled cells) in series. Just because the average cell voltage is say 3.8 V, does not mean that no cell is exceeding 4.0 V, and that's bad for the cell. That's what battery management systems are about.