Super-fast EVCPs?

Jon Steward:

Lithium batteries tech is very young. Lead Acid chemistry gives 1.2V per cell and requires smart conditioning to stop early death from over and under charging.

 

At the risk of appearing a bit of a nit pick, not quite so.


NiCd (nickel Cadmium) and NiMh (Nickel Metal hydride) are the ones that are more like 1.2V per cell, (oh and NiFe (Nickel Iron) but there will not be many of those left ,except perhaps on very old milk floats)

All batteries of these families have alkaline electrolytes.

These can all be constant current charged at a rate of C/10 or less, as once fully charged, the water electrolyses to hydrogen and oxygen, but the nickel catalyses their recombination back to water, just making the cell warm, so a few 100% overcharge at low current rate is not usually an issue, nor is leaving flat for a few weeks. The problem is that they are quite heavy for a given capacity. The NiCd was Invented in the 1890s,  various forms these have been around commercially since between the wars, but modern 'chip fabrication' methods now allow plates to be thinner and textured to give more area, so that capacity per cell size is about 3 times what it was in 1970. NiMh have largely driven out NiCd from common use in the last 25 years or so.


Lead Acid is sulphuric acid based and manages about 2-2.3 volts per cell. The original  wet cell concept is about 150 years old, but the modern compact ones use lead coated plates made of other things, and may have the acid in a gel or glass-fibre mat to allow it two work when not upright. Lead -acid cells must not be let to go flat, or the plates dissolve ('sulphation') and there is no cure for that. Sealed cells must be charged up to a voltage limit, and then the current cut back, or they outgas, and can blow up. Open cells may be allowed to outgas, but then you need to add distilled water to compensate. At one time all garages had a hygrometer to measure the acid strength to see how much water to add.. Now most are sealed.


Various Lithium based batteries at 3.5 to 4.2 V per cell have been around since the 1980s appearing first in a military setting, but have only really come out commercially in the last 20-25 years for phones  (where 3V CMOS allows a 'one cell' design) and laptops where sticks of 3 cells in series to give 10-12V or 4 cells for 12.5-16V  are the popular configurations.


The modern ones do not have exposed lithium inside, and the electrolyte is not a liquid but a flexible and conductive polymer, so the fire risk is not as high as the early metal plate ones (though the polymer burns nicely, it does not self ignite.).

Like lead acid they must not be allowed to go flat - falling below 2,5V off load is usually fatal, nor overcharged, so a mix of voltage limited and current limited charging is needed, with the limits being cell temperature dependant. Modern electronics can handle this surprisingly well,and if the cells are only charged to 4.1V not 4.2, and not run fully flat or over charged, you may look forward to a 10 year life or many thousands of charge cycles which ever occurs first. (for best results,  series sticks need a 'charge balancer' to leak charge from whichever cell reaches 4.2V first, so charging can continue for the other cells without over-charging that one - making the 10 cell stacks used in electric bikes quite a thing, as connections are needed to monitor each cell in the stack. Quite often this is the same chip that locks the battery off if any cell gets to the lower voltage limit, or the total charging voltage is too high.)


M.




 

 

Jon Steward:

Lithium batteries tech is very young. Lead Acid chemistry gives 1.2V per cell and requires smart conditioning to stop early death from over and under charging.

 

At the risk of appearing a bit of a nit pick, not quite so.


NiCd (nickel Cadmium) and NiMh (Nickel Metal hydride) are the ones that are more like 1.2V per cell, (oh and NiFe (Nickel Iron) but there will not be many of those left ,except perhaps on very old milk floats)

All batteries of these families have alkaline electrolytes.

These can all be constant current charged at a rate of C/10 or less, as once fully charged, the water electrolyses to hydrogen and oxygen, but the nickel catalyses their recombination back to water, just making the cell warm, so a few 100% overcharge at low current rate is not usually an issue, nor is leaving flat for a few weeks. The problem is that they are quite heavy for a given capacity. The NiCd was Invented in the 1890s,  various forms these have been around commercially since between the wars, but modern 'chip fabrication' methods now allow plates to be thinner and textured to give more area, so that capacity per cell size is about 3 times what it was in 1970. NiMh have largely driven out NiCd from common use in the last 25 years or so.


Lead Acid is sulphuric acid based and manages about 2-2.3 volts per cell. The original  wet cell concept is about 150 years old, but the modern compact ones use lead coated plates made of other things, and may have the acid in a gel or glass-fibre mat to allow it two work when not upright. Lead -acid cells must not be let to go flat, or the plates dissolve ('sulphation') and there is no cure for that. Sealed cells must be charged up to a voltage limit, and then the current cut back, or they outgas, and can blow up. Open cells may be allowed to outgas, but then you need to add distilled water to compensate. At one time all garages had a hygrometer to measure the acid strength to see how much water to add.. Now most are sealed.


Various Lithium based batteries at 3.5 to 4.2 V per cell have been around since the 1980s appearing first in a military setting, but have only really come out commercially in the last 20-25 years for phones  (where 3V CMOS allows a 'one cell' design) and laptops where sticks of 3 cells in series to give 10-12V or 4 cells for 12.5-16V  are the popular configurations.


The modern ones do not have exposed lithium inside, and the electrolyte is not a liquid but a flexible and conductive polymer, so the fire risk is not as high as the early metal plate ones (though the polymer burns nicely, it does not self ignite.).

Like lead acid they must not be allowed to go flat - falling below 2,5V off load is usually fatal, nor overcharged, so a mix of voltage limited and current limited charging is needed, with the limits being cell temperature dependant. Modern electronics can handle this surprisingly well,and if the cells are only charged to 4.1V not 4.2, and not run fully flat or over charged, you may look forward to a 10 year life or many thousands of charge cycles which ever occurs first. (for best results,  series sticks need a 'charge balancer' to leak charge from whichever cell reaches 4.2V first, so charging can continue for the other cells without over-charging that one - making the 10 cell stacks used in electric bikes quite a thing, as connections are needed to monitor each cell in the stack. Quite often this is the same chip that locks the battery off if any cell gets to the lower voltage limit, or the total charging voltage is too high.)


M.