Optimising on-the-go charging

[ir_fuel]

We have some hyper milers here that take a (fast) charger with them on their trips to charge when taking a break. Now the question is: how can we optimise charge time?

As most of us know, a charger pumps out max current until the charged battery reaches a certain %, then the current decreases until we reach the point where it becomes really really low at constant voltage to get the battery perfectly charged. There is a point, I think, whereby so much time is lost waiting for those last % that we might as well just start riding a lot earlier because the waiting time is disproportionate to the extra range gained from, guessing here, 5 extra percents of charge.

 

Has anyone got numbers on this and a way to calculate what the optimum charge would be (I presume we can simply determine this by looking at the per cell battery voltage) to waste as little time as possible charging? Charge it to 75%? 80%? 90%?

 

[meepmeepmayer]

I believe it isn't that complicated.

The optimum charge is reached when the current starts dropping (when that is depends on the charger). Because you can't charge faster than the max current (limitation of the charger), but you certainly can charge slower (with a reduced current). So time charging with a lower current could be used more effectively by charging with the full current.

So look at what percentage your fast charger starts dropping the current and that's where you should stop charging, ride more, and later charge with full current instead.

[Mono]

18 hours ago, ir_fuel said:

Has anyone got numbers on this and a way to calculate what the optimum charge would be (I presume we can simply determine this by looking at the per cell battery voltage) to waste as little time as possible charging?

This is not a well-posed question, AFAICS. Why would you want stop charging anyways unless you want to start riding? Now if you want to start riding as soon as possible you need to charge just enough to reach the next destination. Otherwise, as long as the maximal charge current is flowing, you don't lose any time given you will have to recharge again or drive the battery empty (otherwise you lost time with an unnecessary charge). Finally, waiting time per Wh is inverse proportional to the current which you can measure with the charge doctor.