Charging - Miles per hour

[APGSDL]

This is some testing I plan to do (When I get a Sherman) but wondered if anyone had already done this or even has an idea of it.

The Sherman seems to be an all day wheel in terms of range, but if you are out doing a LONG ride and you stop for lunch and manage to plug in, what will an hour of charge do to your range?

I know it can be calculated in theory but just wondering about real world as it's not always quite as it is on paper.

Correct my maths if i'm wrong, but assuming the use of the 5amp charger and that the stated 5amps is at charge voltage and not the input mains voltage it should add around 500Wh in one hour if the battery is low enough that full charge rate is accepted for the hour.  Then lets say a riding consumption of 25Wh/mile, this would give us a 20miles per hour charge rate.

Am I any where near close with this for those that have the wheel and experience with it?

(Basically i'm bored while waiting for a Sherman to arrive!  So planning ahead for some long ride days)

[supercurio]

Haha that's a good idea to have this math in mind before going for a very long ride.

On my first long ride with the Sherman (150km) I had a two chargers: the original 5A and Begode's 3A for a grand total of 8A. I waited to be at something like 10% to stop and charge.

That made me realize that it wasn't good enough, and I has to stop a second time to extend the range. When looking at the graphs on EUC World, it appeared that I even at moderate speed the wheel was discharging the battery faster than it was charged at 8A, which meant spending longer stopped charging than riding from then on.

Following this experience I got a 2300W max charger, and typically charge at 12.5A during long range rides. It's a lot better than 8A, but it's still not that fast in terms of distance/h.

My Sherman slows down charge beyond 12.5/13A. I thought I could be charging at 14 or 15A if not looking continuously but it can't be sustained throughout.

[Chriull]

3 hours ago, APGSDL said:

assuming the use of the 5amp charger and that the stated 5amps is at charge voltage and not the input mains voltage it should add around 500Wh in one hour if the battery is low enough that full charge rate is accepted for the hour.

If one looks at a li ion  charging curve, for example in https://batteryuniversity.com/article/bu-409-charging-lithium-ion there is a constant current with rising voltage up to max voltage and then decreasing current.

So 5A x 100V = 500W is only reached once during charging, most times it's notable lower...

[APGSDL]

11 minutes ago, Chriull said:

If one looks at a li ion  charging curve, for example in https://batteryuniversity.com/article/bu-409-charging-lithium-ion there is a constant current with rising voltage up to max voltage and then decreasing current.

So 5A x 100V = 500W is only reached once during charging, most times it's notable lower...

When you say it's only reached once, what do you mean?  

As I understood it the charge current tails off as the cell voltage approaches it's charged state (maybe 80% or so) which should mean the battery pack should be able to accept full charge current until the latter stages of the charge when it tails off and then goes through it's cell balancing.  Have I got it wrong?

 

[Chriull]

14 minutes ago, APGSDL said:

When you say it's only reached once, what do you mean?  

You have full voltage and full charging current only once during charging.

[APGSDL]

5 minutes ago, Chriull said:

You have full voltage and full charging current only once during charging.

Yes, but that 'once' could be for hours though no?  That's what I was stating in my first post, that the battery was depleted enough so it could take a full rate charge for the hour.

So for example, say you stopped with the battery at 20% charge.  Surely there's more than one hour of full current charge at that state before it tails off the current for the final stages.

[agranner]

The key to understand here is the voltage and current are both variable in the charge cycle. So for the first “phase” you have max current, but less then max voltage depending on state of charge. The charger voltage follows the cell voltage. Only when max voltage is reached, current rapidly tapers off in the next “phase.” They call this Constant Current - Constant Voltage charge cycle but they could also call it Variable Voltage - Variable Current. 
Put another way, there is one “moment” when you get near max current and voltage at the same time. Before and after that moment, the actual power transfer is less then max. 
To get the most miles per charge hour, you want to stay under the greatest area of that curve. That’s why the recommendation when “destination charging” electric cars (which everyone seems to be obsessed with road trips versus daily driving) to charge from 30% to 80%. That gives you half range with the best average rate. Or near enough. YMMV

Edited May 20, 2022 by agranner

[APGSDL]

I've got a reasonable understanding of battery and charging theory, that wasn't really my question, it was more about peoples real world experience of what a short period of charge will get them in terms of added range.  Obviously if this is done with a battery already at a reasonably charged state then the returns will be minimal, but for a long day's riding where you may stop to charge briefly while resting and the battery is below 50% what sort of range boost will this offer.

Again, I don't mean the theory of it, more whether anyone has actually measured it or has a feel for it from experience.

[agranner]

In my experience with a V8S, Inmotion app states average lifetime 33Wh/mile. I don’t know how this is calculated and I know from monitoring pack voltage that my calibration is off. I assume that’s on the high side because I’m heavy (200lb plus gear), I ride the beeps in traffic, and almost always charge from about 75% SoC to full since my daily commute is only about 6-7 miles total per day. I have never tried destination charging. Remember everything is extremely variable including our “measurements” (in-app mileage, SoC, etc) so unless you tracked a lot of miles with stopwatch, GPS, etc, it would be very difficult to test in the real world. 

[Tawpie]

1 hour ago, APGSDL said:

more whether anyone has actually measured it or has a feel for it from experience.

I haven't been on a ride where I felt the need to charge in route but many of the locals charge during breaks—and plan breaks to recharge. Odd thing is, they go mostly on 'feeling' rather than measured data. This 'feels like' enough battery voltage to get me where I'm going. Or more likely… I'm ready to get back on the road, let's go. It seems in their practice, it's more about reducing range anxiety as a general idea than actually knowing there's exactly this or that much charge in the wheel.

Starting with theory should keep you from getting stranded. If you pay attention to your range at various voltage levels (don't use % SOC, it's computed and not terribly reliable), you'll learn what your approximate minimum voltage is that will assure you that you're going to make the next 25 miles. Likewise, a few charge plots of voltage over time will give you a good clue as to how long you need to plan to get from too-low to should-be-ok voltage. Charging is pretty consistent (temperature is a variable, but probably a handful of minutes per hour difference).

Edited May 20, 2022 by Tawpie

[agranner]

I may be beating a dead horse, but this just occurred to me: 
If you "feel" like the wheel is getting "weak" (probably lots of voltage sag) then already your charging rate is going to be slow. You've "fallen off the voltage curve". I can "feel" this difference at about 72V standing still on my V8S. Stop before you reach this point, and you will get the best charging rate (probably). If you wait until it's about to die/tilt you off, your charge is going to be pretty slow for a while. Again, no first-hand experience here, just thoughts.