LR versus SR motor, charging speed etc

[Coulomb]

from what I read the SR has a more powerful motor, significantly so. Is it higher geared so that the motor will wear better?

My understanding is that the motor and motor controller are identical between the two models, but because the SR model has a higher voltage battery, my guess is that field weakening happens at a higher speed. The difference in peak power isn't massive, it's 13% (130 kW versus 115 kW).

So up to the field weakening point for the LR model (usually very roughly 40 mph), the two models would perform identically. Then for the next 5 mph or so, the LR model will be limiting its field excitation and hence torque (to keep the back-emf less than the battery voltage), while the SR model will still be running at full torque. By the speed that the SR model has to limit torque, it will be moving at about 13% more speed. Speed times torque equals power, hence the peak power of the SR model is 13% higher than that of the LR model. Both models will have roughly constant power beyond their field weakening points.

The reason for the difference in battery voltage is merely an accident of the cell chemistry and the way the cells pack into the battery space available.

So this won't affect the speed of the motor, including top speed (which is probably software limited anyway). So I believe that the motor bearing life will not be different between these two models.

[ Edit: added toque curve. ]
[ Edit: moved to new ZS EV topic for easier finding ]

 

[BrianG]

My understanding is that the motor and motor controller are identical between the two models, but because the SR model has a higher voltage battery, my guess is that field weakening happens at a higher speed. The difference in peak power isn't massive, it's 13% (130 kW versus 115 kW).

So up to the field weakening point for the LR model (usually very roughly 40 mph), the two models would perform identically. Then for the next 5 mph or so, the LR model will be limiting its field excitation and hence torque (to keep the back-emf less than the battery voltage), while the SR model will still be running at full torque. By the speed that the SR model has to limit torque, it will be moving at about 13% more speed. Speed times torque equals power, hence the peak power of the SR model is 13% higher than that of the LR model. Both models will have roughly constant power beyond their field weakening points.

View attachment 8778
View attachment 8782


The reason for the difference in battery voltage is merely an accident of the cell chemistry and the way the cells pack into the battery space available.

So this won't affect the speed of the motor, including top speed (which is probably software limited anyway). So I believe that the motor bearing life will not be different between these two models.

[ Edit: added toque curve. ]

Thanks for the explanation. In the case of a higher battery voltage, does that mean quicker rapid recharging? Weighing up whether to go for the LR is the speed of charging! At my age I cannot see me dashing 400 plus miles in a day any more, but 350 yes. So the SR should require a first recharge around 160 miles on motorways in fair weather. That is in line with my constitution and need for caffeine. If it will charge at 75 kW for 25 minutes to add 30 kWh I could move on to 290 miles for another break and recharge.

Given a higher voltage to recharge it ought to add more power all the way through the charging curve to 80%?

 

[Coulomb]

In the case of a higher battery voltage, does that mean quicker rapid recharging?

I think that the effect of battery voltage [ edit: on charging speed ] would be limited. I'd expect a difference only when current limited, e.g. a 50 or 75 kW charger with a connector limited to 150A. Those would be rare, I think. When not current limited, the limit would be the charger's power limit, or the limit due to battery chemistry or highest cell voltage.

I was a little surprised to find that ev-database.org lists the SR at 75kW max and 260km/h, while the LR is 94kW and 420km/h. If that's true, on a long trip you'd be spending 60% more time charging an SR than an LR.

MG ZS EV Standard Range

All details and specs of the MG ZS EV Standard Range (2021). Compare price, lease, real-world range and consumption of every electric vehicle.

ev-database.org

MG ZS EV Long Range

All details and specs of the MG ZS EV Long Range (2021). Compare price, lease, real-world range and consumption of every electric vehicle.

ev-database.org

Standard range drivers: are you finding rapid charging slow?

 

[drmcw]

Makes sense I suppose as the to 80% times on a 100 kW charger are only different by 6 minutes between SR and LR on the MG web site despite difference in capacity. Annoying thing is that the LR was touted as 76 kW max speed for ages. I imagine working for MG UK is mushroom management at its best!

 

[Whiskery]

Standard range drivers: are you finding rapid charging slow?

Not too bad at all. This was on my 1st trip from the dealer in Chorley down to Swansea where I had to make a stop in Ludlow (I didn't have to stop in Ludlow but this was a rapid on my route).