Shallow cycles V full cycles.

I am having a discussion with someone over charging the Nissan leaf to 80% when you don't need the full range, or even 70% and not below 30-40% if you don't need to.

Steve Marsh from Seattle turned 100,000 miles on his Leaf a while back and has lost 20% capacity, so he would have to charge about 1,333 times to reach this based on an average 75 miles range per charge. He was using 100% or close enough.

So if you got say 1333 cycles to 80% if using 70%-40% about 60% of the battery would get you what ,3000 cycles ?

Anyway the guy I'm talking to this is saying that it wouldn't matter if he charged to 80% he would still have 80% capacity after the same mileage and 2000 cycles I'm saying he would reach the same mileage but with shallower cycles.

What do people think on this ? Sure shallow cycles make a difference but if you're going to rake up 100,000 miles and use 60% of the battery it may give you 3000 cycles but it would take 3000 cycles to do the mileage ? ( off the top of my head figures) so while you gain cycles you have to use them ?

I think this only works of you are not doing the mileage and you think, (ah sure what's the point in charging it every 2 days when it doesn't go to low battery warning for 3 days) in that sense shallow cycles will extend the life greatly.

However if you're not doing big mileage, does it really matter at all if it will take the guts of 10 years to clock up 100,000 miles ?

In Steve Marsh's situation he's buggered no matter because he's doing such high mileage and it isn't possible for him to do such shallow cycles.

It's pretty cut and dried that batteries wear out slower if you don't use 100% at the top or the bottom. But I don't think it takes as conservative a use pattern as is typical for a lead powered car.

However, don't they design the charging and low voltage cutoffs for those cars to be a pretty conservative dod anyway?

Depending on the charge cycle set up in the car, He might not gain that much more by adding more conservative dod, or taking it off the charger sooner. It might already be pretty much doing the equivalent of RC lipo from 3.7v to 4.1v. So doing even more conservative might not do all that much.

I would tell him, that when he is in the last few miles left, don't drive full speed if possible. Try to be very gentle on the battery in that last 20% of dod. That is something he can control, and going easy on the car in the last miles to home should be easy. Ease out of that stop sign, or just cruise a tad slower if on the freeway. Whatever can be done without being a real pain or a dangerous thing.

Obviously, if it was real convenient, he'd charge more often. If he's going without charging each night, then he is a fool. But if he just can't charge at work, what can you do? Go someplace after work to charge for two hours? No way.

The leaf has about 20 kwh usable out of 24.

Thing is though for the 100,000 miles if the LiMn204 has an 800 cycle life to what, 70% end of life, and charging to 70% and down to 40% increases those cycles to 2000 or even 3000 to end of life.

Does it mean that in Steve Marsh's leaf that hit 100,000 miles that by him using the 70-40% he would have to charge 3000 times anyway to make up the 100,000 miles so in effect still loosing the same 20% capacity ?

I think it only matters if you do not need the range and a charge would do you 3-4 days that it would then be wise to use the 70%-40%, because if you intend to keep it a long time it will only matter then ?

But even if you keep the car 10 years, and have only 60K miles you'll have cycled it less anyway or does it still mean that after the say, 3000, cycles you could do more than the 100,000 and have maybe 90% left ? I guess we'll never really know.

You'd have to run an expensive experiment, to really know.

Find out what each way's use pattern yields in total mileage.

If it was my car, I'd charge fully when possible. I'd not worry about undercharging it, but I would try to lessen dod as much as could be done without going to huge pain in the ass. In other words, definitely don't go, " I don't need to charge tonight". Charge at every convenient opportunity. But like you said, he's doing enough miles to have to charge every night. Best thing he can do is drive slower, and use less that way. And like I said, maybe slow down only on the return trip, when the battery is closer to empty. Cruise it slow the last 5 miles or whatever.

I think they have picked the low hanging fruit already in the charge level and the dod setting. It might not yield enough more to bother with to do more.

The way to go with EV's may be to trade them in before the battery goes anyway.

What year is Steve's Leaf ?

o00scorpion00o said:

But even if you keep the car 10 years, and have only 60K miles you'll have cycled it less anyway or does it still mean that after the say, 3000, cycles you could do more than the 100,000 and have maybe 90% left ? I guess we'll never really know.

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Surely just sitting there for ten years the calendar life will probably have dropped the capacity to 80% even with low cycles. They will figure out some nice middle ground.

dogman said:

...I would tell him, that when he is in the last few miles left, don't drive full speed if possible. Try to be very gentle on the battery in that last 20% of dod. That is something he can control, and going easy on the car in the last miles to home should be easy. Ease out of that stop sign, or just cruise a tad slower if on the freeway. Whatever can be done without being a real pain or a dangerous thing. .

Click to expand...

I believe the Leaf, like most PIEV's already has a "restriction" programmed in to limit the battery load when it nears the low charge situation.

Great, a car that goes slower as it turns toward the barn. Just the opposite of the horse. Anyone remember those, folks?

Like I was thinking, the leaf engineers already picked the low hanging fruit when they designed the battery system. Drive it, charge it when you can.