Graham wrote:
I would bet the house that they manage the stated capacity in software at both the high and low end. When new what it displays as ‘100%’ and caps charging at will be less than 100%
There’s actually a very good reason to do this: LiFePO4 batteries will do a lot more charge cycles if not charged all the way to 100% and not discharged all the way to 0% (the difference isn’t slight either, it’s difficult to find hard numbers for this but doing some searching shows that the difference may be going from 2000 cycles to 6000-8000 cycles).
LeSving wrote:
But, I have had poor voltage in the 12V battery a couple of times. The first time I had no clue what was going on, the car was dead, nothing worked. Called help, and out of the truck came a dude with a jump starter. I said, look, that’s an electric car, and he just laughed and said, of course it is, and this jump starter will fix it. What happened was the 12V had low voltage for some reason (severe cold for instance). Everything (except the motors) run on the 12V, and when the voltage drops, nothing works, not even charging the 12V.
The same thing has happened to me. Extremely embarrasing. (But I did realise the 12V battery was at fault.)
alioth wrote:
There’s actually a very good reason to do this: LiFePO4 batteries will do a lot more charge cycles if not charged all the way to 100% and not discharged all the way to 0% (the difference isn’t slight either, it’s difficult to find hard numbers for this but doing some searching shows that the difference may be going from 2000 cycles to 6000-8000 cycles).
That’s well-known and not in question. What I’m getting at is that the software is almost certainly, over the life of the vehicle, moving the definitions of where various % points on the actual battery capacity lie in order to disguise degradation.
Graham wrote:
in order to disguise degradation.
You can just as well say that it does it to prevent degradation for as long as possible.
Airborne_Again wrote:
You can just as well say that it does it to prevent degradation for as long as possible.
It does both. Clearly the manufacturer wants to optimise the battery life, so it implements measures to ensure / encourage use within the 20%-80% band. But even then the level of unavoidable degradation remains unpalatable to the customer, so it implements further measures to disguise it.
I used to make up A123 (LiFePo) battery packs for my model helicopters. I crashed once from letting the pack discharge fully and it was startling how quickly the power output reduced. Its not at all like the gradual drop-off that you get with other types of cells. I worried about reverse biasing the weakest cell, but the battery still seems good.
Bringing this thread somewhat back to its original topic, I thought I’d mention that I went to the Paris Air Show at Le Bourget last week (and still have the sunburn).
As you walked into the main exhibition hall, there were electric drone-like things that are going to save the planet as far as the eye could see. At least half a dozen, probably more. They all look more or less the same, a helicopter-like passenger cabin and some kind of structure on top to support a bunch of rotors.
Just one of them actually flew as part of the show – the Velocopter. This one has about a dozen rotors arranged on a huge circular ring above the cabin. It looks a bit like a flying VOR (the kind that has a bunch of antennas held on a structure above the ground like SJC, not the more common bowling-pin design like SFO). In reality it can fly for 20 minutes, with another 10 minutes of reserve. The commentator was super enthusiastic about how it was going to save the planet and so on, being able to do amazing things like move injured people rapidly in a congested city. (Hmmm, I thought helicopters were pretty good at that).
Needless to say they are all waiting for the miracle battery technology that will give them useful range.
One of them is called a Joby. I hope they’re not expecting great things of the Australian market. Though maybe they could team up with VW/Audi – the Audi electric cars are called Etron, which is French for the same thing.
The show itself was interesting, but that would be off topic.
😄😀😀
johnh wrote:
In reality it can fly for 20 minutes, with another 10 minutes of reserve
johnh wrote:
Hmmm, I thought helicopters were pretty good at that
Here is a good video showing why helicopters will never go out of fashion vs multi-rotor. At least for real size aircraft, where efficiency is a major parameter.
There are electric helicopters as well, but they don’t look as “futuristic” as a multi rotor. One of the most successful military drones is the tiny Black Hornet Nano. It’s a helicopter for a reason: as small and light as possible and with as long a hovering time as possible.
One thing that really strikes me about multirotor RC drones as opposed to my electric RC helicopter (I have a fairly large one, a T-Rex 600) is that the multirotor drones really are brute forcing their way into the air. At least the electric RC helis are flying and get a decent amount of translational lift, and can even autorotate just fine (I’ve had one save when my receiver failsafed when one of the power leads started chafing through, I managed to get the heli down from about 20 feet without taking any damage although the landing was not pretty).
The noise from multirotor drones is also really annoying because of all the weird beat frequencies from all the high RPM props running at slightly different speeds, rather than one large single rotor and smaller tail rotor (which always run in sync as they are connected by gears and torque tubes). I’m pretty sure the racket these multirotors will be sufficiently unacceptable that you’re not ever going to get more of these over a city than you get helicopters. Add to that the inability to autorotate (meaning in case of a mechanical failure, the only option is a BRS and to hope the machine doesn’t land on someone) I think there’s a lot of unjustified hype about them.
