Everything that uses batteries slows down as the batteries wear down. How bad is this in electric cars ?
the discharge curve of rechargeables like nickel-metal hydride (NiMH) and lithium-ion (LiIon) are pretty flat, they stay close to rated voltage until almost completely discharged. This is unlike alkalines, whose discharge curve is much more of a slope; their voltage continually drops as you discharge the cell. edited to add: a good example would be cordless drills; if you’ve ever run one flat you might have noticed this. they’ll run at full speed until the battery is nearly flat, then once it starts slowing down it only has a couple of minutes of run-time left.
also, electric vehicles generally have pretty sophisticated battery management. I can’t speak for Tesla, but hybrids like the Prius and Volt only charge the battery to about 70% total capacity, and don’t discharge it below 30%. This maximizes the longevity of the battery.
Well, my PC runs at exactly the same speed until its batteries are flat. (It’s easy to think of many other examples.)
Essentially all modern electric cars have sophisticated battery management, so the car performs as it should throughout a charge cycle, and as the batteries age over time. The big issue is range, which does indeed grow shorter - at around 1 mile per mile in the first case and slowly in the second.
No, this only happens with primitive devices that don’t regulate the battery output, and therefore the performance is limited by the battery itself. If a light bulb is connected directly to a battery, for example, the bulb will get dimmer as the battery is used up. But add a regulator, and the bulb will stay at the same brightness until it suddenly goes out.
Probably not what stosh was thinking of but just before the Nissan Leaf totally depletes the battery it goes into “Turtle Mode” to get the most mileage out of the remaining electrons. In Turtle Mode, the Leaf is restricted to about 30 mph.
Thanks for all the answers. I used to work at a place where we had an electric fork lift. we plugged it in when ever we were not using it and I always wondered what would happen if it ran low.
those usually use lead-acid batteries which do double-duty as a counterweight. Lead-acids slowly drop voltage during discharge due to lead sulfate building up on the plates. The faster you discharge them, the steeper the discharge curve.
In the cold storage plant where my dad worked the old fork lifts, lead acid batteries, ran normal until the battery depleted considerable. Speed control was by resistors and a governor. As long as battery voltage was above the minims they operated normal. When they began to slow down the operator knew he had to plug in soon. This was in the late 60’s. Then they got a new fork lift, speed control was by transistors. One operator found out the hard way to keep an eye on the voltage gage. When the battery hit the minimum voltage the fork lift died, stopped moving. Problem was forklift was on the ground moving bins around and the charging station was on the dock.
It shouldn’t do that unless it’s broken. Modern laptops should all dynamically increase/decrease CPU speed several hundred times a second in order to maximize battery power.
But this should not gradually decline as the battery discharges - right?
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It shouldn’t do that unless it’s broken. Modern laptops should all dynamically increase/decrease CPU speed several hundred times a second in order to maximize battery power./QUOTE]
Xema probably needs perceived speed. Things like timer coalescing help manage times when the CPU should be fast (high energy) and not, too.
This. Good LED flashlights incorporate circuitry that provides a constant current supply to the LED, even as the battery voltage varies considerably. The result is a flashlight that maintains constant brightness until very close to the end of the battery’s life.
Right. A computer should perform the same with a full battery as with a nearly empty one.
Unless you’ve set up your computer to go into a low-power mode when the battery is low. I can’t remember if Windows has that ability, but some laptops come with power management software to do this (e.g. Lenovo).
And other types of devices are often programmed to do this. Some regulated LED flashlights go to a reduced brightness when the battery is low, to stretch the run time and to serve as a low-battery warning.
it’s irrelevant. even when the power source is a battery, the actual electronics inside the laptop are powered through a regulated DC-DC power supply. as long as the battery still has sufficient power your laptop will run the same. once the battery is near flat, you’ll get a warning and shortly after the laptop will power down.
Basically this. I think some laptops (and especially phones) do throttle the cpu down because the battery is low, but that’s got nothing to do with the battery voltage. The voltage regulation circuitry gives the electronics an almost flat voltage up until it can’t, then it just forces a shutdown.
My point was that computers are one (of many) exceptions to the OP’s assertion that “Everything that uses batteries slows down as the batteries wear down.”
Yes, some things may change (e.g. warnings, powersave modes). But the basic scheme is to keep operating normally as long as possible, not to gradually slow down.
My hearing aid batteries are like that. They work great for three days, then I get a warning tone and ten minutes later they die.
With a steady purely resistive load you will see the raw performance of the battery. They vary in the curve of discharge. Different devices respond differently to discharge. Some will die fast with just a slight change of voltage. A lot of devices have a convertor system between the battery and load. As the battery changes voltage produced, the convertor varies the current drawn. It draws more current, converts it to voltage. This makes the output seem to be steady until a very steep drop off. Convertors can be designed to modulate current and or voltage. Changing one to the other as needed.