some of the stop-start systems are kind of like that. Mazda is working on such a system, but I don’t know how close it is to production.
Thought experiment: take a car with a manual transmission. Put in a new, completely dead (but still chargeable battery). Fill the gas tank. Push start the car, run it until the battery fully charges, then turn the key to Accessory mode. Where did the power that is running the radio come from? The sun -> Proterozoic phytoplankton -> [time passes] -> the engine -> the alternator -> the battery. Musicat and Crafter_Man are just choosing to stop at different places in the chain.
No, the battery is used as a big battery.
Not totally correct. Alternator-equipped cars bump-start (push or slope) just fine. Never tried a hand-crank in a long time, but the principle is the same. You don’t need a big battery just to do this.
Doesn’t have to be a thought experiment. The alternator will not charge a fully dead battery (0V) and as I said before there has to be energy in the field of the alternator for it to generate electricity. Unlike a DC generator there are not permanent magnets in an alternator so until you supply electricity to excite the field which creates a magnetic field it does not generate any electricity.
Without a battery you’d have no key remotes for doors or starting either.
Yeah, what Rick said. If you’ve got a completely flat battery, the car isn’t going to start. There’s no power to the PCM. So, no fuel, no spark.
It’s true that you can’t roll start a car with an alternator and a dead battery, but it has to be well and truly dead. I’ve been able to roll start alternator-equipped vehicles with batteries that were so dead that the warning lights on the dash wouldn’t come on, but there was still enough juice to run the alternator (and then eventually the ECM and fuel pump after it rolled for a bit). You would only need a tiny battery for a roll start only car.
I am not convinced the battery is so heavy that eliminating it is that worthwhile a task if the only reason you are doing it is for weight saving. There are a lot of other areas you could save weight in more easily without having to rethink such a major part of how a car works.
If you look at the figures for Jaguar since they started to use All-Aluminium construction there body shells like for like are said to be 300 lbs. lighter than a steel body shell. Now that is a weight saving worth making. Losing 30 lbs of battery weight is Ok but as can be seen if you are really serious about weight loss there are much better ways to go about it. When you are talking about just 30 lbs then how much the driver weights is going to be just as big a factor as the battery weight.
Technically, I think you are correct, But that’s because you carefully placed the words “ultimately” and “basically”.
Yes, all of the electrical energy ultimately comes from the alternator, because the alternator charges the battery. So the electrical energy which the lights and radio and doorlocks receive directly from the battery, does ultimately come from the alternator.
And yes, you are also correct that the battery is basically used as a big capacitor. It holds the charge from the alternator, and distributes a nice even flow to the lights and radio and doorlocks. Would you really prefer the radio to be connected directly to the alternator, so that while you are driving the volume will keep getting louder and softer and louder and softer?
A really cost-effective way to save the same amount as the battery weighs would be for the average American driver, such as myself, to lose that much weight.
I think PCMs are spec’ed to be able to operate down to like 9.5 volts.
it doesn’t work that way.
The battery also keeps system settings and memory alive during periods of vehicle inactivity. I’d hate to have to reset my radio, clock, not to mention the Bluetooth data each time I started the car.
The main purpose of the 12v battery in a Prius is to keep the computer alive (I don’t remeber if it also is used for lighting), the gas engine is started by the main battery pack (at a much higher RPM than conventional cars)
Brian
Battery as source vs. alternator as source:
They are connected in parallel folks. Exactly like a municipal water system with a well feeding a distribution network and a big storage tank at a high point. When the engine is turning at decent speed, the alternator output current supplies the loads without first charging the battery. Only a minimal ripple current is first put in the battery, then supplied to the load.
It is much better to connect large steady loads (like an RV charging connection not a winch) at the alternator, because on modern vehicles, the voltage regulator is inside the alternator, and thus regulates the voltage at the alternator terminal, not the battery. If connected at the battery, the load current causes a voltage drop in the wire from the alternator output to the battery, lowering the battery charging voltage, which will reduce available capacity, increase charging time, Nd may shorten life of battery.
When loads are connected at the alternator terminal, the load current never flows through the charging line, so there is no voltage drop due to load, so the battery can charge to the full alternator output voltage.
Note that charging voltage is fairly critical for a lead acid battery. 100mV drop would be about all you would design for, and 500mV would cause trouble.
Well if you insist on ultimately and basically then I would argue that the electricity comes from the dead dinosaures we pour into our tank. After all the alternator does in convert mechanical energy RO electrical energy.
I’m not mechanically minded and I’m car-blind (I can’t tell different makes and models apart) so I expect chiming in here is a blunder of epic proportions, but here goes anyway…
When I go out to my car, I use a remote to unlock the doors and the interior light comes on automatically. The clock is still running and doesn’t need to be reset. I open the glove box or the boot (trunk) and the lights in both come on. With my key in the ignition I turn on the battery (without starting the engine) and my radio starts, and my heater/fan (but not the a/c) works. When I turn my car off, the interior light comes on again for a minute, and I’m able to put my electric window back up.
How many of these fuctions would I lose in a batteryless car?
I would venture to guess that if some automaker were to come out with a “battery-less” car, the modules themselves would have a small backup battery to make sure they retain settings.
Sure, why have a single point of failure when you can have 15 or 20? 