114

You're asking about the technical tradeoffs surrounding the selection of a traction motor for an electric vehicle application. Describing the full design tradespace is far beyond what can reasonably be summarized here, but I'll outline the prominent design tradeoffs for such an application. Because the amount of energy that can be stored chemically (i.e. in ...


90

Relays are much more stable temperature-wise: a sealed relay has essentially the same characteristics at -30°C and +70°C, both temperatures being common for cars. A transistor works quite differently at -30°C and +70°C, so the schematic has to be designed to account for those variations. I once worked on a product with temperature range starting at -55°C, ...


77

You'd be surprised. This is actually topic of ongoing research, and of several PhD dissertations. The question which radar waveforms and algorithms can be used to mitigate interference is a long-fought over one; in essence, however, this breaks down to the same problem that any ad-hoc communication system has. Different systems solve that differently; ...


71

So, obvious answer first: why do batteries still weigh 20kg? Because they're still the same lead-acid batteries. Simple as that. No other technology came near the low cost per Ampere (and ampere-hour) of those, near the reliability and near the ease of handling. 20kg isn't that heavy, if you consider that "fuel economy" still means your average new car ...


63

So, now after the answer to your literal questionto your real question, that you sadly didn't ask Battery technology has moved so far in the last 100 years. The lead-acid starter battery became common in cars in 1920, lead is essentially poison, and sulphuric/lead acid isn't any less dangerous. They tend to fail in cold temperatures, especially if not ...


48

"Ground" is just a code word which, in this case, refers to the "current return common" circuit node. There is a complete circuit because everything electrical in the car, such as the starter motor, also connects to ground in order to return current to the minus terminal of the battery through the ground. The car's chassis is used for this return network, ...


45

A car is (still, in the modern era) an electrically harsh environment. The "12V supply" is typically 13.5 to 15 V, and may occasionally spike to 80V or more. There may also be some high-frequency junk on the wires from the spark plugs. Relays put up with that abuse somewhat better than transistors, at least for "a similar price point."


43

...and now why Tesla uses induction motors The other answers are excellent and get at the technical reasons. Having followed Tesla and the EV market in general for many years, I'd like to actually answer your question as why Tesla uses induction motors. Background Elon Musk (cofounder of Tesla) comes from Silicon Valley (SV) thinking, where "move fast and ...


39

A wrench does not have a resistance of 0.5 ohms, it's way lower. Your basic multimeter cannot measure resistances to better than an ohm or so, the resistance of leads, and the unreliability of contact resistance make it impossible. The way resistances as low as a wrench are measured is to use a 4-terminal Kelvin method. What you do here is to pass a ...


33

Hint: resistance is not just a matter of cross section, but also of length. Would you expect the jumper cables to work if they were say, 10 meters long? What about 100 meters? You got my point. Even if the contact surface is very small, the effective length of the contact is very short. One could argue that having flat, rounded surfaces would lead to a ...


32

Every car that I have seen had center-positive cigarette lighter 'sockets'. All (as far as I know) modern cars use negative ground systems, so the outer negative 'body' is vehicle ground and positive center is battery You would expect this polarity to be maintained even with positive ground vehicles made by any sane manufacturer (and most insane ones as ...


29

With frequency control, there is not just one torque curve, but an infinite number of curves, one for every operating frequency. The voltage needs to be proportional to frequency. If the voltage is carefully regulated using a mathematical model of the motor with motor operating voltage, current and power factor information, the torque curve can be made to ...


26

It's hard to say what the engineers' exact reasons were without being on the design team, but here are a few thoughts: Both motors require similar drives. Brushed DC motors can run directly off a battery but the type of motor you are looking at in an electric vehicle is a brushless DC motor. The drives for an induction motor and a brushless DC motor are ...


20

Knowing that all sorts of weird stuff can happen in automotive power circuits, and not being especially knowledgeable in those systems, I'd err on the side of caution and use an opto-isolator. simulate this circuit – Schematic created using CircuitLab Pin 1 = Car 12v R1 Pin 2 = Car Ground Pin 3 = NC Pin 4 = Arduino Ground Pin 5 = Arduino 5v R2 Pin 6 =...


20

The latest batteries are much lighter and cost less over a vehicle lifetime than ones of yore. But they do not use LA (lead acid) chemistry. A LiFePO4 (Lithium Ferro Phosphate) battery will do what is required at acceptable whole of life cost BUT at higher initial capital cost - which makes it unattractive to car manufacturers. Low initial capital cost ...


19

Have you noticed how the clamps get hot after a jump-start? That means power is lost, it ends up in those clamps. You're right the connection isn't ideal so power is lost but not so much that anything melts or explode. What is there to explode anyway? Nothing :-) You wouldn't want to make that huge starting current flow for more than a minute as the clamps ...


18

The - end of the charged battery is already connected to the chassis, the engine, and, particularly, the starter motor. The whole car is designed to work that way. Everything use earth return. All the lights have one wire, and one connection to the chassis. The spark plugs have one wire, and one connection to the engine block. And so on. OK, on a modern ...


18

Lithium starter batteries exist, primarily for racing or other performance or luxury applications where the weight savings or bragging rights are worth the cost. As others have noted, however, the demands of the application are rather extreme and lithium technology needs a lot of special development and care to be able to reliably and safely fulfil the ...


17

A load dump is what happens to an automobile electrical system when a large load (such as the headlights) switches off. The problem is that the charging system (primarily the alternator) has significant inductance, and any attempt to rapidly reduce the current draw results in an "inductive kick" that creates a large voltage spike on the 12V bus. This kick is ...


17

By decoding your question, this is what I arrive at: You are using the two resistors as a voltage divider, with the LEDs wired in parallel connected to the junction of these two resistors. simulate this circuit – Schematic created using CircuitLab This is not a valid approach, the voltage divider will not provide the 1:4 (approximately) voltage ...


17

The main reason for connecting to the positive terminal on the battery first is to do with volatile gases possibly being emitted from the battery. If you connect to both terminals at the battery terminal this will usually cause some kind of spark as you first touch the cable to the terminal, whether you do positive or negative first is irrelevant. Connect ...


17

My question is this: is this phenomenon something that truly exists, or is it simply an internal "old wives tale" with little to no basis? Well, do the math. If you sink let's say 100 A into a steel conductor of let's say 50 mm² diameter, what is the voltage over 10cm of that conductor due to ohmic resistance? So yes, Ohm's right, and if you put a lot of ...


17

There's only any point in trying to protect a circuit with a fuse if there is enough headroom between the operating current, and the fault current, to ensure that the fuse won't blow in normal operation, and will blow under fault conditions. Unfortunately, once you have included all the tolerances, there is no current level you can choose that is ...


16

There's not an electrical reason, but instead a weight reason. By using the existing metal structure as a ground, it effectively reduces the number of wires by around half, and therefore saving a great deal of weight. (For example, otherwise each tail light would have to have two wires instead of one.) Remember too, that some electrical loads in an ...


16

Having a power fuse blow on the circuit that is going to the engine starter can result in a serious safety issue, especially in marine systems where the inability to start the engine can mean limited or no navigation capabilities. On cars, it can mean not being able to start in an emergency situation. Some cars used to have it. I once rear ended an old ...


15

You specified a current draw of 800mA. The voltage drop is 12-5=7V thus the regulator will consume 0.8*7=5.6 Watts. That will likely burn your regulator from the board. Even if you take a different type and a heat sink, you don't want a big heat source in your car. I strongly suggest you use a ready-made 5V switching regulator. They come in a bit larger ...


14

You don't get shocked because you're talking about DC with no connection path back to the positive terminal of the battery. If you touch something metal on the vehicle you're now at the potential of the negative terminal of the battery (or the car's ground voltage). If you're also touching earth ground, then a very slight current will flow to balance out ...


14

The answer is very simple: Because we haven't found anything better. A car battery needs to hold its charge over a long period of time, be able to deliver a huge current and fit into a small space. And it would help if it's not too expensive. Lead acid is still the best solution for those requirements. You could use a Lithium based chemistry, they can ...


13

The battery is forcing a difference of potential between the - terminal and the + terminal. The chassis (- terminal) is somewhat isolated from the Earth because of the tyres so theoretically the potentials are different however as shown on the attached simplified equivalent schematic, there is nothing in particular forcing a voltage across your body (you ...


13

The voltage in a car is only about 12V, which means that even moderately powered components can draw large currents. The dash in my car is illuminated by four 12V 2W bulbs. They draw a current of 666mA just to light up the dash! If you look at the fuses for all the circuits in your car, even the smallest will be 5A. Most will be 10-20A range and some even ...


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