I’ve been shopping around for an emergency jump starter to carry around in the car. I’ve found jump packs that are roughly a little larger than a cell phone, and produce 1000 amps or more. What is keeping them from being a main car battery?
In: Engineering
Its the amount of energy stored, not the amount of energy produced.
A car battery holds 10 to 20 times more electricity inside of it then even a good cellphone battery.
You can get lithium batteries for cars, but they are expensive, and wear out quickly. They tend do be much more temperature sensitive too. Both to the cold, as to the heat of the engine. The lead-acid battery chemistry is very robust and simple. And in a 1k5 kg automobile, the savings of a few kilo’s is not really worth it.
Capacity. Emergency starters need to start your car once. Car batteries can’t recharge enough on shorter drives so they slowly lose charge.
You can crank your car with a normal battery like 50 to 100 times before it goes flat. The small emergency jump starters can crank a car from zero to five times depending on the size of the battery and the size of the engine.
Also, a lot of those jump packs don’t actually produce anywhere near as much as they advertise.
Supposed to be eli5.
Those new age mini jump starters are lithium chemistry, of the good ol fashion lithium ion style, not to be confused with the more deep cycle variant : lithium iron phosphate.
These little things exploit the power to weight ratio of lithium ion but do so such that you dont destroy it from regular mass high current events.
Theyre able to start a battery but not capable of safety doing it over and over again, due to the 1 main danger of lithium,; thermal runaway!
Thermal runaway is when current starts to flow, is then restricted by something, then starts to flow even more to counter for the lack of voltage, to output the same watts of power and that heat creates even more resistance so the cycle continues until it heats up to the point it melts and explodes.
Lithium iron phosphate is much safer, and similar to a carb battery, but doesnt have the cranking power delivery required. Li-ion does but is dangerous, hence we continue with ol faithful lead a id
Another factor to consider is range anxiety. My car has a small-ish battery that can theoretically range 280 miles. Yet only once did I have to use a fast charger while driving. Car manufacturers have to reach an autonomy similar to a tank of gas even if the cases one empties a tank in a single day are the exception and not the norm
Car batteries aren’t just for starting the vehicle. They act as a power source when the engine isn’t running (think modern vehicles with stop/start features) and act as a capacitor to handle surge loads to help keep the voltage stable which is important for the electronics which run modern cars.
Jump packs are limited capacity often only able to do just that, jump the vehicle when the battery cannot supply enough current. Often a jump pack can only be used a handful of times before it needs a recharge itself.
That all being said, we can afford the older lead acid design because the extra weight simply isn’t that huge of a concern and the added capacity makes up for it.
Pb batteries are simpler to keep connected to a running electrical system. If you kept a lithium battery constantly connected to 14.2 volts, there could be problems including cell damage and maybe fires without complex cell management.
Also, lithium jump packs aren’t meant to be used cold. At least, that’s the impression I get from lithium motorcycle batteries. You can keep your jump pack indoors and bring it out when you need it. Pb batteries may lose capacity when cold, but they’re still simply robust.
Speaking of motorcycle batteries, look at how much a lithium battery (like antigravity) costs compared to a traditional Pb battery.
Cost. To make them durable enough to withstand the extremes cars are designed to, they will cost significantly more than a lead acid battery. That being said, they are starting to show up in high end performance cars.
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