In a typical hybrid car (that’s not a plug-in hybrid), the batteries get charged from the engine running and from regenerative braking. They then power an electric motor to assist with locomotion. You might park your car in the garage with the batteries at 90% capacity, or 70%, or 50%, or whatever.
When you pull back out, the batteries are then still at that “whatever” level. Doesn’t really matter. So how does the car’s battery bank know or care whether it was topped off via shore power while parked in the garage? Why is having an onboard charger for shore power (or a plug for a wall charger) such a difficult engineering feat? Seems like it would just require the addition of a part that costs a few hundred bucks.
RVs and boats have a “house” battery bank that generally functions this way. Maybe it’s getting charged by the alternator, maybe by solar panels, maybe by shore power. But hybrid cars having a shore power option (i.e. PHEV) seems like a real premium option that is not easily built.
What am I missing? Why does the battery bank care where it got its charge from?
In: Technology
Most of the gains of a hybrid come from the ability to store energy when slowing down and reinject that into the drive-train when you are accelerating again. It gives them much better city mileage and crucially doesn’t add much weight to the vehicle.
A standard Prius has a 1.3kWh battery of which half is useable – that’s about 1% of the available capacity of something like a Telsa. The hardware to allow that to be wall charged would probably add as much weight as the battery itself, and the extra efficiency of always leaving the house fully charged would be very small.
Something that the other comments have missed: PHEVs (usually) have a “battery only” mode.
A standard hybrid will use battery power to *assist* the engine to get up to speed, but is almost entirely moved by the engine. It can’t move the car on it’s own, at least not very fast and definitely not for very long. You’d have to recharge the battery every 2-5 miles, and you’d only be going 10-20 MPH. If you’re only using the battery to give the car a quick push, you don’t need a big battery or motor.
A plug in hybrid will have both a bigger battery and a bigger electric motor. Most work like an electric car, using only the electric motor to move and using the engine to recharge the battery. You could drive highway speeds without using gas, and some can drive as far as 50-70 miles using the battery only.
By having a larger battery, larger electric motor, and the additional hardware to plug into a wall, PHEVs are more expensive and heavier than standard hybrids. Both hybrid types typically get about the same gas mileage if you are running them in hybrid mode, but the battery only option is why many people chose a PHEV.
A non-plugin hybrid just has a much smaller battery. This is because for that model of car the price and efficiency decisions came out that way. The cost, weight and environmental impact of the charger are not worth any gains that topping it off at home would have. It’s not that it’s technically difficult to add, it’s that it was intentionally left out because adding a battery big enough to make the charger worth it would place the model in a different price point than the manufacturer wanted.
Beyond the fact that the battery is too small to make it worthwhile, every battery has a finite capacity and cannot accept more energy from regenerative braking when fully charged. So a fully charged hybrid would have to use friction brakes instead, negating any possible efficiency advantage. PHEVs and Battery-only EVs deal with this by having a buffer and not allowing you to actually fully charge the battery.
Plug-in hybrids are my favorite configuration. It’s an electric car but on the rare long trips, it has a bvkup generator on board.
However, the larger battery is heavy and more expendive.
The most successful parallel hybrid is the Toyota Prius. The city mileage is better than the highway, so they work well as taxis.
The electric battery can only run a short while, so the engine/generator must come on often.
That being said, they often get 50-MPG, and also last 400K miles.
The worst fuel economy and worst emissions are from accelerating from zero up to cruising speed. This is where the Prius electric motor does the heavy lifting.
The famous second-gen Prius sold new for under $20K. 2004-ish?
The Toyota RAV4 plug-in hybrid is $45K in 2023 dollars
In addition to all the technical/mechanical explanations, another reason is also just because of cost. It costs more to make a plug-in hybrid over a regular hybrid, and a non-plug-in hybrid is still an easy way to get a more fuel efficient car to customers at cheaper prices while also inflating your fleet’s average MPG.
Plug in hybrids require a much bigger battery, and big batteries are expensive and heavy.
There is indeed some benefit from making a car a plug in hybrid, especially if the driver typically doesn’t drive more than the battery-only range. This allows for a lot less gasoline usage than a regular hybrid. However, actual cost savings depend on the local prices of gas and electricity.
With a regular hybrid, the battery is only really used when you’re accelerating, so during the last few seconds/minutes while you’re decelerating into your garage, it’s being constantly charged by the gas engine. It never gets low enough to the point where it needs to be charged via plugin.
Many hybrids don’t work that way at all actually – there is an electric motor and a gas engine, but *both* are connected to the drivetrain and power the wheels.
Gas engines consume a lot of fuel and experience more wear during stop-and-go driving, but electric motor efficiency isn’t really affected by this. Gas engines are much more efficient when kept at a constant RPM to maintain your speed, electric motors don’t benefit much from this.
So, the car is actually swapping between using the electric motor and the gas engine to power the wheels. During acceleration, it swaps over to full electric, or uses the electric motor to assist the gas engine. During highway cruising, it’s mostly powered by the gas engine, which is also recharging the batteries while you’re going.
A major inefficiency in cars is the loss of kinetic energy when braking.
The point of non-plugin hybrids is to store this energy via regenerative breaking (and be able to give some added torque). So they only need batteries that can store the energy gotten from braking from ~70mph down to 0 (or conversely the energy required to get your car up to highway speeds).
Many non-plugin hybrids can barely make it 10 miles on the battery alone, and that’s in very ideal conditions (I.e slow acceleration, coasting down hills, no braking etc.) So you would only gain a maximum of ~10 miles of range by charging them up (if people even bother/remember).
Plug-in hybrids on the other hand are meant to be able to run off the battery for most city driving (~30+ miles), and use gas for long drives. So someone can go months without fueling up, if they’re only driving short distances (e.g. to work and back).
Because hybrid cars predate the existence of plug-in charging stations, therefore the original hybrid cars were designed to only accept gasoline as a fuel (with the gasoline engine charging the electric battery).
> Why is having an onboard charger for shore power (or a plug for a wall charger) such a difficult engineering feat?
Household electrical current systems predate hybrid cars by a long time. The electric current and voltage would be very insufficient to charge a car.
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