Battery size vs. power from MG
 

The nerd in me got to thinking this morning about various hybrid batteries out there in the market and couldn't figure what 1) battery capacity is vs 2) electric motor power rating.

1) my 2013 450h has 37 kw battery capacity. I think this means amount of power stored.
2) MG2 is rated at 116 kw and MGR(rear) is rated at max output of 50kw.

What I don't get is: How does the 37 kw get used over time???? is this kilowatt per hour? does that pump out all 37 kw in 2 seconds and done with it? how sustainable is that 37kw before we need to go to regen mode? And why do we have a 116kw motor when we don't have 116kw electricity available anywhere???

Some more information from Mercedes Benz hybrid GLE (as a comparison)

its battery is 9 kwh (note the "per hour" figure) in capacity and the electric motor's max output is 85kw (note the absence of "h") in there. How in the world is the 9kwh battery gonna power the 85kw motor????

This one is easy to explain.

For simplicity lets assume there is no loss [there is always a loss of energy, but for now lets assume there is none].

Amount of energy stored in battery [9kwh] is 9K watts that can be sustained for 1 hour before being depleted [assuming no charge is done. There is another leap that I am making here that the chemical reaction is no longer regenerating energy .. treating the situation as a large Capacitor]

Motor can produce a max of 85K watts ... [once again assuming no loss it can consume 85Kwatts to produce 86Kwatts of turning power]

Now assume you mate the above battery with the above motor you can produce 86Kwatts for 9/86 hrs ~ 1/9.6 hrs.

Seems like a short time, but realistically you do not put the demand on the motor to produce max power. The sustained current most likely will not be supported by the actual wires. What is being quoted is the actual max specs.

Salim

I've only had my 2010 RX450h for six months, but as an engineer I've looked at lots of YouTube videos in order to try to understand the brilliant Toyota hybrid system.

In short, it's much more complicated than one would first think. I don't think of it as an "electric" car, but rather a gas-engined car that maximizes the efficiency of that gas engine. The HV battery is not meant to drive the car along, but rather to provide instant (unnoticeable) engine starts (dozens or hundreds in a typical trip) and to accommodate regen braking. I imagine Toyota experimented with various battery sizes and picked the one that was the best balance of cost, weight, performance, and life. Similarly they probably sized the MG2 motor based on different criteria. MG1 and MG2 are both motors AND generators, and the computer blends their operation with the operation of the gas engine to deliver transparent power--and combines all that with a CVT-style "transmission" effect. Remarkable.

Errrrr. Come again????

Sorry, what I mean is that the electric system is not meant to "primarily" power the car. All the energy moving the car comes ultimately from combustion of fuel in the engine. All the supporting stuff is designed to help that engine run in its most efficient mode. A full-throttle start uses both the engine and the stored electical energy, but that maximum effort can't be sustained, nor was it meant to be. By contrast a plug-in or EV car assumes that most or all of the required energy comes from the mains.

As for the CVT effect, the hybrid does not use a conventional cone-and-belt mechanism. Instead, both the engine and the Motor-Generator are on a planetary gearset, and the Motor-Generator is driven in such a manner that the engine runs at an rpm appropriate for the amount of power needed at that moment. Very clever. And no belt to wear out, it's just a planetary gearset.

Think of the system as a closed loop system and clearly the energy input into the system is from the gasoline engine. The battery produced electrical energy [chemical] and get replenished by the charging system. The beauty is in shutting down the gasoline engine [stop/long-decellaration] and recovery of energy during braking.

Salim

then, what does this mean:

Hyundai Sonata Plug-in only has 9.8 Kwh battery - seems very small, with an MG producing 50 kw of power only. Yet, this can go so far without gas as well as to produce pretty good 0 to 60 times. Something doesn't sound right. Our EV range is pretty much parking lot only...... yet, our battery and MGs aer much bigger....

One thing to note is that you can't compare the Sonata's 9.8Kwh battery with the RX 37Kw battery. One is a capacity measurement, the other is a power measurement. The RX battery may be able to put out 37KW of power, but that doesn't say how long it would last, could be only 1 or 2 minutes. In practice the vehicle electronics only permit about 20-40% of the total battery capacity to be used, which is probably why it's rarely advertised. Capacity is more important for plug-ins and electric cars, in hybrids the power rating is the main concern, how much power can I get for a couple of minutes under max acceleration, after that the battery will be recharged. Hybrids never do well flat out top speed.

I noticed it too. RX uses just quotes Kilowatts, which doesn't mean much on its own and Sonata says Kilowat-hour.

kW = power
kWh = energy

RX can deliver 37kW of power. I believe the 4RX hybrid battery is carried over from the 3RX and it's rated for 1.9kWh... which is why you can't get far under electric power only.

1.9kwh is not that much. I wonder how other cars have so much more energy stored in them. and more importantly, why Lexus can't have as much battery capacity like that of the Sonata. in fact, I think our batteries are actually bigger (physically)

Most plug-ins with larger battery capacity sacrifice a good deal of trunk space. The Sonata plug-in uses lithium cells to offset the size it would have gained had they used NiMH.

You can get approx 50 HP* out of the battery to drive one or both (or three, if AWD) of the motors, afterwhich the ICE is called upon to provide power to the wheels via MG1 (using up to approx 25% of the ICE as a generator) plus up to approximately 75% of the torque to the wheels from the ICE.

The planetary gears of the eCVT are approximately 25% to MG1; and approximately 75% (78%, IIRC) to the engine.

Depending upon the programming, the driver's input, and the alignment of Neptune with The Moon, the mix of electricity from the battery, MG1, MG2, the ICE, and even the motor in the rear of the AWD motor contribute to forward propulsion of the vehicle at any given time.

It's simply a bit shy of magic.

*37 Kw converts to 49.6 HP

...because once the battery is depleted, all that is left to power the car is the ICE's power (less the conversion losses during electrical generation and transmission)!