Hybrid cars and regenerative charging of batteries

You are absolutely right!!! A single mistake (even in metric units) can lead to bogus calculations. Should have spotted that myself. Ah well, "to err is human". Some days I'm just more 'human' than others ;-)

daestrom

daestrom: Very tricky, those dc motors/generators. thanks for the crash class on them., i'll keep it in mind.

=AEoy

what i know about motors & generators is that the magnetic flux in motors is induced mostly or all by electricity, with generators it is imposed on the metallurgy or you'd get no excitement or hysterisis curve.Not that they are all that harmonic, duhhh..... you must think I'ma dolt......

=AEoy

so I don't know it all, who does, but, still the drive mechanism employed must shift the power off the motor, and transfer the (any) output generated, back into the batteries through a controled charge circuit, (whatchu macall it) and the best charges should still be durng coasting or motor free axle spins.

how they do it I haven't seen..

Anyone have a website with specs or do I need to activate my IEEE student membership to dig around files?

=AEoy

To four decimal places! ;-)

I sometimes wish for the old days of slide rule use! I used one all through college and took my P.E. exam with one. You had to place the decimal point with a mental calculation. It also prevented assuming four-place results from two-place inputs, a common tendency now-a days. :-(

Please Mr. Kelly you are standing too close to the Rift

----------- And you are trying to look up from the bottom.

I've run (many times) motors as generators and generators as motors-- no problem. The only real difference is the direction of power flow. Direction of rotation is unchanged. polarity of voltage is unchanged. (note: IF a DC machine has a series field, then it is necessary to reverse the field to avoid voltage reversal.- this is not necessary with a PM, shunt or separately excited machine). For AC machines, there is also no problem. In fact there are many places where ordinary induction motors are used as generators. In some locations they are connected to small water wheels and are started from the grid, run up to speed as a motor, then the water valve is opened so they are driven above synchronous speed and generate. AC synchronous generators can be and are used as motors. I can suggest some references for you, if you wish.

regenerative

requirements

manufacturers

regenerative

-------------- If, as it appears, they are using the motors as generators driven by the gasoline engine, they probably do have a fairly good and efficient method of controlling the charging. In addition the motors may be as I have seen in one experimental hybrid vehicle, using PM field magnets so field control is out. These motors were surprisingly small physically for their rating (which I forget- it was over 20 years ago). Given electronic controls for normal operation, addition of regeneration control should be relatively cheap and simple.

By the way, thanks, I had called regenerative braking = dynamic braking- theoretically dynamic braking is regenerative - but not in the standard terminology as you have pointed out.

I have made the following calculation for a panic stop: Assume that you have a vehicle of 1000 kg (2200 lbs) and you are going to decelerate it from 100 km/h (62 mph) to a stop in 50 m at -8 m/s^2 (about 0.82 g). This requires 400,000 J (watt-seconds) of energy and takes about 3.5 seconds.

The Toyota Prius uses a 274 V NiMH battery with a capacity of about

7 Ah (3 hour rate). If you wanted to dump all that energy into the battery, you'd have 115.2 kW over the 3.4 seconds, or 420 A. Compared to the battery capacity, this is a lot. I seem to recall (but can't cite) a number that only 10 to 20% of the braking energy is recaptured by the regenerative system, and that figure would seem to be a more reasonable rate to recharge that battery.

The Prius battery does have several thermistors embedded in it, a forced-air cooling system, and its own computer to decide how it will be charged. While I agree that charging at a too-high rate is not good for any battery, this "battery" is not just a box of chemicals. It can stop charging itself if the rate is too high. (Also, the target state-of-charge in most hybrid cars is not 100%; it's usually somewhere between 50% and 80%, so there will always be someplace to dump some of the energy when braking.)

Another clue is that Toyota warrants the battery and hybrid components for 8 years or 100,000 miles. The 2004 and up Priuses use the same battery as the 2001-2003 Priuses, but use it more extensively to get better fuel economy, so Toyota must be comfortable that the battery will last at least that long.

Matt Roberds

You're quite right. Apart from a couple of constraints the only difference is efficiency.

Newsey

I read somewhere "Chrstie Industries=AE" was bringing an EV Production Line into the US but nothing there after >>>> any body know of it ?

=AEoy

I understood that NiMh batteries have a shelf life of around 3 years. In other words, they'll have a relatively low capacity after that period. Also NiMh lose their capacity from heating, so I wonder how do Toyota expect their NiMh to last for 8 years? Everyone who has been through the experience of having to repeatedly replacing their laptop computer battery after hardly using it knows about this. Silver-oxide and the new titanium batteries have a shelf life longer than eight years. Do they have some sort of special NiMh battery?

Sig: Work saves us from three great evils: boredom, vice and need. -Voltaire, philosopher (1694-1778)

the braking energy is not nearly as much as the downhill coasting energy that is recovered. on my echo, the fuel is entirely cut off at closed throttle and 1440 plus RPMs. it makes a big difference as there's no idle fuel being used during this time. i was surprised at the reduction in fuel flow when i coast to a stop, (out of gear, idling ) and gearing for higher rpms and closed throttle. we have a lot of ups and downs in western PA. if i could recover the downhill energy it would be even better. sammmm

To me, "shelf life" means "sitting on the shelf, not doing anything." A battery that is being used, and maintained by a relatively smart system, ought to last longer than that. I do know that Toyota specifies an extended charging procedure when the vehicles are first delivered to the dealerships, so the battery should be fully charged while the vehicle is on the lot. (Not that it's there for long; Priuses are back to a few-month waiting period...) My Prius was built in late 2000, and I bought it in spring 2001, and I've had no problems with the battery so far.

The pack does have forced-air cooling. Air is drawn in from vents in the rear parcel shelf, blown across the battery, and exhausted through the left C-pillar. The blower doesn't run all the time... only when needed.

I think Toyota has better rockets than the coyote...

It's made up of 38 7.2 V modules. Each module is a skinny rectangular thing, about the same proportions as a VHS tape, but a little smaller. They are clamped together in a big stack with long bolts. The original Prius, sold only in Japan, used cylindrical NiMH cells, and its pack was of a lower capacity than the later US model. Any FUD you hear about the "turtle light" almost certainly derives from early US road tests of Japanese-model Priuses.

Matt Roberds