Energy Dump?

[gallde]

Any thoughts on how the Prius decelerates normally when the batteries are already fully-charged? What happens to the energy generated as it places the intentional drag on the drivetrain? Or, does it not even supply drag and "glides" instead? I wonder if that's why the battery compartment has a cooling system: maybe it just keeps dumping energy there.

[mshappe]

Originally posted by gallde
Any thoughts on how the Prius decelerates normally when the batteries are already fully-charged? What happens to the energy generated as it places the intentional drag on the drivetrain? Or, does it not even supply drag and \"glides\" instead? I wonder if that's why the battery compartment has a cooling system: maybe it just keeps dumping energy there.

(Not sure why this is in Audio & Electronics...)

Keep in mind that the battery meter on the MFD represents a relatively narrow window on the range the battery pack can be charged. The top of the meter represents about 80% of the HV pack's actual capacity; the bottom about 40%.

Why? Because the HSD is designed to try to keep the pack in roughly that range, to extend the pack's longevity. Full charges, and deep discharges, actually have a more detrimental effect on the battery's life cycle than just keeping the charge level somewhere in the middle.

So, when your meter appears to be 'topping out', you're not actually fully charged, physically; and when the meter 'bottoms out', you actually have a fair amount of slack.

The upshot is, in normal usage, it's actually going to be a pretty rare case that you're ever going to truly top out your battery!

[jamarimutt]

I frequently drive down a long hill in which all the bars turn green way before reaching the end of the hill. The meter indicates that the battery is fully charged but continues to charge it. When reaching the bottom of the hill I can drive for a longer time before losing the first bar than I do when all bars turn green in another shorter hill.

Thus, mshappe is right. After al the bars turn green the battery is not yet fully charged.

[efusco]

moving to an appropriate forum

Response:
When the battery gets near full--all green bars--one of two things usually happens.

1)If you're stopped the ICE will cycle off and on several times in a row. MG1 uses guite a bit of electrical power to turn the ICE over and it uses that to drain the battery slightly to make room for more charge.

2)If you are actually on the move--ie coasting down a hill, the ICE will spin up and race...it's a bit frightening and sound like something's wrong, but there isn't, it's just a mechanism to prevent over chargeing.

Sort of a 3rd thing is that the fuller the battery is charged the more the hybrid system will utilize battery power, the lower it is the more it will use ICE power--particularly in flat/cruising conditions.

[jamarimutt]

Evan: I see all green bars two or three times a day, on the move and stopped at a light. I have not yet noticed the behaviors listed in 1 and 2.

[efusco]

Originally posted by jamarimutt
Evan: I see all green bars two or three times a day, on the move and stopped at a light. I have not yet noticed the behaviors listed in 1 and 2.

All green bars meaning all available slots filled? Remember, the bars turn green when the second from the top bar is reached, but you won't see the energy 'burn off' at that state, only when the battery shows all the bars to the top of the digital battery. Even then, it won't 'always' do that, but if a certain SOC threshold is reached, it will.

BTW, if you're seeing that condition several times a day you can probably alter your driving pattern a bit at the places where you routinely see that state and improve your mileage. Basicly, you want to encourage EV mode more in the mile or so prior to the places where you see all the green bars.

[Mirza]

Thanks for the explanation Evan! I thought that the engine turning was some kind of rare bug, but now it makes sense. I've experienced it a few times (very hill area). A full green battery wasn't uncommon in my semester.

[Frank Hudon]

furthur to Evan's #2, the engine runs at a faster speed to bring the MG1 speed down to a point were it's almost stopped and that decreases the output to the inverter/battery.

[DaveinOlyWA]

according to the tech specs a the battery indicator range is 70%-30%. so when the indicator says the battery is fully charged, it actually can take another 30%.

this is done because overcharging and undercharging the battery will greatly reduce the battery life. keeping the SOC in this range is the reason why this battery pack will last nearly 3 times longer than an average car battery.

iow, it aint the battery, its the computer controlling the charging circuit to the battery that is responsible for its long life. if the battery pack was treated like battery packs in laptops, etc. its life would be just as short as the laptop.

if you feel that you might be overcharging your batteries, turn on the headlights, crank the stereo, blast the air. it will all help burn off the charge. but unless the hill is huge, i wouldnt worry about it. the car's computer is set to guard against overcharge conditions.

[gallde]

I have noticed behaviors 1 and 2, after coasting down a long hill to my house following a flat, slow driving segment. I come to a light, and the ICE starts and stops several times briefly. I thought the current sensor was flaky, but I guess it's just trying to use up the extra power generated on the hill. Now if it had an auxiliary flywheel storage unit...