Synergy drive technical questions...

[sorka]

1) How can you tell when the brake pads engage. i.e. I'd like to brake as hard as possible but without engaging the pads. Is there an indicator light or some other method for knowing when you're wasting energy on braking?

2) Is the management software smart enough not to completely charge the battery while in motion? I'm assuming that the system is smart enough to leave enough room in the battery for a full regenerative capture when braking? If it wasn't, then you'd waste energy by braking with an already fully charged battery.

[effwitt]

1. No indicator light, but light to moderate braking doesn't use the brake pads until you drop to 7 MPH.

2. A lot of work was done to make the management software very smart. Even if you have all the bars, the battery is only 80% charged. It doesn't take very long to use a bars worth of energy.

[JimboK]

Originally Posted by sorka

1) I'd like to brake as hard as possible but without engaging the pads.

Why? Light to moderate braking is more efficient. See this for more.

Originally Posted by sorka

2) Is the management software smart enough not to completely charge the battery while in motion? I'm assuming that the system is smart enough to leave enough room in the battery for a full regenerative capture when braking? If it wasn't, then you'd waste energy by braking with an already fully charged battery.

Effwitt is correct about the 80% level being "full." (Actually I've seen it go as high as 82% after a long descent out of the mountains with continuous regeneration.) Taking it a step further, the car aims for an optimal charge of 60% (six blue bars) to allow just what you suggest -- headroom for any upcoming regeneration.

[archae86]

Originally Posted by sorka

1) How can you tell when the brake pads engage. i.e. I'd like to brake as hard as possible but without engaging the pads. Is there an indicator light or some other method for knowing when you're wasting energy on braking?

I wish that the standard display on the Prius supported that function but it does not.

I can get a pretty good approximation using my ScanGaugeII. With a cool battery at moderate charge level it will allow you something like 95 amperes of regeneration. If I modulate the braking level a little, and see the regeneration current change, I figure I'm not at maximum yet. This is necessary because the actual maximum value drops with a hotter battery or a higher state of charge.

While some folks posting here would have you believe that you're not likely to exceed the regeneration maximum unless you are braking pretty hard, watching the SG2 has taught me that at higher speeds on downhill it is really quite easy to go past the maximum. 90 amperes of regeneration at 70 mph does not feel like very strong deceleration at all. On the other hand at 25 mph it is quite robust.

[JimboK]

Originally Posted by sorka

1) How can you tell when the brake pads engage.

I had forgotten about this, but in researching something for an unrelated thread I rediscovered this, in case you're at all inclined to a DIY hack.

[bushface]

I go down a 12% grade (per state road sign) for 3 miles every workday, at the top I shift the Prius to "B" to help with braking. Half way down the grade when my battery shows full, the motor speeds up like my jeep manual drive when I gear down. Or at least that what it sounds like. What is going on? I suspect that the ICE is doing the braking without regen the battery. I wish that I could not have the battery at 4 or 5 bars at the top of the grade but at 2 bars.

[qbee42]

Originally Posted by bushface

I go down a 12% grade (per state road sign) for 3 miles every workday, at the top I shift the Prius to "B" to help with braking. Half way down the grade when my battery shows full, the motor speeds up like my jeep manual drive when I gear down. Or at least that what it sounds like. What is going on? I suspect that the ICE is doing the braking without regen the battery. I wish that I could not have the battery at 4 or 5 bars at the top of the grade but at 2 bars.

That is exactly what is happening. Once the battery is full, regenerative braking no longer has a place to dump all of the generated electricity, so it uses the excess electricity to spin the ICE. The ICE is being used as a big friction device by pumping air with the valves in a high drag configuration.

You deserve some sort of prize for being one of the few Prius drivers to correctly use B mode. This is exactly the application for which it was designed.

You might be a good candidate for an EV switch. That way you might be able to keep your SOC low before you hit the top of the hill.

Tom

[sorka]

Originally Posted by JimboK

Why? Light to moderate braking is more efficient. See this for more

....because you're not engaging the brake pads. What I want to know is if there's a way to tell when the brake pads engage.

[sorka]

Originally Posted by JimboK

Effwitt is correct about the 80% level being "full." (Actually I've seen it go as high as 82% after a long descent out of the mountains with continuous regeneration.) Taking it a step further, the car aims for an optimal charge of 60% (six blue bars) to allow just what you suggest -- headroom for any upcoming regeneration.

That is very cool. So of course they did the right thing. That's awsome.

[David Beale]

First, be aware the pads are brought to the rotor as soon as you press lightly on the brake pedal. They are not pressed against it however, just placed in a "ready" position.
So far, the only way anyone has come up with to tell if the braking is friction or not is the DIY circuit posted above.
At slower speeds most reasonable braking is regen. If you panic stop (quick and hard application of pedal) it is purely friction. Be careful, in this situation the car will just about stop on its' nose.