Energy Dump?

[efusco]

Originally posted by 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...

You, my friend, are a perfect candidate for an EV button!! You could use it on that flat slow segment. That energy dump is just that, wasted energy. You should also try to master feathering the pedal to encourage EV only driving along that segment so that you're actually draining the battery and not having the ICE charge further with it's 'excess' energy. I think you'll notice a small but noticable improvement in fuel economy if you can master that little trick.

[plusaf]

Originally posted by DaveinOlyWA
<snipped>
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.

Dave, don't the a/c, stereo, headlights, etc., run off the 12v system?
how do they draw power from the 200v+ battery?

it struck me that if the battery got too charged on a L O N G downhill stretch, say, from Donner's Pass to near Reno, couldn't MG1 and MG2 "buck" each other to consume energy, and perhaps pass that heat on to the radiator in front of the engine? i've wondered where heat from MG1 goes during a high-speed cruise. (or is it MG2... i keep forgetting)



ps. 47 mpg and round trip from Cupertino to Mendocino, plus some sightseeing there, ON ONE TANK! woweewoweewow! and handling on route 128 was super! loving this car more and more each day!

[gallde]

A/C runs on the HV battery, other accessories on auxiliary 12v power. But as long as the power is in the "IG-ON" mode, the HV battery "charges" the aux battery through the step-down inverter, keeping the aux voltage at 13.8 volts, so you won't run the aux battery down. Clever system!

[gallde]

I read it is as simple as momentarily grounding H14-27. Do you know where I can pick off the status of EV mode to operate an LED?

[efusco]

Originally posted by gallde
I read it is as simple as momentarily grounding H14-27. Do you know where I can pick off the status of EV mode to operate an LED?

That is exactly what it is. But, unfortunately I don't know how you can get it to operate an LED. I suggest you post the question under another thread (mods probably). Someone like Brosnan might be able to help you out there as I lack the technical expertise to do so. Also, I and others would like to know the answer as it would be handy to have a little reminder LED to let you know when you're in EV or not.

[jamarimutt]

I experienced behavior 1 for the first time this morning. After going down a long hill and stopping at a red light, the ICE began turning on and off; it had done it three times before the light turned green. Thanks for pointing this out, Evan; I would have otherwise been afraid that something had gone very wrong.

[efusco]

Originally posted by jamarimutt
I experienced behavior 1 for the first time this morning. After going down a long hill and stopping at a red light, the ICE began turning on and off; it had done it three times before the light turned green. Thanks for pointing this out, Evan; I would have otherwise been afraid that something had gone very wrong.

You're welcome...now you can start thinking even further into this and try to figure out how to prevent that energy dump by minimizing regen or maximizing EV/stealth driving before that area where you're seeing the full SOC. No need to waste energy if it can be prevented.

[aforkosh]

Sometimes, it is almost impossible to prevent without major route changes. Here is my typical scenario that results in a 'full green':

1) Climb a 4% grade for 2 miles to a 1/3mile tunnel with a 2% dowgrade.

2) After the tunnel, coast down the freeway (at up to 70mph) 5% grade for 1.5 miles.

3) Brake to a stop on a long, almost level offramp to a traffic signal.

4) Coast down a 6 or 7% grade for 3 blocks.

At the end of this, I am almost always 'greened up'. If I lived in this neighborhood (the Rockridge district of Oakland, CA), that would be the normal final condition of the car when returning from work.

I actually proceed a few more miles to my home. I operate in stealth a good part of the distance, although one of my typical erands sends me up a 10 to 12% grade, giving the ICE a bit of a workout.

[efusco]

Originally posted by aforkosh
Sometimes, it is almost impossible to prevent without major route changes. Here is my typical scenario that results in a 'full green':

1) Climb a 4% grade for 2 miles to a 1/3mile tunnel with a 2% dowgrade.

2) After the tunnel, coast down the freeway (at up to 70mph) 5% grade for 1.5 miles.

3) Brake to a stop on a long, almost level offramp to a traffic signal.  

4) Coast down a 6 or 7% grade for 3 blocks.

At the end of this, I am almost always 'greened up'.  If I lived in this neighborhood (the Rockridge district of Oakland, CA), that would be the normal final condition of the car when returning from work.

I actually proceed a few more miles to my home. I operate in stealth a good part of the distance, although one of my typical erands sends me up a 10 to 12% grade, giving the ICE a bit of a workout.

Certainly there will be times...I don't mean to imply one is doing something wrong if they're topping off at green routinely. Rather, I suggest that if you find you're doing it routinely then perhaps you should look for means to avoid that where possible. That much of a descent for the entire route would certainly cause difficulties. Still, that 70mph stretch provides a good opportunity to practice the feathering technique and gliding rather than using the ICE which will, almost certainly in those conditions, have excess power it sends to the battery.

Also, that long off ramp if you can glide as you approach that and slow while gliding to avoid regen there you'll maximize energy saved as well.

Given all that, it still may be impossible and I don't want to imply you're a bad hybrid driver if you can't achieve that, but I certainly would use the commonality of that route to really try to maximize efficiency.

[DaveinOlyWA]

its situations like that where a larger power storage would come in handy.

the full charge indicator for the battery actually only represents a rather small range of charge. it is this range where the optimum life is achieved.

i think it would be nicer to have a battery pack that could say do 5-10 miles safely without the ICE. it could be used for short trips in town (these kill my mileage rating as i am positive i can exceed the EPA if not for these types of unavoidable trips and as the cold weather approaches i know my mileage will suffer even more)