Theory: Use EV mode just before home...

[ZTrekus]

Still waiting to pick my space ship up from the big T so I can't test my theory out but what do you guys reckon?

The theory goes like this:

1) All batteries left unattended will self-discharge to some extent;
2) But batteries with a greater charge will discharge at a greater rate (at least initially - that is non-linearly);
3) Therefore to conserve fuel - one is better off storing the car with minimum charge in battery (ie - better to leave energy stored as petrol in tank rather than as charge in battery).

THUS - better to run the battery down as much as possible by shifting into EV mode a mile or two before home every time - or before any extended period of inactivity...

Since I don't have my car yet, this is alas a thought experiment for me - but any seconders on this theory or am I just blowing hot air?

[ZTrekus]

There is another advantage of course.

They say most accidents occur on the way and close to home (the carelessness factor creeping in). Well when close to home and switching into EV mode to run the battery down, I am guessing it would have to be a real challenege to actually keep the car IN EV mode for that last mile. That's got to slow the driver down and cause her/him to be more careful at that risky accidental statistical danger zone thingo...well you get the drift.

[Ogo]

Self discharge rate of Ni-MH battery is quite low. And this procedure does not make much sense for parking your car over night. Even over weekend.

Ogo

[CivicQc]

Originally Posted by ZTrekus

The theory goes like this:

1) All batteries left unattended will self-discharge to some extent;
2) But batteries with a greater charge will discharge at a greater rate (at least initially - that is non-linearly);
3) Therefore to conserve fuel - one is better off storing the car with minimum charge in battery (ie - better to leave energy stored as petrol in tank rather than as charge in battery).

That is a very interesting theory - not easy to test though. My main concern would be that the instruments in the Prius are probably not sufficiently precise to provide you with the data that you would need to support it. I believe a battery does not loose much power during a single night. So you would need to find a way to measure very precisely the charge level of a battery.

[CivicQc]

I have several other similar things I want to test myself. For instance: I live on top of a hill. I know in the next morning I will be able to recharge the battery when going back to work (going downhill). The hill is 400 m long, and slope peaks at 18%. I wonder what charge level I should aim for when parking my car in the evening in order to get full charge the next morning at the bottom of the hill (to make sure I dont use brakes), this way optimizing the use of battery.

[rahamanmd]

Originally Posted by ZTrekus

Still waiting to pick my space ship up from the big T so I can't test my theory out but what do you guys reckon?

The theory goes like this:

1) All batteries left unattended will self-discharge to some extent;
2) But batteries with a greater charge will discharge at a greater rate (at least initially - that is non-linearly);
3) Therefore to conserve fuel - one is better off storing the car with minimum charge in battery (ie - better to leave energy stored as petrol in tank rather than as charge in battery).

THUS - better to run the battery down as much as possible by shifting into EV mode a mile or two before home every time - or before any extended period of inactivity...

Since I don't have my car yet, this is alas a thought experiment for me - but any seconders on this theory or am I just blowing hot air?

I agree with your theory. I have had similar thoughts recently and started this practice myself. The engine runs and warm up in first start of the day, and will recharge an undercharged battery anyway.

[qbee42]

Not a good theory, and in fact it will be counter-productive. The self discharge rate for the NiMh battery is very low - not even a factor over such a short time. A much bigger factor is the cost of generating electricity, storing it as chemical energy, converting it back to electricity, and using that to move the car. There are a lot of losses in the conversions, which should be avoided if possible. Your proposal increases the required conversions, which will cost you mileage.

A second disadvantage is that you will be doing the recharge at the ICE's least efficient point: warm up. It is better to start with a higher SOC and let the ICE take it easy during warm up.

One other minor point relates to self discharge rates and how they vary with charged batteries verses discharged batteries. With the Prius, the HV battery SOC swings over a narrow range in the middle of the charge curve. Seldom does it swing very far, and never does it charge up and discharge like you would with a flashlight battery. That would be too damaging to the battery and would severely limit its service life.

Tom

[Muhahahahaz]

The negligible amount of self-discharge may not be a very good reason to use EV.

However, since the ICE needs to warm-up during the next start anyway (and will thus charge the battery), using EV during the last leg may still end up being more efficient.

That's how I see it anyway, although I have only owned my Prius for about a week. Also, my Prius is from 2007, so I don't even have an EV mode right now. However, I may add the Costal eTech solution sometime soon.

Edit: Sorry, I didn't see Tom's post since I opened a bunch of threads together some time ago...

[rahamanmd]

Originally Posted by Muhahahahaz

The negligible amount of self-discharge may not be a very good reason to use EV.

However, since the ICE needs to warm-up during the next start anyway (and will thus charge the battery), using EV during the last leg may still end up being more efficient.

That's how I see it anyway, although I have only owned my Prius for about a week. Also, my Prius is from 2007, so I don't even have an EV mode right now. However, I may add the Costal eTech solution sometime soon.

Edit: Sorry, I didn't see Tom's post since I opened a bunch of threads together some time ago...

I think 100 yards of EV into the garage at the end of the day cannot be bad. Helps reduce emission fumes in the garage too! After all why was the EV mode created in the first place?

[royrose]

Originally Posted by CivicQc

I have several other similar things I want to test myself. For instance: I live on top of a hill. I know in the next morning I will be able to recharge the battery when going back to work (going downhill). The hill is 400 m long, and slope peaks at 18%. I wonder what charge level I should aim for when parking my car in the evening in order to get full charge the next morning at the bottom of the hill (to make sure I dont use brakes), this way optimizing the use of battery.

I am in the exact same situation, almost identical distance and slope. Mine is a little curvy as well. I can't go very fast up the hill, so the speed limit of EV would not be a problem.

So, I wonder if the electric motor, with it's plenty of torque, would be more efficient going up the hill vs the ICE. In fact, I assume the electric motor would be assisting the ICE going up the hill in normal mode.

one of the posts criticizes using regen on startup, but with my hill, breaking is necessary down the hill, so why not get regen going down and therefore, why not use EV going up? I assume that poster was responding to the first post, not your uphill/downhill question.

Edit: come to think of it, some loss of charge would probably happen going up the hill in normal mode, so it is probably a matter of degree. Time and experimentation will tell.