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#1 (permalink) Old 03-01-2009, 12:18 PM
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Default Battery Charging

Hi,

I have had my 2004 Prius for only six days now, so there is a lot I don't understand about it. The vehicle has 162k on it. I discussed something the car does with a friend, and he says it doesn't sound normal to him. When the battery gets a high charge on it and I come to a stop, for instance when I am stopping on a steep downhill grade, the engine will rev up a keep charging the battery. Then when I take off again, the battery will be used quite a bit. I have noticed my average mpg does go up for the next few minutes. Is this normal? I have no idea how the computers decide to charge the battery, use the gas engine, etc.

Thanks,
Dave

2004 Prius 162,000
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#2 (permalink) Old 03-01-2009, 03:16 PM
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Default Re: Battery Charging

That particular thing sounds normal. The computers work to keep the battery charge within a fairly narrow range (30% - 70% of total capacity) to maximize its life. If the battery has a lot of charge one of the electric motors may spin the engine without fuel as an air pump to use up some energy. (By the way, don't use "B" in normal city driving. It reduces fuel economy and should only be used to avoid riding the brakes on very long down grades.) What MPGs are you getting?

After five years some details of Prius control theory remain mysterious even to the most learned and fanatical of amateur gurus.

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#3 (permalink) Old 03-01-2009, 03:18 PM
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Default Re: Battery Charging

It's normal. When the HV battery gets a full charge, the ICE (internal combustion engine) will spin up to take the excess charge off the battery. It's not using any fuel during this time.

You can get some good Prius info from John's site here http://john1701a.com/.
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#4 (permalink) Old 03-01-2009, 03:32 PM
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Default Re: Battery Charging

Thanks guys!

That makes a lot of sense. I didn't have the impression that there was a problem, but spinning the engine without using fuel makes sense. I'm so used to ICE only cars, so when I hear the engine revving I thinking that gas is being burned.

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Dave

2004 Prius 162,000
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#5 (permalink) Old 03-01-2009, 04:14 PM
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Default Re: Battery Charging

Richard,

I'm getting about 46mpg according to the computer, so I think everything is working efficiently. Although I calculated my mileage by hand and got 51mpg. It's possible I'm not filling the tank all the way, but I haven't been on any significant kind of slope while fueling.

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Dave

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#6 (permalink) Old 03-02-2009, 02:02 PM
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Default Re: Battery Charging

You're doing well. The displayed MPG figure is accurate within a couple percent, much more so than any single or small number of "manual" MPG calculations, for reasons that are discussed ad nauseum both here and at http://priuschat.com

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#7 (permalink) Old 03-02-2009, 06:09 PM
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Default Re: Battery Charging

I am doing better than I expected. I was averaging 48mpg, but then I drove quite a ways loaded down with people and stuff. So it made sense to me that my average dropped to 46mpg by the time I filled up. I was initially hoping to average 44mpg, so I'm very happy. My 4runner gets 18, my van gets 20, and my volvo get 23. 46 is very nice!

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