My 2009 Prius experienced very high idling after decending from a 1/4 mile steep hill. The battery was indicating a max full charge at the bottom and the engine was revving higher than normal. I was stopped at the stop sign for maybe a minute or so before the engine just cut off completely. Was this an attempt for the car to burn off the excess energy produced from the hill decent? The car ran just fine the rest of my drive and being that was the only large hill, I'm thinking that might had something to do with it. Could I've damage my traction battery from this over charging or does the car not overcharge and have internal regualtors to prevent that? I also had my heat set to 72 degrees F, medium setting with an outside temp at 27 degrees F. I drive this hill 5 days a week and this was a first.
Yes, it was running off the excess charge. Yes, it minds itself; it would be a very poor design that depended upon the driver to manage the battery state of charge.
Yes, the HV ECU was using battery power to make MG1 spin the engine in order to reduce its state of charge. If, for example, you had turned off the car and let it sit for an hour when you got to the bottom of the hill, there would be the possibility for battery overheating and damage, but the car does a pretty good job at taking care of removing heat, as long as it is turned on and the HV battery fan is not clogged. The fact that this was a first in an otherwise daily routine for the past 3 years could be the first indication of battery wear, or it is just a random occurrence.
Thanks for the infomation, the extremely high engine idle had me worried too(a first), in the past at the hill the engine would idle like a normal engine would, say at 600rpm for example, this was more like 2,000-2,500rpms. I'm using this as an example since I didn't have a tach. I'll check the HV fan vent too to make sure it is not clogged. Is there anything as a user that I could do to prevent the build up of energy to the battery?
You don't want to "prevent the build up of energy to the battery". The computer will take care of it for you. Keep in mind that when the ICE spins off the excess energy, it is not using any fuel.
Yes. If you know that a descent will charge the battery to the limit, use B mode for all or some of the descent. Tom
Hi jgod12. Yeah this is totally normal behavior to dump excess charge. You'll find that it's not even burning any gas when this happens, MG1 is just spinning the engine to burn off some of the battery's energy. I've got one hill around here that frequently causes that exact thing to happen to me. It's a fairly steep hill, about 3/8 miles, and with a set of traffic light right at the bottom. If I get the green light and don't have to stop then I usually wont top 7 bars (or maybe just hit eight) and no charge will get dumped. If however I get the red light then the extra regen to stop there usually tips the balance and it starts dumping the charge. I usually come to a stop, look up and see all eight green bars, then two to three seconds later the engine starts spinning. It's pretty annoying becasue after those lights it's all flats and I can usually go about a mile just on electricity if I don't get the red light.
Had something like that happen to mine yesterday, coming down Monteagle and all of a sudden, the engine started revving really fast, and sounded different than when it does it accelerating. Threw me for a loop for a second and then I saw the SOC indicator and it was FULL, never saw it completely to the top before. I noticed if I shifted to B, the engine sped up even more. I am often amazed at the technology this thing has and how well it works.
I used the B mode this morning and didn't have any kind of engine idile at the bottom compared to yesterday. Same situation, same speed, the outside temps were a few degrees higher, heat set at 72 degrees, etc. I didn't realize the engine doesn't burn gas when burning off excess energy, how is this possible? Just wondering.. Thanks everybody for the posts!
One of the motor/generators of the HV traction system (MG1) essentially can function as a big starter motor for the engine. It's actually what starts the engine as it cuts in and out as you're driving around. Imagine if you took a regular car and disconnected the fuel pump and then just sat there cranking it over until you'd drained the battery. That's kind of what's going on, except obviously it's only trying to drain a part of the battery charge.
No, it won't. There is *less* regen in B mode. People often get this confused. B mode will produce more regeneration without touching the brake, and in a few point of the mapping it is more aggressive, but its main purpose is to toss away energy that would otherwise go to the battery. Tossing away energy does not recharge the battery faster (obviously). Use the brake if you have room in the battery. Tom
This happens to me often in the summer. Its fine. What I don't like is how the engine goes on and off and on and off repeatedly while I'm at a stop. People next to me look at me wondering whats wrong with my car.
There's no point in trying to use "B" to protect the battery; the battery takes care of itself. You use "B" to protect the brakes so that they don't overheat and fade. It takes quite a long downgrade before that becomes a concern.
