What is the highest SOC you have seen?

I often see 80% coming down mountains, at which point it stops charging the battery. I hypermile, so I avoid getting low SoC (it reduces your mileage, in general), but today I hit 45%, which triggers the engine to come on and charge the battery (A/C was draining the battery quickly, and I was moving at about 10 mph, so running the engine was pointless). Those are the normal ranges - I don't think there's any way to get over 80%. To get below 45%, you'd probably have to be in Neutral and the computer will start yelling at you to shift to Park or Drive so it can avoid damaging the battery.

If you really did see 33.3% in normal driving, I'd wonder if your gauge is programmed incorrectly... Or maybe it's scaled to show 0% when the real SoC is 45%, and 100% when it's really 80%.

 

You must have a SGII because I only get bars to tell me what my SOC is.

 

I believe you, but I don't fully understand all the reasons behind this fact. Can you please explain more? Thanks!

 

Under normal driving conditions only a small amount of energy is generated by braking. The majority of energy stored in the HV battery is generated by?

Answer this question and you will find the answer to your question.

 

I don't worry if my SOC gets low just before I head up the hill to my home since I know that the engine will be on & charge the battery on the trip. Now if I could figure a way to get up the hill & not drop my mpg like a rock I would be happy.

 

How many bars does the car itself show? If it shows at least 2, then I'd suspect your gauge is wrong. If it shows 1 bar, and if the MFD gives you warnings (like "Low traction battery, shift to P position"), then the gauge is correct and your car should be checked out.

 

And strictly speaking, braking doesn't generate any energy - only burning gasoline does. So the simple fact that you recovered some of the energy while braking just means that you burned too much gasoline in the first place.

To answer markabele's question less coyly, except for cases where the engine is extremely inefficient (parking lots, very slow traffic jams), it's better to use the engine briefly and then coast. This directly uses the engine's power to propel the vehicle. If you use electric power, then it has to be replaced at some point in time by the engine. Doing this has all the same inefficiencies (limited thermal efficiency of the engine, drive train loss, etc.), plus many more (converting the mechanical energy from the engine's driveshaft to electrical energy, converting the motor's alternating current to direct current, converting the direct current to chemical energy in the battery... And then the reverse process to use the chemical energy again).

So you're better off using power directly from the engine most of the time - and when you're not better off, you won't be using very much power from the battery, so it's not going to draw your SoC very low.

Well, if your SoC is low, the engine will work harder because it's charging the battery while you go up the hill. I can notice a difference in engine RPMs relative to position on the HSI when the SoC is as little as 2% away from the 60% level the computer tries to maintain. If the hill is gradual enough that the extra charging means the engine runs at 2000 RPMs instead of 1500, that might be a good thing. If the hill is steep and the engine has to run at 3500 RPMs instead of 3000, then it might really hurt your efficiency going up the hill.

When I was down around 45-50% SoC the other day, I noticed that I was hitting ~2100 RPMs (my typical target while accelerating) when the fat part of the HSI was about 3/4 full. Normally, at 60+% SoC, I'm up to maybe 1/4 of the way through the PWR bar at those RPMs. The extra engine power was going to the battery, and I was having to run the engine for longer at my target RPMs to get up to speed.

 

And all that said, the Prius computer does pretty well if you just drive it like a normal person. Sometimes, trying for high efficiency is even counterproductive, resulting in lower mileage. However, I am not a normal person, I'm a huge nerd. You may be more normal than I, in which case the "Just Drive It" mantra applies - it really does work very well.