HV Mode question

You can do this with "HV Charge" mode. It will essentially maintain the battery at about 60%. Unfortunately, it won't stay in this mode after you turn the car off, so every time you drive it you have to remember to put it back in the mode you want (if the desired mode isn't EV).

You could also use HV mode (and a little EV when you want quiet operation) and then just pick times to use HV Charge to build the battery back up to 60%.

 

Not quite. You'd have to remember to push the button for HV every time you turned out on, and it can't actually keep the charge at the exact same point. On a trip from Texas to Alabama, HV all the way aside from a few consecutive seconds before I push the HV button after stopping for gas, it still goes through plenty of the battery. At 15¢/kWh, for about 3 miles per kW, means gas at 45 mpg must be below $2.25 to match. But if you don't have a plug at all... It does get great mpg on gas for being a big roomy sedan, and you can always switch to "HV charge" if you're worried the battery is too low.

 

For your situation I’d recommend the following.

1) After a full charge, use at least one bar off the top of the battery gauge, or 3-4 miles of EV range. This will prevent regenerative braking energy from starting the engine.
2) Remember to press HV every time you “start” the car. Otherwise, you’ll burn those precious EV miles.
3) When the battery gauge gets to 2-3 bars, engage HV Charge. Ideally, at a time when you can drive for 30-60 minutes at a sustained high speed (45mph or better) to allow for a “full” charge, 60%.
4) Seek out public “free” chargers whenever possible.

You will likely lose a few percentage points of charge every time you turn off the vehicle. Long, but true story. So, the more frequently you turn the car off and on, the sooner you will need to recharge.

 

I raised this issue about a year ago and everyone speculated that I would lose enough efficiency in the changeover that I should just drive long distances in regular HV mode. I’d like to report that I have essentially used Landshark’s strategy on all my long distance trips with really excellent results. My caveats are 1) It takes alot of minding to be switching back and forth, 2) I have to stop and reboot to go from HV Charge back to EV (?), and 3) on a long road trip, using the hybrid motor getting north of 42 mpg on level freeways seems pretty easy and virtuous, especially if you leave enough emergency electrons in the battery.

I see no benefit to starting my car in HV. I haven’t had instances where my car wanted to switch to HV as long as I have some EV left, even when I’m on the highway. My goal is to use EV as much as possible, recharging as I go. When I get near the end of the battery, then I recharge with HV Charge.

 

Yes, the battery will drain as you drive in HV mode. As @Landshark said, the biggest hit is that it will use some EV every time you stop the car and restart, even if you immediately go into HV. But even just driving in HV, it has been my experience that EV range will slowly go down. HV Charge will get back any lost miles up to 60% and from what I have seen using HV Charge at speeds from 40-60 MPH on level roads won't hit efficiency and might even increase it a little above HV only.

 

In my experience, HV mode does pretty well at holding the state of charge.

As others have stated though, every time you stop and restart, a new set-point gets established which is almost always a little lower than it was before you stopped. And of course, if you forget to re-engage HV immediately, you will lose some charge before you get around to hitting the button.

Also, depending on the terrain, there may be situations where the charge droops farther below the set-point (a sustained up slope). If you level out for a while or reach a down-slope, I find that it does recover back to the desired point.

I have found that you can drive indefinitely in HV on a reasonably flat road at normal speeds and not lose any battery charge. Some have reported that their vehicles constantly lose charge. It is unclear why there would be differences like this.

 

I’m not familiar with the nuances of the Volt. To elaborate, in HV mode, the Clarity will “maintain” the SOC that existed at the time HV was engaged. This is commonly referred to as the set point.

It has been discovered that the SOC typically drops ~4% from the set point before the engine/generator begins to recharge the battery. Under certain conditions, high power demand for example, the SOC may drop more than 4% below the set point. Since the car uses energy from both the battery and engine in HV mode, it would be next to impossible to maintain the SOC at a precise level. Given sufficient time, the car will restore the SOC to the original point.

The takeaway is, unless you manage to only turn the car off at the exact moment the SOC has been restored to the set point, the car will always start up at a new, lower, set point.

 

When Clarity was a new model, a common complaint was that the dealers would leave the car at zero charge on the lot, possibly for a few months or so, and the concern was that this could damage the traction battery. Some dealers presumably didn't want additional cost of installing their own level 2 charger and it was also speculated that it would be no-good to use the level 1 charger that comes with the car. i.e. want to keep it new.

I now know enough (from ~3 years of driving Clarity), that there was a simple solution-> HV Charge. Dealers could of simply put enough gas into Clarity to run HV charge to keep EV range while the car waited to be purchased. I also know from experience you can go from EV range of 0.0 hold the HV button and HV charge will absolutely take the car up to about 50% charge.

This also means folks who never plugin can maintain a reasonable charge. This may be because electric is costly where they live or they simply lack access. I find Clarity drives great as a hybrid. Just get in and press HV before each trip (unfortunate only that this setting isn't 'sticky'). And if and only if the car has more than 10 miles of EV range. I am not a proponent of leaving the EV range at zero and driving that way. It's a way better experience to have at least 10 EV miles all of the time. I say this as you'll see the car "borrow" against EV range as it goes up a grade/hill, then on a typical trip it will try to replenish the EV range back to what it was.

BTW I do realize folks mileage/experience does vary. My Clarity has always lost a little EV range even in HV mode, so I do at intervals require HV charge mode. This isn't new for my car, it was like this since day 1.

 

LOL, after owning the Clarity for about a year, now I know about engaging HV charge by holding down the HV button, thx to this thread. I might not need it, but it's nice to have and nice to know it exists

 

Our Clarity makes a brave attempt to hold a “set point” in HV mode. Starting over a mountain with 10 EV miles remaining, it can drop as low as 6 while climbing, but will recover back to 10 when descending on the other side.

That said, on a round trip to Florida we kept track and watched a gradual degradation over time:



The above chart also confirms the Honda’s mpg estimates are consistently about 12% optimistic, which I still think must be intentional - and deceptive.

 

Over the last three years, I used HV for a high percentage of driving. I too have little access to a charger and bought the vehicle because of carpool stickers. Even when the vehicle is in HV, electric car miles drop. For example, if I drive up a steep grade, EV miles will drop significantly.

Get a Chargepoint card. I would count on charging it periodically.

 

This behavior has been well documented on this forum. Have you driven the car a sufficient distance on flat terrain, after driving uphill and observed EV range? It may take 5 or more miles, but it will return to the set point.

 

I am very familiar with HV mode and regen braking. I have driven the vehicle 30,000 miles, roughly 90% in HV mode. I press the HV mode as soon as I start the vehicle and it's on at all times. The climate is very moderate, and I'm not making any significant use of either the A/C or ventilation or heat.
1. If I fully charge the battery and then immediately drive it in HV mode on the freeway at 65 MPH, even on flat terrain, it typically immediately loses a few miles of charge.
2. After driving in HV up a steep hill, and then driving 20 miles or so on fairly flat terrain (or back downhill) at less than freeway speeds, the vehicle still has lost a few miles of EV charge.
3. Driving in urban areas at low speed in HV, the vehicle loses a bit of EV mileage each time. It can come close sometimes, but still losses.

The end result for me has been that in a mix of driving situations always in HV, the EV mileage drops continuously (but not abruptly unless on a hill) over a week. I can either recharge the car or use HV charge mode when it gets below about 57%.

 

This also is typical. The reason, it is believed that this occurs, is so that the car can utilize full regenerative energy capture without starting the engine.

This is unusual, in my experience.

 

Those MPG calculations are brought to us by the same people who brought us, CMBS, RDM and LKAS. It could just be, that it’s the best they could do. At least it’s consistent.

 

The vehicle is very economical to run, especially considering its size and weight. However, I would not want to be in some remote area far from refueling options, relying on the displayed "optimistic" range.

 

I'd like an explanation of point #1 - how or why would regenerative braking energy start the engine. ?!?
I rarely charge our Clarity to 100%, but several times (when I have) I noticed the engine had started very soon after driving away from our house, and I could not see any reason why it would be running the engine!! (It makes no sense to me for the car to start the engine with 100% SOC.) Driving thru our subdivision I'm certainly not "getting on it" with the accelerator, just nice and easy.
Explanation, please?!?
Do I have to drive 3-4 miles without using the brakes after 100% SOC to keep from starting the engine?

 

Honda's Insight and Accord hybrids, use the starter motor/generator turn a deadened engine to use up excess regen energy that cannot go to the fully charged battery. That ploy wasn't continued in the Clarity PHEV. Perhaps it has something to do with the Clarity's greater weight; perhaps it has something to do with the Clarity's larger battery--I cannot think of any other differences. What the Clarity does is burn gasoline running the engine to use up excess regen energy that cannot go to the fully charged battery. No one from Honda has explained this mysterious behavior.

So you have to not only avoid braking, but also the regen paddle to prevent unwanted engine start-up after fully charging your Clarity's battery. Although in frustration you may be tempted to pull over and turn your Clarity off and on again to stop the engine, it's a better idea to let the engine warm up and get the oil circulating before it decides you've suffered enough internal combustion and shuts off the engine.