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Discussion Starter · #1 ·
Today, in HV mode, at the light, my engine started charging my battery while my battery was over 80% charged. I was not it HV Charge mode. I knew I was not in HV charge mode because not only did it not say "Charge" on the dash, but when I tried to engage HV Charge the message said it was not available due the how charged my battery was already, but continued to charge. I then put it in EV mode, no change. Then turned the car on and off to get it to stop. Is this normal? Im on my first month of ownership of a 2020 clarity. Any ideas?
 

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Not very common for it to do that. You are saying the engine turned off when you stopped at the light, then it came back on while you were sitting there? About how long were you sitting at the light before the engine started, half a minute, several minutes? How long had you been driving in HV mode prior to this, long enough for the engine to have warmed up? Was the A/C running at this time and if so how hard? Don't infer anything from my questions I am just trying to get a picture of the situation.
 

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It can. If the engine is generating more power than needed the excess is fed back into the battery.
 

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Discussion Starter · #4 ·
Not very common for it to do that. You are saying the engine turned off when you stopped at the light, then it came back on while you were sitting there? About how long were you sitting at the light before the engine started, half a minute, several minutes? How long had you been driving in HV mode prior to this, long enough for the engine to have warmed up? Was the A/C running at this time and if so how hard? Don't infer anything from my questions I am just trying to get a picture of the situation.
No- the engine was engaged while driving in HV mode. I was driving between 30-45mph up a long but not very steep gradient. I had been driving on that road, that way, for a few min before I came to a red light. When I stopped, the engine continued to run and send all the energy into the battery (long green line from engine to battery). My Air was on, but on low. I had been driving for about 5 min total, most of the time in HV.

Any ideas? Since I was at a light anyway I ended up turning off the car and turning it back on and it was fine.
 

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I had been driving for about 5 min total, most of the time in HV
This is the key piece of information, and why I was asking. When you first switch to HV the engine will come on but it first goes into a warmup period where it will just idle as it warms up. During the warmup period the engine will produce little if any electricity. You can see this by observing that your EV range will continue to decrease while the engine is warming up. After the engine is warmed up then it will start producing electricity. If the car is stopped at a light after the engine is warmed up the engine will usually shut off. In most cases that is.

Your situation was different because you were climbing a slight grade during the engine warmup period, so it used up more than the usual amount of battery power during that time. Even though you had plenty of charge (80% as you said) the way HV works is that when you first activate HV it creates a "set point" at whatever SOC you are at when you activate HV. From that point forward as long as you remain in HV mode the engine will come on as needed when the SOC drops below the set point. In normal situations when you stop at a light you would at the most be only slightly below the set point and so it won't turn the engine on while stopped. But in your case I think it's the fact that your SOC would have been way down due to the slight but long upgrade, again during a time when the engine was contributing little if anything due to it being in warmup mode. So in that less than common scenario it's not surprising that even while stopped at a light the engine remained on to continue charging the battery. It is however slightly surprising that when you turned of HV while sitting at the light that the engine didn't turn off. But I suspect that's because the engine was still not fully warmed up, and since the SOC was pretty far below the set point, it decided to keep the engine running to charge the battery while it continued warming up the engine.

There is no official documentation of any this by Honda. I suspect that they consider this level of intricacy about the operation of the system to be proprietary information. So we can only infer things from what we observe, and by noticing what the usual patterns are. Then if things work differently in a particular case we can try and think what may have been different this time, in this case a slight uphill climb during engine warmup ending at a stop light. Now if you see it happening in other situations like flat driving and a fully warmed up engine, then something else is causing it.

If you are interested in the workings of the Clarity you can get an inexpensive OBD-2 scanner and a free bluetooth app for your phone, which will show engine RPM and coolant temperature among other things. Of course the great thing about the Clarity is that you can also just drive it and not think too much about these type of things, unless you find it interesting.

A good thread to read about an OBD-2 scanner and free app is located here:

 

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The manual says the battery will only charge to 57% on HV mode. If your battery state of charge is higher then it won't be available until 56% or lower. I used it on my drive from Los Angeles to Southern Utah a few times when on level ground or slightly downhill stretches. The engine will rev a little higher and your fuel economy will suffer a little, but you get it back when running in electric mode.
 

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Discussion Starter · #7 ·
This is the key piece of information, and why I was asking. When you first switch to HV the engine will come on but it first goes into a warmup period where it will just idle as it warms up. During the warmup period the engine will produce little if any electricity. You can see this by observing that your EV range will continue to decrease while the engine is warming up. After the engine is warmed up then it will start producing electricity. If the car is stopped at a light after the engine is warmed up the engine will usually shut off. In most cases that is.

Your situation was different because you were climbing a slight grade during the engine warmup period, so it used up more than the usual amount of battery power during that time. Even though you had plenty of charge (80% as you said) the way HV works is that when you first activate HV it creates a "set point" at whatever SOC you are at when you activate HV. From that point forward as long as you remain in HV mode the engine will come on as needed when the SOC drops below the set point. In normal situations when you stop at a light you would at the most be only slightly below the set point and so it won't turn the engine on while stopped. But in your case I think it's the fact that your SOC would have been way down due to the slight but long upgrade, again during a time when the engine was contributing little if anything due to it being in warmup mode. So in that less than common scenario it's not surprising that even while stopped at a light the engine remained on to continue charging the battery. It is however slightly surprising that when you turned of HV while sitting at the light that the engine didn't turn off. But I suspect that's because the engine was still not fully warmed up, and since the SOC was pretty far below the set point, it decided to keep the engine running to charge the battery while it continued warming up the engine.

There is no official documentation of any this by Honda. I suspect that they consider this level of intricacy about the operation of the system to be proprietary information. So we can only infer things from what we observe, and by noticing what the usual patterns are. Then if things work differently in a particular case we can try and think what may have been different this time, in this case a slight uphill climb during engine warmup ending at a stop light. Now if you see it happening in other situations like flat driving and a fully warmed up engine, then something else is causing it.

If you are interested in the workings of the Clarity you can get an inexpensive OBD-2 scanner and a free bluetooth app for your phone, which will show engine RPM and coolant temperature among other things. Of course the great thing about the Clarity is that you can also just drive it and not think too much about these type of things, unless you find it interesting.

A good thread to read about an OBD-2 scanner and free app is located here:

Thanks. that was a great answer. I appreciate it.
 
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