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I was driving on EV mode with the battery well charged. All of sudden I saw the EV sign went off and heard the loud noise of the engine running. On the screen for vehicle energy, I saw a straight green line, indicating that engine was running to charge the battery. The whole episode would go away in a minute or so and the the EV sign would come up again. First it happened only once a week or so, but today it happened three times in my commute home. Does anybody know what this is?
 

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Two batteries to charge

In one of the three manuals available on the car, I read the 12v batterie is charged by the engine. I just did an on-line scan and couldn't find it but when I have the time I'll try again with my paper manuals. That could be one of the reasons the gas engine runs on occasion when it appears the traction batteries are well charged. The A/C and heater systems are powered by the traction (high powered batteries) batteries.

All of the cars run the engine in this manner, it's not abnormal. Remember to smile when you pass gas stations :smile_big:.
I was driving on EV mode with the battery well charged. All of sudden I saw the EV sign went off and heard the loud noise of the engine running. On the screen for vehicle energy, I saw a straight green line, indicating that engine was running to charge the battery. The whole episode would go away in a minute or so and the EV sign would come up again. First it happened only once a week or so, but today it happened three times in my commute home. Does anybody know what this is?
 

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In one of the three manuals available on the car, I read the 12v batterie is charged by the engine. I just did an on-line scan and couldn't find it but when I have the time I'll try again with my paper manuals. That could be one of the reasons the gas engine runs on occasion when it appears the traction batteries are well charged. The A/C and heater systems are powered by the traction (high powered batteries) batteries.

All of the cars run the engine in this manner, it's not abnormal. Remember to smile when you pass gas stations :smile_big:.
It would be impossible for the engine to charge the 12v battery since there is no alternator or even a fan belt. I believe the 12v is charged by the traction motor battery via the dc-dc inverter.
 

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Page 4 in online manual, main battery charges 12 volt

From Honda PHEV 2018 manual page 4, under Battery Type:

Battery Types
There are two types of batteries in this vehicle. A standard 12-volt battery, which powers the airbags, interior and exterior lights, and other standard 12-volt systems; and a high voltage lithium-ion battery, which powers the propulsion motor and recharges the 12-volt battery.
http://techinfo.honda.com/rjanisis/pubs/QS/AH/ATRW1818OG/enu/ATRW1818OG.PDF

I thought the Generator would have supplied a charge for the 12 Volt battery, but apparently the lithium-ion battery does.
 

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I see someone found another passage in the manual indicating the traction battery charges the car. I don't dispute that but I did read somewhere the 12v battery is charged by the engine running. I need to find it, I know it wasn't on page 4 but deeper in the book. It may have meant the 12v is charged from the generator (there is a 2nd generator/motor) when the engine is running. I still believe that, as the 12v needs a way to be charged when you're traveling cross country and only keeping the traction batteries charged via HV/charge. Maybe it gets it's charge both ways?

Either way, Honda figured it out. The 12v even runs the electric power steering.
It would be impossible for the engine to charge the 12v battery since there is no alternator or even a fan belt. I believe the 12v is charged by the traction motor battery via the dc-dc inverter.
 

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It would be impossible for the engine to charge the 12v battery since there is no alternator or even a fan belt. I believe the 12v is charged by the traction motor battery via the dc-dc inverter.
I meant to say dc-dc converter not inverter since it's already dc voltage and inverters basically inverts ac to dc. My understanding is that the dc-dc converter powers ALL 12v devices in the car passing current thru the battery and out to the 12v devices. The 12 v battery does not have the capacity to power the headlight, heater, ac, power steering, wipers,defroster,radio, and power seat if they all came on load at the same time.Any 12v load is taken from the 348dc traction battery by the dc-dc converter and sent to the battery where it's taken out by the 12v devices. It is also my understanding that the ONLY job of the 12v battery is to close electrical contacts to "wake up" the electrical system to get the car ready for duty.
 

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Two batteries to charge

In one of the three manuals available on the car, I read the 12v batterie is charged by the engine. I just did an on-line scan and couldn't find it but when I have the time I'll try again with my paper manuals. That could be one of the reasons the gas engine runs on occasion when it appears the traction batteries are well charged. The A/C and heater systems are powered by the traction (high powered batteries) batteries.

All of the cars run the engine in this manner, it's not abnormal. Remember to smile when you pass gas stations :smile_big:.
Sorry but I believe the 12 volt battery is charged by a power inverter from the high voltage motor battery. The engine has no alternator like a normal gas powered car. It gets power from the motor when it's run off of the engine like a generator.
 

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Sorry but I believe the 12 volt battery is charged by a power inverter from the high voltage motor battery. The engine has no alternator like a normal gas powered car. It gets power from the motor when it's run off of the engine like a generator.
but somehow my 2018 Clarity gasoline engine turns on without the hybrid mode by itself even when the big battery is fully charged, I thought it is for charging the 12v battery.

Any feedback will be appreciated.
 

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but somehow my 2018 Clarity gasoline engine turns on without the hybrid mode by itself even when the big battery is fully charged, I thought it is for charging the 12v battery.

Any feedback will be appreciated.
The gasoline engine can turn on for various reasons even with a full traction battery. But charging the 12V battery is not one of them. The 12V battery is charged by the traction battery via the DC-DC converter. This occurs anytime the car is in READY mode, even when the engine is not running.

The gasoline engine will turn on with a full HV battery if you press the accelerator past a certain point. Even if you only do this for a brief moment, once the engine starts it will remain on for a few minutes until it warms up, then it will shut off again.

Another situation is when you leave home with a full battery and within the first mile or so do any kind of regen like using the paddles or pressing the brakes, since the HV battery is full it has no place to store the electricity being generated by regen so it spins the gas engine to dissipate the energy, this causes the gas engine to start up and once started it will run for a few minutes until it is warmed up.

Some people drive relatively short distances each day and almost never use the gas engine. After a month or so of not being used the gas engine will start up on its own and go through a warmup cycle.
 

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but somehow my 2018 Clarity gasoline engine turns on without the hybrid mode by itself even when the big battery is fully charged, I thought it is for charging the 12v battery.

Any feedback will be appreciated.
The gasoline engine is definitely not turning on to charge the 12v battery because there is no alternator on it that would facilitate this. Most likely it is running either because the load you’re imposing on the hybrid battery is too high or the car thinks the engine has not been running enough to circulate oil or burn gas that is getting too old.
 

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If you press hard enough fast enough on the gas pedal the engine will come on to add additional power to help improve acceleration. It may not rev up right away due to a warm up phase. Try flooring the gas pedal and you will see the engine will come on. (One possibility I can think of).

Other possibility (I'm guessing) is something I learned about recently on this forum, sticky buttons, foreign material got underneath and is activating the mode.
 

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If you press hard enough fast enough on the gas pedal the engine will come on to add additional power to help improve acceleration. It may not rev up right away due to a warm up phase. Try flooring the gas pedal and you will see the engine will come on.
The best way to observe it is to watch the power meter. As long as you keep it in the blue area it will stay in EV. You can press the accelerator and bring it right up to the gray area, but as long as you keep it in the blue it will stay in EV. But the moment that you cross over into the gray area the engine will come on. But you likely will barely hear it as it immediately goes into warmup mode at low RPM. The only time you really hear the engine is if you press the accelerator well into the gray area. But if you just barely go into the gray area, especially if it's just for a brief moment, then you likely won't even hear it. Then what happens is a couple of minutes later you notice that the engine is running, and it seems like it was totally random because we don't always connect it with the slightly high acceleration that we did a couple of minutes ago, which by then we have probably forgotten about. I think this is what leads to a lot of the perception that the engine just comes on at any random time for no reason, when that is not the case. People still insist that it comes on totally random, but unless they post a video showing the previous five minutes of driving, then I reserve the right to believe that they did something inadvertently to start it.
 

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Page 4 in online manual, main battery charges 12 volt

From Honda PHEV 2018 manual page 4, under Battery Type:

Battery Types
There are two types of batteries in this vehicle. A standard 12-volt battery, which powers the airbags, interior and exterior lights, and other standard 12-volt systems; and a high voltage lithium-ion battery, which powers the propulsion motor and recharges the 12-volt battery.
http://techinfo.honda.com/rjanisis/pubs/QS/AH/ATRW1818OG/enu/ATRW1818OG.PDF

I thought the Generator would have supplied a charge for the 12 Volt battery, but apparently the lithium-ion battery does.
This is typical of most E.V's. 12 volt battery will drain fast, of not continuously charged. Traction battery always charges the 12-volt battery. As for why the engine runs in E.V. Mode, it does say in the manual, that if you do not run the gas engine for a long period of time, that occasionally the engine will start to keep the oil circulated. However, it does not define how long it has to go without running to initiate this feature. I have gone up to 2 weeks of back to back E.V. driving, & not had the engine start, even once. Especially if it did it, on your car, 2 days in a row, it's probably for a different reason. I'm not sure.
 
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