driving on a depleted battery

Discussion in 'Clarity' started by ProspectiveBuyer, Oct 26, 2018.

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  1. I've mainly driven with a charged battery. But tonight I ran out of charge and was alarmed at the strain on the engine when it transitioned to gas only. Mind you, I was going uphill. But it wasn't that steep a grade. Does it make a difference that I was still in EV mode? Should I have switched to HV and would that have made it drive smoother? I didn't think quickly enough to switch to HV mode.
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  3. jdonalds

    jdonalds Well-Known Member

    The car will switch to Normal mode when the battery is depleted. If you don't have charge in the battery it won't make a difference what mode you put it in. The engine will run.
    insightman likes this.
  4. PHEV Newbie

    PHEV Newbie Well-Known Member

    That's the Dr. Jekyll and Mr. Hyde personality of the Clarity that's caused the car to be misunderstood, sometimes resulting in bad reviews. If you hold a significant charge in the high voltage battery, the car is an excellent performer in either EV or HV mode. Once the battery is depleted, it can run adequately in most circumstances but it is very power limited resulting in a very unsatisfying and potentially dangerous experience when you need power. Here, the car relies almost entirely on the ICE to generate electricity to power the traction motor to avoid drawing from what's left of the battery, protecting it from damage. Note that the Honda Accord Hybrid has a much bigger, more powerful ICE to generate electricity to its otherwise identical drive system even though the car is nearly 700 lbs lighter than the Clarity. Why? Because it has a Li ion battery a tenth the size of the Clarity, which cannot provide much power on its own. That Honda installed a much smaller ICE in the much heavier Clarity says that it is not meant to be driven with a depleted battery, because you won't receive the full performance of the drive system. I don't know how much power you have relying entirely on ICE/generator but it's likely to be significantly less than the peak 103 horsepower that the ICE can produce near the redline (i.e., if it is screaming), possibly only 61 hp (battery alone can produce 120 hp; battery + ICE produces max 181 hp). Just think about it. Driving a 4,054 lb car with less power than the minuscule two seater Smart Car puts out. It's no wonder why some reviews have been terrible. They were driving the Clarity with a depleted battery. You should avoid driving the Clarity with a depleted battery if at all possible. It could even be dangerous in emergency situations. In addition, HV mileage seems to be much better if you keep a major charge in the battery so it's better for the environment and your pocketbook.
    Last edited: Oct 26, 2018
    Dan Albrich and ClarityDoc like this.
  5. insightman

    insightman Well-Known Member Subscriber

    The ICE + electric power = 181 hp calculation has always been a mystery to me. Why is the total not 103 + 121 = 224? Is 61 (~45.5 kW) hp the maximum the starter motor/generator can produce? Is the Clarity's mechanical-to-electric energy conversion process so inefficient that 103 mechanical horsepower is reduced to 61 horsepower? Are the horsepower curves of the ICE and the electric motor so different that 61 hp is the peak power of the combo when the ICE is at full revs?

    Or is 103 hp available in "angry bees" mode, the only time the ICE is operating at full tilt and 61 hp available when the ICE is operating at the lower RPMs used when supplementing the battery's power?
  6. PHEV Newbie

    PHEV Newbie Well-Known Member

    It's a mystery to me too. It's possible that the traction motor is limited to 181 hp so the combined output from battery + ICE could power a more powerful traction motor. The other possibility is that it's the maximum electric output from the generator, which is less likely because I would think that Honda would have installed a sufficient generator to maximize output from the ICE. The big question is what is how much horsepower can the traction motor produce if all the electricity is coming from the ICE/generator. I imagine it must be less than 103 hp because you lose some energy converting that power to electricity and again when converting electrical energy to kinetic energy. Regardless of what the actual power is, it's far less than you can have when combining total power from combining the ICE and a charged high voltage battery.
    insightman likes this.
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  8. Bas

    Bas New Member

    It was my understanding that the battery can provide 121HP to the traction motor. And the ICE can provide a total of 103HP. However, the generator is only designed to supply 60HP of the 103HP to the traction motor. (bringing the total of the traction motor to 181HP). The other 40HP of the ICE becomes available at higher speed when the mechanical clutch directly couples it to the output shafts.
  9. PHEV Newbie

    PHEV Newbie Well-Known Member

    The ICE delivers 103 hp at 5500 rpm and 99 ib ft torque at 5000 rpm. These figures are from the engine itself, not at the drive wheels or the traction motor. It is unclear how much horsepower can come through the traction motor if the only electricity comes exclusively from the ICE producing electricity through the generator, but it's not very much.
  10. Bas

    Bas New Member

    It was my understanding that the battery can provide 121HP to the traction motor. And the ICE can provide a total of 103HP. However, the generator is only designed to supply 60HP of the 103HP to the traction motor. (bringing the total of the traction motor to 181HP). The other 40HP of the ICE becomes available at higher speed when the mechanical clutch directly couples it to the output shafts.
    It would be great if the traction motor power curve was published. I assume an almost standard torque till it reaches max HP (still under the understanding that is 181HP with the ICE assisting the battery). And then following a constant power curve until it reached max speed of the motor. It would also be nice to know what the ratio is of RPM of the traction motor vs speed of the car. And at what RPM the traction motor starts following the power curve. If we would have the same info for the traction motor, then we could probably figure out everything we like to know.
  11. kcsunshine

    kcsunshine Active Member

    Numbers aside, I think driving the Clarity requires some planning especially for longer trips when you know you can't charge soon. I would try to maintain a charge on the highway by using the HV mode. When you need some power, turn off the HV mode and let the car decide what to do. I think if the car is in HV mode, it will try to charge the battery when you need the power. If the battery is already low, turn on HV charge mode while cruising. If you are near your destination and can charge soon, run in normal mode. Of course there will be times when you can't maintain a charge. I spoke to a Prius Prime driver and it sounded like it was even worse. Once the car is out of charge, it lacked power.
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  13. insightman

    insightman Well-Known Member Subscriber

    The i-MMD system operates in 3 basic, underlying drive modes: EV Drive mode, Hybrid Drive mode, and Engine Drive mode. In EV Drive mode, the Clarity PHEV produces up to 121 hp. In Hybrid Drive mode, when the battery and ICE are both powering the traction motor, the Clarity PHEV produces up to 181 hp. Honda claims 212 hp max for the Clarity, so that peak must come from Engine Drive mode, when the clutch locks the output from the ICE to the single-speed transmission.

    Apparently, if you stomp on the accelerator while in Engine Drive mode, the Clarity PHEV switches from Engine Drive mode to Hybrid Drive mode to achieve greater acceleration than the high gear ratio of the single-speed transmission can provide even with 212 hp.

    So the difference between the max hp in Engine Drive mode and the max hp in Hybrid Drive mode is 212-181=31 hp. This calculation doesn't jump me to a new conclusion, but perhaps someone smarter than me can make sense of it.

    Interestingly, Honda also claims 212 hp for the Accord Hybrid despite it's larger, more powerful ICE.
    Last edited: Oct 26, 2018
  14. KentuckyKen

    KentuckyKen Well-Known Member

    I can tell you from experience that you don’t have to turn off HV mode to get the power you need on a steep hill. I did a 500 mile round trip in HV mode with a full battery. On a long steep hill, the ICE reved up to a mild lower mid range rpm and the power display showed power going from battery and engine-generator to the wheels. I had plenty of power with no angry bees and it switched power flows automatically. After the climb it put the juice back in the battery.
  15. bfd

    bfd Active Member

    Clarity has the same engine as Honda uses for the Fit hybrid…
  16. I hear what you're saying, but what do you do if you have no choice? There are times when there's no way to keep a charge. Such as going on a trip beyond the limited range. How does everyone else cope with this issue? Is there any recourse or is it just the buyer's responsibility?
  17. insightman

    insightman Well-Known Member Subscriber

    If you keep your Clarity in HV Mode, you'll preserve your battery's charge. Then, if you blow past the last gas station without realizing you're almost out of gas, you can use the remaining charge to either turn around and go back to that gas station or, hopefully, make it to the next gas station.

    As far as buyer's responsibility, it reminds me of the time 30 years ago when one of my housemates ran his 10-year old car out of oil and wrecked the engine. Another sarcastic housemate asked him, "What? Didn't they put enough oil in at the factory?"
    Richard_arch74 likes this.
  18. su_A_ve

    su_A_ve Active Member

    Well, at least we have the gas engine. If this was a BEV, we would be SOL. I noticed lately that my EV range has been too conservative and more often than not, I end up running out of power so the last few miles are done in HV/EV mode (car switches on it's own). Coincidentally I recently filled the tank for the first time adding a whooping 5 gallons. HV range is 1000 but getting the SB applied at this time...
  19. John Fritzen

    John Fritzen New Member

    I was driving in the Adirondack's with the battery "depleted" - 2 bars on the charge indicator.
    Going up a big hill, started losing power, engine screaming, barely made it to the top. Noticed that the charge indicator was down to 1 bar. My guess is that the system keeps a "buffer" of charge in the battery to handle most driving conditions. This buffer failed in the conditions I was driving. Now I keep about 1/3 to 1/2 battery charge if driving in hills.

    BTW, I was able to charge up the battery going downhill in the "HV-Charge" mode.
  20. insightman

    insightman Well-Known Member Subscriber

    Very interesting! This is the first report of 1 bar AFAIK.
  21. Bas

    Bas New Member

    A few months ago I saw in a thread that somebody depleted his battery to 0% (whereas normally it will not go down lower than 10%). I think it was after a hilly ride. At that moment I assumed that the last 10% are exactly for those circumstances were you need to scale a decent slope for a decent distance. If the system would let you go down to 0% battery available, and then you would need to scale that same hill, then all you would have available is the ICE. And since it doesn't clutch to the shaft at lower speeds, you would only have about 60HP available. Can't imagine how to lug a 4000+ ride up a hill with only about 60HP, and no gearbox to shift down!
  22. insightman

    insightman Well-Known Member Subscriber

    I've heard that a Li-Ion battery dies if it's allowed to be fully discharged.
  23. KentuckyKen

    KentuckyKen Well-Known Member

    Yes, complete charge to 100% and complete discharge to 0% is the kiss of death to a Li-ion battery. Honda has programmed the BMS to not allow this, otherwise they would loose their shirt over the warranty replacements. Thus we only get to use about 70 to 75% of the total capacity of the battery pack and see 0 EV at 2 bars and only rarely see it go to 1 bar.
    Bas and insightman like this.

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