I guess I haven’t been driving it enough (car won’t start)

[MrFixit]

@JCA
There is one situation that you didn't encounter in your test.
It is not quite as simple as you conveyed (EV always 14.x and HV always 12.x).
When I did my test, there was clearly a mode in HV that did produce 14.x.
For me, it was at night with the headlights on. This produced 14.x while the engine was running (HV mode invoked with the button).

I also think it is still likely that this charging system really only has 2 states (I will call them 'float' and 'charge'). In 'float' the system just holds the charge (12.69 in your test). In 'charge' it operates like a standard alternator (14.7 in your test). The only exception that occurred was when the vehicle was plugged in, so that's not really part of vehicle operation (your 13.5).

 

[vicw]

So I was going to post how those claiming different charging voltages were crazy, that the DC-DC converter should just put out single voltage, and any discrepancies had to be either in your head, from reading a screen wrong, or something. But before I did, I thought I’d test it myself, with a pretty accurate multimeter and an old lighter cord I had cut apart for something else and an experimental drive. Well, sure enough, you’re right! Here’s what I observed, in my 2020 Base:

• When starting and driving EV-only, the voltage remained at 14.7V the entire time, including a 15+ minute EV drive.

• As soon as I got the engine to run (either using the HV button or just kicking the accelerator past the detent), a few seconds later the voltage went to 12.69V and stayed there until I shut down the car, even when the engine was off and back in full EV mode. No matter how long I drove in EV (another 10+ minutes) it stayed at the lower voltage.
  
  
• When I plugged in the charger (L1 but shouldn’t matter), I measured 13.45V at the battery; that should be enough to charge the battery.

• When off/not charging, I measured 12.2V at the battery, so at least when running at 12.69V that means power is indeed coming from the DC-DC converter and not draining the battery, but it may not be effectively charging it either.

I wonder if people who’ve had more dead battery problems tend to have the engine run early in their drive, thus never really getting a good charge while driving. And when they take it to be tested, the car starts in EV and the charging system puts out 14.7V, so it *looks* fine.

It’s weird, because the engine running should have nothing to do with this -- there’s no 12V alternator or starter since the engine starts and generates electricity right to/from the HV system, and that wouldn’t explain why it stays low after the engine shuts off. I can’t imagine why they would have designed it this way intentionally, but there may be a reason. Pure ICE cars draw significantly from the battery every time they start, so there’s more need to replenish while driving than our cars.

I doubt there’s any real intelligence here -- once the DC-DC converter voltage is there the car can’t tell the 12V battery’s state; so I don’t think it’s actively deciding to charge or not charge. I’d bet the above behavior is true regardless, but I was wrong with my initial thought so who knows.

No idea how we’d get Honda to explain, acknowledge, or fix this (if it’s indeed broken).

@JCA I'm pleased that you took the time to check out your Clarity before posting that we are crazy (perhaps we still are, but not because of this).

My experience with my 2018 Clarity Touring matches what you reported in your four bullet points. I observe about 13.3v when L2 charging - essentially the same as yours on L1.

I hadn't yet posted about the behavior your described in your second point, regarding the Clarity remaining at the lower charge level when in HV mode, and not reverting back to the higher 14.6-7v level when you switched the car back to EV mode while driving. That one really startled me, but I had tried that only once, a couple of days ago, and I wanted to try it again once or twice more before posting about it.

I also agree with your comments regarding people who have had 12v battery problems, perhaps exacerbated by the HV thing, where subsequent testing won't properly diagnose it, because EV charging operation masks it.

If you plan to dig any deeper, and do any more testing, you might consider installing a battery monitor. I put in a $35 Battery Tracker from Antigravity Batteries, which you can just connect to the battery terminals, and capture data from your battery 24/7. Were it not for that device, I never would have been aware of this odd problem.

I expect the same little device might be sold under different names, but it's much more convenient than trying to capture and record voltage readings while driving, and it retains 30 days of data. I can check the Clarity 12v battery voltage levels on my phone at any time, and capture the screenshots for reference. I've got about a zillion screenshots of it so far during the several weeks of monitoring and especially testing for the Low vs. High charge levels related to HV operation.

I'm currently trying to deplete my battery enough to get the HV operation to sustain a higher 14.6-7v charge level, as @MrFixit has described. So far, I haven't been able to do that on mine. I would also really like to establish how low the battery can go, before it no longer can start the car, but I don't want to destroy my new battery in the process.

 

[JCA]

@JCA
There is one situation that you didn't encounter in your test.
It is not quite as simple as you conveyed (EV always 14.x and HV always 12.x).
When I did my test, there was clearly a mode in HV that did produce 14.x.
For me, it was at night with the headlights on. This produced 14.x while the engine was running (HV mode invoked with the button).

I also think it is still likely that this charging system really only has 2 states (I will call them 'float' and 'charge'). In 'float' the system just holds the charge (12.69 in your test). In 'charge' it operates like a standard alternator (14.7 in your test). The only exception that occurred was when the vehicle was plugged in, so that's not really part of vehicle operation (your 13.5).

Good point -- I didn't play with loads on the 12V system much other than trying the fan speed. I will hack my lighter plug and the trusty and awesome Radio Shack multimeter that I bought in the 1980s and do some more experiments when I get a chance. I'm trying to think of other big 12V loads other than the headlights and fan; the heat and AC should be on the high voltage side. I'll do it during the day so I can see if it stays at 14V after the headlights are off with and without being in EV mode again.

I agree it sounds like some sort of intentional "float", but I can't figure out why yet. I'm not aware of regular car alternators switching voltages like that; they just output one voltage, and our battery is the same as the one in my Civic. And if it is intentional, why float when the engine is running vs not? Unless there are some 12V loads like power steering/brakes that are driven directly from the engine when it's on (taking the load off the 12V system) -- but I don't think that's the case. And even then, it wouldn't explain not bumping back up when the engine shuts off. Such a mystery...

 

[bpratt]

When my battery would not start the car it measured just under 9 volts.

 

[vicw]

Considering @MrFixit's experience getting HV mode to sustain the 14.x voltage charging level to the 12v battery, while driving at night, with the headlights ON, and the possibility that the Clarity was making the decision to charge at the higher 14.x level, or not, perhaps because of the need for charging, low battery voltage, I decided to try something.

I just took a short drive, about 3 mi each way, at about 10:52 am on a very sunny day, no clouds, around 56 degrees outside. For the outbound trip, with the battery at a 12.52v, I started the car, turned the headlights ON, put the car in HV mode, and drove.

It sustained the 14.x charge level throughout the drive. Note the 14.x voltage on the chart until I stopped at 11:02 am.

I waited for about 10 minutes to let the battery settle and put the headlights back to Auto, so they would not come ON again during that drive.

The battery level showed as at 12.47v. I then started the car, at 11:13 am, put the car in HV mode and drove again. It started at the 14.x charge level, but within about 90 seconds, it reverted back to the 12.x level and stayed low for the rest of the drive, ending at 11:22am.

I think we can reasonably discard the theory that the Clarity is making the decision for 14.x vs 12.x charging levels due to the need for charging, since I started the initial run with the battery at a relatively high level of 12.52v.

It seems that the HV mode charging decision may be simply based on the headlights being ON, but that rule doesn't apparently apply when driving in EV mode.

There are a bunch of What-If contingencies I can think of to determine what the car will do under a variety of sequences and circumstances, but it seems reasonable for starters that I will want to have the headlights ON when on long drives, running in HV mode, to assure that it will apply the 14.x charging voltage, especially if I am on a long trip, or plan to leave the car at an airport for an extended period.

 

[vicw]

When my battery would not start the car it measured just under 9 volts.

Thanks for that @bpratt. When mine failed, I didn't think to check that. I was totally fixated on jump starting it.

 

[Landshark]

Many modern vehicles equipped with alternators, now have “smart” alternators that can control voltage. Even the dumb alternators can control current while maintaining a fairly steady voltage.

The Clarity has a fuse protected 12V battery sensor circuit. Presumably there is a shunt that measures current going in and out of the battery. This information would be used to determine when and how the battery would be charged. The DC/DC converter may be, just a converter. There are DC/DC converter/chargers they are capable of performing multi-stage charging with programmable protocols.

I suspect that our DC/DC converter may be the dumb variety, but there is a moderately intelligent component, somewhere in the car, that determines when to turn the dumb on or off.

 

[socalclarity]

I have a 2018 Clarity with 29K miles. I started having starting problems a couple of months ago and brought it in to the dealer who replaced the battery under the warranty. Now the same problem has resurfaced. After driving 50 miles, then fully charging overnight, the car won't start in the morning. When I hook up my starter battery charger it then starts immediately. Has anyone else experienced this and does anyone have any advice? I will take it back to the dealer next week but it is pretty frustrating having reliability problems with starting the car.

 

[MrFixit]

If you have the capability, I would suggest measuring the battery voltage.
You should have 12.x volts when the car is off, and 14.x when the car is in "Ready" mode (On, and ready to drive). If you don't get 14.x, then the vehicle's charging circuitry (not an alternator in this case, but a DC to DC converter operating from the HV battery) may be suspect.
A battery certainly shouldn't fail after a couple of months, but stranger things have happened. At least you are still under warranty.

 

[Landshark]

After driving 50 miles, then fully charging overnight, the car won't start in the morning. When I hook up my starter battery charger it then starts immediately.

I’d say that you have a defective 12V battery. It is my understanding that the 12V battery gets charged when the HV battery gets charged. I’ve left the car sitting for more than a month and it started right up. The only time it didn’t start was after sitting for 6 months. It did start with the aid of a lithium jump pack and has started every time for the past 9 months.

The car doesn’t require a 12V battery with a huge CCA rating to power up. It just needs a 12V source to flip a switch. When driving the HV battery charges the 12V battery via a DC/DC converter. So, after driving 50 miles, the 12V should be fully charged, even before you plug it in to charge.