[Armin]

Surprisingly, we never really had a threat dedicated to this all too familiar issue.

I just wanted to discuss the relation of the occurence of recals to warm weather. In the winter, I had about one or two recals, and they appeared only when the battery was discharged to below 1/4, so they might be excusable. Now it's getting warmer and I already had three recals in the last 1000 miles.

There is one curiosity I noticed on my amperemeter, that many of us might not be aware of: Hidden charging (like force charge, but without lighting the green bars on the charge gauge) is _a lot_ more frequent in cold weather than in when it's hot!

When the outside temperature is around or below freezing, I see 5A to 10A charge current almost always when cruising. In warm weather, this hidden charge only happens sporadically. When it turns on, it usually continues until the battery is 19 bars full, but it rarely starts with the SoC is above 3/4.

In fact, after my last recal, even the force charging is getting rare. The battery stayed around half for a long while with no force or hidden charging. The only charge I got into it was from recuperative braking.

Any comments/opinions/observations?

 

[Rick Reece]

Ampmeter

Just curious where you are sensing from for the ampmeter. Most of us only have the charge/discharge guage and thus only see what is occuring according to the guage. Have fun, RIck

 

[Tim Maddux]

Good idea for a thread.

I've noticed the net positive float into the IMA battery on long cruises (with no green light) before, it never seemed to be correlated with temperature. On your ampmeter can you see the IMA charge/assist cycling to reduce engine vibration? I've always figured the net positive float was simply from nonlinearity of that activity (a little more charge than assist).

Temperature dependence of recals makes sense if you consider the temperature dependence of the voltage - state-of-charge (SOC) relationship. In warmer weather the system would be more likely to halt charging early because the batteries are getting warm, which would lead to a tendency to overestimate the SOC in warmer climates. Plus, when it's cold I've noticed system visibly (with green bars) charges the battery pack to warm it up.

I haven't had a single recal this incredibly cold winter. Also I see my battery pack get charged to 100% full (ALL bars) much more frequently. When I lived in SoCal, I never saw all bars lit on the battery SOC meter. Not once in 45k miles. It wasn't until I drove across country and drained the battery on a big hill in Arizona that I first saw the battery fully charged (on the way down the hill).

 

[Armin]

My Amperemeter

I tapped into the leads to the OEM battery current sensor. The sensor is a hall-effect type sensor mounted on the busbar that connects to the battery. I simply wired it to an LED panelmeter and calibrated against a clamp-on amp-probe.

Tim, I don't see the engine vibration dampening, that is too high frequency. All I can see is DC-current. But the hidden charging is more than an assymetry from the AC current. It is just as strong as force charging with the green bars lit (5 to 10A, depending on rpm and a few other things). I also observed that the current is controlled in "steps". Almost never does it go below 5A. Rather it shuts off entirely.

As for the temperature dependence, my original theory was that the car is trying to heat the battery in extremely cold weather by charging it. This would explain the almost constant hidden charging activity. The lack of it in warm weather can't be explained by over-temperature protection, since it happens during my normal all-highway commute where there is little stress on the battery and it should stay cool.

But I'm not convinced. There may be finer ways that temperature gets figured into the battery management.

 

[Rick Reece]

Battery Management

Armin,

Great investigative work. I don't know about current on the 144 volt side but I do have a real voltage meter on the 12Volt side. My experience is somewhat different than what I have seen others post.
While driving the car (and I always have a load on the 12 volt battery) I see the DC to DC converter cycle on and off. The car voltage will run around 13.8 to 14.1 for a while then drop to 12.5-12.3 where it will slowly drop (I assume due to my accessory use) to the 12 or 11.9 and then it will go back to 13.8 to 14.1. I figured the DC to DC converter monitors battery voltage to know when it is needed. Others have suggested the converter is always providing power to the 12 volt system but if that were the case I should not see a large variance in the battery voltage. As a last comment the Civic VX used an alternator that cycled by need and engine load so the Insight could use a similar approach. Have fun, Rick

 

[Armin]

DC-DC converter

Rick,

I agree. I haven't looked while driving, but I confirmed the same behavior in auto-idle-stop. My theory is that the DC-DC is shut down, once the load current drops below a certain value. It would be too inefficient to operate it with low load. Then, once the 12V voltage drops, the DC-DC comes back on to keep the little battery topped off.

 

[Tim Maddux]

Re: My Amperemeter

It is just as strong as force charging with the green bars lit (5 to 10A, depending on rpm and a few other things).

Wow. How many CHRG bars does it correspond to? I'm surprised that the software apparently chooses not to show this to the driver.

 

[Will M]

Stuff I've learned about electricity from living in a solar electric house, applied to the Insight:

1. Charging systems work under the simple principle that two batteries of different voltage levels wired in parallel in a circuit will tend to result in a circuit that has a voltage level between the two different battery voltages. The higher voltage battery will drain while the lower voltage battery will charge.

Replace the higher voltage battery with some other power source and it works the same way. Solar panels are basically batteries that get their electricity from sunlight instead of from chemicals changing from one compound to a different compound. Alternators are basically batteries that get their power from mechanical motion instead of chemicals. The DC/DC converter is a battery that gets its power from a different battery converted from a different voltage.

2. Since the DC/DC converter is electronic, it probably produces only one voltage, and since it has to charge the 12 volt system, that voltage is higher than the voltage you really want the 12 volt system to achieve. The same is true for an alternator or any other charging source. Solar panels for 12 volt system can produce more than 17 volts, for example.

Whenever you have a charging source of higher voltage than you want the system to be, you add electronic controls that do for voltage what your thermostat does in your home with temperature. You don't want your house as hot as your furnace, but you use the furnace's heat to add heat to your house until the thermostat says, "Enough" and the furnace turns off, until the thermostat tells the furnace it is cold enough to start again.

So, the DC/DC converter senses that your 12 volt battery is down to 12 volts and it flips a switch turning on the more than 14 volt DC power from the DC/DC converter. The voltage in the line is then between the 12 volts and the voltage coming from the DC/DC converter. Once this in-between voltage climbs up to 14 or so (my 12 volt house shut off at 14.4 volts for my deep-cycle batteries), then the DC/DC converter turns off and waits for the voltage to drop back down to 12 volts.

As for your accessories putting a load on the 12 volt system, remember that the car's computers, fuel injection controllers and ignition are 12 volt, too, so by just running the car, there's a load on the 12 volt system. You don't have to have any accessories turned on to have a 12 volt load.