HCH-II Recalibrations (Recal). What are they ?

[msantos]

HCH-II Recalibrations (Recal). What are they ?

We often hear about recals from Honda Hybrid owners and we learn to fear them based on the reports of an impending traction battery failure. As the HCH-II ages, reports of these "recals" are likely to become more regular and often send other owners into a panic mode. Is this a reason to worry? Certainly not !!!

What is a recal (recalibration) on the HCH-II ?

The HCH recalibration is an automatic process that is purely instrumented. In other words, there is a sub-system (BCM) in your HCH-II that is responsible for monitoring and managing the charge level of the hybrid battery pack and because of the errors incurred in measuring not only the pack's charge level but also how much energy enters and leaves the battery pack, in time this measurement becomes less precise.

To better explain this relationship let's depict a typical charging and discharging scenario:

1. When you depress the brake pedal your car will capture a given amount of energy which is then sent to the battery pack. The car's system measures that amount of energy and assumes that (let's say) 1600 watts-hour worth of energy was send to battery pack. But because of the energy losses due to converting electrical energy to chemical (with heat as a by-product) and the approximated method of measuring this energy, the real amount of energy ends us being a little lower than measured... perhaps just 1460 watts-hour actually made it into the battery pack. Yet the system does not necessarily see it that way. The SoC is incremented as a function of this estimate of energy that "was" added to the pack.
2. When you depress the gas pedal and you get electric assist to move forward, the system will obtain energy from the battery pack and will attempt to measure how much of this energy is flowing into the power-train. This measurement is also an approximation and the charge level of the battery pack will be adjusted to reflect the energy that was consumed. Also, do not forget that AC use will help deplete the battery pack a faster rate too which further compounds the instrumented error.
3. Finally, the measurement of the battery pack's charge level is in itself an approximation not only because it is affected by the estimate of how much energy was stored in it but also how much energy was actually obtained from the pack.

You can see that over time, the battery charge level will be inaccurate and the car's governing system may evoke a recalibration. Basically, a recalibration simply invalidates the current charge level by "setting' it to a low enough charge level that is enough to trigger a forced regeneration process. Often we will see the charge level dipping rapidly towards an SoC reading 1 or 2 bars only, which is equivalent to the lowest safe voltage permitted by the Battery Condition Monitor (BCM).
Because of this induced and fake low charge level, a forced regeneration (charging) will be triggered and will stay in effect until the car's SoC reaches 7 or 8 bars. When the highest safe voltage is detected (SoC at 7 or 8 bars) the BCM will request the cancellation of the forced regeneration.

Now, if these recals are very frequent then these events could indicate a possible condition caused by any of the following:

• If the battery pack is too cold or too hot, the system expects measurement errors to be magnified and the chance of a recal increases. Very cold weather or very hot weather with AC use are typical scenarios. Please do not panic. This is absolutely normal.

• A problem with one or more cells in the battery pack can also cause a recal. A single faulty cell can cause precocious fluctuations in the battery pack's SoC and these fluctuations in turn, can cause the detection of either extreme of the permissible charge level which inevitably leads to a recal. This is not normal and will likely be a symptom of a fault condition. In this situation you WILL see an IMA warning light appear on the dash and when it does you should schedule an appointment with your dealer for a detailed assessment of the problem.

What if we are getting frequent recals, especially in moderate weather but no IMA light appears? You may try any of the following:

• Perform a power reset procedure.
• Check with your dealer for any software updates for your car.
• Maintain a detailed summary of these incidents and report them to your dealer if they persist.

In summary:

Just because we a get a recalibration it does not mean that our battery pack is going downhill. Do keep an eye on it, but also enjoy your car. For additional details please read Understanding your HEV NiMH battery pack.

[Jess]

Thank you MSantos for this information, this definitely gives some perspective of what's going on, which makes me feel a little better. Just a couple of questions:

1) Does this forced charging add wear and tear to the battery pack, shortening the life?
2) If the system is not sure how much energy is in the pack to begin with, why does the system force charge for what seems to be the same amount of time, regardless of how much energy is truly in there?

(btw, no recals today and a 11 mile morning commute of 73mpg)

Jess

[GardenWeasel]

Never for mine - 'course now I've said that it'll probably happen during tomorrow's commute!

[msantos]

Originally Posted by Jess

Thank you MSantos for this information, this definitely gives some perspective of what's going on, which makes me feel a little better. Just a couple of questions:

1) Does this forced charging add wear and tear to the battery pack, shortening the life?
2) If the system is not sure how much energy is in the pack to begin with, why does the system force charge for what seems to be the same amount of time, regardless of how much energy is truly in there?

(btw, no recals today and a 11 mile morning commute of 73mpg)

Jess

Hi Jess;

1- Yes it does (as any charge/discharge cycle would) . But, is it significant given the instrumented range that the BCM monitors? No. Have a look at the following picture to get an idea of what the instrumented range is.



Now, as the battery ages its capacity also diminishes (as it should) and the BCM is very watchful of this. On a future cycle (Cycle N) the discharge curve is visibly more abrupt than the one on Cycle 1 and this is a fundamental aspect of a NiMH battery pack life cycle. Please note that the detection of the "potentially low" SoC occurs within a very small margin and if you factor in the accumulated instrumented error, the BCM is clearly acting on the safe side of things by being conservative and triggering it a bit earlier than needed.
As we notice the SoC crash is sometimes short lived because the charge process really is not doing much at all as all it wants is to find the upper limit of the instrumented SoC which typically occurs at 7-8 bars.
To make matters even more interesting, the 7-8 bar upper limit also occurs at different voltages depending on the ambient temp. The chart shown above is only applicable to an ambient temp of 21C.

2- Again, it depends on the ambient temps and also the pack temps, and sadly under some conditions not all of the regen is used in the charge process. As you know charging generates heat and the BCM walks a fine line while in the charging process especially when the pack is already hot. That is why we always recommend we keep our regen braking to the lowest number of bars in order to avoid inefficiencies due to discarded energy that never makes it into the pack.


Glad to hear you are getting good numbers. I've been having to much fun with my 06 and in this type of weather each commute is graced with 70+ MPG without much effort either. Yes, these SoC crashes do take a toll on a commute or two but it is hardly enough to spoil the tank and quite frankly, when it happens I actually give it a little hand by helping to keep the regen low. On this note the episodes are short lived and relatively benign


Cheers;

MSantos

[Jess]

Hi MSantos,

Sorry for the delay. I had to read and reread to better understand what the table was showing and what you were explaining about it. I think I got it now. Very cool.

The past 2 days I have had no re-cal. What I've done differently is to change the initial part of my route. Now, when I first leave, I drive a route that has a flatter elevation before I get to what was my second incline on my previous route. I'm wondering if driving this route allows the system more time to warm up and better monitor where the SoC is at.

My previous route had me initially go down a hill and then climb 2 inclines thereafter. I'm thinking the BCM wasn't fully warmed up and, by the time it was, (I had already been using 2-3 bars of assist to climb those 2 inclines, nearly one after the other), it was better off re-calibrating and starting over at 8 bars than to try and figure where the SoC was at.

Thank you so much for the insight. I truly appreciate it. I think I have a much better idea of what is going on now.

btw: Have you taken yours in for the new update? I've yet to myself. I'm really not sure if I want to though. What do you think?

[Kacey Green]

I appreciate and respect the ReCal, however, the car doesn't need to do one if I'm not moving and if I stop moving, cancel the recal until I start again and when you cancel, GIVE ME BACK MY AUTO STOP!

Today (about 5 min before I started this post) the car goes into a recal at about 89F according to the display and after about a min at the light it stops the recal and idles when I start moving again, I'm still force charging all the way occasionally I get 1 assist bar.

When I get to the next light the car is still doing the recal.

By the time I get to the rim of the bowl I live in, the car is at 7 bars and will reliably give either 1 bar or glide with 1 bar of regen, if I pushed harder it would continue a normal force charge, so I EVed it to the crest of the bowl and of course we're at 8 bars promptly, I have to take the car down to 6 bars to take this hill normally, and if I FAS it I get going way too fast with kids playing and all, and would have to restart to climb my street and driveway.

I think the car may have been punishing me for a short trip, which had been good up to that point 65ish MPG. The trip would have been too long and unsafe by bike, the place I went is dangerous in a car at rush hour (4-9:15 on a Friday) and the sun was setting fast. That and I don't own a bike anymore (it never made the trip up from FL)

[msantos]

Originally Posted by Jess

...
btw: Have you taken yours in for the new update? I've yet to myself. I'm really not sure if I want to though. What do you think?

I received the update already in mid June during the an oil change visit.

As before, I get these updates a little earlier than most folks but what surprised me is that this particular update was also later accompanied by a TSB. While we've had a couple that followed the approach, there are many others that do not and are in reality silent updates. Interesting.

Cheers;

Manuel

[msantos]

Originally Posted by Kacey Green

I appreciate and respect the ReCal, however, the car doesn't need to do one if I'm not moving and if I stop moving, cancel the recal until I start again and when you cancel, GIVE ME BACK MY AUTO STOP!
...

Hi Kacey.

I know what you mean. However, one way I have to defuse that type of behavior is to execute a FAS. As long as the SoC remains at 5 or less bars, the car will remember the forced charge routine and resume after the power-up.

[Kacey Green]

So I would have been fine during both events. But if I do it at 6 I may cause the system to do it again at an inopportune time because it wasn't necessarily a true 6 bars?

[psyshack]

We had our first recal/crash two weeks ago.

The SoC was at 6 bars then samba'ed down to 0. It would drop 2 bars then give one back. Then drop 3 and give 2 back. It was interesting to watch it work it's way down to 0. Then the force regen started. The A/C was on when it happened set to 80f Auto. Soon as it started the A/C was turned off. It took 10 miles of hilly 100 degree open window hwy driving for it to sort its self out. The segments mpg was crushed.