Battery fully charged going uphill at 70 MPH

My idea is this: Don't take what you see on the hybrid-system display as real data. What you may be seeing is a result of a higher voltage being applied to the hybrid battery, not the actual charge-state of the battery. In my case, the battery-indicator changes from showing the level of the EV battery partition, to the level of the HV battery partition, once the EV range hits zero. There is no indication of what the battery-indicator is actually showing, other than your own assumption, based on what mode the car is running in.

 

If your HV battery is still the original battery, it's just showing signs of age and lost capacity. It's equivalent to a 12v battery being completely dead and once hooked up to a charger, it's fully charged in 15 minutes.

 

Greg, this looks to be a gen 2 non-phev

OP: This is not uncommon, I've observed it in my gen 2 climbing the Mogollon Rim out here in AZ. As I understand it the hybrid controller steps the ICE rpms in discrete steps. If the power the ICE is putting out at the selected rpm is a little higher than you are currently requesting (via position of the gas pedal) it will use MG1 to put the excess back in the battery. If its a little lower than what you are requesting, it will use the battery to power MG2 to supplement the ICE power. This is all when the battery is within its normal SOC operating range of course. You can see this anytime, but its particularly easy to see on uphills due to the extra load. As you slowly press down on the accelerator you can see the indicator go from charging to discharging, then the ICE will step up an rpm notch and go back to charging, then discharging, then another rpm notch etc.

So in your case all that means is that on that grade and rpm, the ICE was still putting out more power than needed to climb that grade at that speed, and so was putting the extra in the battery. Interestingly you could have discharged the battery either by trying to go even faster, or by going a bit slower (dropping the ICE rpm and requiring electric power to maintain speed). Its a handy thing to be aware of, as on a long climb you can use this knowledge to keep the battery from getting to a low SOC and dropping you into a low power mode while it brings that battery back into a normal SOC range. When that happens its easy to no longer have enough power to maintain speed on a long climb, or have reserve power for passing. By watching the battery and adjusting speed and pedal position a bit you can ensure that you have plenty of reserve battery power all the way up.

While some folks have experienced this low power mode and thought the Prius doesn't have enough power to climb big hills, my experience is that if you understand what's going on and manage the battery appropriately the Prius (even gen 2) can often be one of the quickest vehicles up steep grades, even when having to accelerate back up to speed after getting caught up behind slower moving vehicles.

If you know what comes after that steep climb, you can also make some intelligent choices about managing the battery SOC on the climb. If its flat after the climb, just keep the SOC in the normal range. If its a long gentle down slope, arriving at the top of the hill with full bars will let you run "warp stealth" (high speed EV only, or high mpg EV assisted) for a long time. If its a steep down hill that follows, managing it so as to arrive at the top with 2-3 bars will keep you from getting into that low power mode on the uphill, but give you plenty of room in the battery to recover and store regenerative braking energy.

Rob

JC, I believe a weak HV battery will usually appear to discharge faster on an uphill and recharge faster on a downhill. In both cases the combination of elevated internal resistance and reduced capacity will cause it to hit the recalibration voltage limits resulting in a rapid SOC recalculation. Increased internal resistance will cause the voltage to sag lower under high load (usually uphill) as well as hit the lower limit sooner than expected due to reduced storage capacity. Increased internal resistance will also cause the voltage to increase during high regen (usually downhill) and hit the high limit sooner due to reduced capacity.

In this case (charging to full on a long uphill climb) I don't think anything out of the ordinary is happening as explained above.

Rob

OP, to your other question, I don't believe the Prius has a preset regular recalibration routine like the Honda's do. The Prius uses coulomb counting to estimate SOC (tracks amps in and out and compares Ahs charged/discharged to how big it knows the battery to be) combined with high and low voltage limits that trigger recalibration (often called SOC drift). From what I've seen its very rare to hit these voltage limits in normal operation. As I recall we only found out about them due to experiments being done around plugin conversions in the mid 2000s. Where they have perhaps started to show up is in the symptoms observed in older high mileage cars whose HV batteries are failing. Then you can start to see apparent rapid fluctuations in battery SOC that to me seem consistent with hitting these voltage limits and triggering the SOC drift recalibration program as described above.

Rob

 

I have what you are describing on my 2006, up a hill, it'll discharge very fast and downhill, it gets full bars from empty in less than 2 miles.

 

If it makes you feel any better, just Monday I experienced the same thing, but it was at 60 mph. I'm just sitting there listing to the little 1.5 rev like crazy and it doesn't use hardly any power from the battery (stayed at 6 bars all the way up)

 

Hmm, could be getting weak but doesn't sound too bad. Regen on a downhill can generate ~100A / ~10kW. At that rate it only takes 2-3 minutes to completely fill the usable portion of the battery. When it gets really bad you can start to see it dropping from 7-8 bars to 1-2 just in the 10-15 seconds it takes to accelerate from a light, and vice versa on a single deceleration, or even see the SOC bars moving in the opposite direction to the charge / discharge arrows.

Whether its weak or not, it would be interesting to see if you can avoid the discharging on uphills by using the trick above.

 

There is a stretch when I drive to Las Vegas that depletes my gen2 battery everytime. Regardless of speed or technique. Once I start climbing, it goes down 1 bar every 10 seconds or so. But when I drive my gen3, it never depletes.

I have 10k miles left on my gen2 warranty, hoping it'll fail me sooner rather than later.

 

op doesnt state what climate he lies in, doesnt that make difference? I way overcharge going down lonnng hills to dez.

 

Getting to full charge is no big surprise on a long down hill, as mentioned above the regen can kick out 10kW on a steep down grade and the usable portion of the battery I think is only around 400Wh. That's only about 2-3 minutes of max regen.

The OP was noting that he noticed he was charging to full on a long high speed _uphill_, which is less common but very possible.

Rob

 

miscrms,

Thanks for the informative information on this observed behaviour. It makes a pleasant change to read something authoritative rather than some of the nonsense offered by armchair theorists that some times appears on forums, both here and elsewhere.

Cheers.

Thanks for answering that. I read in the Gen I forum of a "balancing cycle" that had been observed and wonder whether this also existed in Gen II/III programming, and asked in another thread. I didn't get any response at that time, so good to get an answer this time round.

 

My question to the op;

Was anyone sat in the rear seat where they could have potentially blocked the rear battery vent? If not a person, maybe a blanket or a box or coat etc?

I had found on my gen3 that if the rear vent was inadvertently blocked for some time or if the car was under load, the HV battery state of charge would climb to 8/8 bars. It would quickly fall back to normal if the vent was cleared.

 

I tried the trick you mentioned and it worked. I made a good 15 mile climb today and didn't run down my battery for the first time. I was able to maintain speeds of 60 to 72 mph while climbing for 15 miles and the battery never got under 4 bars.

Before when I used cruise control, it would flatten out my battery in about 3 miles and the climb would be very difficult from that point.

I wasn't able to maintain 70+ mph on the climb, when I needed more power, it seemed to start draining the battery. I just maintained the highest speed while keeping from pulling power from the battery

This method you mentioned of keeping a good SOC going uphill and keeping the battery from draining, really depends on how healthy your HV battery is. If your HV battery is weak and can go down from a full charge fairly quickly, the car will not have enough time to "kick up to a higher rpm" while the battery is providing power. If the power is deplete too quickly (in the case of using cruise control and keeping the speed constant), the car will go down to 1 battery bar and go into reduce power mode.

I drove 500 miles yesterday and I was able to test this many times but although very useful in keeping my SOC above the middle mark, I was not able to maintain a higher speed because my car would not kick up to a higher rpm fast enough. If I kept the higher speed, my battery would have depleted and I would have very little power climbing the long hills. I was able to keep speeds above 60 though, so I wasn't too concerned. But definitely wasn't able to keep it above 70 during climbs.......especially using cruise control