CAN View Users (Charge/Discharge Limits)

awesome experiment... actually not necessary. i was willing to take your word for it.

 

just an update. still not anywhere on the Max charge and discharge. but do notice that i get the most movement before the ICE is properly warmed up. a couple times i have gotten the discharge rate down to zero or near it and all those times, it was when ICE was at 135º or colder. after the ICE is warmed up, i cant get the discharge to change nearly as much even when all other conditions are the same.

im beginning to think we need to figure out what makes the max charge rate move and also think summer will provide more and better data to ponder

 

Regarding the charge/discharge limits. While driving to work today I saw numbers that indicates that they are mismarked. It looks like the charge limit is actually the discharge limit and vice versa.

While going down a long hill on the freeway (in traffic), about 25mph, with a light touch on the brake pedal (for optimum regen) and I noticed the ICE start up. I tried to stop it with EVb but it denied EV mode. I checked on CAN-View and the SOC was 79%, and the Discharge Limit was 0 amps, the Charge Limit was +100 amps, and the battery current was -4 amps. The ECU was using the ICE to discharge the battery even though I was braking downhill which normally provides +20 amps into the battery.

At this point I did a few experiments. I stomped on the brakes to see if I could get any regen but battery amps stayed at -4. Releasing the brakes, still -4 amps. Sharp acceleration drew current from the battery -40 to -60 amps (even though the discharge limit was 0 amps).

The SOC dropped to 78% and the discharge limit went from 0 to -10 amps. At this point I was able to get some regen while braking but only up to +10 amps.

At the bottom of the hill the SOC continued to drop and the discharge limit continued to climb. At about 75% SOC the discharge limit was back to 100 amps. And full regen was available when I used the brakes.

During this time the discharge was never limited, I could accelerate and was able to see a draw of 20-80 amps from the battery several times.

Unfortunately I didn't have a recorder hooked up to the serial output from CAN-View so all the numbers are from memory. I could probably duplicate the situation with a PC hooked up to the serial output to capture some more exact data.

 

ya, i guess the discharge limit relates to the current to batt direction.

 

looking at the current draw on the battery I'm wondering if -4 amps is what is displayed as 0 when the BSOC is 80% and MG2 is powering MG1 with the ICE forcing the MG1 to turn in the opposite direction and it is being use to "plug" the output from MG2 in effect being the brake. The computer by disconnecting the HV battery from the circuit and the minor draw, 4 amps in this case is what the comverter is using to power the 12 volt side of the car. That could possibly be the reason for the "0" discharge reading.

 

I have not seen my limits change yet from the ordinary increases during warm upl

But if limits go to 0 for discharge it could mean either that the battery was too low and it wanted to charge up more for equialization or a memory erasure cycle.

Or it coud be mislabeled and mean it can't charge more til the level is brought down.

So testing limits when they are different seems like a safer way to see which is which.

 

Max Discharge goes towards zero when SOC goes up. so that must indicate discharge TO the battery. it would be easier if we could determine what causes MAX charge to move. havent really seen much of that yet. but willing to bet that Max Charge will drop on long uphills when the SOC is dropping below say 50%??

 

"Discharge TO the battery" is what we usually call "charging the battery".

Anyway, the same thing happened today on the same hill (80% SOC, 0 amps Discharge limit). When it did, I reset the CAN-View limits (so the Min and Max shown are starting from that moment). Then I put the car in N and pulled over and got some photos of the display while the ICE was being spun to bring down the SOC on the HV battery. Here is a sequence of photos showing the SOC dropping and the Discharge limit changing (what I think should actually be called Charge Current Limit).

Here the SOC is 77%, Voltage 235v, Discharge Limit -30A, ICE spinning at 1000rpm. Note that the Min column shows that the Discharge Limit had been 0A while the Min Battery Amps was -4A.


Now SOC is 76%, Voltage 234v, Discharge Limit -36A, ICE still at 1000rpm.


SOC is 76%, Voltage 233v, Discharge Limit -55A, ICE still at 1000rpm.


(Sorry for the lousy pix, I was facing the sun and using just a point and shoot camera)

 

4 amps is too much current for just normal consumption of the DC-DC 12v converter, that's 936 watts which equates to a > 60 amp load on the 12v side. See my data in this other thread for baseline numbers on consumption: Power Consumption. Under this circumstance, all accessories off, it should be less than 2 amps.

 

I too would like a rational conclusion to this. Suppose I simply swap the charge and discharge limit labels. This then fits in nicely with what you observe.

Can we agree that when the Prius is wam we can expect to see 105A and 125A limits?

So if my swapped charge limit is now increased to 125Amps, why have I never seen over 105 amps charge?

And if my swapped discharge limit is now reduced to 105Amps, why do I often see close to 125 amps?

Neither solution neatly fits both sets of observations. Is it possible these are NOT limits to which the inverter adheres? But some unrelated function?

 

not nessasarily, the converter is just a stepdown transforrmer with a regualator and filtering and we have no actual way of finding out how much current it actually uses to power the 12volt system. Unless you've actually clamped the 12 volt circuit when it does this to see what the actual amperage is going in or out of the battery it's just speculation. The other thing is on the "low" reading 76% state of charge and only 204 volts seems low to me, I would have thougth more like 220-225 volts would be more the norm.

 

the more i track this, the less i understand. i have resigned myself to not understanding anything until i can get the Max Charge to change. now that i have had the flash done, EV mode works much better so it is easy to run the SOC down to 45% (something that i could never do before unless running up a very very large hill)

i thought that this would run Max Charge to zero, but it actually creeped up from 100 to 103...at the same time the max discharge went from zero to -100 as SOC went to 45% from 77%

 

Did the labels for these two fields get swapped in the latest CAN-View code?

Last Sunday I left my Prius parked in the sun for a few hours on an 80°F day. I also forgot to put in the reflector in the windshield so it got really hot in the car. Later when I started it to leave I noticed it refused to go into EV mode (usually it's no problem to get it into EV). I finally figured out that it won't do EV mode when the battery temp is 114°F and CAN-View was showing the Charge Limit was at 30 amps instead of its usual 105.

I continued to watch the battery current, and the limits, and saw that the regen would not go over 30 amps even with hard braking and it never used more than 30 amps when accelerating. It took a long time for the battery temp to drop on the drive home. Eventually the Charge Limit went up from 30amps and then current usage and regen went back to normal. Based on this one case it appears the the Charge Limit field actually limits both charge and discharge based on battery temp.

 

<div class='quotetop'>QUOTE(kk6yb @ May 9 2006, 09:11 AM) [snapback]252166[/snapback]</div>

Nope, no change, there has been some discussion but to avoid confusing everybody, it seems safer for now to leave both labels (right or wrong) as they have always been. There are convincing arguments for both cases. Your observation is one more clue to what these values really are. Its becoming obvious that neither is 'just' a charge limit or a discharge limit alone.

As an aside, I am working on adding a Trip screen which lets you record total trip, time, distance, average speed and average fuel consumption. But the maths is really eating up the code. (and my brain)
Hopefully a new download available in the next couple of weeks.

 

<div class='quotetop'>QUOTE(eflier @ May 9 2006, 08:49 PM) [snapback]252584[/snapback]</div>

Yes that would be great!!! It is the only thing I miss from my ScanGage. The how did I do this time? I hope it comes off.

 

<div class='quotetop'>QUOTE(eflier @ May 9 2006, 08:49 PM) [snapback]252584[/snapback]</div>

Norm would it be possible to add a % run time indicator such as % ICE time or % in Stealth time to the trip screen. That would really let us hone our driving skills.