HV Batt SOC below 40 percent

That's extremely interesting! Was the car in panic mode, sending a lot of charging current to the battery via the ICE, leaving you with no power? Did you also happen to notice it dropping suddenly from 40-something down to 29? Was the battery fan running?

 

Have you read this thread: http://priuschat.com/forums/gen-ii-prius-main-forum/95641-power-loss-low-battery-during-climb.html

Anyway, were you forced to drive slower behind trucks because the car had no power in spite of redlining i.e. panic mode? Also, I assume that you have a ScanGauge or similar device. Do you make this trip regularly? Maybe you could monitor btA and cell soc delta when it gets in this state?

 

Yes on 12v. I just put an new Optima in my 2006 and it seems to be helping MPG/HEV battery a lot. But I am thinking my SOC always goes to purple (2 lines) climbing up a mountain, if you go faster that would force more power back to charge up the HEV batt.

 

One big question, was the AC on? That is a very big drag on the system even when new and especially uphill.

 

Was the "below 40 percent" from the battery screen or do you have some method of actually measuring SOC?

If we are talking about the battery SOC display, I've taken mine all the way to the bottom on occasion when climbing through high mountain passes.

Tom

 

I still can't believe you have 2005 Prius with 170K miles on orig 12v battery, if I got that right. You gotta be pushing that 12v batt life. Be sure to make some of the simple 12v battery load tests discussed on the site here.

 

If you take a lot of long trips and never drain the 12v battery, it can last a long time. My 2004 Prius is at 205k miles on the original 12v battery.

JeffD

 

I think your HV battery is weak, and the drop in SoC below 40% catches the computers off guard. If Toyota would publish their SoC algorithm, we could pick this apart, but in your case and Tone88's, a plausible explanation is that SoC falling below 40% triggers a demand on the already stressed engine to charge the battery. At this point, instead of drawing current from the battery and pulling the voltage down, it is now adding current to the battery and pushing voltage up. Charging SoC calculation is different from the discharging calculation. This would fall under a different lookup table. In addition, the battery ECU is also trying to smooth the SoC calculation over time. So it makes sense, to me anyway, that you could find SoC dropping slowly to 29% even though charging current is coming from the engine.

This is more or less what happens in Hondas when there is a negative recal. Now Honda does not equal Toyota, but they do share Panasonic EV as the battery suppliers.

The long term implications for your car in particular remain to be seen, but it should help extend the life of the battery to avoid the low SoC, high demand situations. Like, turn off or put on low recirc the A/C, and drive slow but steady, avoiding acceleration, up the grade.

 

I think you are under estmatine the demand that the AC puts on the system. I live in San Diego and travel to the SF Bay Area often. I drive 80 MPH on the straight and level I-5 through the valley and often find the battery display down to one or two bars with the AC on. Couple that with what seilerts said in his post above and the engine is doing triple duty, propelling the car, running the AC and trying to recharge the battery. P.S. When I run the AC even in town, I drop 10 MPG's.

 

We need to know how you know it was below 40%. CAN reader?