I haven't been tracking TSBs but one of the folks in the Prius_Technical_Stuff group has. Also, let the folks over there know how things work out, especially after you get the car home for a couple of days.

If you can, get copies of the work sheets and describe everything they did. We're very curious.

Bob Wilson

 

To "equalize" a multicelled battery you charge it up fully. Because some of the cells will be closer to full charge than others, they will be susceptible to overcharging (overheating is the result with NiMH cells). So to minimize the impact of this, you charge at a low rate, which allows the excess heat to dissipate without the cells reaching dangerous temps (for their health). This also translates to dangerous internal pressures. Usually a 24 hr rate or thereabouts is used.

Charge rate is specified as battery capacity (AHrs) divided by time, giving a charge current. For example, a 5 AHr capacity battery charged at a 24 Hr rate would receive a 208 mA charge.

I'm not sure what the Prius electronics would think of this. It tries to keep the battery between about 40% and 80% charge, and does so mainly by monitoring the charge mathematically. If you disconnected the battery and fully charged it, the system would have to reset itself, or perhaps it is required the tech reset it after charging.

 

Speculation on my part but due to NiMH self-discharge, I suspect the battery controller calculates the SOC each time the car is started. If I were doing it, I would use the initial, no-load voltage and the dV/dI, internal resistance, as a function of starting current load.

Bob Wilson

 

That is reasonable, except NiMH battery voltage actually varies as much from temperature as from state of charge "in the zone" (40%-80% of full charge). That's why Toyota has the system calculate the SOC. They -may- also do as you say, using temp readouts to estimate the temp/voltage effect.

Just to clarify what I'm saying, a NiMH cell starts out at about 1.2V close to full discharge (at "room temp" - 70F or 20C). It then quickly reaches 1.25V as you charge it and slowly rises to about 1.35V until it starts to heat up a lot at about 80% charge. Then the voltage drops slightly from the heating, masking the still increasing charge state. Once fully charged the cell presents about 1.5V, though it quickly drops from that value over time or when you load it with discharge. In discharge it quickly drops to about 1.3 V and then slowly drops from there to about 1.25V while "in the zone". "The zone" being the preferred operating SOC.

Now, if you wanted to build a charger for a Prius battery, you might design it to output a max. voltage of 1.5V times the number of cells. You would also want to limit the current to perhaps 200 mA, and I'd add a second "safer" current of 100 mA. You would also have to use the proper plug Toyota uses for the battery connection, and supply 12V to activate the relays in the battery pack. To be really "cool", connect to the temp sensors and cell pickoffs and use those outputs for debugging problems.

 

Folks offered both cautionary and encouraging comments on my service concerns, but after nearly a month, I finally turned in the loaner and picked up my 2001 Prius… done just right!

The dealer started out doing an injector repair required by a code stored in the ECM, and they explained that the delay was due to the coincidental occurrence of 3 problems: the fuel pump died while finishing injector replacement; the HV battery died while repeatedly trying to restart the car; then Toyota management in Georgia squabbled over the only HV battery charger in the southeast.

So still, “I Am The Luckiest Dog In The Known Universe” because I got a lot of free stuff, including a thorough inspection, a service history review, valve adjustment check, labor, loaner, and materials. With new injectors and associated materials, engine computer, fuel tank with fuel pump, and small battery, my Prius is completely up-to-date, for free! The tech even says all the HV pack cells vary by 0 volts.

The upshot is, if Toyota takes away your Prius for repairs for a long time, it REALLY pays to be patient.

And, I think we all learned that Toyota needs to have more than one HV battery charger in the southeast.

So if your Prius needs work in the Charlotte NC area, the best place to take it is Scott Clark’s Toyota on Independence Boulevard. They certainly went out of there way to satisfy me, considering how extremely impatient I was.

 

Hmmm, interesting-but dying at 99,000 miles at a cost of maybe $3500 isn't too bad. $3500 is roughly what it costs to get a complete transmission rebuild done, and many vehicles have 50,000 miles transmissions(Dodge minivans being one).
I would brag about a $3500 maintanence cost at 100,000 miles, but it isn't waaaaay out of line. On the bright side, there are very few reports of low mile dead batteries in any Prius.
Luck,
Charlie
PS-Bob, have you started stockpiling battery packs? There should be enough of them out there, that the cost for a used Classic battery pack with under 50,000 miles might be under $500 or so? Even if your bp never died, you could use it as an aux pk to double range.Does the Classic have an EV only mode?
The 2004 BP might end up being cheaper-used-since there should be a fait number of then-wrecked- out there. This would be a cheaper route to plug in-with 3 or 4 extra "stock" BPs-.Should get maybe 10-12 all electric miles-enough to get many folks to and from work on cheap 10cent KWH ELECTRICITY-I think we can get about 5 miles on a KWH-2 CENTS A MILE- or 150 mpg at $3/gal.