Full-battery downhill engine start is a pain!

Is the engine warm during this time? The engine starts up to heat the catalytic converter and other critical components up initially, regardless of battery state.

 

By the way, i have taken to going down my hill in neutral if the battery is full when I leave my house. It's the only way to stop the ICE from starting. and yes when it starts, it is running and burning fuel, unless my scangauge is lying to me about fuel flow being nonzero.

Kinda burns my butt since I don't get to recapture that potential energy, but oh well. and my brakes will wear out just a wee bit faster I suppose.

 

With your Scanguage, are you also seeing that the ICE starts when the SoC reaches 84% as well? On Torque, I never actually see it reach 84%. I see it go up to 83.9% and stay there for a few seconds (while regenerating) before the ICE starts. So I always just assumed 84% was the magic number. Just wondering if the Scanguage displays anything more or less.

 

I think I've seen greater than 85% (like 85.3%) before the ice starts. I have not driven in a few days but next time I take the car out I'll let it start and note the soc.

 

Get a heavy duty appliance timer.

 

i don't see how this helps unless i am always starting from an empty battery. in any other situation i would have to calculate the amount of time needed to charge the battery to just below the "full" threshold. i could do this, since i have a scangauge but in all honesty this is the kind of thing the car's computer should do since it has all the information.

 

Guys just a word of caution: Do NOT interrupt the charging process just to finish short of a full charge.

As with any EV vehicle charging system, the last phase of charging is when all the cells are balanced to finish with the same SoC, the so called equalization phase of charging.

On the european model we see the AC input wattage going down from around 2100W to 650W, don't know if the US model does uses the same values, presumably yes with higher current and less voltage.

If you want your battery to live longer, always let it equalize till the end of the charging process!

 

That's a good point.

 

i would like to know more about this, i don't believe there are any warnings in the manual.

 

As with many other stuff that we are able to do in the car and shouldn't, so no big deal about a warning not being present in the manual.

In fact I don't know of a single EV having the equalization warning there, except for Vectrix perhaps, I seem to remember it there, a recommendation to perform a full charge till the end of the process every once in a while, don't know how often.

This is a very technical detail that probably no manufacturer will deem big enough to put it there. In their defense one can argue that it would be a whole lot of bad luck to have someone consistently aborting the charging process on the equalization part... that's what I thought when I saw this thread course, and decided to give a fair warning.

 

Here's a printscreen of the final phase of charging of a PHV on the Portuguese 230V (European) grid:



The time to charge varies slightly as you all know, but usually takes about 1h20, the last 13m or so being the equalization phase.

Just for comparison here's another "equalization signature", this time from my BMW C-Evolution, with a slightly different (but more common) back-down in power during the last 28 minutes:



As you can see Brisco, this is not something exclusive of the PHV. It is quite common and known in the EV world.

 

Is the Prius top-balanced? Can you describe the BMS behavior in more detail for our PiP?

I know the battery is never fully charged, but I don't know if that would affect the way balancing is implemented.

 

thanks jprates, that's great info!

 

This chain was very useful, although I didn't see anyone comment that the problem only started in 2021. I bought my Prius Prime in January 2020. I drove a whole year down a very long steep hill just after a full charge and the range would peg and I could drive a few kms before it would start to drop. Sometime in 2021, after a few regular maintenance checks by Toyota (and possible software upgrades), that's when the EV would drop out going down that hill. B mode definitely doesn't resolve it, neither did switching to park at the light at the bottom. I could shut down if I hit the red at the right time and restart, but that just isn't right. So, wondering if the cause was a software upgrade, the batteries degrading forcing the change or some algorithm that tracks performance.

 

The issue dates from 2017. It's nothing new and so far there hasn't been a solution that covers everyone.
Back in 2017 I believe most owners that posted about the issue solved their ICE startup going downhill with a full charge by unplugging their EVSE before the cars charge session was completed.
If you can test over may days ( it may take that long ) safely ( test may require very slow speed ) - test by reducing the cars speed as it reaches the crest of the hill, until the ICE doesn't fire on the decent.

Speed that ICE switches on is also determined by temp. so what works when it's 80 F doesn't always work when it the temp is 40 F and similarly what works at 40 F doesn't always work at 20 F. And many more temp variations than listed above.