Battery recharge threshold mod?

[redtrebor]

My commute consists of going many miles up a steep hill and then many miles back down -- at highway speeds. About half way up it decides that the battery is too low (only a quarter down) and starts running the gas engine harder to recharge the battery. In this case this is wasteful because half way down the other side the battery is full and the remaining braking is lost.

I would like a mod that lets the battery run down more -- ideally selectably. This must just be a threshold value somewhere on the PROM. I've searched for a few hours now and I can't find anything like this. I've looked through lots of stuff about the EV switch, which this wouldn't be -- the gas engine is needed to go up the hill.

Any pointers would be appreciated.

(2005 Prius)

[ken1784]

If you understand the Prius and think of the battery life , you don't want to do that or Toyota may void the warranty.

Ken@Japan

[McShemp]

Ken is right on. Taking the battery to a lower DOD will definitely shorten the cycle life. The Prius battery isn't meant to be deep cycled, as you desire. The car knows what to do and how to do it ... just go with it.

Ken - You have some inside info on the working of Prii. I've read on here - from people with CAN view - that the upper limit for SOC is 80% and the lower limit is 40%. If these are accurate, I guess I just don't get it.

Upper limit - Why so low? I realize large power spikes could occur during regen, but it seems like they could have gone to at least 90% SOC for a little more storage capacity. 80% seems a little too conservative. The car's software could attenuate the regen depending on SOC, and I know Toyota and PEVE have developed accurate SOC algorithms (probably in the 1% range).

Lower limit - Again, why so low? Not so much as "why" but "how"? All of the prismatic data I've seen (AABC papers and the like on gen 1 and gen 2 modules) suggest this level of DOD wouldn't provide enough cycles to get the battery life we're seeing. It looks like a 15-20% differential from max to min SOC would be the limit. Can you explain?

[redtrebor]

Thanks Ken and McShemp!

McShemp, I'd like to know the answer to your questions as well, but what I'm looking for I don't think is as radical as that. It starts recharging when about half the bars remain. If the display top is 80% charge and the bottom is 40% charge, this is around 60% charge (though I know the bars aren't a linear measure). It is starting to recharge when it is well away from the lower part of the acceptable range -- which would be a reasonable thing for it to do if it had to keep climbing -- but I know the summit (and lots of charging going down) is just a few minutes away.

[Frank Hudon]

<div class='quotetop'>QUOTE(Red Trebor @ Jul 3 2006, 11:26 AM) [snapback]280581[/snapback]</div>

Thanks Ken and McShemp!

McShemp, I'd like to know the answer to your questions as well, but what I'm looking for I don't think is as radical as that. It starts recharging when about half the bars remain. If the display top is 80% charge and the bottom is 40% charge, this is around 60% charge (though I know the bars aren't a linear measure). It is starting to recharge when it is well away from the lower part of the acceptable range -- which would be a reasonable thing for it to do if it had to keep climbing -- but I know the summit (and lots of charging going down) is just a few minutes away.
[/b]

when you say recharging the battery I assume your looking at the energy screen and seeing the arrows going back to the battery as well as MG2. Don't assume that there is a lot of charge going into the battery, it's probably under 10 Amps. MG2 can't use all the energy that the ICE is forcing MG1 to produce so the excess is available for charging the battery, but it's a very small amount. As you have a 2k5 your a candidate for a CAN-view so you could see all the charge/discharge rates and temps etc. Even my Classic puts about 7 Amps into the battery on a very steep hill over and above what MG2 uses to climb it.

[ken1784]

<div class='quotetop'>QUOTE(McShemp @ Jul 3 2006, 10:32 PM) [snapback]280472[/snapback]</div>

Ken is right on. Taking the battery to a lower DOD will definitely shorten the cycle life. The Prius battery isn't meant to be deep cycled, as you desire. The car knows what to do and how to do it ... just go with it.[/b]

Thank you for your comments.
I think you understand Prius very much.

Ken - You have some inside info on the working of Prii. I've read on here - from people with CAN view - that the upper limit for SOC is 80% and the lower limit is 40%. If these are accurate, I guess I just don't get it.[/b]

I just have the Toyota Tech Manual, and the internet info is my friend.

Upper limit - Why so low? I realize large power spikes could occur during regen, but it seems like they could have gone to at least 90% SOC for a little more storage capacity. 80% seems a little too conservative. The car's software could attenuate the regen depending on SOC, and I know Toyota and PEVE have developed accurate SOC algorithms (probably in the 1% range).[/b]

I saw 84.5% SOC max. The battery temp was 50C, which means it becomes almost full.
I think the 90% SOC level is dangerous and I believe Toyota did a lot of testing to find the reasonable upper limit for both performance and battery life.

Lower limit - Again, why so low? Not so much as "why" but "how"? All of the prismatic data I've seen (AABC papers and the like on gen 1 and gen 2 modules) suggest this level of DOD wouldn't provide enough cycles to get the battery life we're seeing. It looks like a 15-20% differential from max to min SOC would be the limit. Can you explain?[/b]

Prius is just a hybrid vehicle which does not require big battery capacity.
Please understand Toyota reduced the battery capacity...
NHW-11 273.6V * 6.5Ah = 1778Wh, NHW-20 201.6V * 6.5Ah = 1310Wh
However, both vehicle performance and mileage number are improving on the NHW-20 Prius. That's the technology innovation.
Also, note that the plug-in hybrid vehicle is completely different animal. Prius is not a good candidate for the plug-in hybrid.

Ken@Japan

[hobbit]

If you're able to temporarily slow from "highway speed" to under
34 mph for the last bit of your climb, an EV button would allow you
to use up the battery down close to that 40% level if you timed its
invocation right. Also, depending on how hard you push it on the
up side, you may be asking the system to supply more *from* the
battery in the first place to help move the car -- but you have to
be running the ICE up around 3000 rpm before that starts happening,
which may be too aggressive in your setting.
.
If you must maintain highway speed on both the up and the down, why
do you have a need to brake that much on the backside? Air resistance
should be able to hold you back, and if you need to provide any
motive power at all then it should only be at the warp-stealth level
[which very slowly *uses up* battery power, but no fuel] and just
coasting along otherwise.
.
I'm sure that with a little thought and more familiarity with how
the system works, possibly coupled with an EV mod if you're into
that sort of thing, you'll come up with the best way to conquer
the hill.
.
_H*

[McShemp]

<div class='quotetop'>QUOTE(ken1784 @ Jul 3 2006, 08:00 PM) [snapback]280719[/snapback]</div>

Thank you for your comments.
I think you understand Prius very much.

I just have the Toyota Tech Manual, and the internet info is my friend.

I saw 84.5% SOC max. The battery temp was 50C, which means it becomes almost full.
I think the 90% SOC level is dangerous and I believe Toyota did a lot of testing to find the reasonable upper limit for both performance and battery life.

Prius is just a hybrid vehicle which does not require big battery capacity.
Please understand Toyota reduced the battery capacity...
NHW-11 273.6V * 6.5Ah = 1778Wh, NHW-20 201.6V * 6.5Ah = 1310Wh
However, both vehicle performance and mileage number are improving on the NHW-20 Prius. That's the technology innovation.
Also, note that the plug-in hybrid vehicle is completely different animal. Prius is not a good candidate for the plug-in hybrid.

Ken@Japan
[/b]

Ken - I was just questioning the SOC swing and the lower SOC level of 40% (I still have a hard time buying that number). No NiMH life cycle info I've seen on PEVE modules supports taking them that low and still getting the number of cycles demonstrated with the Prius. I don't have anything in front of me now, but I'd guess <100,000 cycles when taken down to 40% SOC. I know each cycle on the battery isn't all the way down to 40%, but the car does a ton of discharge cycles in everyday driving.

As for the capacity differences between the NHW-11 and NHW-20 Prii, I think that is just a result of a lower bus voltage (likely due to changes in the electric motor/generators between Prius models). The PEVE modules still have the same capacities (6.5 Ah) and the same nominal voltage (7.2 VDC). However, fewer modules are needed at the lower voltage (28 vs. 38). I think this explains the lower capacity.

BTW - Prii are great candidates for plug-ins as long as it's the "extra" battery approach (like CalCar's).

[redtrebor]

Thanks Hobbit for your suggestions.

The highway is California State Hwy 17 a windy mountain highway (two lanes in each direction) that rises from sea level to 1800 feet in a few miles, and which Wikipedia calls "one of the most dangerous highways in the state". Driving 34mph would get me hate stares (I don't want Prius bad PR) and a ticket, driving without braking would get me a ticket in the unlikely event that I survived

I'm likely to try an EV button, for other reasons if not this.

I don't understand what you mean by:
<div class='quotetop'>QUOTE(hobbit @ Jul 3 2006, 06:30 PM) [snapback]280733[/snapback]</div>

Also, depending on how hard you push it on the
up side, you may be asking the system to supply more *from* the
battery in the first place to help move the car -- but you have to
be running the ICE up around 3000 rpm before that starts happening,
which may be too aggressive in your setting.
[/b]

[ken1784]

<div class='quotetop'>QUOTE(McShemp @ Jul 4 2006, 11:50 AM) [snapback]280778[/snapback]</div>

Ken - I was just questioning the SOC swing and the lower SOC level of 40% (I still have a hard time buying that number). No NiMH life cycle info I've seen on PEVE modules supports taking them that low and still getting the number of cycles demonstrated with the Prius. I don't have anything in front of me now, but I'd guess <100,000 cycles when taken down to 40% SOC. I know each cycle on the battery isn't all the way down to 40%, but the car does a ton of discharge cycles in everyday driving.[/b]

I think the zero bar of the battery level on the energy screen is 40% SOC.
I have never down to 45% or less. I know it is not good for battery.
I don't know how PEVE did the cycle test.

As for the capacity differences between the NHW-11 and NHW-20 Prii, I think that is just a result of a lower bus voltage (likely due to changes in the electric motor/generators between Prius models). The PEVE modules still have the same capacities (6.5 Ah) and the same nominal voltage (7.2 VDC). However, fewer modules are needed at the lower voltage (28 vs. 38). I think this explains the lower capacity.[/b]

The NHW-20 Prius requires higher voltage. Please remember it has step-up circuit up to 500V.

BTW - Prii are great candidates for plug-ins as long as it's the "extra" battery approach (like CalCar's).[/b]

If your commute is short distance, the plug-in vehicle is almost an EV through out a year.
Why we have to carry a heavy 1.5L engine all the time on such EV like vehicle?
Also, Prius consumes a lot of electric power, 250Wh/mile, on the other hand a good EV consumes less than 200Wh/mile.
My ideal plug-in hybrid is an EV based series hybrid with small (less than 1L) engine.