How to extend LIMITED SERVICE LIFE of Prius PHV traction battery.

The Volt requires liquid cooling vs the air cooling in the Prius Plug-in. To me, this indicates that the Volt batteries are under higher stress signified by the greater amount of heat generated during discharging/charging.

 

The liquid is not just cooling, its full TMS. Keeps the battery warm when its cold as well. Very important if you want all EV mode to have range. The Prius PHV will use the engine early to keep it warm.

Keeping the battery in the right range has significant impact on range/power, see http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/aabc_lv.pdf

Even for cooling, to me it indicates that they cautious path to ensure it will last a long time and allows them to have a 8y/100,000 mile warranty on the battery. Its uncertain how well any technology will last.. accelerated testing is always iffy.

 

i will definitely read the manual cover to cover. hopefully, for long term storage, it's just a matter of leaving it on the charger. that's what all my other rechargeables recommend. and maybe that will take care of the 12v as a bonus!

 

What was good advice? He had none. He said you can't make these predictions without knowing about the cells in question. He is wrong. Any lithium battery will have more capacity if stored at a lower SOC. If you store it at full capacity it will make it wear out faster. Any lithium ion battery on the market.

It indicates they want less thermal stress. That is all it indicates. Ford is doing liquid cooling. Tesla is. Fisker is. GM is.

Who isn't doing liquid cooling? Toyota, Nissan, and ?

It is simply a design decision. If you want the vehicle to cost less you leave out liquid cooling. If you are Toyota and plan on using the ICE often then it works out well. You can keep the batteries from to much strain with ICE and save the cost of a more robust thermal management system.

 

He DID give advice. He said a lot of effort to protect the battery will have little result. He said the owner's manual will be a good place to consult. Go back and read post #79.

The PiP will not be allowed to charge to 100% The Toyota engineers are likely to be well informed on this subject which will be reflected in the owner's manual. What they say is worth considering.

 

Mitsubishi, if you were looking for another. But the new Toyota RAV4-ev has liquid cooling, so, you can't really say one manufacturer prefers one BMS over the other. BTW, your statement below is either based on speculation or just a guess.

Since neither I, nor you nor anyone on PC are engineers for both Toyota and Nissan, and Ford, we can't say with any authority WHY the vehicles are either liquid or air cooled. Another valid reason (beyond the "cost" guess) to go with either air or liquid could just as easily be based on safety requirements. Some lithium chemistries may simply require liquid cooling to help assure they don't experience thermal runaway / catch fire (a la Volt). So, to state cost is THE reason whether to use air or liquid cooling, I'd like to see a link to read up on that, if it's really 'THE' reason.

 

Dup.

 

They are both required to max discharge rate of about 7C (7.0C for prius and 7.3C for Volt), for me this is a good indication for similar stress (and i did not say same in the original post).

Of course, there are other factors influencing, but one can only judge and estimate based on the data known.

I think your assumption that the Prius battery is delivering its max power at constant speed of 60 mph is wrong, its probably only half of it.

 

Thanks I knew there was another one. Anyway you missed what I am saying. The RAV4 will have liquid TMS b/c it is better for cell life and Toyota knows it is better. It just costs more. I am not saying that Nissan and Mitubishi will only ever do air cooling or that the others will always do a liquid TMS, just that at this exact moment in time a liquid TMS will extend the life of lithium ion cells in a given design unless the current draw is so minor that the additional energy used in pumping fluid is a large proportion of the energy used by the pack over its life.

The PiP is partially based on work they already did for the regular prius and they don't want to radically change it to accommodate liquid cooling. It is undoubtedly a cost issue, but that doesn't mean it is a bad decision. Everyone seems to get all upset if you mention cost. All manufacturers make tons of decisions based on cost. The decision as I said here was possible b/c they use the ICE often to keep the pack safe. There is nothing inherently wrong with that. BTW The volt caught fire because of liquid cooling, it wasn't a necessity to prevent thermal runaway. The advantages I see for liquid TMS is that it prolongs pack life by keeping the cells at a better temperature, it theoretically could enable a denser pack hidden farther into the recesses of the vehicle since there is no need for high rates of air flow, faster thermal regulation, and acoustics might be better. The disadvantages are that there is another pump, more tubing, another liquid level to check, problems if you have a leak, possibility of messing up the connections (a la fisker) and it is cheaper. I personally think Toyota is making the right decision given the other parameters they are working from, but that doesn't mean that cost wasn't a factor in their decision. I would be disappointed with them if they had not considered cost.

 

Thanks for your kind words, Allan.

As Allan already pointed out, my advice was to consult the owner's manual and follow its advice, rather than assuming you know better than Toyota's engineers.

Wrong. The Rav4EV will have liquid cooling because Tesla is building the battery pack (as well as the drive train) and Tesla uses a battery chemistry that requires it.

Lithium is not all the same. Lithium ion laptop batteries (the kind used by Tesla because they are less expensive AND have greater energy density AND are more readily available from a variety of manufacturers) experience thermal runaway if they get too hot, and therefore must be cooled for safety. LiFePO4 batteries (the kind in both my Xebra and the ill-fated electric Porsche, whose problems, BTW, had nothing to do with the choice of battery chemistry) do not experience thermal runaway, and can therefore operate safely without active cooling.

I do not know the chemistry used in the Volt, Leaf, and PiP, but I do know that all three are proprietary, and all are different, and that therefore you cannot make assumptions about one based on the others. Volt and Tesla have active temperature management, Leaf and PiP do not. Leaf and Tesla allow charging to 100% (or nearly) at the owner's discretion, but warn that this will shorten battery life. Volt and PiP do not. Because you CANNOT charge PiP to 100%, the analogy to Leaf as regards storage is invalid.

Because the chemistries are different, it makes more sense to follow the recommendations of the manufacturer of your car, rather than making general assumptions about all lithium batteries, or extrapolating from one car to another.

 

I chose not to respond previously b/c in my post I specifically said that Toyota had this worked out. I said one should follow their recommendations, and that these little decisions individually are not that important. I did no see how repeating the same thing was useful, but obviously some learn from repetition and need to hear the same thing over and over.

I know I was going to write about Tesla being the only one that needed it b/c they used lower quality cells in the roadster, but I did not want you to get upset so I left that part out. Sorry for the omission. So yes the only company that truly needs liquid cooling to prevent a catastrophe is Tesla. Congrats on that. The wonderful world of cobalt oxide batteries.

Fisker uses LiFePO4 batteries and has a liquid TMS. It is I REPEAT for battery life. It is not for thermal runaway. They are doing it to prolong the life in all of the other scenarios, from ford, from fisker, from GM. We will see in 5 years the difference when comparing the Leaf and the Volt, the Sonic, etc...

It is the cathode and anode we are talking about. Lithium is lithium

 

Scotty,

You seem to distrust Toyota engineering but think Volt is better engineered. That's what I am getting from your posts.

One thing not discussed yet is under extreme temps. Prius PHV would gladly run the gas engine. Volt will hold out as much and as long as possible trying not to run the gas engine.

 

I apologize for not being more clear then.
I trust both their engineering teams (oh noes!)

Toyota uses the ICE to make it possible to forgoe a liquid TMS.
If Toyota wanted to increase the EV capability with the same sort of cells we have access to now they would use a liquid TMS most likely (in my opinion).

However what Toyota is doing actually makes more sense for the average person.
Use a smaller less capable cheaper battery pack and the ICE to make it work. When battery technology improves and gets cheaper they can get a higher capacity pack. If cell technology improves we may be able to lose the liquid TMS across more capable vehicles.

I like the voltec power train more myself b/c I like a more EV like vehicle (that doesn't mean I think it is better for the average person). However I like the PiP more b/c the glider is more to my taste (it has 5 seats and more clearance etc... and once again this doesn't apply to everyone). However none of this means that a liquid TMS would not improve the service life of the pack in the PiP. I think it likely, however the cost increase, and the energy use pumping the fluid around would make this a poor choice in this given vehicle.

 

But it may shift gear if you have a lead foot resulting in up to 3 seconds lag because the traction motor was not engineered like a BEV.

If you push the accelerate pretty hard, Prius PHV will use two fuels (gas and electric) but Volt will shift a gear with mechanical (clutches) transmission. There is no other EV that shift gears as they are all single speed. Even the Prius has a single speed.

 

You don't seem to understand the Volt design. The traction motor is the same type of motor used in a BEV..

If you accelerate hard it uses 1 motor, the 111kw traction motor. I only uses 2 moters in a power-split approach when it seeks efficiency. I've done 0-90 and there is no "shift" (And I've done 75-100 and there was no shift then either).

Watch this video around 1:10-2:00 (and especially at 1:40 when they say you can do 0-100 in just single engine mode).
[ame=http://www.youtube.com/watch?v=343-NQKOvLg]Chevy Volt Powertrain Deep Dive | Part 2 - YouTube[/ame]


Here is a video of a volt doing from 0-95.. where do you see it shift?

There is only 1 place where one can "feel" a shift.. going from 2-motor efficient mode to 1-motor acceleration. While it has cluches.. it does speed matching before any of them are used so its seamless when it does change from efficient 2-motor to 1-motor driving, but can present a little lag when going from cruising speeds to acceleration. I find it about 1-second before the real power kicks in.

 

7C is nothing compare to Prius Alpha/+ Lithium HV battery pack. It has 1kWh pack and it needs to provide 27 kW (to match NiMH spec). That's some 27C but it is a high power chemistry.

 

Very interesting video (Deep Drive). Thanks for posting that. While others have asserted that there is a power lag from the clutches, my concern is reliability: I consider HSD, with no clutches, to be more reliable than Voltec, with three clutches.

And although she kept stressing efficiency, 35 mpg does not seem all that efficient to me, compared to the prius's 50 mpg. (Or 45 for mixed driving.) The Volt's only saving grace is that 35 mile EV range, five miles less than my Zap Xebra had with its LiFePO4 battery pack.

But for all that, the video is very interesting, especially since it's the first time I've seen a diagram of the Voltec power train.

BTW, the Chevy dealership where I test-drove one told me categorically that the ICE never connects to the wheels. Not surprising that Volt salesmen are as ignorant of their car as Toyota salesmen were of the Prius in the early days.

As for the other video, looks like someone's been breaking the speed limit.

 

Ok, so it goes to overdrive when cruising. If you alternatively accelerate hard and cruise, going in and out of overdrive with there will be 1-3 seconds gearshift lag.

 

Volt gets 40 highway which is really the only time it uses the "efficent" setup. For city driving it pure serial setup. (BTW, that was video 2 in a 3 video sequence.. though I'm pretty sure you guessed that).

It never formally connects to the wheels. Ice connects to the generator that connects to the ring that connects to the carier that connects to the reduction gear that connects to the wheels. But of course that is semantic and every chevy salesman I've met was an idiot that would not understand the difference. My 2 visits neither had even charged the volt let alone really knew anything.


The reliability of the clutches could be an issues but they elements are all speed match before the clutches change. The good thing is that it means items are isolated when not in use. For example in the PiP what stress is put on the ICE engine by always being in the gear setup while not running. In the Pure Prius that is not all often, but in the PiP it could be (ideally) not in use most of the time. The engine will need to passively supply torque to hold still. From that view I like that the clutch takes the ice off of the system, since I don't plan on using it much at all. (For the Volt with the bigger battery its even more important).

 

Well, nothing but an in-wheel motor "really" connects to the wheels. Having a direct geared path to the wheels is what I call "connected." When the ICE is connected to the generator and the generator is connected to the PSD, and the PSD is connected to the wheels, that is "connected" in my mind. As opposed to ICE connected to generator, then only an electrical path from the generator to the motor, which is what that dealer claimed was the only way the ICE supplies power to the wheels.

But it sounds like your dealers are as ignorant as the one I visited.

I understand your points about completely isolating the ICE when not in use, and about the clutches being synchronized before being engaged or disengaged. But I still view a clutch as a more complicated mechanism.

But I also consider both Prius/PiP and Volt to be overly complicated compared to a pure EV, and therefore less reliable. Just based on general experience, I consider Toyota to be more reliable than GM, and on top of that I regard the Volt as too complicated.

And even 40 mpg for the Volt on the highway, compared to my 50 mpg for my Prius on the highway, looks poor in my opinion. As I've said, I'd have bought the Volt four years ago, when nothing else was available. But I think there are better choices now. In order I'd pick: Tesla, Leaf, Xebra, Volt; and for long trips, I'd pick the Gen II Prius (or Gen III as a very close second).