does anyone have details on how the software works in regards to battery charging? I am wondering if something could be done like have an isolated battery that you charge up at home then during operation have it switched in to the connect with the hybrid battery charging system (to allow it to keep the hybrid battery always charged). I am wondering if the computer would complain? Does it only allow current to flow from the regenerative brakes? I have heard that it locks you out if you try to charge the hybrid battery while it is parked. Just curious to maybe try something as a project. I am installing solar at my house and if I could use some of that on the Tahoe that would be pretty great. I'd have to find a battery from a larger hybrid, maybe a Chevy volt and come up with a circuit to allow it to slowly charge the Tahoe hybrid battery to keep it always topped up, that way the Tahoe would always have some battery reserve to use.

 

Bad idea on every level. Not even a valid concept. First, the usable capacity of the hybrid battery in terms of electrical energy (240S*1.2V*6.5Ah*40%=749Wh) is less than the total capacity of the 12V under the hood (6S*2V*70Ah=840Wh).

You are attempting to drive off the equivalent electrical energy as the 12V under the hood. Try to wrap your head around that. That's approximately 1% of the energy contained in a gallon of gas according to the EPA formula in which 33.7kWh of electricity is equivalent to 1 gallon of gas.

A GREAT way to kill a battery is to charge it to full every day. The battery only uses 40% of its capacity for life considerations. Expand that amount of utilization, and the battery life drops substantially.

The battery is kept at a medium state of charge to ensure it has sufficient capacity to capture regenerative braking energy - a primary advantage of hybrids - recapture your kinetic energy as stored kinetic energy.

Ever seen a Volt battery? Try lugging this around:

https://gas2.org/2015/10/14/chevy-vo...-problem-free/

let alone secure it so it doesn't kill everybody in the vehicle in the case of an accident.

You do NOT have an EV or anything even remotely close. You have a gas car with a kinetic energy recovery and release system.

 

thanks for the reply, I think I didn't explain my idea very well. Totally agree that the vehicle is not designed to be driven exclusively off battery power (except for the tiny bit of driving under 60 amps load and until the tiny battery is too low). I am not thinking of changing anything fundamental about how it is designed. My understanding (correct me if I am wrong) is that the second mode in 2 mode (the first being all electric parking lot speed) is hybrid mode where the battery and gas engine work together. My idea was if the hybrid battery always has some energy it can operate in 2 mode far more than now reducing the load on the gas engine.

I also completely agree on a couple of points, any extra energy put back into the battery would have to be within its optimal range (not charging it 100%) so as not to shorten its life span and to allow room for big in rushes of current during braking.

Also I just googled the volt battery and yes its a monster and not what I am looking for, if this concept is plausible I would probably get something less than a quarter that size and stick it somewhere outside the passenger compartment, maybe where the spare tire goes.

the thing I am not sure about is if the computer would accept a small amount of charge going into the battery (while only keeping it within its valid range)

 

You explained it fine. It's not a valid idea. Your understanding of 2nd mode is correct; however, you haven't wrapped your head around the implications of additional electrical energy storage. Do you know how big the hybrid battery is? It won't fit where the spare tire goes - not even close. Even with the higher power density of lithium, you're still not going to be storing much more energy - perhaps 1-2 miles of additional high mode-2 EV assist the FIRST time you use the vehicle after charging. After this, you've exhausted any useful energy and have to charge.

You haven't thought through the complexity of interfacing the "spare" battery into the system and what to do about regen. Essentially, you're looking at a thousands of dollars solution to get you a couple of miles of enhanced EV-boosted driving with negligible environmental or economic benefit.

Consider also that NiMH batteries are filled with caustic KOH electrolyte (24% solution with WATER). They are NOT flammable. Screw up Lithium by pulling or pushing too much current or exceed voltage limits, and you risk a massive chemical fire. You also need provisions for keeping ALL cells in the Lithium battery balanced, so they're all operating at nearly identical voltages.

There are two sensible ways to maximize the performance of your vehicle:
1) replace the hybrid battery with a new one.
2) replace the vehicle with an EV or PHEV.

Every other conceivable option has massive cost with minimal benefit.

 

thanks for the input, true this is definitely not a fully baked idea lol, one thing I am curious to see if I can figure out somehow, maybe with the Torque app how much current and thus power is drawn from the hybrid battery during 2 mode operation and how that impacts fuel consumption vs. what fuel consumption is in the exact same driving conditions but purely on the gas engine. Basically a calculation/measurement to determine two things: how much energy the battery is providing and how much it is reducing fuel usage. Mostly for my curiosity, I am seeing here that actually trying to increase the time spent in the second mode is probably not worth the effort required. It would be interesting to see what percent of the total energy required to move the car forward comes from the battery in 2 mode and what percent comes from the engine though.

Also, not quite sure I understood why it would only be 1 or 2 extra miles of travel? If a chevy volt battery can propel that car on 100% electric power for 40 miles, even a Tahoe which is twice as heavy with a booster battery 1/4 the size and providing say 25% percent of the total energy needed (I just threw that number out there, no idea if its even in the ballpark until I attempt to do what I mentioned above, that and I suspect its highly variable) would be 20 miles if I did the math right and assuming its linear.

A lot of huge assumptions here but just for the sake of argument if I commuted 20 miles a day and got 25% better fuel economy by charging a 'booster' battery overnight, that would be significant but would it be worth the cost and all the extra effort? probably not, I'd have to have nothing better to do lol.

 

25% mpg improvement is massive. that's what the hybrid system provides above the non-hybrid. You'd need to provide enough energy for 5 miles of pure EV travel. Let's say 1/4 of a gallon. That's about the equivalent of a Ford Fusion Energi PHEV battery. That will take your entire trunk space.

You're talking about a booster battery that fits in your spare tire well. That's why you're only getting 1-2 miles out of it.

 

Adding any second or third battery to the system without re-programming the hybrid and battery controllers will only result in a Check Engine Light and Service Hybrid message. The system is smart enough to figure out something is different.


It's a hybrid NOT an EV!


The battery is sized to take in up to about 35 kW during Re-Gen and provide almost that much for lower speed EV and boosting.


You are also assuming that it only uses the 2 modes. There are four ( 4 ) fixed gears.


Lastly, increasing the vehicle mass with another large battery will only further reduce fuel economy.


The Volt goes 40 miles on only electricity because it was designed to. That liquid cooled Lithium battery lets you use about 15 kWh of power compared to less than 3kWh available from that NiMh in the 2-mode.


NOTE: The GM battery uses the same cells as Prius, just 6 more of them.

 

12 more than Prius (gen2-gen4)...
TWO more than Prius Gen1, but those modules are slightly different.
6 more than Camry/Avalon/Altima
20 more than Prius C
Same # as Lexus GS450h

 

WoW. I did not know all that. So newer Prius reduced number of modules?

 

With the Gen1, the modules had higher resistance, so they needed higher voltage/lower current. With the Gen2 in 2004, they dropped it from 38 to 28, and it's been that way ever since. The only exception is the "C", which can get away with 20 given its diminutive size. But even the larger V uses the same 28 module pack as the 2011-2015 regular Prius.