Looks like they "right sized" their packs depending on mass of vehicle and driveline requirements.

 

Indeed they did.

Unfortunately, starting with the Camry/GS450h (2010-2015 Prius), the Gen3 Toyota hybrids are much harder on their batteries. I think they decided that the Gen2 battery was "overbuilt", so they dialed up the utilization while simultaneously introducing cooling issues to all models, which shortens the life of the battery and causes cycle/heat damage in the lower 1/3 of the country. The GM packs have the same cooling issue (IMHO).

 

The cooling design on those packs shows me that nobody knows air flow.

Now the VW Toureg pack has an air flow system that will make a Corvette jealous.

 

I know this is an old thread but it seems like an opportunity for a good discussion was derailed. I think your idea is valid but the application is tricky.

What I suggest is building a large custom Lithium Ion battery and use that battery to charge/recharge the individual cells inside the hybrid battery using individual DC-DC converters. I don't know enough about these hybrid batteries to start making precise voltage claims but "In General".

Build a 36v lithium ion battery using modern hybrid batteries. There are better ones to use besides Chevy Volt batteries. I like the once from a Ford C-Max.




Using these simple DC to DC converters for each cell pack in the hybrid battery.



The output voltage can be adjusted to the highest voltage which doesn't cause any issues with GM's safety protocols. 14v, 15v, 16v. Whatever? The DC to DC converters only allow the power to flow in one direction.

The second battery would keep the primary hybrid battery charged to ~65% overall SOC without touching the 300v system. The secondary battery would also help keep the primary cells balanced.

With a "full" hybrid battery, the vehicle should try to use the battery as much as possible for the most efficient driving experience.

Once the lithium Ion battery is depleted to a safe level, the BMS will shut down the DC to DC converters and the vehicle will behave like normal. Charge the secondary battery at night it will recharge the primary battery to start the next day. It seems simple enough.

 

The main flaw in your thinking is that NiMH can be voltage balanced effectively. They can't. They don't have the direct linear voltage to SoC relationship typical of LiPo. Your trickle "balancers" won't balance to any significant degree, and they would likely worsen any existing imbalance due to the typical disparity in SoH between the various modules. NiMH can only be balanced at a voltage AND current of significance OR at 100% or 0% SoC.

In short, your solution would be complex, expensive, time-intensive and ineffective.

A quicker, cheaper and more effective solution would be to simply use DC-DC converters capable of converting 12V to 336V (might need 2+ with their outputs in series) at a low current of < 0.3A to charge the entire pack and provide a means for driving the cooling fan.

 

I should have taken more time in my original post. I was tired and I didn't want to loose my train of thought.

Having balanced cells wasn't the main point of my thinking. It was a unintentional side effect. The main points of my thinking are:

1. Start the daily commute with cells packs near or at the maximum SoC allowed by design.

2. Provide a way to recharge or supplement the high voltage battery with a secondary battery.

This is very true under load but NiHM voltage vs SoC becomes "more" linear under rest. Also, this doesn't mean there are no effective ways of trying to maintain a voltage slightly higher than nominal. Which isn't perfect but a much better indicator of a properly charged cell. Anything would be better than nothing.



The dc to dc converters I'm referring to "claim" a maximum output of 3a.


We all know there is a difference between "claims" and actual performance. IF (big if) the converters are able to produce 3a of output they would be able to carry the entire load of the max 60a (3a x 20 = 60a) placed on the battery from the Hybrid system.

When the accelerator is pressed and the voltage of the HV battery drops below the threshold set in the DC to DC converters, the DC to DC converters would start to supply current to the cell packs. The current from the DC to DC converters would essentially "flow over" the cell packs and go straight to the controller. If the current demands are more than the DC to DC converters can supply, additional current will be pulled from the HV battery.

In this scenario, the HV battery essentially becomes a slave until the secondary battery is fully depleted. Once the secondary battery is depleted, the system returns to normal operation.

If the converters used in this example aren't enough to provide a significant current, there are others that can. The converters linked in this thread are 10 for $13.99. I picked these for the simplicity in their design and operation.

I'm assuming all the cell packs are healthy. I would be wrong to assume I could fix unhealthy cell packs.Large disparities in SoH would have to be addressed differently.

Complex, A little.
Expensive, A little.
Time-intensive, Yes.
Ineffective, Maybe.

Building custom batteries out of used hybrid cells is easy and common. DIY powerwall guys build 24v, 36v and 48v batteries all the time to run off grid and grid tie inverters. I built this 52v nominal battery to power an off grid inverter for my travel trailer when shore power isn't available.







The box fit snugly between the wheel wells of my old Suburban. The cells are from a Ford C-Max hybrid 7.6kWh. The entire HV battery assembly cost me $650 and I tore it down myself. The battery management system was like ~$50 from China. I have another $50 in copper bus bars and misc wiring.




Do you think a setup like this would be completely ineffective to improve the performance of the GM 2-Mode hybrid? I'm not claiming the application I'm describing in this thread is the best way to do it. I'm just trying to keep the conversation going.










Link?

 

1. 240S * 1.2V/S * 6.5Ah = 1.9kWh of capacity. Of which about 40% is usable of which only about 50% is available for "enhanced" driving. That puts you at 0.37kWh of "play" capacity. This would equate to about ONE MILE of pure EV operation at slow speed (< 25mph).

2. See #1.

The assumption of a healthy battery in a GM hybrid is a poor one. The vast majority are working with severely deteriorated batteries just above the threshold of failure.

You have some big errors:

1. Total current pull on a NiMH pack can be 130-150A. Even moderate acceleration is routinely 70A+
2. You don't get to add the 3A. You're only applying 3A to a block. To get 3A at the pack, you have to apply 3A to ALL blocks, which is what you're doing. To put it another way, with your proposed devices, you can ONLY supply 3A of current to the entire pack, NOT 3A * 20A = 60A.

Concerning your off-grid option: I'm assuming you're 14S6P on your off-grid battery (don't want to count). I did a similar thing with Energi cells in a 7S12P config with a 24V/2kW inverter of the same brand. However, I retained the original module frames since they are fireproof, and I opted not to surround Lithium with flammable material. Due to present and future current requirements (at and slightly above 100A now with a future pull of over 200A), rather than a cheap BMS, I went with true "balancers" that can shuffle 6A between cell groups as most cheap BMS only bleed off excess capacity at the top, and I couldn't find anything cheap that could handle 100A.

I also charge the bank with about 2kW of panels, but it's limited to about 1700W due to the solar controller. I have acquired a total of 6kW of panels and 37.8kWh of Energi packs (5) that will soon be deployed with 2X Victron 5kW inverter/chargers providing split phase 220V for total off-grid power for 2X RVs and an then eventual permanent dwelling.

The experience above and my knowledge of the workings of the NiMH packs forces me to conclude that efforts towards extending range in the manner suggested are high effort, high cost and very low (if any) reward.

 

1 miles is better than no miles.

Agreed. Any unhealthy cells would need to be addressed.

Yeah. I'll go back to my corner...

My idea would require much larger chargers per cell block to regain any real range while driving. hmmm

So I would image you have gone through any possible scenario/solution to convert a 2-Mode GM Hybrid to a pseudo PHEV?

I don't own a GM 2 mode hybrid. But I would like to own a GM PHEV Truck or SUV. Short of finding a Via Motors VTRUX I just have to wait for GM to release one?

 

Correct. 14s6p

Fire proof? If a cell explodes inside the original module frame nothing is going to stop it from causing the adjacent cells from exploding. I plan on removing the cells from the wood box to build smaller modules in 14s2p configuration for portability. I sized the box to fit inside the wheel wells of my Suburban but I never got to test it. The box was too heavy to move from my basement to the garage and I sold the Suburban.

That is why I went with 14s. 14s cuts the amp requirements in half for the BMS, cabling, bus bars, etc. And it's a low enough voltage I still feel comfortable handling.

Awesome! #goals. I've built a couple of smaller custom batteries using 18650s. It didn't take me long to figure out that I didn't want to use 18650s for a DIY power wall. These Energi cells are great because they can output a ton of current and are easy to configure/reconfigure.

I need a 220v split phase solution. Do you have a link to your setup for more information? I'll promise to not bug you too much.

 

14S was always the final destination, but I cheaped out and went with 24V for the initial configuration. I regret it. Even so, I knew with 48V, my 10kW final configuration will still pull > 200A and even higher with surge currents. Split phase is pretty simple. You have to buy two inverters that can run in parallel. They're spendy.

I'm in the process of acquiring 2X Victron 48/5000 Inverter/Chargers that can operate in split phase mode:

https://www.victronenergy.com/invert...argers/quattro

They can also charge the battery from one of 2X simultaneously connected AC sources (e.g., generator and grid) if I have too many consecutive cloudy days.

My main motivation for split phase is for the eventual DEEP well pump we will need. Those are always 220V due to the hundreds of feet of wires. My neighbor has to run his diesel generator to run his well pump. I'm trying to avoid that. With that as the goal, then things like electric heat become more realistic as I truly want to minimize the carbon footprint (will have propane backup!).