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bwilson4web · 11-23-2010, 03:19 PM

Hi,

Thanks, I often get lost in what I'm doing and forget that folks aren't mind readers. Some background information is important.

The 2001-03 Prius, NHW11 model, introduced the first prismatic, NiMH batteries in a hybrid electric vehicle. The first generation NHW10 sold only in Japan used strings of "D" cells. But like many first generation products, field use revealed some weaknesses:

weak terminal seals - under high temperatures and internal pressures, the seals can leak electrolyte.
single cell-to-cell connectors - located at the top of each cell, this concentrated the heat in a 'gas' space leading the higher than necessary temperatures.

Notice the black material around the terminal. This is the rubber seal that has melted and oozed out around the terminal. This provides a path for latent gas escape under high load and high temperature operations:

These latent defects would not be a problem unless someone operated their NHW11 Prius in hot climates, speeds over 65 mph and in hilly terrain where the exothermic charge cycle can 'heat pump' the battery to high temperatures and generate gas.

With the 2004 model NHW20, Toyota and Panasonic changed the design by making the case stronger and putting a second, cell interconnect near the bottom of each cell. This distributes the I**R load and with the stronger terminal seals all but eliminates the loss of gas, H{2} and O{2}, that dries out the electrolyte:

Taylor Automotive buys the traction batteries from salvaged NHW20s and ZVW30s (2004-current) and surveys the modules to establish an inventory of matched modules. They then rebuild NHW11 traction battery packs using the much improved NHW20 modules.

Now most folks wait until their NHW11 traction battery fails, usually one or two modules and then go after a replacement. But it occurs to me that an alternate approach is to replace the NHW11 traction battery and 'retire it' to the much easier life of a PHEV battery:

active charge balancing - so all modules are paired for optimum performance
wider dynamic charge/discharge range - the Prius battery controller is supposed to limit charge to 80% to prevent over charging the strong modules and a discharge level of 40% to prevent a fatal reverse charge. But in a PHEV, the battery no longer has to respond to driving conditions as much as provide additional energy to reduce fuel consumption
tailored charging - instead of 'drain me till I'm dead', a more strategic approach that seeks to minimize inefficient fuel burning makes a lot of sense. So cold engine starts and warm-up receive extra energy until the ICE becomes efficient. Then the remaining PHEV battery energy is saved for the next cold engine start where it can do maximum good. Also, a custom battery controller could store excess kinetic energy that the existing traction battery may not be able to handle.

There are some other things I'd like to do but first I need to pay attention to the basics and get the NHW11 battery mounted where I want it . . . after some refurbishment including balancing the charges. <GRINS>

Bob Wilson

ps. Is that 'brief' enough?

11-23-2010, 03:19 PM	#3 (permalink)
bwilson4web Engineering first Join Date: Mar 2009 Location: Huntsville, AL Posts: 843 17 i3-REx - '14 BMW i3-REx Last 3: 45.67 mpg (US) Blue Bob's - '19 Tesla Std Rng Plus Thanks: 94 Thanked 248 Times in 157 Posts	Hi, Thanks, I often get lost in what I'm doing and forget that folks aren't mind readers. Some background information is important. The 2001-03 Prius, NHW11 model, introduced the first prismatic, NiMH batteries in a hybrid electric vehicle. The first generation NHW10 sold only in Japan used strings of "D" cells. But like many first generation products, field use revealed some weaknesses: weak terminal seals - under high temperatures and internal pressures, the seals can leak electrolyte. single cell-to-cell connectors - located at the top of each cell, this concentrated the heat in a 'gas' space leading the higher than necessary temperatures. Notice the black material around the terminal. This is the rubber seal that has melted and oozed out around the terminal. This provides a path for latent gas escape under high load and high temperature operations: These latent defects would not be a problem unless someone operated their NHW11 Prius in hot climates, speeds over 65 mph and in hilly terrain where the exothermic charge cycle can 'heat pump' the battery to high temperatures and generate gas. With the 2004 model NHW20, Toyota and Panasonic changed the design by making the case stronger and putting a second, cell interconnect near the bottom of each cell. This distributes the IR load and with the stronger terminal seals all but eliminates the loss of gas, H{2} and O{2}, that dries out the electrolyte: Taylor Automotive buys the traction batteries from salvaged NHW20s and ZVW30s (2004-current) and surveys the modules to establish an inventory of matched modules. They then rebuild NHW11 traction battery packs using the much improved NHW20 modules. Now most folks wait until their NHW11 traction battery fails, usually one or two modules and then go after a replacement. But it occurs to me that an alternate approach is to replace the NHW11 traction battery and 'retire it' to the much easier life of a PHEV battery: active charge balancing - so all modules are paired for optimum performance wider dynamic charge/discharge range - the Prius battery controller is supposed to limit charge to 80% to prevent over charging the strong modules and a discharge level of 40% to prevent a fatal reverse charge. But in a PHEV, the battery no longer has to respond to driving conditions as much as provide additional energy to reduce fuel consumption tailored charging - instead of 'drain me till I'm dead', a more strategic approach that seeks to minimize inefficient fuel burning makes a lot of sense. So cold engine starts and warm-up receive extra energy until the ICE becomes efficient. Then the remaining PHEV battery energy is saved for the next cold engine start where it can do maximum good. Also, a custom battery controller could store excess kinetic energy that the existing traction battery may not be able to handle. There are some other things I'd like to do but first I need to pay attention to the basics and get the NHW11 battery mounted where I want it . . . after some refurbishment including balancing the charges. <GRINS> Bob Wilson ps. Is that 'brief' enough? __________________ 2019 Tesla Model 3 Std. Range Plus - 215 mi EV 2017 BMW i3-REx** - 106 mi EV, 88 mi mid-grade Retired engineer, Huntsville, AL Last edited by bwilson4web; 11-23-2010 at 04:42 PM..