In-vehicle Trickle Charging a Dead Traction Battery ?

I loaned a family member my 2007 Prius without telling her that the gas gauge is drastically inaccurate. (Two bars means you're close to walking).

As you might guess, she ran it out of gas and continued to drive until the traction battery was depleted. There is no longer sufficient charge in the traction battery to start the vehicle. I had it towed back to my garage.

I recently purchased a Meanwell-branded LED driver module (called an "E-ballast" in the old linear fluorescent days) intended for driving LED lighting strings in the range of 150-250VDC. Its output current is roughly 300mADC. I have electrical engineering training that allows me to work on a 210VDC Prius traction battery without getting shocked or burned.

Question #1: Someone elsewhere in this forum suggested that disconnecting the 12VDC battery will cause the engine computer to reset and, when 12V is re-applied, the computer will reboot itself with the false presumption that the traction battery has 60% state of charge. The poster believes this will cause the vehicle to attempt to restart one last time.

Does anyone know if this is true?

Question #2: How can I use my 350mADC LED driver to trickle charge the traction battery sufficiently to re-start the ICE? Specifically, does trickle charging require removing the traction battery's cover or can its 210VDC terminals be accessed elsewhere in the vehicle? I assume that the high current relay in the traction battery enclosure makes trickle charging difficult.

Thanks to anyone with advice to offer.

Jim Olson
Indianapolis, IN US

 

Thanks for the great feedback, gentlemen.

I studied up last night (using internet resources) on the design of the Gen 2 battery pack, and Mr_guy_mann is correct that there is no easy access to the battery stack's terminals.

In fact, I was surprised that the high current loop out of the battery pack to the inverter is not connectorized. I can imagine that Toyota engineers doubted the long term reliability of a 150 amp connector, a reasonable fear.

The most convenient solution for my depleted NiMH problem would have been a low current (~1 amp) charging port integrated into the removable shut off plug. The plug was a custom-molded device anyway at the beginning of the Prius program.

That there is no conveniently-mounted low current charging connector for the NiMH battery shows that Toyota believed the self-discharge rate of their battery was extremely low. They certainly understood that business circumstances (recalls, parts shortages, etc.) would strand some unsold Prii in parking lots for months.

The hot trick would have been a simple circuit in the main inverter that, upon software command or via a hidden metallic switch, would have used the 12V battery rail to trickle charge a depleted traction battery. This charging method would necessitate an external charger on the 12V battery during use, but it would be a clean, zero labor solution to depleted traction batteries.

 

John, thanks for the thoughts, and let me use them as a soapbox for my own.

I'm a bit disenchanted with Toyota's customer experience from vehicle purchase to scrapping it, and might consider another brand when I buy an EV. But, in fairness, I think Toyota probably isn't much different from other manufacturers except maybe Rolls or Bentley.

As a car buyer/user I see Toyota as a besieged corporation living in a walled fortress, driven there by state and federal governments and plantiff's lawyers. (Ex: 600 page owners manuals that warn you the dashboard gets too hot to touch in the sun.)

Toyota cautiously builds cars and pushes them through the fortress wall to dealerships who (mostly) set their own rules and define the customer-facing experience. The recent "market adjustment" pricing stuff is a good example of dealers going their own way.

Modern business schools teach graduates to keep their eyes on high-level performance metrics and de-prioritize the crisises of the day. Translated, if market share this year is a half point higher than last year's it doesn't matter that customers think you suck. Numbers are what matter.

Dealerships act as if their targeted customer is a 75 year old senior flush with cash, never owned an air compressor or wrench, never patronizes the parts department except to purchase rubber floor mats, and simply wants a pristine driving experience to match their hoped-for stress-free retirement. Dealers apparently think that any deviation from that sterile business model encourages Toyota to franchise a new dealership down the street.

I would love to see a mainstream car manufacturer bold enough to sever their parts and service functions from their car selling entities. Frankly, most car purchasers just endure the dealership experience and acquire parts and service elsewhere.