Salvage Traction Battery

Recently, a thread on transaxle replacement was inadvertently hijacked with a discussion about salvage parts, particularly traction (high voltage) batteries. Patrick Wong and jk450 still have some questions, so I decided to start a new thread.

Around Christmas, I took delivery of a couple of batteries. All that I want are the cells, which are being re-purposed. The two batteries came from the same yard.

The average junkyard is, shall we say, less than conscientious about the details. The batteries had the terminal/relay cover (Toyota calls this battery carrier panel No. 6) floating loose. Once removed from the car, there is no way to attach this panel other than nuts+bolts or zip ties. One had the orange service plug floating loose as well.

The other battery had the orange service plug installed.



The service plug completes the circuit in the 28 module battery string via a fuse, 120 amp if I remember correctly. If the service plug is installed, then the battery side terminals of the system main relays are at the full potential of the battery. Normally, white plastic caps cover the terminals for added protection, but these are miscellaneous bits not likely to be included by the junkyard.



To Patrick, the frame wire side terminals of SMR2 and SMR3 can only be energized when the car is in Ready. But the battery side terminals of SMR2 and SMR3 are always hot.



To jk450, since the battery side terminals of SMR2 and SMR3 are hot, a good reference for the hazard level would be the two hot legs of a 220V circuit. But in this case, the only human protection is a 120A fuse, which is really no protection at all! For lack of the #6 panel and the terminal caps, it is quite possible for someone to brush a hand up against those terminals during handling and receive a fatal shock.

To everyone, please do be careful around traction batteries! The orange plug should ALWAYS be removed as soon as possible during any service involving the high voltage system, and should NEVER be installed unless the battery is bolted down inside the car with all connections and safety covers in place. The pictures in this post are to illustrate the potential risk, and even using Cat III gloves and multimeter it still made me nervous. Toyota goes a step further safety-wise in recommending that the socket for the service plug be taped over with electrical tape whenever the plug is removed.

 

This one came out of an '04 with 95,000 miles. The physical appearance is pristine: no electrolyte leakage, swelling, etc. I love the pack assembly -- it is a home run compared to an IMA battery. I'll run some capacity tests eventually.

The two exposed terminals are where the leads for the service plug connect.



The bottom side of the battery. The wires are thermistor leads.

 

Honda has two problems: inferior module construction, and poor battery management. Honda uses D cell NiMH batteries that are spot welded into "sticks" in groups of 6, which are then arranged in a 3 x 7 grid inside the battery case (with one empty slot), and there is a large muffin fan which draws cabin air across the modules to cool them. As a result, the heat dissipation is uneven.

Battery management is poor for two reasons. There is no provision for rebalancing modules, other than "recalibration". If one module runs lower than the rest, i.e. hits near-zero SoC, that triggers a negative recal, where IMA takes engine power to recharge the entire pack, not just the affected modules. Over time, the imbalance divergence grows, and the stress on modules at the extremes increases, ultimately resulting in a failed module and the IMA light coming on. Whereas, the Prius can rebalance modules in the background, and failures are much, much less frequent. I wonder if Toyota has or licensed a patent somewhere on balancing. On the thermal side, the fan goes into high gear at a higher temperature than on the Prius, and only has 4 states: off, low, medium, and high. High kicks on at 53C. When NREL published testing results on an Insight in 2001, they were concerned about the thermal effects on long term reliability, and it is possible that real world results are even worse than they thought at the time.

Few of the early Honda hybrids made it past 150,000 miles on the original battery pack. I purchased my Insight with 159,000 miles on the clock and having a bad pack, and it was already a pack that had been replaced at least once. I think it is very rare for at the early Honda hybrids to go more than 150,000 miles on the original pack.

So, yes, I am planning to put 20 Prius cells into my Insight. It sure beats giving Honda $2600 for a new pack, or trying to refurbish the old one along the lines of hybrid-battery-repair.com. But there are challenges, such as getting them to fit in the existing form factor, and making sure that they are adequately cooled. It's a long term project.

 

As far as I know, they still use cylindrical NiMH modules, but fewer of them in the newer cars. I thought I read somewhere that Toyota has an exclusive agreement with Panasonic for prismatic modules, but I can't find the reference now.

 

Right, the Accord has the same rough config as the Insight and HCH, but a different module construction. It was the 2010 Insight that seems to have dropped down to 84 cells.

Have you had any problems with your Accord traction battery yet?