I've been considering my options, posting to the Mark 1 Prius Yahoo group:
http://autos.groups.yahoo.com/group/Mk1 ... ssage/5536
(Note: I think that registration is required (free, but slow) for this group).
While I've been wondering about this, I was contacted by someone with an ailing NHW10 with just 41,000 km on the clock, and one of the last '10s made (2000 manufacture). It's a bit ironic that while low mileage is generally good for a car, it's probably bad for the hybrid pack. I had ideas of this Prius being the first customer for a sort of "Prius Import Rescue" business.
In the above thread, Mr Mik kindly offered to "brain dump" all he knows about the NHW10 model. He has three of them; two are daily drivers and one is a repairable writeoff that he uses for parts. He also came across four NHW10 packs for $100 some time ago, so he's got lots of cells to play with. (These are all old packs, from cars that had their packs replaced with new or refurbished NHW10 packs from Japan. So someone knew how to import replacement packs from Japan!) Unfortunately, the novelty of rejuvenating NHW10 packs has worn off for him, and there are other demands on his time, so things haven't progressed for a year or so.
As it happens, one of his daily drivers is showing the triangle and turtles, and so it needs a slow equalisation with his charger. To do that, he needs to take the front off the pack, and he had the day off today. If I'm going to start this rescue business, I'll need to know all I can about the NHW10 car, so I begged Weber for a day off from MX-lightning duties, and visited Mr Mik's "Prius Farm" today.
I certainly learned a lot today, and I'm very grateful to Mr Mik for taking the time to teach me some of the tricks he's learned. One big realisation for me is that life would be pretty miserable without the Toyota S2000 scanner, which he grabbed one of for "only" $1200. This is one of the few machines that will talk to the NHW10s, which seem to have OBD-1 ports (most cars have OBD-2 ports). Without this scanner, the only way to get the stick (strings of 6 cells manufactured into a sort of rigid tube) voltages would be with a multimeter on the ends of the sticks. I envisaged this as a fairly simple exercise, but alas, the only practical way is to take the battery box (almost the width of the car and weighing some 60 kg) out of the car, and take out the two half-packs from the removed box. This makes the "instant diagnosis" part of the business plan rather difficult.
(BTW, the readout of the S2000 scanner is all in Japanese; it's taken the NHW10 community some time to decode the menus. Fortunately, the numbers are in English, so after a while, you get to remember the sequence of numbers to get to a particular menu option.)
Mr Mik was working with a colleague from New Zealand on attempting to crack the protocol of the S2000 scanner. He had the S2000, a Jaycar kit OBD2 scanner, and a sort of "Y" cable to enable the Jaycar scanner to see what packets the S2000 was sending. But that was never completed. If it was, and something home-made could interrogate the stick-pair voltages (the Battery ECU measures the voltage of each pair of sticks, or 12 cells), then the rescue idea might be feasible.
Though now that I post this, it occurs to me that something that connects to the wiring that monitors the cell voltages (perhaps with a different sort of "Y" cable) would be able to monitor the cell voltages. Well, two "Y" cables, since each half-pack would need its own "Y" cable. Maybe it needs a small computer with a USB connection and a 20 to 1 multiplexer to scan the various string-pair voltages... oh. Of course, it would have the usual problem of increasing common mode voltage; parts of the circuit would have up to 360 V difference to other parts. So that would be tricky to wire up. It's all done safely in the battery ECU already... but we can't easily get to it. It's frustrating.
Another thing I learned is that the NHW10 will drive quite happily with the warning triangle, and even turtles coming on and off. Things must be pretty drastic to get the 20 km/h limit.
We also decided to fire up the repairable writeoff car, since it hasn't been used for some time. It would be in a similar state to the cars I'd be trying to rescue. We used the boost charger to get the engine running. We used the scanner to find the weakest stick-pair, pair 9. It would have the lowest voltage during discharge, and the highest voltage when charged. After running a short while, the motor (edit: I means "engine") started running at a higher speed. I had guessed that this indicated the start of an equalisation charge, but not in this case at least. The current went to zero. We found that the "delta SOC" value had gone up to 58% (or perhaps higher), which is apparently alarming enough that the hybrid ECU decided to not continue charging the pack. We repeated this a few times, with the same result.
This made me realise that there are plenty of reasons that the engine will not charge the pack, so any recovery would have to be on the bench. However, the car would presumably still be drivable, so I suppose that's not so bad. It just means that the rescue will almost always result in a drive back to the garage, where either a long slow equalise might fix it, at least temporarily, or bad sticks, or the whole pack, can be replaced. I was hoping that at least some of the rescues would result in a running vehicle the same day, which would make the customer happy, and they'd cheerfully fork over some money for the service. The more expensive options they might have to think about long and hard.
We talked about that aspect over lunch. For example, maybe I can figure out a good way of putting 1.4 NHW20 packs of prismatic cells (which are far more reliable then the D cells in the NHW10s) into a NHW10 box. Would customers be willing to pay around $5000 for a reliable pack that should last the life of the car? Would used car buyers pay around $5000 more for a NHW10 with a reliable pack? Sadly, I can't see it. I think that there will be enough used NHW20s around, some at low prices, that would be more attractive than the older NHW10s. So I think that the business model for the rescue business is flawed.
The idea of converting NHW10s to plug-in or full electric seems flawed for the same reason. It would add more value to the car, but at an even higher cost, and the Prius battery ECU can't be guaranteed not to attempt an "equalise charge" of the pack, which could be disastrous for a lithium pack.
I'll let the ideas rattle around in my head for a little longer, to see what might still work out. I've taken home an empty NHW10 battery box, in case I want to try to fit the NHW20 cells into one. Mr Mik has so many of these (seven) that he'd have to take some to the dump soon anyway.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.