We have an extra battery block sense cable harness. Has anyone spoofed the ECU with a voltage divider network so it always thinks the 19 blocks are balanced on a gen I battery system? For grins, I entered the schematic of the HV Battery, with 19 battery blocks, but instead of battery blocks, used 1K resistors instead, and then attached the output of a HV Battery to the endpoints of that voltage divider network. The circuit analysis showed a balanced output between each of the sense lines, and very little current loss through the circuit. Meaning it would take a long time for the divider network to self discharge the HV Battery if not driven or plugged into the grid for a long duration. Sure seems like this would work, if you were able to at least monitor the after market HV Battery with your own BMS.
I'm quite sure you would be the first to do something like that. Sure seams like it would work, although I can't think of a good reason so actually do it other than if you were to run some battery type that is not NiMh.
Yes, it would be interesting to us anyhow, to see if we could build up say a 20 or 40Ah LiFePO4 battery pack, with it's own charger/bms, then send that power to the input of the Prius's OEM electronics. But we'd need to spoof the Toyota's battery sensing of the original 19 blocks of NiMh so it thinks everything is AOK. Of course before going through the expense of the LiFePO4 pack, we'd like to test this theory with our small test bed of Pb Acid batteries we currently are using to boost the failed OEM pack of NiMh batteries.
Took the chance and made up the spoof circuit board today and installed it. Series set of resistors and capacitors, soldered onto the Battery ECU sensing cable, with connection to the add-on lead acid bank of batteries works.
Yes, this has been done by the early PHEV pioneers. There is much info about it out there with a search. I for one, think this is too clunky. I simply built my own replacement battery ECU. (gen II) This should be similar to implement on gen I. Then you can implement any kind of algorithm you like, and also report higher SOC numbers up front so the system will use more electricity. I first did a detailed teardown and analysis of the battery ECU, including what data it sends, so I could implement my own. If someone wanted to do this on Gen I it shouldn't be that different.
Looks like you are on the cutting edge of design there. Really good/impressive work. What is simple to you though, is way over my head. A handful of resistors, capacitors, and a relay was much easier to implement, which has the car running on a completely different battery , using the OEM electronics. Not as efficient, in getting the Prius to use more electricity in combined mode, but the goal was to remove the deceased NiMh batteries, and utilize something entirely different which was achieved. We can now focus on deciding what chemistry and Ah pack to go with for long term use. Thanks again for your input, it's very impressive the work you have done. I only wish I had the mental ability to duplicate it....
Update: So far the car has logged aprox 500 miles with the spoofing circuit installed with great success. No error codes have been thrown, regen is applied to the aux battery/capacitor banks without issue. Of course this will need to go through testing over a years worth of seasons to see if anything acts up due to temp variations.
Can you provide an update now after all this time? I like your idea because it provides the easiest and quickest fix/upgrade with the least amount of alterations. Also, I think that leaving the SOC and charge algorithm stock would possibly work with a LiPO4 battery as long as it was designed for a lower working voltage (e.g. 3.7v instead of 4.2v) so that the stock invert and ECU wouldn't overcharge it. There is little difference in the NiMH and LiPO4 charging algorithm up to about 80% charged state. After 80%, the two algorithms differ significantly which results in a LiPO4 battery exploding if put into a NiMH charger for too long. I did find this Fujitsu document on their work for the Gen3 Prius Plug-in ECU which I thought was interesting. They jumped through a lot of hoops to use the onboard systems with the 'Start' off and disable the 'Start' moving into gear with the charge cable plugged in. They also reworked the ECU to use LiPO4 batteries which was interesting. Fujitsu document attached.
