General questions about troubles with converting hybrids or upgrading BEVs

[0tik]

I read a lot about this stuff and the conclusion this-
> Replacing OEM battery without using OEM hardware is major pain in the ass to make it work with stock HEV/BEV. Nobody makes replacements boards for CMU and BMU that work with the rest of OEM components of HEV/BEV
> Replacing NiMh with li-ion or Lifepo4 is impossible due to voltage not being scalable and Toyota's BMS seeing series of 6 cells/ monitoring 7.2v packs. Therefore not being able to monitor single cells of liion/lifepo4
> Upgrading OEM capacity is troublesome too because of the way BMS counts battery capacity. For example shutting off battery before it really depletes. Someone tried that with I-miev so we have a proof of concept that it doesn't work. Besides that, Only Leaf and imiev/Outlander have guts easy to work with. I admit I have never looked into zoe or bmw i3 batteries. Other cars have water cooling and/or unconventional cell dimensions which makes it difficult to work with.
> Can't find any info about ABS or ESP and other traction assists so I assume any DIY BEV cars/conversions are incapable of those features. Is this true?
> The only way for easy (as in someone who doesn't know anything about CAN programming) modification is to add second battery in parallel to original one. Just add a board to act as a bms for secondary battery and wire it to contactors that cut it off in case:
-something is wrong during charging
-something is wrong during drive
-to make sure both batteries have same voltage
It is safe to cut off second battery because the car is designd to work with original one. So nothing bad should happen... Apart from doubling amp draw from battery but that's an extreme case and unlikely scenario. This is what we have fuses for. Can't have it wired to cut off both batteries because that could cause reverse current from a motor to blow up HV electronic. I don't think it would be an issue during charging because charger would be wired to my board and shut off in case of second battery failure. Second battery in case of Toyota could be lifepo4+orion bms. Now correct me if im wrong here but I think that in case of BEVs it would be the most reasonable to add second OEM battery + OEM BMS with one way CAN communication. That way ECU can tell BMS to close contactors. If that doesn't work that the idea of doubling OEM battery is still the most convenient one because it's easy to relay cell data from OEM BMS CAN to homemade control board and chemistry is the same. To clarify- when i write about BEV batteries i mean 2 units of the same, stock battery.

To give you a better picture about text above I have to say about myself. I only own an I-miev and have not done any modifications to it yet.
Yes, there are people who upgrade i-miev capacity or install second battery(or even replace OEM one) to prius but it's their business, they must have done some CAN hacking and therefore won't open source their projects.
https://www.ozdiyelectricvehicles.com/

Ps. If someone could explain all the over-engineering of PIS Kit. Was it buck boost converter in second battery? Was it lower voltage than OEM one? Project is dead and therefore can't find any details on it. Didn't they just add parallel battery with matching voltage and a charger to charge both batteries?
ps.2 In case this thread goes places, for future readers, here's a guide on parallel strings. One must know that doing that requires more "safety breakers". https://www.orionbms.com/manuals/pdf/pa ... trings.pdf

[ZooKeeper]

I read a lot about this stuff and the conclusion this-
> Replacing OEM battery without using OEM hardware is major pain in the ass to make it work with stock HEV/BEV. Nobody makes replacements boards for CMU and BMU that work with the rest of OEM components of HEV/BEV
> Replacing NiMh with li-ion or Lifepo4 is impossible due to voltage not being scalable and Toyota's BMS seeing series of 6 cells/ monitoring 7.2v

Actually, it is totally possible to replace the NiMh with a Li based pack, but you have to LIE to the Toyota BMS about cell voltage so the vehicle will function. Basically the Toyota BMS leads would connect to a series resistor string across the Li pack selected to return the correct cell voltage at full charge. Voltage dividers are a well documented method, of course this would require adequate isolation as it would need to be connected to the pack directly.

[0tik]

I know about the general idea of that concept but wouldn't software spoofing of voltage be more simple? I'm more concerned about abs and esp systems and making the whole converted car in a state that all modules are working.

[0tik]

Actually, it is totally possible to replace the NiMh with a Li based pack, but you have to LIE to the Toyota BMS about cell voltage so the vehicle will function. Basically the Toyota BMS leads would connect to a series resistor string across the Li pack selected to return the correct cell voltage at full charge. Voltage dividers are a well documented method, of course this would require adequate isolation as it would need to be connected to the pack directly.

I have found out that Prius have coulomb counter too and can't see more than 6.5ah. One Russian guy had this problem but I don't know what happened next. I'd link the thread but I'm not on my PC now. I see that people are successfully swapping their NiMH batteries in Prius for LFP. No idea how they do BMS stuff with them or how they overcome 6.5ah limit.