I recently owned a 2000 Prius 1st Gen with a damaged HV battery. It turned out that one cell almost exploded (the side of the battery melted). Obviously, corrosion and voltage distortion on the BMS caused the problem. I replaced that cell with one from a 3rd Gen Prius (all cells balanced, of course), and the battery works. However, I noticed that the other cells weren't very good either, so I started considering an alternative. I noticed that you can buy a complete Li-ion battery from a 5th Gen Toyota RAV4 for ridiculously cheap (at least in my country). Prices start at $300. I'm wondering if it would be possible to build a battery pack using these cells for a 1st Gen Prius. Theoretically, I would need 76 Li-ion cells, which would require buying two RAV4 batteries, but it's still much cheaper than replacing all the stock NIMH batteries. I wonder if this would even work.
You got to know the base voltage of rav 4 Prius is like 200 220 Dc volts . You should be able to Google the RAV4 I don't if that makes it plug in or
In theory you can't do what you're suggesting because you will need a much more elaborate BMS than the stock NiMH battery ECU provides. There was a guy who started selling Li replacement modules that ran on the stock battery ECU and he nearly bankrupted himself when all that batteries start to fail after not even two years. Then there is the potential fire hazard when the battery has a thermal runaway from poor battery management. You need to consider that there is no putting out a Li ion fire, you just got to let it burn while trying to avoid the hazardous toxic fumes. There was another member here who was looking into developing a Li-ion battery BMS (@mudder) who you could Start a Conversation with to see where he is at and whether his solution can work for you.
I agree. I agree. I'm working on my replacement Toyota BMS project full time right now. Initial support is for Prius Gen3, Prius V, Lexus CT 200h, and related. FYI: I'm not publicly documenting my progress like I did while developing my similar Honda product... ...but behind the scenes there's lots going on, and lots that I would love to talk about but choose not to for reasons. At some point my product will just start existing, but don't expect to hear too many specifics before then.
I'm aware of the dangers posed by Li-ion batteries. I thought the BMS for NIMH cells would be able to handle it, especially since there are plug&play Li-ion replacements, but after reading your posts, I've read more about these replacements and they are indeed quite unreliable. I think I'll pass on these Li-ion batteries and simply replace faulty NIMH cells as they become available.
Definitely avoid the Li-ion batteries! In theory it could work, but you would need to reconfigure the inverter for a different battery voltage, step up and step down etc. And you need a Lithium BMS designed specifically for the car; The main issues with Lithium batteries is that they are extremely efficient when charging, while NiMH batteries waste ~20%?, or a fair few % at least, of energy as waste heat. The NiMH Prius uses this inefficiency to keep the battery healthy: the efficiency changes with state of charge, and it turns out that the normal charge/discharge cycle when driving tends to bring the cells into balance with each-other. The Prius also keeps the battery between (IIRC) 40%-80%, where 40% is ‘nearly empty’, and 80% is ‘absolutely full’; this reduces the chances of cell reversal when the battery charge is low, and excessive overcharging, Another bonus of.NiMH is that overcharging usually just produces waste heat. It also produces some gases, which can recombine in smaller amounts. The Prius has emergency vents to release pressure if needed (very rare, hopefully). The NiMH chemistry allows the Prius to charge the entire battery as one unit - just apply 276 or 320-ish volts to the entire pack. Lithium batteries are efficient, so they don’t tend to self-balance like NiMH. Any slightly weaker cells or stronger cells will slowly drift further and further away, voltage-wise. Li batteries hate being overcharged; they just produce gas (which damages them very badly). Also, discharging them too much damages the internal structure / chemistry, causing issues when trying to recharge. Also, charging below freezing can damage the internal structure / chemistry / cause lithium to crystallize; On my Leaf, the car actually does charge the battery ‘all as one unit’ like a NiMH Prius, One difference is that the BMS refuses to let you overcharge the battery. And most importantly, it has ‘shunts’ controlled electronically, which are constantly taking charge from cells with a higher state of charge, and transfers it to cells with a lower state of charge. This is vital, and NiMH BMSs can’t do that (the Prius uses blocks of 14 cells; Lithium is often 1, sometimes 2 cells in a ‘block’, to allow individual cell balancing by the BMS. The final issue is that Li batteries are like a plastic toilet roll, with Lithium (flammable) between the plastic layers - with other chemicals also. Damage to the structure / chemistry can cause tiny short circuits, causing heat, igniting the plastic and lithium, also releasing toxic flammable gas and oxygen. Li without a BMS will ignite, sooner or later!
