[PROJECT] Lithium battery for Prius

Hello everyone, since the fall of 2023 I have been developing a high-voltage battery for a Toyota Prius.

Code:

I am not a native English speaker, so sometimes I use a translator.
I am in north California, you can meet me and see the prototype live.

At the moment, I have already driven 8 thousand miles on the prototype of the first version.
Everything works great for me, now I am in the process of finalizing and optimizing the appearance.

My enthusiasm is fading a little, and I decided to start this blog to add information, maybe you will give me some new ideas.

1. The goal of Prototype 1 was to make the high-voltage battery ECU work with lithium cells, a small device was developed to do this.
2. In version 2, a device was developed with connectors, so that it could be connected to the HV Battery ECU without interfering with the car wiring. At any moment you could return to the original state.

Spoiler: Prototype v2

In version 3, the functionality is added to monitor the state of each cell by voltage, and when certain values are exceeded, an error is generated and displayed on the auto. (Also installation of additional temperature sensors.)
In version 3 I encountered a large number of wires sticking out during installation and the board had to be redone from scratch..

Spoiler: Version 3

In addition, housings for the cells that are used in version 3 were developed.
Different cells were tested.
All cells used are high current, automotive grade.
Version 1 uses 4.6 Ah cells.
Version 3 will have 5.0 Ah cells
Version 5 will have 5.5 Ah cells

Now about fuel consumption.
Test car Toyota Prius second generation 2005, with a mileage of 200 thousand miles.
On average my consumption is 40 MPG.
On the highway, it's about the same. If you drive with acceleration and 75 mph, it comes out to 37 MPG.
I don’t like to drive economically; in a Camry hybrid I got 25 and 22 MPG, but now my wife drives consistently at 30 MPG.
In any case, I started this project not to save fuel, but to forget about the existence of a high-voltage battery for a long time.


Plans and what I want to implement:
Version 3
Complete testing of version 3 with as careful wiring as possible.
Test the system in emergency situations

Attention!
Lithium cells are susceptible to fire and possible property damage and personal injury!
I carry out all tests on my car in compliance with all safety rules.
I strongly do not recommend performing tests and interventions on a high-voltage battery if you do not have the necessary skills and knowledge.

 

I can immediately foresee a question.

You can't just take and install a lithium battery from a new Prius! They are different in voltage, and increased voltage on the cells can lead to a fire!

I cannot give a detailed answer to some questions, please treat this with understanding.

 

In any case, the project will continue, but if before I worked on it every day after work, now only on weekends and it’s hard to force myself

 

Version 3 Installed in the car.
Next week there will be full tests on long runs.

PCB V4 has ben ordered.

 

Today I was stuck in a traffic jam for a bit, the speed on the highway was 70+ miles per hour, where the consumption dropped it was a traffic jam. It’s strange that in traffic jams my consumption is significantly lower than when driving on the highway.
It's a pity that the Prius doesn't record the average speed.


I had an idea and decided to assemble a battery for a Prius 30. After assembly, I’ll try to find an enthusiast willing to test it. See how the battery behaves for a person who knows how to drive more or less economically.

 

The version 4 board arrived, everything works as planned, I connected to the computer. Next, I'll set up the configuration.

 

The one that exists is not of very good quality, watch the video of disassembling the elements, what’s inside and how it’s assembled..

 

1st problem is soldering.
In automotive design you CAN'T use soldering because of vibration.

2nd problem is balancing board
It is based on cheap chinise chip. WITHOUT any safety featyre. For example, one cell is unsoldered. In this case, another cell will take on the entire load.

3rd and main problem is cells.
Inside NexCell they use 5s2p circuit. The Prius Gen 2 the maximum discharge current that I have seen is 120A.
Each cell with a capacity of 3.5 Ah must have a charge/discharge rating of 18C.
I have not found cells with a similar characteristic in open sources.
There is also a problem with the location of the cells; they lie close to each other, which indicates poor ventilation.
In the new version they made holes at the bottom and top of the case, but in my opinion this will not help much.

 

1) Contact welding
2) You're right it was a typo 5s2p. But anyway, I calculated right 120А / 2S/ 3.5АН = 17,2 ~ 18C

 

Board version 4b has been developed.
- The size of the PCB was reduced
- Reduced number of connectors.

Further plans include developing a case, board configuration, and installation in the car for testing.

 

My lithium has no problem with high current.
Also, I have some plans to test brand new cells from China. I already tested them with my equipment, but now I'm focused on the control board.

 

You indicate peak values; in general, I am more interested in current (A) values that last from 3 to 15 seconds. In any case, thanks for the information.