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Hybrid electric vehicals, batteries going serial or parallel Answered

Can I wire 7000 lithium ion battery cells (about 75kwh) in parallel, and then use a lightweight bike engine hooked to a DC generator and connected in series to the batteries to boost voltage? Are there any flows in this design concept, for use in a hybrid race vehicle to increase the longevity of the batteries?

I am trying to develop a race track car which is hybrid, thus utilizing electric motors immense torque.
We build original race cars with common petrol engines but now I’m seriously thinking of developing a next generation race car. I know batteries don’t last long in high drain situations and thus any race car I sell will need a battery replacement after a race season. I’m sure this will be bad for business. Thus this is why I’m thinking of ideas to prolong the battery life by reducing current drainage. That’s why I want to have an engine generator with its sole purpose is just to boost voltage, and about 20,000ah worth of batteries connected in parallel so I reduce current demand per battery cell to well under 1C.

Giving a Tesla p100d as an example I would require about 1200 amps and 400 volts to produce 480kw of power. If wire all 7000 battery cells in parallel to produce the same amount of current then each cell will need to provide about 0.18amps that’s very low to sustain longevity of the batteries.

The generator is then connected in series to help boost the system voltage to 400v

In extrem simple terms, (the batteries provide the current, and the engine generator provides the voltage)

I hope you understand why I’m looking at it this way. I know it might not be the most efficient way, but is it a practical doable way?




9 months ago

I think your main problem will be safety.
Massive bus bars for the power are one thing, same as individual charge and protection cicuits for the batteries.
But keeping track of cells that are slightly out of specs from the rest will be hard.
Simial story for adding a generator.
In the ideal case it would only "boost" power when required - but how to control this amount of current and the required voltages?
Here it comes down to the same problem everyone face when trying to charge batteries while they are in use.
The input must match and somehow be diverted between batteries and motor controllers.
You can't just try to add the generator to boost the voltage as without current there will be no gain at all.
And with enough current from the generator you are again faced with the problem of handling and diverting it.
Normal battery eliminators are only good for about 120A, beyond that region normal relays won't do it and expensive electronics are required.

You calculations are also slightly flawed I am afraid.
If you want to reduce weight and demands then you need a quite high bus voltage.
So a lot of 3.7V cells need to be in series for this.
To reach the currents you require a lot of these series strings need to be in parallel.
And how many you need to make it around the track long enough is determined by the drain rate and what power you will use during a race.
Take a simple example:
Replace a 12V starter battery with 1.2V AA cells.
We need strings of 10 to reach 12V.
To get to at least 100 ampere from AA's with a reasonable drain rate we need about 120 of these strings.
Makes 1200 batteries :(
Add the losses from the bus system and you might even need 130.
Replacing the AA's with d-cells and you might only need 40 strings but a much sturdier bus system between the cells.
In your case you might not want to go for 400V but instead for 1000V and use a buck converter or inverter to get the 400.
Gives stable supply voltage and again reduce the demand on the batteries.

Apart from the bad examples charging will be a nightmare too.
Replacing a petrol engine with an electric motor is not hard.
Replacing the fuel tank with batteries is ;)
But I wish you all the luck and genius ideas you need to make your dream a reality soon!