Interesting stuff Jagodo, I know a few of us have considered the electric route, and of course Marek has a complete but not totally fettled example in his Delage. I am very happy that you are going down this route and will be following your progress and findings keenly. I hope your build journal de-mystifies electrickery for me.
JimR

I had a question about batteries on my build thread. I think it would fit better here.

Could you use the 48v battery from an ebike?

That depends on 3 main things: The current limit of the pack, the total energy capacity of the pack, and safety.
Note: I assume the question is about road-legal ebikes, off-road bikes are different as there are no rules and no power restrictions and may well be user designed.

Current Limit
========
UK CycleKarts are limited to 3kW continuous/ 5kW peak (which typically means for 10 seconds before the motor overheats).  Road legal ebikes are limited to 250W continuous. So we are using 12x the power. This means that road legal ebike battery packs are not intended for the sort of currents that a CK will draw. 5kW peak is the CK motor mechanical output but its electrical input will depend on the motor efficiency, if this is 75% then the battery needs to provide 6.7kW, which is about 140A at 48V. Whether that will quickly destroy the cells in an ebike battery depends on the particular cells used and the number of cells in parallel in the pack.

Battery Capacity
==========
Also a CK battery will typically need to last for a minimum of 10 mins of racing (but some events may be longer, e.g. 24 minutes so a battery swap might be needed). During a race, drivers are usually on full power for about 60-75% of the time, so 10 mins of racing is about 7.5 mins on full power. 3kW output means 4kW of electricity which translates to 83A at 48V. This means the pack needs to be able to supply 500Wh before its voltage dips significantly. What fraction of discharge represents a significant drop in voltage will depend on the battery chemistry but it is likely to be between 60 to 80% discharged. So you probably need a nominal capacity of 700-800Wh but more would be better. I don't think that typical ebikes batteries are in this range.

Safety
====
There are many different Lithium chemistries and most of them need special care and some are particularly sensitive to over AND under charging. Under failure conditions they can result in serious fires and explosions. There is also the danger of crash damage causing short circuits, battery rupture etc leading to fires. On a ebike, the rider is likely to be thrown clear in a crash, not so in a cyclekart. Other racing clubs (I'm thinking of the Hacky Racers) have virtually restricted the approved chemistries to only LiFePO4 by imposing restraints on other types. LiFePO4 is much safer because its electrolyte requires much higher temperatures to ignite and generally needs an existing fire to get it going. LiFePO4 also has other safety benefits when handling the cells and when abused. It also has a long life, long shelf life and it maintains its voltage longer under discharge. But LiFePO4 has significantly lower capacity for a given volume or a given weight, which means that it is probably not used in ebikes - but I've not checked.

Note: this is my view, others might disagree...

I have not been able to get past 2 major drawbacks.
1. The cost of the drive system will be at least £1000, more than my entire kart.
2. How will I recharge the battery fast enough to make a day’s racing achievable.

1) The cost...
I have spent £370 on a 3kW motor and a matching controller through Alibaba from a company called Wuxi Helanda Mechanical & Electrical. That was the total cost including delivery, import duty and various other charges, but I was very pleased with this price. It is intended for a large 3 wheeled transport that is common in China but it remains to be seen if this is suitable for a cyclekart.

I have currently spent about £450 on the batteries, which was £300 for the cells, £130 for a BMS. I got the cells 'new second hand' for a very good price because they were surplus from another project and had cost over £1,000 new in 2020. I noticed that similar cells are available through AliExpress with 60% off making them only a little higher than the price I paid.

I have also bought a 15A charger specifically for my battery configuration from AliExpress for £110.

So I am standing at £930. I am actually going to split my cells to make 2 batteries, so I'll need another BMS which will bring the total to just over £1,000. But I recognise that the implementation is completely unproven and I might well end up reworking it (i.e. spending more money).

2) By my estimates, a typical 10 minute racing session will use about 12Ah at 48V. My cells are 15Ah (Headway 40152's), so I can get away with using a single string of 16 cells. Note: the cells can happily delivery 150A, so I don't need to parallel them.

As I have 56 cells in total, I am intending to make a second battery that uses 32 cells in a 16s2p arrangement, so that I can take part in longer events (~20 mins). I intend to make these batteries interchangeable (although I doubt it would ever be as fast as a F1 pitstop). So with my 15A charger running full time charging one of the batteries, I can drive for 10 mins per hour all day. I'd expect to arrive with both batteries charged and to always swap the batteries, to keep the charger running. However, I might move up to a higher power charger (I've seen a 30A one) because even the single string can be charged at more than 15A.

That all assumes that power is available and that I am allowed to use it. If not, and for places that are off grid, then I think I'll need a 3KVA petrol generator - so about another £300 into the mix. I might claim that the generator is to cover home power cuts, as we have had 2 in the last year, so I can put that expense in a different budget!

A higher power charger and a generator are going to push the cost of going electric close to £2,000. But I'm not going to invest any more for now until I know 1) that the cyclekart works, and 2) that a rule change won't make my hardware obsolete.