Electrathon Vehicle Testing Issues

Hey all,
I am a High School student and have been working on an electathon vehicle as my in school project and I have a race in the next few days and have encountered an issue during testing. While I was testing about 15-20 min in the vehicle suddenly began to rapidly lose power and after letting the car sit for a few min it would regain some of this power back and the batteries had already each lost 1 volt. I am completly unaware of what the problem could be any suggestions would be awesome.
Some basic specs are:
the battery setup is one that we created, it uses nine like e-scooter batteries arranged in 3 packs of 3 for a total of 36 volts 42 amphours. Our speed controller is an altrax SP48300 and our motor is a 95r motor, 12-48v dc, axial flux, both the motor and speed controller are from shiftev.com.

Tman0315 said:

Hey all,
I am a High School student and have been working on an electathon vehicle as my in school project and I have a race in the next few days and have encountered an issue during testing..........

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Hi Tman0315, welcome to ES!

Things like sudden power loss can be a lot of things; anything from a faulty connection to a bad battery cell. Here are a few things I would look for:

1. Check all connections carefully to make sure they are well connected.
2. Make sure that your battery is fully charged and balanced. If your cells are unbalanced the controller or bms might detect a low voltage and cut off the power. It is known as LVC or low voltage cutoff.
3. After a long charge, maybe an overnight charge, test all your cells individually to make sure they are within manufactures specifications. Your battery needs to be charged and balanced. Then give your vehicle a good run and after the run, test the cells again to make sure that none of the cells have had a marked reduction in voltage causing LVC. A battery with out of balanced cells will cause a LVC.

Good luck and let us know!

After just 15-20min of running seems pretty short for 42ah of batteries, but what kind of running? Hard running or trying to conserve energy? Your team will definitely need to learn the difference to be successful. What kind of energy consumption measurement do you have?

It sounds like your controller is cutting back due to voltage dropping to the LVC (Low Voltage Cutoff). What voltage do you have that set for?

Unless you are running fairly conservatively, I doubt those batteries are up to matching the power potential of your motor and controller. After running for a while at the maximum performance you plan to use, you should check the batteries for signs of warmth. If the batteries are heating up then they aren't up to the task you demand of them.

In addition to making sure your LVC is set properly, you need to run a capacity test of your battery pack. To do that you first need to get it charged and well balanced.

Also, now is the time to learn about battery life. ie the only time you should ever 100% charge your battery pack is immediately before a competition. All other times you should charge much more conservatively to ensure maximum capacity for the competitions where you want to make sure your pack is charged and balanced to get the most juice out of it.

A good understanding of lithium batteries could be a real key to success in electrathons, especially since they've gotten away from the lead acid battery pack requirement. Your team should spend a couple of man-days reading in the battery section of this forum to get somewhat up to speed. You'll even learn how to get much more out of your cell phone battery while you're at it.

Tman0315 said:

the battery setup is one that we created, it uses nine like e-scooter batteries arranged in 3 packs of 3 for a total of 36 volts 42 amphours.

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what specific batteries?

are they arranged all in parallel, or are some in series and some in parallel?