Energy dump / overvoltage protection

Discuss hardware related to the VESC such as the NRF nunchuk.
TilmanBaumann
Posts: 15
Joined: 15 Feb 2018, 16:50
Location: Germany

Re: Energy dump / overvoltage protection

Postby TilmanBaumann » 15 Feb 2018, 17:13

Fantastic. I was very much concerned about going into an over-voltage regime. Mostly of the controller, but quite frankly also of the battery.
We should really not be dumping any brake current into a battery that is already fully charged.

When I first realised the issue I thought surely a 60V zehner cannot be the solution, it would go up in flames immediately. But I didn't think that through. :)
Having the option to dump excess power into a resistor is actually brilliant, because operation of the brake remains available. (Until the resistor or driver burns:) )

Would you say this type of current dump would allow me to push VESC safely into higher voltage regimes? Due to the motor I have I'm somewhat forced to use higher voltages as VESC would really like.
I would be happy to use 14S Which with 68V only leaves minimal margin to the 60V Ceiling.

How much headroom would such a circuit allow?

arvidb
Posts: 234
Joined: 26 Dec 2015, 14:38
Location: Sweden, Stockholm

Re: Energy dump / overvoltage protection

Postby arvidb » 15 Feb 2018, 23:12

I'm sorry to say I don't think this will help you at all at 14 cells compared to just using a battery "dump". I'm guessing you need the 10 V of headroom that you've got with 12 cells to handle the inductive spikes from switching the motor coils.

You might get lucky, but the right solution for higher voltages is to not use the DRV chip, and design everything to handle the intended voltage, with the required headroom.

This energy dump is intended for running a motor on the lab bench, from a lab power supply that cannot absorb regenerated energy. It would also allow you to do regenerative braking even though your batteries were fully charged if used on a vehicle (and if it was carefully dimensioned for the load), of course.

TilmanBaumann
Posts: 15
Joined: 15 Feb 2018, 16:50
Location: Germany

Re: Energy dump / overvoltage protection

Postby TilmanBaumann » 15 Feb 2018, 23:31

I have looked a little deeper into the subject.
Generic crowbar circuits should catch transients just as well as as larger current dumps.
The main difference would be not to dump the load into resistors but burn it ruthlessly into silicon chopping off anything going over voltage.

Still not convinced it will work. But I wonder why it wouldn't.

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Energy dump / overvoltage protection

Postby rew » 17 Feb 2018, 15:36

The DRV is a 60V chip. It breaks when you go over 60. Going for 68 is sure to fry the chip.

There are also diodes around the DRV that are rated for 60V. Those might be the cause of the DRV getting fried.

TilmanBaumann
Posts: 15
Joined: 15 Feb 2018, 16:50
Location: Germany

Re: Energy dump / overvoltage protection

Postby TilmanBaumann » 17 Feb 2018, 17:22

Sorry that 68v was a typo.
The max pack voltage is 58V, which what I meant to type.


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