Some friends of mine are building a big rover, and they’re hoping to use the VNH carrier boards as the motor drivers. The motors run off of 24V batteries, so I’m thinking the VNH2s are no good, but they’re already committed to using motor controllers (no drivers) that output at 20kHz, twice the max frequency spec of the VNH3s.
They’re going to do their own tests when parts come in, but in the meantime has anyone tried running a VNH3 at such high PWM frequencies? What were the consequences?
Uh-oh; that’s not going to work at all. The VNH3SP30 has shoot-through issues that get quite bad past about 18 V, making the drivers useable only at low frequencies. Even at a few kHz, they will most likely destroy themselves since the shoot-through currents peak faster than the protection features get triggered.
However, we have some new discrete motor drivers coming out that will be able to do 24 V, 20 A at 20 kHz. We’re waiting for one chip to ship from the manufacturer, so we’re at their mercy, but we hope to be able to ship by the end of next month.
Sounds neat (except for the being at the manufacturer’s mercy part). Unfortunately my friends’ project is over at the end of August, so I don’t think they have time to wait.
What about running VNH2 chips (they’ve already ordered some of the dual carriers) at 20kHz off of a 14.8V battery pack (it would be about 16.8V for just a bit at full charge). Would they still have to worry about shoot-through?
The VNH2’s are working great off of a 4-cell Lithium Ion pack at 20kHz.
Another thought, do you foresee any negative consequences to increasing the current-sense resistor value to amplify the output voltage? We’re trying to get higher resolution in the ~1A range, but all the spec sheet seems to say about it is that the absolute maximum voltage on the current sense pin is 15V. Would switching to a 4.7K be reasonable? How about a 10K? To be safer I’ll try it on just one driver of the dual board first, like how they perform eye surgery on just one eye per visit!
I think it should be safe to put in the bigger resistors, but we don’t have any experience with doing something like that. Just doing one first sounds reasonable. I got both my eyes fixed at the same time.
