Are commercial VFDs tweakable?

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Are commercial VFDs tweakable?

Post by luke_jenson » Tue, 04 Apr 2017, 13:06

Does anyone have experience with commercial VFDs regarding driving them with lower voltage DC than designed to use, and or lower AC voltage or Hz?

I have a used 75 kW Lenze VFD that I'm trying to use to accomplish 2 things: ... erters.pdf

short term: lower the rpm to lower diesel use and less noise

long term: add battery pack, connected to the DC-bus

Other reason for asking: I'd like to know if my 15kW motor can be run from a higher voltage vfd. ... Motors.pdf

Any experience from others might save me lots of time and potential costs if things fail.

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Are commercial VFDs tweakable?

Post by woody » Tue, 04 Apr 2017, 13:22

The VFDs I've looked at (Mostly ABB) have low voltage alarms which would be the lower end of your DC bus voltage - but they seem to vary quite a bit in range - e.g. I recall some having alarms at 400 and 900 volts.

Lenze's: Johnny on this forum has one in his car and will be more familiar with them.

Lower RPM - The VFD should handle a lower RPM but you will lose power capacity - a 15kW motor at half speed is a 7.5kW motor or less as the currents will be the same but the fan speed/cooling will be less.

Lower voltage - most 3 phase motors have 6 wires which means they can be connected in "Star" or "Delta"/"Wye" configuration- the "Star" voltage will be 1.7 times higher than the "Delta". In Aus usuially 415/240. or 690/415. the currents change in the opposite direction; e.g. 17 amps nominal in Star would be 30 in Delta.

Similarly your 75kW VFD is limited by voltage and current - if you are using it at half voltage it is only a 37.5kw drive but that doesn't worry you if you've got a 15kW motor.

Motors are easier to come across than VFDs usually.
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Are commercial VFDs tweakable?

Post by Johny » Tue, 04 Apr 2017, 15:48

Hi Luke. Woody's final comment is the key. The current a VFD can provide is the main factor.
As for running lower DC Bus voltage on a Lenze. That would be a pretty major re-engineering project. The Lenze drives run entirely from their DC Bus which means they have lots of switch-mode power supplies built in.
I run the earlier 9300 series and the drive pretty much drops out at 450 VDC (from early testing I did). I run a 600-650 VDC pack (192S2P LiFePO4).

Running AC motors on higher voltages is fine - in fact desirable. For instance to get twice the speed out of the motor at the same torque as nominal speed, you must run twice the motor voltage. The faster you can run the motor with the same torque, the more power you get. Final drive gearing becomes the issue with a DIY (assuming no gearbox).

The Lenze drive are VERY configurable. You have function blocks, Analog comparators, OR, AND, NOT gates etc. I have mine set up for an elaborate Torque/Speed control that gives me a seamless transition from acceleration to regenerative braking. It also controls brake lights, motor cooling fan, battery packs alerts. (The 9300 comes standard with more I/O than the later 8200 series.)

The 75kW in a monster - size wise.
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You will also find tonnes of discussion on this forum about AC motors - it takes some time in searching though.

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