# Maximum Voltage for Voice Coil Servo

1. ## Maximum Voltage for Voice Coil Servo

Hi all,

Be warned, mechanical engineer here. I'm working on a project with a DC non-commutated linear moving-magnet voice coil, controlled with a servo drive in current mode, and I can't seem to get a straight answer from the manufacturer on the maximum voltage the device is rated to.

The rated current is 2.4 A continuous/7.2 A peak, the back-emf coefficient is 83.6 V/m/s, the DC resistance is 12 ohm at 20 C, and the inductance is 6.5 mH at 20 C. The magnet wire is AWG 22, Type-E rated to 600 V. As a worst-case operating point at peak current and max velocity could be as high as 1.9 m/s. Accounting for a 50% higher resistance due to increased temperature, the highest voltage I could see is ~160 V_bemf and ~130 V_R (ignoring the L*di/dt term) for a total of 290 VDC. I only really plan on leaving it at 2.4 A, so this voltage is likely higher than I'd see.

I've sized a servo drive and power supply that are able to deliver this voltage, but my question here is: is the high voltage itself bad for the voice coil? What issues might there be even if I use the servo drive to keep the continuous current below 2.4 A and the voltage stays below a reasonable safety factor on the wire rating?

Thanks,
Paul

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2. ## Re: Maximum Voltage for Voice Coil Servo

Hi,

your voltage calculations seem to be correct.

But for safety reasons you have to consider the wire isolation, the coil winding technique (isolation layers), the winding core, clearance and creepage distances and so on..
Iīd say itīs about impossible for you to decide. But in my eyes the manufacturer should know you the answer.

Maybe some high voltage tests can give a clue. but donīt hurt the isolaton barrier with too high voltage.

Klaus

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3. ## Re: Maximum Voltage for Voice Coil Servo

Hi Klaus,

Thanks for your response. I'm having a hard time getting the motor manufacturer to understand my question.. Or maybe I don't understand the answer :/ He says that at 10% duty I should stay below 120 VDC, and at 100% 40 VDC. But doesn't 40 VDC seem awfully low for a continuous rating when you take back-emf into consideration? That would mean you're only moving at 0.13 m/s (after subtracting off the V=I*R and dividing by K_e).

Paul

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