Jim Coate wrote: > So with my 176 volt pack I just need to add a FET to turn it on/off > at 60 Hz to make a crude square wave inverter?
Rod Hower replied: > You'll need at least 2 FETs, or you could use 4... your standard > H-bridge... Or you can replace Fet's 3 and 4 with capacitors > and pulse Fet 1 and 2 complimentary (make sure you have some dead > time in between turning one on and the other off. If you use IGBT's > make sure you have anti-parallel diodes on every device. The simplest inverter is probably just an H-bridge (4 semiconductor switches). It intrinsically delivers a square wave. You'll want some inductance in series with the load (which can be the motor itself if you only use it for driving motors). You'll also need some capacitance to filter the sharp edges and voltage spikes. The larger the L and C values you can stand, the closer the output can approach a sinewave. If you use only 2 switches with 2 series capacitors for the other two legs, the capacitors have to be HUGE at 60 Hz and high power levels. But, it has the advantage of being intrinsically current-limited. The capacitors also guarantee no DC offset. If the DC input voltage happens to be different that the peak AC output voltage, you'll need an autotransformer (or transformer if isolation is also needed). At 60 Hz, a transformer will be big and heavy. The size of an autotransformer is proportional to the voltage difference it needs to provide; if you only need to boost the AC output voltage 10%, the autotransformer is 10% of the weight of a transformer. -- Lee A. Hart Ring the bells that still can ring 814 8th Ave. N. Forget your perfect offering Sartell, MN 56377 USA There is a crack in everything leeahart_at_earthlink.net That's how the light gets in - Leonard Cohen
