R
[email protected]
- Jan 1, 1970
- 0
The original post was to design the inductor for a LPF to allow a 19.2v
electric drill charger to operate from a "modified sine wave" 12/120v
inverter.
I received my 'scope from EBay with only CH2 working but using that I
was able to look at the voltage waveforms of my three dc/ac inverters
and the input current of the charger when driven from 120v rms line.
The two smaller (~90w) inverters have similar output waveforms with ~
2ms dwell at zero and 2microsec rise and fall times. The 140w sample
had narrower alternating pulses with ~ 4ms dwell at zero but of course
higher peak voltage such that the rms value was still ~120v.
Using 0.9 ohm sampling resistor in the neutral return of the charger I
measured an alternating pulsed current ~ 3a pk with ~ 3ms zero dwells
and narrow leading edge spikes of 4.6a pk.
I calculated the average current (Simpson's rule) as 1.35a which agrees
with the measurement using an old Avo 8 rectifier multimeter and taking
rms/av = 1.11.
Crudely sampling this current on paper with a 120v rms sine wave gives
247.6va, a far cry from the 75w on the charger label! No wonder the 90w
inverters complained.
I tried a surplus Corcom EMC filter with 012 e-3H chokes and 9 e-9F
capacitors as someone suggested but the charger wouldn't run even with
the 140w inverter.
It seems incredible that the charger takes so much current and that
with an almost fully charged 19.2v battery pack. If I had both channels
available on the 'scope I could see if the phase was such that 247.6va
is only 75w. I bought a 7 mFd oil capacitor and a transformer to
rewind as a choke but assuming 100va size core area, Perhaps I should
re-simulate with a 60 ohm load i/o the 176 ohm load for 75w. Any
suggestions?
Dick
electric drill charger to operate from a "modified sine wave" 12/120v
inverter.
I received my 'scope from EBay with only CH2 working but using that I
was able to look at the voltage waveforms of my three dc/ac inverters
and the input current of the charger when driven from 120v rms line.
The two smaller (~90w) inverters have similar output waveforms with ~
2ms dwell at zero and 2microsec rise and fall times. The 140w sample
had narrower alternating pulses with ~ 4ms dwell at zero but of course
higher peak voltage such that the rms value was still ~120v.
Using 0.9 ohm sampling resistor in the neutral return of the charger I
measured an alternating pulsed current ~ 3a pk with ~ 3ms zero dwells
and narrow leading edge spikes of 4.6a pk.
I calculated the average current (Simpson's rule) as 1.35a which agrees
with the measurement using an old Avo 8 rectifier multimeter and taking
rms/av = 1.11.
Crudely sampling this current on paper with a 120v rms sine wave gives
247.6va, a far cry from the 75w on the charger label! No wonder the 90w
inverters complained.
I tried a surplus Corcom EMC filter with 012 e-3H chokes and 9 e-9F
capacitors as someone suggested but the charger wouldn't run even with
the 140w inverter.
It seems incredible that the charger takes so much current and that
with an almost fully charged 19.2v battery pack. If I had both channels
available on the 'scope I could see if the phase was such that 247.6va
is only 75w. I bought a 7 mFd oil capacitor and a transformer to
rewind as a choke but assuming 100va size core area, Perhaps I should
re-simulate with a 60 ohm load i/o the 176 ohm load for 75w. Any
suggestions?
Dick
