Post by Nigel on Feb 25th, 2008 at 2:51pm
Will is right, generally speaking things will work ok on true sinewave inverters and decent quality generators. The problem will come if your device needs more power than your inverter/genny can provide - typically washing machines cause this problem. The voltage and/or frequency goes unstable and so all sorts of odd things start happening - including self destruction.
The problem is (as Will says) much worse with modified sinewave inverters. Usually the first thing to blow is the pressure control unit on water pumps (typically in a few seconds/minutes) followed by various other devices - typically ones that have microprocessors controlling them. The reason is due to the design of the power supply circuit that these devices use.
For anyone interested in the reason, here goes:
You can see the circuit design for a really cheap DC supply from AC shown below. The problem with modified sinewave inverters is that they have a number of switching stages to simulate AC - anything from 4 (really really cheap) upwards. The AC is generated by switching these stages on and off in sequence - each having a higher or lower voltage, basically the waveform output looks like an up/down staircase (see Modified Sinewave Intended).
As these stages switch on/off there is a large transient spike, and lots of harmonics with high voltages, that occurs on the switching edge - far in excess of the designed output voltage of the inverter but of such short duration as to be insignificant (see Modified sinewave actual) UNLESS you are a capacitor ( C1 ) in which case your design voltage is exceeded and you start to break down inside, shorting out the plates through the dilectric. Eventually C1 dies completely and the full inverter supply is dumped across the remaining bits (if you're unlucky, which tends to be the majority of cases) or C1 goes open circuit and so no supply arrives at the rest of the circuit. Whichever happens, usually C1 ends up as a charred lump, taking several other bits to the scrapyard with it.
In some cases the device can be repaired, in others not, but the advice is not to use anything sensitive on modified sinewave inverters or invest in a good quality pure sinewave inverter!
Nigel
supply5.gif (Attachment deleted)
The problem is (as Will says) much worse with modified sinewave inverters. Usually the first thing to blow is the pressure control unit on water pumps (typically in a few seconds/minutes) followed by various other devices - typically ones that have microprocessors controlling them. The reason is due to the design of the power supply circuit that these devices use.
For anyone interested in the reason, here goes:
You can see the circuit design for a really cheap DC supply from AC shown below. The problem with modified sinewave inverters is that they have a number of switching stages to simulate AC - anything from 4 (really really cheap) upwards. The AC is generated by switching these stages on and off in sequence - each having a higher or lower voltage, basically the waveform output looks like an up/down staircase (see Modified Sinewave Intended).
As these stages switch on/off there is a large transient spike, and lots of harmonics with high voltages, that occurs on the switching edge - far in excess of the designed output voltage of the inverter but of such short duration as to be insignificant (see Modified sinewave actual) UNLESS you are a capacitor ( C1 ) in which case your design voltage is exceeded and you start to break down inside, shorting out the plates through the dilectric. Eventually C1 dies completely and the full inverter supply is dumped across the remaining bits (if you're unlucky, which tends to be the majority of cases) or C1 goes open circuit and so no supply arrives at the rest of the circuit. Whichever happens, usually C1 ends up as a charred lump, taking several other bits to the scrapyard with it.
In some cases the device can be repaired, in others not, but the advice is not to use anything sensitive on modified sinewave inverters or invest in a good quality pure sinewave inverter!
Nigel
supply5.gif (Attachment deleted)