8
\$\begingroup\$

I have rampant power failure in my country. So to mitigate, we have an inverter that basically converts the charge from a big lead-acid battery to AC. But as far as i know this doesn't produce pure sine AC. It is something close to sine.
The output voltage is 220V nonetheless so it is hard to find out when the power is out.
Sometimes, i use my laptop on AC. My question is, will using laptop on inverter affect the components since output is not pure sine?

\$\endgroup\$
  • 1
    \$\begingroup\$ Just a thought... you could use an in-car laptop PSU which runs from 12v (car) or 24v (truck), it would be more efficient overall and probably nicer to the equipment. \$\endgroup\$ – John U Feb 7 '13 at 12:01
12
\$\begingroup\$

I assume the question is not about power efficiency differences with a system on sine-wave power versus not-quite-sine-wave power.

Recent laptop power bricks and desktop power supplies are switched mode power supplies (SMPS). An SMPS typically rectifies the power line voltage, then uses a high frequency oscillator to "chop" this DC, a small transformer to step this switching voltage down as well as isolate it from the power line, and finally regulates the output voltage to the required levels using an integrated sense mechanism feeding back to the high frequency oscillator.

An SMPS is not particularly sensitive to power line waveform, as the rectifier stage turns it all into a ripply form of DC anyway. Yes, the high voltage section immediately after power line rectification would see a difference in voltage due to waveform change, but that doesn't matter very much: Many "universal" SMPS designs are rated for 90-250 Volts 50/60 Hz operation anyway.

If the power line supply is a square wave, the higher harmonics might stress some components in the high voltage portion of the SMPS beyond their ideal design parameters. Also, there is a tiny possibility of higher-harmonic noise sneaking onto the output rails.

However, typical inverters, even the poor quality ones we have analyzed for some projects, tend to deliver at least a somewhat smoothed trapezoidal waveform rather than a square wave. Adverse impact on the SMPS is negligible in such cases.

If the SMPS is reasonably well-designed, the actual computing hardware (laptop, or desktop motherboard) will not face any problems due to non-sine power line waveforms.

\$\endgroup\$
  • \$\begingroup\$ Square wave output inverters do still exist, and they are known to be very hard on input rectification components in a SMPS. @AnindoGosh, have you ever evaluated the effects of square- or modified sine-wave inverters on Power Factor Correction (PFC)-equipped supplies? \$\endgroup\$ – HikeOnPast Nov 5 '12 at 17:22
  • \$\begingroup\$ Mr. Anindo i assume you to be from india just like me so you'd know the scenario very well. I have an extra large size Exide Tubular battery and yes, i guess the wave form is just flat on the crest. My laptop is HP. so any specific advise? \$\endgroup\$ – Fasih Khatib Nov 5 '12 at 18:00
  • \$\begingroup\$ @FasihKhatib Yes, I am in Mumbai, India. The answer given above applies... I know people who have been running computers on no-name "local-made" inverters for years without any trouble. Use a good quality, high power-rating spike-guard though - some of these inverters spike for as much as 400 Volts when the supply power comes back on. \$\endgroup\$ – Anindo Ghosh Nov 5 '12 at 19:07
  • \$\begingroup\$ Component temperature rise from ripple current in capacitors is a big accelerating factor on MTBF failure rates. It may be improved if the inverter is stable thus rendering closer to DC when full wave rectified than a sine source. Unless your load has PFC. DeanB makes a good point about input rectification current and method of manual switching may also provoke more stress. Inverters are also prone to audible noise from load current and voltage regulation. Only forensic details on any design can tell for sure. \$\endgroup\$ – Sunnyskyguy EE75 Nov 5 '12 at 20:14
  • \$\begingroup\$ @DeanB Yes, we did evaluate one square wave inverter for an industrial deployment. After examining the higher harmonic spikes being pushed through the SMPS to the equipment, a line conditioner, essentially a hefty and fancy spike guard, was added to the set-up. This isn't sufficient evidence to take as a norm, hence we'd rather avoid square wave inverters entirely, now that the price difference is marginal to none. Even Indian local no-name inverters these days are decently wave-shaped. \$\endgroup\$ – Anindo Ghosh Nov 6 '12 at 7:26
3
\$\begingroup\$

Such inverters usually produce "pseudo sine wave" or "modified square wave" output. Not quite a square wave but a swuare wave with off period so the overall form factor and RMS values are closer to a sine wave.

Image below from here

Very good writeup of aspects involved here (despite heading) What is power inverter
Diagram below is from that site.

enter image description here

A SMPS with active power factor correction may not like "pseudo sine wave" input.

Some input filter capacitors do no respond well wo PSW input - I once had a unit which made a loud and annoyed 100 HZ buzz (2 x 50 Hz mains frequency) when fed with one such power supply.

A solution which works for me with this sort of supply and other waveform suspect ones is to use a 1:1 mains isolating transformer between supply and load. This is not a perfect filter but dows a reasonable job of cleaning up waveforms. Power rating of transformer needs to be adequate for the load handled.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.