Inverter types

Submitted: Wednesday, Mar 29, 2006 at 13:54
ThreadID: 32307 Views:1759 Replies:10 FollowUps:13
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Hi,

Can anyone tell me why some people on this forum and others say not to use a modified square wave inverter on electronic devices like lap tops etc?? They must have a reason but a few electronics techs I spoken to can't see why the switch mode device being used won't simply clean up and convert to the required voltage.
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Reply By: Member - Sam (NSW) - Wednesday, Mar 29, 2006 at 14:18

Wednesday, Mar 29, 2006 at 14:18
Its mainly due to the fact that some equipment wont actually run at all or wont function properly on a modified sine wave inverter. Some laptop power supplies will handle them without any problems (i used to have a modified sine wave inverter in my HIlux and it worked fine)
AnswerID: 163646

Follow Up By: Austravel - Wednesday, Mar 29, 2006 at 14:31

Wednesday, Mar 29, 2006 at 14:31
I've heard this before but am trying to find out why specifically or is it just hear say. Techs I know think that, up to a point, switch mode units should handle a pretty large range of inputs.
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Follow Up By: Member - Sam (NSW) - Wednesday, Mar 29, 2006 at 14:59

Wednesday, Mar 29, 2006 at 14:59
The only thing I can think of is that the modified sine wave actually looks more like a digital signal

ie rather than a smooth sine wave with smooth alternating troughs and peaks, the modified sine wave is like a square wave where the toughs and peaks are more square in shape and the sudden drop between a peak and a trough as opposed to a rolling change causes electronics to get their nickers in a knot.
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Reply By: Darian (SA) - Wednesday, Mar 29, 2006 at 15:02

Wednesday, Mar 29, 2006 at 15:02
Hmmm..... some kitchen physics..........isn't it all to do with the shape of the wave ? Putting voltage and current aside, it seems that some devices are sensitive to the optimally smooth transition from peak to peak. Hell... aren't there only 50 waves per second ? Plenty of time to drop into some rough spots on the sides ! Might it be too much to ask the switch mode thingies to re-shape the wave ? Whatever..... as you can see, when in the kitchen, maybe I should just stick to cooking........
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Reply By: Steve63 - Wednesday, Mar 29, 2006 at 15:19

Wednesday, Mar 29, 2006 at 15:19
Hi,
The reason is that the square wave generates lots of harmonics. These are reasonably difficult to filter effectively to give a clean 50 hz signal. To some sensitive equipment that is expecting a very clean supply these harmaonics are still significant in the MHz range. If the supply was a high quality supply, designed to be used for laptops etc I can't see why you would have a major issue. The bigger issue may be the cost of the device! If you want a full explaination of the math do a Google search on Fourier Transforms. Square waves are often discussed because of the strength of the harmonics.

The same sort of idea is used for broadband over power ie putting high frequency signals like broadband onto the power transmission lines. Theoretically you can do this (in fact the utilities can do this to control devices on the grid) but many of these trials have been abandoned because they upset TV's and computers.

Steve
AnswerID: 163659

Follow Up By: Austravel - Wednesday, Mar 29, 2006 at 15:28

Wednesday, Mar 29, 2006 at 15:28
Ok, that's a bit clearer. I know when we looked at my modified square wave inverter on an osciloscope everything looked reasonable but we looked at only around the 50 Hz.

Had me wondering and unsure as the general concensus is not to use them but even the Toshiba agent said no dramas to use their lap tops on the square wave inverters. I just wan't sure as there is certainly a premium cost for the pure sine wave inverters.
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Follow Up By: Austravel - Wednesday, Mar 29, 2006 at 15:45

Wednesday, Mar 29, 2006 at 15:45
This is interesting, shows what the output signal is for a UPS. Looks square(ish) but you wouldn't see the harmonics.

web.aanet.com.au/bycompass/toppage1.htm
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Follow Up By: Steve63 - Wednesday, Mar 29, 2006 at 16:04

Wednesday, Mar 29, 2006 at 16:04
Yep,
UPS is usually a switched mode power supply. This is fed to servers (or a PC) whose own power supply can deal with the trash on normal power supply. These usually specifically filter the high frequencies. Some laptops would deal with it too. That is what I was trying to say. If the device is designed to deal with this you will be ok. If it is expecting a clean AC signal it won't.

The harmonics combine to form the square wave so you will not see them. That is the sum of the harmonics is the square wave. The reason it has rounded edges is because the higher harmonics have been filtered out.
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Reply By: wunder77 - Wednesday, Mar 29, 2006 at 15:35

Wednesday, Mar 29, 2006 at 15:35
I did this excercise myself about 2 weeks ago, because my laptop runs at 18.5V not 18 or 19 which you can buy DC adaptors for.
I bought a $69 150W Modified sine, everything works really well. And with the invertor, now I can re-charge my shaver, hair clippers and camera batteries too. Am sure there will be other things I haven't even thought of yet, but considering the DC Adaptor for a laptop is at least $50, I don't think I can go too far wrong.
AnswerID: 163662

Follow Up By: Austravel - Wednesday, Mar 29, 2006 at 15:37

Wednesday, Mar 29, 2006 at 15:37
Hi,

These are the units that the concern is about. modified sine is pretty much a square wave out put. Concern seems to be over the long term not immediately.
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Follow Up By: wunder77 - Wednesday, Mar 29, 2006 at 15:45

Wednesday, Mar 29, 2006 at 15:45
Well aren't you just charging the battery pack that's in the computer anyway? Most of the information I read from around the world on the net about the differnce between modified and true sine waves boils down to the quality of power the device needs, eg medical equipment, laser printers and the like cannot be used on modified. Laptops, shavers and the likes all run on DC power, off a battery, so you only need to worry about charging batteries, in theory.
Well, this is how I understood the mountains of info I read through before buying a invertor.
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Follow Up By: Austravel - Wednesday, Mar 29, 2006 at 15:55

Wednesday, Mar 29, 2006 at 15:55
True but the charger is switch mode which I believe gets upset from the square wave. Don't know just what I've noticed on forums.
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Follow Up By: Member - David 0- Wednesday, Mar 29, 2006 at 17:36

Wednesday, Mar 29, 2006 at 17:36
Yes my Dell laptop refuses to charge on this type of unit. The charger seems to be ome sort of UPS and it simply will not allow the battery to charge. The computer runs as long as the battery will last and that's it
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Follow Up By: Sand Man (SA) - Wednesday, Mar 29, 2006 at 20:21

Wednesday, Mar 29, 2006 at 20:21
David,

A little off topic.

Have you checked out Dell's Auto/Air AC Adapter.
The power pack looks the same as that originally supplied, but this baby has a different input lead, depending on whether you a connecting to a 240 VAC power outlet, or a 12 VDC auto / aeroplane supply.

Plug your Combination Power Adapter into any standard wall outlet, auto outlet, or airplane outlet. This is the only combination AC/DC Adapter that will both power the Dell notebook and charge the battery.

I have ranted on here before that I'm NOT going to buy one, but I couldn't use the Kerio Adapter and they were only about $90.00 delivered.

I'm buggered if I know why Dell don't just sell this one as standard, even if they bumped the total Laptop price up by $50 or so.

P.S. I don't use the original one any more.

Bill


I'm diagonally parked in a parallel Universe!

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Follow Up By: Member - David 0- Wednesday, Mar 29, 2006 at 20:48

Wednesday, Mar 29, 2006 at 20:48
There is much about Dell I don;t understand :-)

I will look into that power supply

Thanks

David O
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Reply By: Member - Mike DID - Wednesday, Mar 29, 2006 at 16:00

Wednesday, Mar 29, 2006 at 16:00
All Laptop Power Supplies are Switchmode - the first thing that happens is the AC input is converted to about 300 volts DC. After this it just doesn't matter what the input waveform was - until you look at it closely.

If you charge a Capacitor from a Sinewave the input will exceed the capacitor voltage only near the peak of the sinewave. From this initial current flow, the input voltage is still increasing slowly, so the capacitor charges up slowly, maybe over 10% of the cycle.

If you charge a capacitor from a square wave the input voltage instantly rises above the capacitor voltage. There is a very large and short current flow that may be only 1% of the cycle.

If the Power supply is well designed it will have good low-ESR capacitors that can cope with this surge without overheating. In a good the voltage spike in the DC will also cause no problems.

So if you have good switchmode power supply, it will work ok off a non-sinewave inverter.

Mike
AnswerID: 163665

Follow Up By: Mike Harding - Thursday, Mar 30, 2006 at 06:09

Thursday, Mar 30, 2006 at 06:09
Thank you Mike. Unusual to see a sensible answer to an electrical thread on this forum.

In my experience all the inverters I looked at the out put of (about 3! :) have a waveform which is much more triangular than square. I would suspect true square wave units (if there are any?) to have problems with a number of 240v items - anything with a transformer for a start!

The only thing I have had problems with on a non sine inverter was the energy efficient lamps - the 12W things - two of those died an immediate death however the third, made by GE, survives to this day. I imagine they use some kind of switcher to obtain the strike voltage and it got upset in the other two makes.

Mike Harding
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Reply By: Kiwi Kia - Wednesday, Mar 29, 2006 at 16:03

Wednesday, Mar 29, 2006 at 16:03
Harmonics ? Anyone had a look at the waveform on their house 230 volt supply ? Harmonics are everywhere along with power spikes when the neighbour cranks up his arc welder.
AnswerID: 163666

Reply By: hl - Wednesday, Mar 29, 2006 at 16:51

Wednesday, Mar 29, 2006 at 16:51
Hi.....
We have run laptops for many many hours on a modified squarewave inverter.
There is no issue to worry about. The input circuits of laptop supplies have plenty of filtering. The only effect you may get is a slight buzzing noise from the supply as there are plenty of harmonics, and the little choke in the supply to filter these out is working a bit harder.
Cheers
AnswerID: 163677

Reply By: Niffty - Wednesday, Mar 29, 2006 at 23:57

Wednesday, Mar 29, 2006 at 23:57
I believe its more to do with the fact that is completly distroys the battery in the lap top.Cant quote the source off hand but I will have a read tonight and get back to you if I solver the problem.Pure sine is the way to go and not that expensive if only running small Watts and dont have auto start and the bells and whistles!The KISS theory works for me.
AnswerID: 163776

Reply By: Chaz - Thursday, Mar 30, 2006 at 01:50

Thursday, Mar 30, 2006 at 01:50
Hi Austravel,
As stated previously, your laptop battery will suffer with a square wave inverter, and apart from some “HUM” in any audio device you may run, there really isn’t any downside. Modified sine wave inverters are nowhere as efficient as pure sine, but there is a substantial cost difference.
I believe that a modified sine inverter will do most jobs satisfactorily at very low cost. I’m running a desktop PC that’s under my drivers seat, using a 150watt modified sine inverter and a 95watt PSU in the PC. Surprisingly, even the sound is good, but more importantly the PC runs great!
Chaz
AnswerID: 163787

Reply By: Dilligaf - Thursday, Mar 30, 2006 at 07:49

Thursday, Mar 30, 2006 at 07:49
we destroyed the battery in our IBM and Dell laptop using modified square wave
Dell would not replace the battery under warranty as they could tell the battery had been charged on modified square wave inverter
bought 150w sine wave inverter for $200
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Follow Up By: wunder77 - Thursday, Mar 30, 2006 at 08:43

Thursday, Mar 30, 2006 at 08:43
how old/antique was you inverter that fried the battery?
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