inverters?

Re: When do you actually need true sine wave

try and jog somebody else's memory .... but here goes ... as far as i can remember, devices which present an active (eg induction) load rather than passive load (eg resistance) will cause the semi-square wave output of an inverter to overload on power-up. any electric motor would be an obvious problem particularly squirrel cage induction motors which most are.

the voltage rise of a square wave consumes instantaneous huge power in an active device whereas sine wave is a much easier monutain to climb .. if you see what i mean ...

this ought to include switched mode power supplies which have switched inductive loads in them but if that was the case, then a telly or vcr should fail to operate with an inverter since virtually all power supplies in a tv are switched mode except that the waveforms inside a tv, eg HV saw tooth, square wave flyback & sync pulses, are internally shaped by the tv's own gubbins. but surprised that the mutiple harmonic frequencies don't bugger the reception.

power tools which must have switched mode psu do fail with an inverter and sometimes catastrophically. So might be somewhere near an explanation? That might also expain the problem somebody had some time ago with using a petrol generator 240v AC output to drive a battery charger - the output would be a 'lazy' square wave which the SMPU of the charger wouldn't like ...


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Re: inverters and laptop

output of "14-22V 45W max"

... this usually means that the PSU has an unregulated, usually DC, output, in that voltage range.

There will then be a charging circuit within the laptop, that will regulate the charging current for the battery using the excess of voltage over 10.8V to effect the regulation. The battery acts like an immense resevoir of energy, and will pretty much 'nail' the voltage at this point to whatever its nominal voltage is (ie. around 10.8V)

The 45W usually refers to the ability of the PSU to dissipate the heat it generates at different current demands - it looks like it will supply a maximum of 2-3Amps, depending upon input (and thus output) voltage.

The laptop battery rating of "10.8V 3500mAh" states it's nominal terminal voltage as 10.8V, and states its nominal capacity as 3500mAh - in this case it means that if the laptop draws 1Amp continuously, it would last for 3.5hours (or thereabouts).

Internally, most of the laptop circuitry will run at 5V and lower, so the battery 10.8V will be further regulated down to that voltage, providing a further degree of protection against voltage fluctuation...

Anyway, in normal use, the laptop itself will effectively be running off the battery, but the PSU and charging circuit will typically be able to supply all the current the battery needs to replace that consumed by the laptop, plus a small excess to keep increasing the state of charge of the battery even with the laptop running.

In all probability, the laptop will continue to run very happily, and maybe even charge too, with raw ships battery (12V) connected to it rather than the PSU, and this is much more efficient than going the 12V->invertor->PSU->laptop route.

I sometimes (on the boards) see dire warnings about the sensitivity of laptop computers, and the likelyhood of 'blowing them up" when directly wired in the boat in this way....

.... well, no guarantees of course, but even during an engine start, where the DC volts may well drop way below a nominal 12V, the laptop itself will run very happily from it's own internal batteries. Effectively, laptops have their own internal UPS (Uniterruptable Power Supply).

In the offices in which I work, we have hunderds of PCs, and dozens of laptops. Whenever we have a power brown-out, just about all of the PCs crash (they usually manage to restart though, after a full power-off; although what it has done to the file-system is anybody's guess) - the laptops *always* just carry on working (of course).....

Alan


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Re: When do you actually need true sine wave

Switched-mode PSUs typically just rectify and smooth the AC voltage, ending up with 320V or so DC, then chop that (usually with a square, rather than sine, characteristic) at high frequency, and use a small lightweight transformer (possible because of the higher frequency) to produce a low voltage, high current AC, then rectify that again to produce the output. They sense that DC output voltage, and feed that back to the chopper to effect voltage regulation at the output.

A well-designed switch-mode should typically have no sensitivity to input waveform or frequency, and indeed should be tested to be immune from various kinds of RF input noise, and high-voltage spikes.

It is only those devices that make assumptions about the input waveform that would give trouble, and that does include some types of electric motor...

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Not all micowave cookers need pure sine wave

It is usually the display and timing defvice which needs the pure sine wave. Turret (analogue) timers are OK with a modified sine wave but digital ones are not. Same is true if you are using an inverter to keep your home central heating going in a power cut. If the timer is analog then it will work on a modified sine wave device but a digital controller needs pure sine wave. Nothing to stop you (safely of course) by-passing the programmer to power the pump and motorised valves directly as you aren't likely to be interested in automatic switching, just keeping warm.

My new 1500 watt "Purewatts" quasi sine wave inverter runs a small domestic TV perfectly well as it does a 650 watt cheapie Microwave which I bought from the local Co-op for a penny off £40

When fitting an inverter on a boat with a "Smart " charger, switching must be provided to make sure that the inverter doesn't try to power the charger. If you just have a switch-over from the shorepower inlet to the inverter output to your 240v AC outlets then the charger will receive output which will damage both it and the inverter but the charger will come off worst, first.

Relying on "mental discipline" alone to remember to disconnect the battery charger from the "mains2 is bound one day to end in sadness - or even flat batteries if you forget to re-connect it when going back onto shorepower. Some people have an entirely separate ring of outlets for the inverter output which will of course not attempt to power the battery charger. This is of course, along with sticking to just connecting mains devices direct to the inverter output alone the safest course.

Steve Cronin

<hr width=100% size=1>The above is, like any other post here, only a personal opinion
 
Re: Not all micowave cookers need pure sine wave

My own boat has a 'Load group 1', and 'Load group 2'.

Group 1 is all the heavy stuff that cannot be run off the inverter (and that includes the charger).

Group 2 includes all the sockets, the microwave, etc etc..

Group 2 can be selected to run either to follow Group 1 (ie.from the Group 1 bus), or from the Inverter.

Group 1 can be selected to run from from shore power, or from the Genset.

Alan

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Re: When do you actually need true sine wave

Could you re-write that in your Celtic dialect than mebbe I might understand.............................

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Re: In Parrot-squeak ...

There was this quiet, conservative man who happened to own a parrot. Unfortunately for the man, this parrot swore like a sailor. He would swear for five minutes straight without repeating himself. This bird's foul mouth was driving the man crazy. One day, it just got to be too much! The man grabbed the bird by the neck, shook him really hard, and yelled, "QUIT IT!" This only made the bird mad and he started swearing even more! The man finally got fed up and said, "Okay for you!" and shut the bird up in a kitchen cabinet. This only served to aggravate the parrot who then began to claw and scratch the cabinet while he cursed even louder than before with a stream of swearing that would make even a sailor blush! At this point, the man became so angry that he threw the parrot into the freezer! For the first few seconds the bird started swearing at the top of his lungs! He kicked and clawed and thrashed all about the place. Then, suddenly it became VERY quiet! At first the man just waited, but then he started to think that the bird might be hurt. After a couple of minutes of silence, he became so worried that he opened the freezer door. The bird calmly climbed on the man's outstretched arm and said, "Awfully sorry about all the trouble I gave you. I'll do my best to improve my vocabulary from now on." The man was astonished! He couldn't understand the transformation that had come over the parrot! Then the parrot said, "By the way, what did the chicken do?"

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Re: When do you actually need true sine wave

if I want to run a laptop (18V 4.5amps 90W) from an inverter how will my battery fair wihtout the engine running. I have a 105A service deep cycle battery. Will the power pack cause excessive power usage due to the ampunt of heat produced, is it better to use a transformer to run direct from 12V system without inverter?

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Re: When do you actually need true sine wave

read what AlanPound has said about driving laptops from the boat's raw 12v supply. I've been doing that for some years and it works.

Inverters are horribly inefficient used in the manner you describe. As much of the power will be wasted in heat energy as will get to the laptop ...

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Re: Not all micowave cookers need pure sine wave

I was advised by two individuals on different stands [they both seemed competent]
that using an impure wave with a microwave would probably be less efficient and might well necessitate a longer cooking time. Your comments are therefore of particular interest & I would ask whether you have noticed such an effect.

Regards,

John G

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Certainly some cheap inverters are pretty hopeless at running any electric motor , I had one that would make even a 'leccy drill run rough & a pond pump ran noisy & slow + often wouldn't start from rest.

There's a lot of difference in modified sine waves....some (more expensive, doubtless) claim to run almost anything, others are pretty rubbish at motors, but may run less demanding equipment adequately.

Even "pure" sine wave ones will probably vary between makes in quality of the sine wave, particularly under heavy load if the makers have skimped on transformer size/design. (same with some diesel & esp. small petrol generators)

If buying cheap, I'd try to get a specific recommendation of one that an owner says works with a particular appliance, or buy from somewhere with a friendly refund policy/bend the distance selling rules & return "unused" if no good.

Think a tv/vcr combo would probably be ok on almost anything adequately sized, but as mentioned earlier, 12V ones available anyway.


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if you have a laptop why not buy Hauppauge WinTV usb tv card and install vcr software (Intervideo Personal Video Recorder) - use for live tv, playing video off hard drive and dvd player and runs off 12v or internal battery? Total cost about £100 and far more versatile.

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