Voltage stabiliser / limiter

[cliff]

While faffing about on the boat recently (rewiring the 240v circuits) during testing of the wiring I was a little worried to note the OC voltage frrom the invertor was around 260~265 volts.As loads were applied the voltage come down until at around 2kw loading the voltage was around 200V. I am a little concerned now about plugging in low consumption loads such as phone chargers etc.

Do any of the electrical bods here have suggestions as where I could aquire a voltage limiter / regulator say with 400w capacity that yould limit the voltage to 220 v or even if such a device exists.

The existing invertor is fine for the higher loads (toaster, hairdrier, vacuum cleaner etc) but I would feel happier if I had a regulated supply for the more delicate "electronics"

 

[Solent sailer]

Hello my experence of inverters is that the wave form is far from a perfect signwave and it it possible that even with a "true sine" inverter the shape of the signwave dosent stabalise untill the unit is significantly loaded. most meters are incapable of giving a true voltage reading with anything other than a pure sign wave (my old inverter not a "true sign inverter" reads 330V on a £300 true RMS meter but works most things fine, lamps are not excessivly bright as would be the case if it were realy giving 330v RMS)
i would put an oscilscope on the output and have a look at the wave form, then contact the manufactures to ask if this is notmal before worrying about fitting a scrubber unit to the output.

 

[cliff]

The invertor drives heavier loads fine, it is the light loads that concern me - would not want to fry the laptop or other light loads hence I was looking for some form of limiter / stabiliser of which I could run the lighter loads.

Will have a look at the wave form before contacting the manufacturer.

 

[nigelmercier]

I was a little worried to note the OC voltage frrom the invertor was around 260~265 volts...

Measured how?

 

[William_H]

AC voltage measurement

As said AC voltage measurement is fraught with problems. The concept of RMS voltage Root Mean Squared is to get a realistic comparison of voltage compared to DC. So a 240vAC RMS should have exactly the same heating power on say a light bulb as 240VDC.
Now it is likely that your Digital volt meter is measuring something more like peak voltage possibly scaled down to closer to RMS. But that may not mean anything if it is not sine wave anyway.
In the now common switch mode power supply of electronic gadgets and chargers it is in fact the peak voltage that does the work.(and damage) So check the peak voltage compared to mains AC on a scope.
good luck olewill

 

[cliff]

Measured how?

1) plugin ac voltmeter, amp meter, power meter (complete with power factor readout)
2) digital AC voltmeter - (not a cheapo one from maplin) on mains only both read the same ~230v but when powered from the invertor both read around 260V until the invertor is loaded to around 1kW at which time the voltage is down to around 240 further loading of the invertor brought the voltage down to around 210 - no noticable difference whether engine on of off except the alternator made lots of funny noises as I was drawing 2kW+ from the invertor when the engine was running

 

[Jean]

That’s a massive load on the batteries (at least 170 amps, and that’s with a unity power factor mains load), and alternator may well get a bit upset with that demand.

Is your meter true rms? (some meters look, for example, at peak, and assume a sine wave, and calculate an rms value based on that)

 

[cliff]

That’s a massive load on the batteries (at least 170 amps, and that’s with a unity power factor mains load), and alternator may well get a bit upset with that demand.

Is your meter true rms? (some meters look, for example, at peak, and assume a sine wave, and calculate an rms value based on that)

Both are (I think) hard to tell as they are a little old - could not even tell you the make or model - seen lots of action over the years

ps 200A over 5 batteries is only 40 amps/per batt - not so much

 

[nigelmercier]

1) plugin ac voltmeter, amp meter, power meter (complete with power factor readout)
2) digital AC voltmeter - (not a cheapo one from maplin)...

OK, but do either of these measure true RMS? The reading of 230V is not the peak value, it's equivalent to the proportion of the voltage that supplies power (0.7071 x the peak, from memory).

A non-standard AC waveform (as on most inverters and generators) will give a false reading, as it isn't a sine wave.

[Later] I see Jean has asked the same thing. If the meters are old, they will not be true RMS.

 

[William_H]

Voltage reduction

Back to your original question regarding reducing voltage. AFAIK a stabiliser is only practical for high power and involves a transformer with multiple taps and switching or motor drive of the tapping to give different transformer ratios at different voltages/loads to give a stabilised output. Plus of course the electronics to determine if increse of reduction is required.
For your situation I would suggest a simple reduction of voltage at 240VAC. Most of your small power battery charges etc will be happy down to 110VAC. So a power transformer stepping 240 down to 110 would probably be easiest to find. Low power for razors etc.
Some power transformers for older radios or amplifiers had a choice of tappings for 220/240 260v. These could also be used as an auto transformer to reduce voltage. ie you feed the output of the inverter onto the 260v tap (and common) and take power out on 220V tapping (and common) to give a reduced AC voltage. NB with a fairly limited power capability ie 40 watts or so.
Or finally for very low power applications a resistive divider might do the job.
So for 10w AC load ie 40 ma of AC a series resistor (fitted in active wire between inverter o/p and load input) of about 2500 ohms and a rating of 5 watts would give a volt drop of about 10v. You should however fit another resistor across the load ie to neutral after the series resistor to provide a permanent or steady load of 10000 ohms with a power dissipation rating of 10 watts. It will waste a bit less than 5 watts but will ensure voltage drop in the series resistor regardless of device load.
Obviously if you do this fit them in a box that is well insulated and do not use it for larger loads than designed. It should be OK for up to 20w load but no more. Allow that the resistors may get hot. Make sure you understand what you are doing.
good luck olewill

 

[nigelmercier]

Some power transformers for older radios or amplifiers had a choice of tappings for 220/240 260v...

I guess that in Oz you are used to problems with over-voltage, I understand it is a common problem. I'd be very wary about putting a non-sinusoidal signal into a transformer that wasn't designed for it. Why doesn't the OP contact the inverter manufacturer and see if (a) the voltage reading on a non-RMS meter is normal, and (b) if it can be reduced.

 

[cliff]

I guess that in Oz you are used to problems with over-voltage, I understand it is a common problem. I'd be very wary about putting a non-sinusoidal signal into a transformer that wasn't designed for it. Why doesn't the OP contact the inverter manufacturer and see if (a) the voltage reading on a non-RMS meter is normal, and (b) if it can be reduced.

Thanks for that Nigel - precisely what I intend to do once I get the details of the invertor.

 

[john_morris_uk]

It would be worth checking with the manufacturers as you suggest - except I bet that they might hedge their bets and suggest you return the unit to them for checking.

Remember that the peak voltage of a 230 volt sine wave is actually about 325 volts. I suspect that there is nothing to worry about and the discrepancy is all to do with the wave form produced by your inverter and the fact that your meters don't measure things that aren't true sine waves accurately.

 

[Ruffles]

I wouldn't worry about laptop adapters, phone chargers etc. They're extremely robust in my experience.
We had a major power outage in my office a couple of years ago after a flood in Tooley street. We brought in a huge genset which turned out to be faulty. The voltage fluctuated between 100 and 300 volts. And was left that way for hours for some reason. Anyway it took out some of the lighting circuits but we had zero failures on desktop PCs and laptops. Out of several thousand.

 

[nigelmercier]

I wouldn't worry about laptop adapters, phone chargers etc.

Indeed, Switch Mode PSUs can take care of large voltage ranges. Anything with an old school transformer in it is going to be unhappy: both with the voltage and the non-sine wave. Also anything with a heating element: toaster, kettle, incandescent light bulbs - but of course some of these will cause the voltage to drop anyway.