Modified Sine Wave Inverters & Flourescent Lights

It sounds like your inverter is working to supplement voltage inadequacies of the grid. This would make the grid the effective load for your inverter. Similar to a dead short as far as mismatched capacities are concerned.

Isolating your supply from the grid while still drawing power from the grid is an uncommon and difficult problem.

Thyristors in parallel on the grid supply might do it, or help.

An AC to AC mixing or regulating transformer could solve your problem at the cost of the unit plus making the grid problem worse. Only thing is, I have never heard of such a critter.

Rolling black outs....?

Best regards,

AAG

Thanks for your comment Mr. Gee, I obviously did not describe the set up clearly enough. The inverter, & the power from the grid, are connected to opposite sides of the DPDT switch. Power can only reach the domestic distribution board from one souce only, either the power company OR the inverter.

It has to be set up like this to prevent power from the inverter going down the companies power lines during a brown out & electricuting a line worker.

The truth is that modified can mean a lot of things: from one square, having the same energy content per alternance (at e.g. 50 to 60 Hz) to some sine like chopped higher frequency (say e,g) 10 kHz in the sine shape.

What does your load see? What does your load do? How does the inverter react? When you are talking a N America style home grid, your neutral will be floating with a 240 Volts unit. Using 2 - 120 Volts units with a common Neutral will have synchro- problems. The way I see it is the use of a conversion transformer.

1. Or 240 in primary to 120 - N - 120 (volts)

2. 120 inverter primary in to the same.

You will need a good pure sine inverter with all lights and bells and horns incorporated.

The modified types without heavy transformer inside work mostly high frequency and plenty of your appliances see only this and react accordingly, sending your experiment ready for repair.

The PJ's (Taiwan - China)you are (maybe) talking about prove to be a good product to me (have more than 20 installed), only ---

stay away from everything modified sine for your application.

when you said you use a DPDT switch, does that mean the neutrals from both the grid and you inverter are connected together and not switched? they should be switched.

and does 270 v from the inverter mean its neutral is floating - not properly grounded?

The DPDT switch was installed by a competent, qualified electrician, the same man who wired the house when it was built. I try not to mess with mains voltages! I'm not qualified & recognise my limitations. I'm ok to connect the inverter to the battery bank & plug the inverter into the input side of the AVR. When a brown out occurs I feel confident enough to switch the inverter on, switch the AVR on & throw the DPDT switch

At the time of the house build the electrician was told of the plans to have an emergency power supply & the wiring runs were laid accordingly. When the house was completed he returned a few months later to wire in the DPDT switch and the lead from one side of it which connects to the AVR.

I'm still seeking the answer to my original question ' Can the flourescent eco bulbs with their built in ballast damage a modified sine wave inverter?'

My thanks to everyone that is considering this question

Answer to your question: YES. The electronic ballasts see or too many DC components in the supplied power/ or in the other (HF) case the switched supply in the Light bulb is completely misinterpreting the switching (spikes) blocks. When I find the time I will make a picture of the supplied pattern. On my oscilloscope It is hard to show, because the flanks are very steep. So this is just my interpretation.

I'm still seeking the answer to my original question ' Can the flourescent eco bulbs with their built in ballast damage a modified sine wave inverter?'

Yes, the manual should say they are not suitable for fluorescent light loads.

You need a true sine wave inverter, but these should also still be easy to import.

_{Jack - Also blew up one of these cheap square wave inverters trying to power a fluorescent light. Yes the manual said it wasn't suitable, but I only read the manual AFTER I blew it up.}

If all you are feeding is the bulbs then it is resonable to suspect them for the inverters damage. Why not just use 12v LED lighting then you will not need the invertors.

dvmdsc - Thankyou! If I understand your answer correctly the ballast in the eco florescent bulbs can do nasty things to the modified sine wave inverter. If I replace the modified sine wave inverter with a pure sine wave inverter then am I correct in thinking that will solve the problem?

Rainmain - I admit the main purpose of the inverter is to provide full lighting during brown outs, but it also powers 32watts of aquarium pumps & filters, a 55watt TV and a 25watt DVD player, together with around 60watts of the 'eco' lighting. I am pretty sure I am only drawing <200watts from the inverter.

I am mulling over replacing all my light fittings with 12v led, disconnecting the mains supply from the lighting trip switches & connecting the battery supply to the trip switches. However there could be a problem with voltage drop as some of the wiring runs could be 10 metres...... If a pure sine wave inverter will solve the problem then this is the easiest path to take. Probably one with at least 2000watt continious power so I can keep the small freezer working as well as the items listed above.

Thanks for your help

We are getting some info:

What inverter you are using? Freezers destroy inverters too. Power? And what about your AVR? Info please.

I'm really curious at to what your "AVR" is. The term AVR that i am familiar with means Automatic Voltage Regulator and is used in conjunction with an engine driven generator to change the generator field so as to maintain a constant voltage. If what you have is some electronic gizmo that is supposed to be controlling the voltage off of your inverter, I would be VERY suspicious of that device. Many of them are NOT designed to be used on anything but utility sine wave power. If you have pseudo AC like what comes from an inverter, the "AVR" may be doing things that cause your inverter output power devices to fail.. That may be the case with ANY inverter you use. Post a mfr and model of what you are calling the "AVR".

Damage to inverters happens during brown outs or blackouts.....not sure why, maybe back emf from the motors?

The inverter apparently feeds an automatic voltage regulator and then the load. Most of those regulators I have seen here in the Philippines are motorized variable transformers and it might be that it is saturating on the peaks of the 'modified sine wave'. Some also are fitted with transient voltage suppressors and I guess that either could would cause nasty current spikes.

As for the "270V" mentioned, that may be what an electronic voltmeter would read on the inverter's output waveform but a moving iron unit would probably read less for true RMS.

Kebang: is this inverter one of those really cheapy units sold for use in cars?

Neil A (Cavite)

JRaef - Yes AVR = Automatic Voltage Regulator. The make is 'Panther'. Its a heavyweight design and is rated to 1000watts I also have a lightweight 'Protec' model protecting my PC. The PC is not used during Brown Out as I like to keep my usage down to around 200watts (treating the batteries gently). The 2500watt inverter I am using at the moment caused all the lights to flash & the TV to pulse when I first connected it. The AVR cured this problem, but from what you say it may be causing other problems!.

dvmdsc - At the moment it is a 2500watt (5000peak) modified sine wave inverter, which I bought of Ebay 6yrs ago but never got the chance to use. Its been repaired twice by a local electronics shop. It has its problems (as above). I didn't realise freezers harmed inverters, is that both modified & pure?

jack of all trades - I am rapidly reaching the conclusion I need a well made pure sine wave inverter!

NeilA - When the 'big' inverter is being repaired I have burnt out I a few 500watt 990peso inverters form CDR King. They don't last long (you get what you pay for!) I've just located a solar company on the net based in Cebu. So I might jump on the ferry & check them out.http://www.sophilcor.com/index_files/SOLARSTARinverter.htm

As you live in Cavite do you know of any good suppliers in Manila? My sister in law lives in Manila, I could send her shopping befor her next visit to Bohol!

Thank you all for your very useful comments

Power fluctuations in the Phil is the number nuissance for electronic devices and your inverter is one good candidate..... auto voltage transformer and good earthing which we usually dont have in normal house wiring are some basic safety features ....

As for the lamps led lamps will fit surely in your system..... led tv , laptop ...

if an old inverter had been repaired inhouse and not by the factory the lifespan shorten.... due to the heat dissipated on other parts .....

china made inverters usually dont last long ... a good avr from kyocera or japan sually are reliable

totoalas

I don't think the LED's would last very long with a modified sine wave.......... I bought one last week & it said on the box 'not to be used with dimmer switches or electronic switches. I think the mod sine wave would fall into the electronic switch catagory.

You are using 7watt fluorescent bulbs in the output circuit of the inverter; that means these bulbs are CFL bulbs. Due to poor quality of embeded electronic ballast in the CFL bulbs,lots of harmonics may be generated and feeded to the inverter. For the harmonics effects, electronic circuits comprising of ICs,capacitors,including transformer may be burnt out. Therefore to mitgate this burntout problem, you must use CFL bulbs with low harmonics content electronic ballast.

Manindra

Thank you Manindra, If the inverter is replaced with a pure sine wave inverter does this solve the problem?

No,Sir, you have to use good quality CFL lamps having low harmonic content electronic ballast.

Regards,

Manindra

Yes my friend has a yacht and I have heard of this before. To answer your questions:

Voltage measurement

Your AC multimeter is calibrated to read a pure sine wave with a form factor (peak ÷ RMS) of 1.11. When you feed it with "a modified sine wave" (which is actually a 2-step square wave or some other hacked output) the form factor is different. You need an oscilloscope or similar meter to have a look at the waveform. My gut feel is that your 270V figure is about right for this stepped square wave in terms of peak-peak voltage similarity. But my gut was designed for other activities and I could be wrong...

Harmonics

Your cheap inverter is exactly that. The mains is a "robust" supply capable of megawatts and absorbing harmonics and spikes. Your inverter has no such capacity. The first thing your CFL does is rectify the input and make DC with a big capacitor. This causes the mains current to become non-linear and "spike", creating harmonics. This is also what every other electronic device does too (like your TV), but filters are installed to control the harmonics, which take up space. Except the little CFL has no space (or value - these things are made as cheap as possible) for such filters.

Inverter rating

Don't believe it. Always look for words like "continuous rating". You won't see them is my bet. And if you do my gut (he's back with the intestines again...) tells me don't believe it anyway! Unless its made by a reputable manufacturer (and thus with a reputation to maintain) take 25-50% off the rated power.

Loads

The 7W CFL refers to output. The rectifier input is really inefficient (at least 50%) so actually you are drawing more than 10W. But you will find the power factor horrendous also (probably around 0.5) so this equals 15 VA. 20 of these means a current load equivalent to 300W for light alone. Remember you meter is not calibrated to measure these currents so you will not see these on your multi-meter. If you have taken 25% off your inverter rating then you need a 400W inveter.

Sine wave output

Paradoxically, as I mentioned almost all devices rectify the income and convert to DC, so the sine wave is somewhat irrelevant. (That said, I would not be happy running my $2000 TV or laptop on a $50 inverter ).

Solution

1. First, try a larger inverter (double the size) and run the lights only on that.

2. Oddly, use larger and branded CFLs! I mean both wattage and physical size. Bigger in size means more room for better components. So lets say a Philips 9W unit is 85% efficient and power factor 0.95 = 11VA or 11W effective load.

3. You could mess with a filter on the output. Don't fancy this. A decent one is going to cost more than the above.

4. Have you the inverter earthed? Many filters dump the harmonics to earth. The inverter earth is floating. However this would only apply to earthed fittings which your CFL is not, and your TV / laptop probably not.

Thanks Baby Guiness, Yep, I've definitely given up with the cheap modified sinewave inverters!

My latest plan is to disconnect the mains supply from the lighting circuits and connect a 12v batterybank to those circuits instead . The battery bank will be permanently connected to a 3 stage battery charger. All the bulbs will be replaced with either 3watt 12v leds (which appear to be expensive) or 7watt 12v CFL's (which are a third of the price but will triple the load on the battery bank during a brown out).

This should give me the advantage of continous lighting even at the commencment of the brownout.

There is a 300watt pure sinewave inverter available from a local solar company, 'SolarStar'. This will be used to power a 55watt TV, 25watt DVD player & 32watts of aquarium pumps. Altho this inverter will be connected to the domestic distribution board by the aformentioned DPDT switch all circuits breakers will be switched of apart from the one controlling the entertainment circuit so there is no chance this little inverter will be overloaded.

kebang