Andy asks:
I have a question about the CFL lamps...
Can they be run from an inverter without a problem ?
I have two types of inverters:
1) An old style square wave inverter 2) A newer style "modified sine wave" inverter...I'd appreciate any comments and discussion on this... Thanks.
Andy in Eureka, Texas
Modified sine wave inverters produce more of a modified square wave.
The usual low power factor CFLs will run a bit dim from the slightly lower peak voltage of the modified sine, and more so from the squarewave - maybe not work too well on a squarewave, with peak voltage of 120V. Modified sine has a peak voltage of 139 volts, while true sine has a peak voltage of 170 volts. This largely affects what the circuitry in a usual low power factor electronic ballasted CFL actually works with.
The peak current through the rectifier and filter capacitor in a usual low power factor electronic ballast CFL wil be high, from the abrupt waveform edges from these inverters. I would ask for an engineer at the CFL manufacturer to find out if this is OK for the CFL - the filter capacitor or any RF filtering choke will get warmer than normal. Any RFI filtering choke may also buzz.
You also need to know if the inverter is rated for those.
It's one of those things where I expect it will usually work, but I can't say for sure that nothing will go KABLOOEY or burn up sometime. I don't have a good feeling that everything will always be fine-and-dandy!
Maybe better is if the inverter is rated for conventional fluorescents or ballasted lamps in general, and get either conventional fluorescents (make sure thay have magnetic ballasts), or CFLs with magnetic ballasts.
Another alternative: Find RV forums and find the good 12V stuff, or whatever the RV crowd says is good. I am not that in tune with CFLs on
12V inverters or whatever RVers use.One more little note: There are 12V A19 lightbulbs. Some auto parts stores have a few of those. They are somewhat more efficient than 120V ones of the same wattage (50W 12V is almost as bright as 60W 120V), due to a couple economies of scale from the thicker filament. They may be where work lights are.
- Don Klipstein ( snipped-for-privacy@misty.com)
On 4/30/2008 7:57 PM Don Klipstein spake thus:
Question (somewhat naive, perhaps, so please bear with me): couldn't a guy turn square wave current into something closer to sine wave just by using a bunch of big honking capacitors as a filter? I'm thinking across the line, but then it occurs to me that if their impedance is too low, too much current'll flow through them and they'll blow ...
I've blown a modified sine inverter in the past with current spikes drawn by capacitors.
There are LC filters, but those tend to be homebrew and experimental and things can go wrong. For example, you have to really know what you're doing to not have them resonate (whether at the fundamental frequency or a harmonic), or get close enough to resonating to deliver excessive voltage. I'm sure one not professionally made and rated for use with inverters would void warranties and safety ratings all over the place. And I don't know where to get any that are rated for this.
- Don Klipstein ( snipped-for-privacy@misty.com)
On 5/1/2008 6:29 PM Don Klipstein spake thus:
So are you saying that an LC filter (say, a pi configuration, two caps and an inductor) *could* work, if one were to select the correct values of L and C? I understand how one would want to avoid resonance (@60 &
120 Hz) here. Should be simple to do, one would think; not exactly rocket science.
A 2-C, 1-L pi has capacitive input - bad for the inverter.
Better would be just one L and one C. Watch for output voltage varying with load even far from resonance. With no load or very light load, output voltage exceeds input voltage for every frequency below resonance, though the gain is minor to negligible for frequencies far below resonance.
Squarewaves have all of the odd harmonics. Modified sine waves (squarewave modified to 1/8 cycle at zero, 3/8 cycle positive, 1/8 cycle zero, 3/8 cycle negative) also have all of them, though notably somewhat less of the 3rd and 5th harmonics than with a squarewave.
You can make the behavior more predictable and damp down resonances by adding a resistive load to the output. However, the resistor load will waste power. You also have to prepare for the load or connections to it failing, or be able to tolerate such failure.
Making an inductor that will handle your load current without saturating requires knowing how to design gapped iron core inductors. This is usually done with a laminated E-I core, and will probably be at least a little heavy and bulky. Otherwise, hope you can find a "reactor" type lamp ballast with the inductance and current capability that you need. (Probably heavy and a little bulky) Air core ones will be huge and probably scramble the color of operating color CRTs a few feet away unless shielded. Ferrite core ones will saturate more easily than iron core ones.
If a setup is going to be something for everyday use in your home or frequent or regular use in your camper, or if it has to work at times when technically qualified personnel are not around and awake and with a fire extinguisher handy, then I recommend something "more-tried-and-true" than something that I consider "experimental" or "science project quality" or even "senior design project quality". Electrical equipment for everyday use should have such reliability and "fale-safeness" (adequately unable to fail or adequately unable to have failures start a fire) to pass the sort of testing that UL does upon electrical equipment of kinds that normally get (or should) have listing/approval of UL or similar safety testing laboratory organization.
- Don Klipstein ( snipped-for-privacy@misty.com)
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