Emergency CFL Lantern

[kplavunkal]

Hai friends
I am planning to assemble an emergency Lantern which will light a 2pin CFL tube of 11 watts with a sealed lead acid battery of 6 volt - 7Ah. there is available pcb in the market for this purpose. but that circuit is not giving sufficiant back up. so i am looking for a circuit with high freqency out put which will reduce the consumption and increase the back up time. like Vinverth Lantern. if anybody have an idea please help. thanks in advance.

 

[things]

hi,
i thought it was ccfl. but anyway if you are using ccfl's i think they need an inverter to run. also what's the backup thing your talking about?

 

[dch222]

You can buy these lanterns off the shelf for about £20.

some of them have a facility that if you keep them permanently plugged in and trickle charging (they usually have sealed lead acid batteries), they will come on automatically if there is a power cut.

I bought one for my disabled mother in case the lights went out unexpectedly.
It worked fine although was never actually needed. Later when I started to use it normally for carol singing one night, both inverters failed. Made in China.

 

[tcmtech]

The typical CFL's will run just fine on DC if its around the rated line voltage and below the peak line voltage. I have not found one that doesn't.
The cheap Chinese brand 'Transport & Distribution Inc.' CFL's start and run all the way down to 45 volts DC!
The better brand ones need close to the line voltage to start though. 100 -110 VDC.

If you have ever taken a CFL apart you would see they rectify the AC line power and then run a tiny inverter to drive the actual fluorescent tube.

I would recommend buying one of those 25 watt cigarette lighter inverters and use that as the step up source.
To gain some additional efficiency take the HV side inverter section out and tie the CFL inverter back in its place.
IF you want longer run time just use a smaller CFL. I have seen some rated as low as 3 watts now!

 

[Hero999]

The problem with running on DC is shortened tube life because the electrons are only sputtered off one filament.

Most fluorescent DC powered light drivers are actually inverters which generate high frequency AC to power the tube. Even then the waveform needs to be roughly symmetrical to avoid the electron sputtering problem described earlier.

If it's a two pin tube you might have problems with the internal RF suppression capacitor bypassing the AC causing it to be dim.

 

[Sceadwian]

TCM the smaller the CFL tube is the less efficient it is, at 3 watts, it's about 1/10th as efficient as a full sides 20 watt tube for lumens per watt. You'd be better off using LED', they beat CFL efficiency if you find the right LED's to replace it with and the drive electronics are simpler.

 

[Hero999]

The drive electronics are also likely to be more efficient for LEDs.

 

[tcmtech]

Never said they were efficient! Just said they made them!

 

[mneary]

The problem with running on DC is shortened tube life because the electrons are only sputtered off one filament.

Most fluorescent DC powered light drivers are actually inverters which generate high frequency AC to power the tube. Even then the waveform needs to be roughly symmetrical to avoid the electron sputtering problem described earlier.

If it's a two pin tube you might have problems with the internal RF suppression capacitor bypassing the AC causing it to be dim.

The typical CFL assembly that I've seen as a direct replacement for an incandescent uses a bridge rectifier to produce DC and then makes its own (symmetrical) high frequency AC for the lamp. Supplying DC to this device should not cause it to operate differently.

 

[Sceadwian]

I'm not sure why you would think that mneary, DC is difficult to current limit and still produce sufficient starting voltage compared to AC. AC at high frequency is extremely easy to current limit all you need is an inductor. Even with DC you need to reverse the polarity every now and then according to Wikipedia at least because the mercury tends to collect at one end of the tube.

 

[tcmtech]

Find a cheap CFL and take it apart. Its exactly like mneary and I have said, they are just tiny inverter devices. Most are simple push pulls or variations of it but some in fact have a full inverter drive IC and all the additional components!

They take the AC line voltage and rectify it to get 170 VDC and then run that through a simple inverter oscillator to get the HF AC that drive the actual tube.

With a little rework and the addition of the right turns ratio toroid placed on the leads that went to the tube ends you can make a small DC-DC step up or step down converter.

The cheap ones from china I mentioned in the earlier post will take a direct DC input and still light up and run at around 45 volts DC. They reach their full brightness from about 90 VDC on up!
They also take over voltage up to the 200 volt capacitor limit of the tiny inverter without problems too!

 

[Hero999]

Sceadwian,
He didn't say it does use DC.

He said a mains CFL converts the mains to DC, then to high frequency AC which powers the lamp.

The cheap ones from china I mentioned in the earlier post will take a direct DC input and still light up and run at around 45 volts DC. They reach their full brightness from about 90 VDC on up!

That must be the US 120V ones.

The UK 230V ones must require 180VDC to reach full brightness.

Still handy if you want to power your house from an alternative energy rig. You could connect 10 SLAs in series and wire it directly to the lighting circuit. I suppose to comply with the regulations you'd need to add waning labels to indicate it's a DC supply and needs isolating separately.

 

[tcmtech]

I have also found out recently that the new HF solid state ballasts for the regular fluorescent tubes (dual 4 ft 40 watt type) will also work on DC with out problems too!
My one shed light ballast went out so I bought a high efficiency solid state one for a replacement.
It too worked on a wide DC input range with little noticeable change in brightness from about 100 volts up to 200 volts!

 

[Hero999]

I have two 8W 24V military vehicle lights in my shed connected to two SLAs which are float charged by a couple of solar panels connected to an LM317 configured to 27.7V out.

If you can get hold of 10 small SLAs and enough solar panels you could do the same. Even tiny 1.2VA batteries should be able to power it for a few hours.