12VDC CFLs vs. mini-inverters

[vtpeaknik]

Hi all.

I am new to this board, this is my first posting.  I am building a backup power system somewhat similar to "RCpilot".  Perhaps I'll post something on that eventually...  Meanwhile:

In a batery-based system where the inverter is not always on (or non-existent), DC lighting seems like a good thing, at least in some key fixtures in the house.  It seems that 12VDC CFLs exist but are hard to find (especially if you're picky on the color rating etc), and expensive when you find them.

Has anybody tried the following alternative approach: there are now dirt-cheap chinese mini-inverters (e.g. 40 watts) flooding the market.  (See e.g. the ebay seller "vastexchangecorp".)  With such, can run regular 115VAC CFLs, available in all sizes shapes and colors, and cheap.  If such an inverter can last longer than the bulb, the bulb can then be replaced with another cheap one.  Before you say "this is a waste", note that a DC CFL must have a mini-inverter built in!  And the cost of a separate mini-inverter plus an AC CFL is actually less than that of a DC CFL alone!  But will those mini-inverters do the job?

Practical issues: Such a mini-inverter is built to plug into a car's cigarette-lighter socket, but should be easy to hardwire or convert to another type of plug.  Also should ideally be arranged to be downstream from the switch.  (Not sure what their idle power cunsumption is - nor their efficiency.)

Alternatively, pointers to reasonably priced screw-in 12VDC CFLs (in the 5-25 watt range, with 2700K color rating) are welcome!

[dbcollen]

7.5 or 12 watt warm cfls @ $7.00 each + shipping

contact me

Madriverwind at gotsky.com

Dustin

[mtbandy]

Running ordinary 'mains' cfls off a cheap inverter is a very good idea IMO.

It's much easier and cheaper to replace the cfls!

One thing I would recommend though:

Rectify and smooth the output from your cheapo inverter, and then distribute the resulting high voltage DC for your lighting circuits. Why? For a start, the output from these cheap inverters is terrible - noisy and full of harmonics which will make your CFLs buzz annoyingly and shorten their life. Also, distributing the output from a cheap inverter over any distance will cause a lot of problems with EMC (i.e. the wiring will radiate lots of nasty RF hash, creating a very electromagnetically noisy environment, which will be heard on TVs, radios etc...

Ordinary CFLs will also be a lot happier with a fairly smooth DC input.

[mtbandy]

As for idle power consumption, about 400mA for the smaller inverters (my 150 watt / 12v measures 430mA)

Efficiency is greatest at near full load, I'd guess at least 80%

[ghurd]

Just my experiences.  It costs more to go the cheap route.

I haven't seen a decent (or even slightly better than junk) Mini-Inverter since the Notepower 50.  Some of the China Name Brands (50 to 75 or 100W?)didn't last 8 hours with a 3~4W load 9W peak, most didn't last a couple days.

Name Brand DC CFLs are worth the price.  They are brighter AND use less power (conservation anyone?). They are available in a couple temperature color ratings. They last an order of magnatude longer too. Well worth the $20.  I only know of one name brand and it's German.  The 11W is my choice over the 7W.

You get what you pay for.

Hard wiring the inverter downstream of the switch will kill most switches.

HF has those mini-inverters on sale right now for $6.99.  I wouldn't give $2 with hope it can keep my cell phone charged for the week.

G-

[scottsAI]

Hello Vtpeaknik,

Wow how cheap the small inverters are! I will buy a couple to play with. Already have a bid in.

10 years ago I bought a cheap 150w inverter, kept it plunged into the vehicle to power my cell phone. ($35 for cell charging adapter at the time) For $30 I got the inverter which powered my laptop also. Lasted about 9 months. Bought a different brand Vector, 150w. It to lasted 9 months. Then bought a 300w vector. After a year I got a new cell phone with car charger thus stopped using it. I now use it for backup lighting power. Bought a second for keeping in the car to power laptops.

Two problems with the DC CFL:

-they are too small in watts.

-Lumins per watt are 80% what a 110v CFL is.

11W may be better than a candle, to light up a large room 23W is the minimum, very hard to find in 12v model or costly at $20 plus shipping. Lumens per watt goes up as the wattage increases. I like the idea of bypassing the AC section of the inverter, little surgery required. Thanks for the info.

I plan to put the inverter at the lamp, switch up stream for zero quiescent current.

I was talking to a friend about electrifying his hunting lodge. They use propane lighting not good in the summer. Entry way wanted a 12v CFL, then get to switch for main 300w inverter for rest of the lodge.

Two golf cart batteries and 30w solar panel + charge controller to charge it up between visits.

Have fun,

Scott.

[boB]

You may be wasting more energy powering the little inverter itself than

if you just ran the DC CFL.  In the long run the DC CFL would most likely

be better.  OR, maybe you have an extra abundance of energy ?  Some ppl do.

boB

[vtpeaknik]

Well I got hold of a couple of these cheap mini-inverters, supposedly rated at 40 watts, and found out that:

• there isn't much inside, see photos below
  
• it ran a 4W night-light bulb rather dimly
  
• after 2 hours of that the heat sink on the power transistor got quite hot
  
• it could not start up a 15W CFL - brief flash, then only an audible whine.
  
  

[Electron Skipper]

You could try wiring past the CFL's circuit board- dismantle one enough to find out what the heater voltage requirement is, and just wire the inverter in as just an electronic ballast in a manner to provide the heaters with their voltage.

A CFL should in theory be able to light and stay lit on just 30 volts which is  something else to consider.

Or you could scale up the Zetex lighting ballast a little bit to double the current.  They give you the instructions on winding the transformer in the application note, so just size up the wire and the core accordingly.  Either drive the CFL luminare portion without base as a cold cathode (both heater leads tied together,) or work out what you need to light the heaters.  Switch the transistor choice over to one of the Fairchild offereings in a TO220 case at 6 Amps.

[yuandrew]

It may depend on the inverter and the bulb. I wonder where the "mini inverter" vtpeaknik has came from. I have a "Power On Board" (I know many here dislike that brand) rated 15 watts and it could start and run an older Philips 20 watt EarthLight CFL for about 15 minutes. It does work nicely with a 15 watt Sylvania CFLs and another Chinese one (Greenlite ?) that I also have.