AC and DC power to light a Bulb

I've re-read your task and found that my end goal of providing enough light does not match well with your proposed experiment to suppliment AC mains.  Unfortunately doing that requires converting your low voltage DC to domestic voltage of more than 200V, which is not a safe thing to do unless you are good at box building, and then 'inverting' that in synch with the mains.  A circuit which can do those, to suppliment the mains from solar is

http://www.ebay.co.uk/itm/290611685881?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Looking inside one of these, it maintains charge on a HV DC capacitor from a MPPT contolled yellow 12V to 340V transformer nearer to the DC end of the box.  Four heavy duty microprocessor contolled FETS in a heric configuration invert HV DC to mains AC.  Downsizing some components left of the HV capacitor near to the centre of the box from 12V 250W to 10V 5W would work in principle but the circuits to generate a sinewave synched to local AC mains won't simplify. The power to run these and a microcontroller might be around 5 Watts, so you'd have a solar cell too small to contribute to mains appliances.  That was why I jumped to 'what on earth could he usefully do with a solar cell of that size' and wrote about using it for DC charger for LED lighting.

You could, for about £600, buy two Sharp NU230 solar panels or Kyocera KD240 or equivalent, and directly connect them to a comparable box to that linked to above.  I have solar panels connected in parallel to the 500W grid tie inverter, operating at 23 to 31 Volts depending on weather.  If you do that, you'll see your household AC bills decrease a little bit when the sun is out, but only by about 1kWh per day and only on reasonably bright days.  You are probably more interested in measuring how much you generate, for which a £12 gadget from Maplin is suitably boxed in to be safe.  This is getting to be an expensive project because it needs 2 x 3.3m of shed roof in bright sun on which to locate the panels.  It would acheive your aim, but not on such a small scale.

Very interesting information on the lamps! It all makes sense now!

As far as my project goes, I know it's quite unorthodox to want to add such a low wattage to power from the grid, so I understand your thoughts D2113F...it's a lot easier to use the low power in a "easier way" to create light, but the goal is to not create light but to leech a small amount of DC power into the AC grid for the purpose of lighting a bulb.

It looks like those options are WAY to expensive for something so little though. I've just gotten into electroincs and it just seems strange that the only way to add a small amount of DC power and mix it with a lot of AC to a would be so complicated and expensive... Perhaps getting a DC bulb, along DC converter (these should be rather cheap they are provided with nearly everything not to mention I have a box full) and adding the DC power to that converter might work. I would really rather a CFL or LED bulb too...for the lower wattage req and that would make my low panel so much more efficient. I'll do some shopping around and some research and let you guys know what I come up with. Your help so far has been invaluable thank you all.

Very interesting information on the lamps! It all makes sense now!

As far as my project goes, I know it's quite unorthodox to want to add such a low wattage to power from the grid, so I understand your thoughts D2113F...it's a lot easier to use the low power in a "easier way" to create light, but the goal is to not create light but to leech a small amount of DC power into the AC grid for the purpose of lighting a bulb.

It looks like those options are WAY to expensive for something so little though. I've just gotten into electroincs and it just seems strange that the only way to add a small amount of DC power and mix it with a lot of AC to a would be so complicated and expensive... Perhaps getting a DC bulb, along DC converter (these should be rather cheap they are provided with nearly everything not to mention I have a box full) and adding the DC power to that converter might work. I would really rather a CFL or LED bulb too...for the lower wattage req and that would make my low panel so much more efficient. I'll do some shopping around and some research and let you guys know what I come up with. Your help so far has been invaluable thank you all.

Hi ,

I agree with one of the other people replying in that adding 10V,500mA in series to the 120 VAC mains will make a virtually imperceptable increase in light level. Moreover, without extra circuitry (a 200V PIV diode bridge at a minimum) to rectify the AC prior to putting it in series with the lamp, you'll likely fry the solar cells as they are not made for high reverse voltages. And if you only use 1 diode, you'll lose 1/2 your 120V power and about 1/2 or more of the lamp intensity as well. WIth the bridge, you put the two AC  wires to the two AC termials of the bridge, then put the bridge plus to the solar cell minus and connect the solar cell plus to one end of the lamp and the bridge minus to the other end of the lamp. Out of the 120 VAC, you'll only lose about 2 V and your solar cells will be safe.

Very Important!!!!!!!!!! Be careful when working around the 120 VAC mains. Never make connections with the AC power on (unless you are already connected to a toggle switch or similar). The 120 VAC can easily kill youi by electrocution. Also, the way you wwre going to connect the circuit without diodes by putting hte solar cells in series with the 120 VAC, you might have had the solar cells shatter and spray shrapnal all over causing possible serious bodily damage. You must know what your doing and be safe by wearing safety goggles and/or using a piece of plexiglass to protect you from exploding circuitry.

Best of luck.

Kamran Kazem