AC and DC power to light a Bulb

You`re asking a really good question here! and happily it has A simple answer.

in effect you`re thinking about a DC current with an AC ripple to make up the rest of the power required by the bulb, I like your thinking, but solar cells are awkward in that respect.

you Are favored by using DC on incandescent bulbs, it`s much "Greener" than AC, by virtue of the fact that the bulbs last longer on DC also.

but your best bet would be to use a battery for storing this electricity  that will be suplemented from the mains power for charging when it`s dark, a simple UPS will do this with minor modifications.

I use this exact same set-up myself, the nice part is that I still have juice when the rest of the street has none in a blackout 6685.contentimage_2516.png

Yes you will need to use a Diode in series with your solar panel, and it must never see AC (it won`t charging a battery).

the problem with a solar cell is that it`s somewhat Dynamic, if you can Promise 100% that it will always have 100% sunshine without varying, then it`s a simple circuit, but this isn`t the case, a cloud passing over can end with lighting your bulb Through a solar cell! (a bad thing).

and anyway, 10v @ .5A is only 5W, so you`de be better off storing that or buying a whole load more.

LEDs on the other hand will lend themselves quite nicely to battery power at low voltages!

this is just my opinion based on what I have here and use, others may have better ideas 2553.contentimage_3.png

500 mA at 10V is 5 Watts.  So, don't expect to run a 60 Watt lightbulb.  I'll go with a presumption that you want to make enough light to read a schoolbook after sunset.  Please let me know if your end use requirement is anything different.

You could charge up eight 1600mAh NiCad batteries with direct connection to this solar cell, though it might be a little safer to have various electronics in to regulate it.  Ignore that for now and get a pile of small batteries on your windowsill fully charged up.  Don't forget to disconnect them when the voltage goes over ten volts or they might blow up from being overcharged.

9 to 10 V worth of batteries is about enough to power three "white LED's" in series (actually blue LED's capped with flourescent yellow) at 3.1 to 3.4 V each.  The 'large' ones are capable of 700 mA so on metal backplates of more than a square inch would tolerate direct connection to your solar photovoltaic. I'd expect battery power to be more useful for nighttime.  Three whites might tolerate direct connection to eight batteries, but DON'T do that without heatsinking them first.  It would be safer to have a 4 Ohm power resistance in series, which can be made from fine steel fence wire nailed to a brick or purchased.  The heatsink bases of LED's tend to be connected to one side of the semiconductor, so you'd need three metal plates for heatsinks and screw them to a brick or something which won't melt.

This sounds rough because it is intended to be copied to Africa and places which cannot go buying heavy duty high quality parts for everyone; a car battery and inverter for example (which this solar cell is too small for).  The solar cell, batteries, and LED lighting are worth having, and everything else is more questionable.

I understand the solar cell is not powerful enough to light a 60 watt bulb.  I also understand that I can use LED's to achieve a lower energy light source.  BUT, the goal of my experiment is to stand outside with a solar cell in the sunlight, feed the 10v 500ma DC power to the 60 watt bulb, and then have the wall plug supplement the rest of the electricity, apparently it will take 55 watts of AC power.  I'm not sure if a lightbulb would just take 60 watts and perhaps be about 5vdc brighter, or if the bulb would be smart enought to just take the 55 watts to reach it's intended peak.  But this is what I'm trying to do, supplement a bulb plugged into a AC grid with DC power.

A regular incandescent lightbulb isn't really "smart."  It is a small length of wire in a glass bulb that heats up and emits light when current is passed through it.

A simple analogy is to equate the lightbulb to a resistor.  It's slightly different from a normal resistor because it is non-linear, but for our purposes, we can call it a resistor.

When the manufaturer says that the lightbulb is 60W, it DOESN'T mean that when we connect it to a power supply it will always draw 60W, and it DOESN'T mean that we need to give it 60W of power for it to produce light.

When the manufaturer says that the lightbulb is 60W, it DOES mean that when we connect it to the mains where the bulb was designed to be used, it will draw about 60W of power from mains.

If we think of the lightbulb as a resistor and this lightbulb was designed for a mains supply of 120Vrms and the lightbulb is rated at 60W, we can calculate the resistance of the lightbulb.  The formula P = V^2/R solved for R with 120 as V and 60 as P will give us R = 240 Ohms.

A lightbulb is simply a "dumb" wire or resistor that will pass both Alternating and Direct Current.  If we took our 240Ohm (60W @ 120V) lightbulb and connected it to the 10Vdc solar panel, the lightbulb would draw P = V^2/R = 10^2/240 = 0.416W.  That power draw will heat up the wire in the lightbulb and it will produce light.  The light may be imperceptible.

What it sounds like you want to do is to utlize all of the power that the solar panel can produce to provide power to the lightbulb in addition to providing AC power from the mains to provide a total of 60W of power to a lightbulb.  We already found out that the lightbulb won't draw the full power of the solar panel with a "dumb" circuit.  The short answer to doing what you want to do is that you will need some power management electronics to boost the DC voltage from the solar panel and reduce the voltage from the mains to provide a total power of 60W to the lightbulb.  The incandescent lightbulb will light with a current that has a DC average and a much larger AC component added to it, but to control the power sent to the lightbulb in the way you want is a lot more complex.

CFL and LED lamps that are meant to plug into the mains are much more complex than an incadescent lamp.  Most CFLs are so sensitive to the voltage and frequency of their power supply that they won't work with dimmer switches; trying to add a DC component to the mains could be bad.

donny662 thanks for all your well explained knowledge!  Thats exactly the answer I was looking for...  You've check my "you learn something new everyday" box, thank you.

From your information here I gather that adding the DC power to that provided from the grid would just make the bulb a bit brighter, and that's not what I'm trying to do (save a bit of energy).  To accomplish what I'm trying to I guess I'd need a virtural AC dimmer switch when DC power is being provided.

I guess I could bypass my AC current issue by using a DC converter, but I don't think they are very energy efficient as they are normally warm to the touch when unplugged from the wall...that's got to be a waste.

On a side note, why do traditional table or floor lamps come with a note that says "60 watt max" or "40 watt max" if its all up to the bulb basically playing the part of a resistor on the grid...  It always seemed to me that bulbs higher than the rated wattage will fail much faster if put in to a lower rated socket.  Just a thought...

Remember that an incandescent bulb is not very efficient at producing light.  A 60W bulb draws 60W from the grid; a few of those watts of electrical power are converted into light power, but the rest of the electrical power is converted into heat energy.

When a floor lamp says "60W max," it is saying that because the fixture can only handle the heat from a 60W incandescent bulb or lower.  Higher wattage bulbs produce more heat, which can be a fire hazard or otherwise damage the fixture and reduce the life of the bulb.  Fixtures rated for higher wattage bulbs are made from materials that can handle the heat and/or have enough ventilation to get rid of the extra heat.

Also, you'll probably notice that CFLs will not last as long in fixtures that are poorly ventilated and rated for lower wattage incandescents. The heat from a 26W CFL may not be enough to damage the fixture, but the poor ventilation will let the CFL get hot enough to reduce its lifetime.

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.

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

First, remember that the light bulb was designed to function using 120VAC because that is what travels into our homes.  Thus a 60W light bulb is way too much for your 5W solar panel.  To be honest, the light bulb has a filament inside that needs to reach a certain temperature and once it reaches that temperature it will emit visible light!  The light bulb could careless if it was receiving AC or DC current as it just needs current!  If you want to have fun, rip open a solar garden light and google ckt's that match the one you have in your hands.  Be careful as newer ones have a big glob covering the brains of the ckt and you pretty much destroy the chip removing the glob.  My advice, grab a very small solar array, diode, light dependent resistor, npn transistor, and nicad AA battery with LED and you will learn more in 4 hours than you could 2 weeks reading about it...