CFL powered off DC - Page 1
Forum section: electronics / projects

author: Harvs
author_rank: Super Contributor
timestamp: April 05, 2013, 06:27:32 am
content: I've been toying with ideas for lighting my firewood shed prior to winter setting in. I live in a semi rural area that backs onto bush, which inevitably means we get every creature under the sun living in our wood pile. Makes collecting a barrow load of wood in the dark an "interesting" experience at times.It's close enough to the house to make running cable out to it ok, however it's far enough to make putting a mains connection down there very expensive. I want to run some garden lights out in the general area as well, so I figure running it off DC (maybe 48V?) would be a sensible solution.I've played around with some LED solutions but have generally been underwhelmed (need plenty of diffused light to see the large eight legged friends as they run up your arms.)Someone posted a tear down of a CFL the other day, and it looks like they've all got a rectifier/cap arrangement on the input. So I thought what the hell, why not just build a DC-DC converter at the shed end and step up the voltage to 340VDC (240VACrms * SQRT(2)).So I tried it out on the bench by modding an old hack of a DC-DC converter I had from building car amps and all seems to work just fine. Although power consumption was about 15% higher than what the globe was rated at. Its rated at 20W, and draws 66mA after warming up. With 340V, that makes about 22.5W. Should I be lowering the voltage? Or is the rating actually the power making its way to the tube and not overall rated consumption?So it seems like a good idea, and designing the converter wont be too hard. But is there anything to do with these CFLs that I'm not taking into account? I really don't know a hell of a lot about them.

author: BravoV
author_rank: Super Contributor
timestamp: April 05, 2013, 06:33:20 am
content: Did you wind both transformers (middle and toroid) yourself ?Post the circuit please.

author: Harvs
author_rank: Super Contributor
timestamp: April 05, 2013, 06:51:12 am
content: Quote from: BravoV on April 05, 2013, 06:33:20 amYeah I've wound many. Actually these ones are quick hacks that I'm not proud of by any means. Attached is a much nicer example of one I wound on the epcos ETD29 core.I don't have the files for it anymore (this was the first car amp psu I built around 4yrs ago and has been hacked for many applications over the years.) However it's a simple 12V unregulated push-pull converter using a TL494 and separate mosfet driver. I'll post the schematics of the finished PSU for this application once I've done it.

author: BravoV
author_rank: Super Contributor
timestamp: April 05, 2013, 09:15:42 am
content: Tidy windings, nice, is that a litz wire ?

author: Harvs
author_rank: Super Contributor
timestamp: April 05, 2013, 09:49:23 am
content: Quote from: BravoV on April 05, 2013, 09:15:42 amNope, just measured out the two lengths, tied them together at one end to something solid, then put the other end in a drill. Then simply wind until you get the turns/inch you're after.

author: BravoV
author_rank: Super Contributor
timestamp: April 05, 2013, 09:57:23 am
content: Quote from: Harvs on April 05, 2013, 09:49:23 amTurns/inch ? Is that matter ? I mean for the overall transformer's performance ? Noob quesiton here.

author: Harvs
author_rank: Super Contributor
timestamp: April 05, 2013, 10:08:02 am
content: Not as far as I know. But I like to be consistent with the same gauge of wire so that multiple windings on the transformer (and across multiple transformers) look the same. Obviously with heavy gauge wires you don't want to over wind them and weaken the insulation.

author: amyk
author_rank: Super Contributor
timestamp: April 05, 2013, 11:38:10 am
content: Have you tried it with more than one CFL? The circuits in them are very cheaply made and component tolerances aren't going to be perfect. I wouldn't be surprised if another draws only 18 or 19W.

author: Psi
author_rank: Super Contributor
timestamp: April 05, 2013, 11:51:38 am
content: The local hardware store here stocks 12V (and i think 24V) DC CFL lamps.They look identical to the 240V versions in terms of their socket, size and shape. (But have different drivers inside obviously.)We're using them in the garage.I ran a 13.8V 20A power feed to the garage using 7 AWG overhead cable to drive all the lighting and battery charger.

author: Harvs
author_rank: Super Contributor
timestamp: April 05, 2013, 12:09:33 pm
content: Quote from: Psi on April 05, 2013, 11:51:38 amYeah they use to, and I do have a couple from that time that I'm going to use somewhere else. But, they don't anymore, and even when they did it was only one brand in cold white and relatively expensive (not that I care that much about a few dollars.) Sure you can still get hold of them from an online retailer, but I like the idea of having a system where you can just use any of the cheap off the shelf items you can get from anywhere.I guess more so is it won't be difficult to design the DC-DC converter, then I can use that design in a number of places around the yard (gate lights etc.)

author: Harvs
author_rank: Super Contributor
timestamp: April 05, 2013, 12:14:12 pm
content: Quote from: amyk on April 05, 2013, 11:38:10 amThat's a good point, I only tried one. I don't have it set up anymore to try others. I'll just keep the design a 340V and see how it goes. 15% over isn't that much anyway (if it only lasts for 10yrs instead of the advertised 15... who cares.)

author: Alana
author_rank: Frequent Contributor
timestamp: April 05, 2013, 12:24:58 pm
content: What is the problem with 240V AC in the shed? Even if permanent wiring need to be done by licensed electrician i think you could power it from wall outlet as if it was long extension cord.

author: C
author_rank: Super Contributor
timestamp: April 05, 2013, 06:23:38 pm
content: Is there some rule or law that says you can not do some or most of the work?Here 240V AC is three wires, where you are it could be two wires.For an extension like this the safety ground should be kept separate, so add a wire to above.Remember, As you decrease the voltage for the same power, the wire size has to increase and increase some more to cover the voltage loss. This increases costs.If you are putting wire in the ground, you should use wire built for this purpose.Be aware, Your creature's like to chew on wires even if under ground.If memory serves, here Power wires in the ground should be a min 18 inches down.If I were doing this I would add some control wires so I could turn off/on separate circuits remotely . For most rules the control wires need to be separated from the AC power wire by ____ distance. If you are creating a trench for power wires this is easy to do and cheap to add some control wires. I would do control wires rated Cat5 or better.Plastic pipe: Makes it easer to change out wires or add wires with out digging. But remember the creature problem, If the creature chews a hole in the top of pipe, the pipe could fill with water.If you have to use a licensed electrician, Ask what parts you could do to save money.If you get an answer like some in this area have from a plumberPlumber: " I will charge you $5000 to run the sewer pipe and connect it to the sewer system"Question to plummer: " and if I install the pipe?"Plumber: "I will charge you $5000 to connect to the sewer system!"You will know you are fighting a government sponsored Racket.C

author: smashedProton
author_rank: Frequent Contributor
timestamp: April 05, 2013, 07:16:03 pm
content: Cant you just use a couple step up transformers to provide a HV bridge between the two points? You could then get away with using tiny wires. It also may provide some protection from the critters to some degree.

author: Harvs
author_rank: Super Contributor
timestamp: April 06, 2013, 01:35:12 am
content: Quote from: C on April 05, 2013, 06:23:38 pmIt depends on the electrician you get. At the end of the day, they have to sign off on it, and if they don't want to they just wont do the job. But, yes, it's a possibility.QuoteYep it's two wire + ground.Remember, As you decrease the voltage for the same power, the wire size has to increase and increase some more to cover the voltage loss. This increases costs.In this case it won't make any difference to the cable to be run. The minimum requirements for mains cabling means it'll need the standard conductor size (which can handle a 10-15A circuit IIRC.) At 48VDC, 100W of lighting will only be 2A, so no big deal.QuoteYep, either way conduit for buried wires is cheap (I was looking at it yesterday, $6 for a 4 meter length) so it'll be a trench with buried conduit and wires feed through it.I'll defiantly be putting down control wires.QuoteBTW when I've said creatures, we actually have very few that chew on things. We have plenty of Oz native mammals, but they're quite different from mice and rats that cities have to deal with. They just go about their business digging smalls holes in the ground and are very shy of humans.Certainly putting a mains connection down to the shed is still a possibility, but there's going to be a DC link anyway for garden lighting, so I'll start out with that and see how it goes.

author: C
author_rank: Super Contributor
timestamp: April 06, 2013, 02:38:45 am
content: Check your rules.here you can normally run power under 50 volts next to controls.Some places you could use long coils of pipe like they use for water, but if unsure us the electrical conduit.if you put in a proper electrical conduit you might find an electrician to finish it. If you do this leave part or all the trench open so the electrician can see it.You may not know this trick, tie a strong string to a part of a soft paper towel. Then use air pressure to blow the paper towel the length of the pipe. You now have a pull string use to pull something stronger or the wire through the conduit.A conduit in the ground with a ready pull cord could make a big difference.Good luckC

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: April 06, 2013, 03:27:07 am
content: Although most of what you C says is true, Harvs cant do the mains wiring without a licence. It is quite strict in Aus.But if the wiring is considered Separate Extra Low Voltage then AS3000 doesn't apply.ELV is defined in AS/NZS 3000 Wiring Rules as "Not exceeding 50 V a.c or 120 V ripple-free d.c."I reckon you could do some good things with 120v dc.Even though I have my sparkies licence I entirely agree thatQuoteOne the subject of rats and native critters, here are two I caught yesterday. The one with the long tail is no longer with us.

author: Harvs
author_rank: Super Contributor
timestamp: April 06, 2013, 03:59:34 am
content: Quote from: HackedFridgeMagnet on April 06, 2013, 03:27:07 amNice rodents. Long tail = imported.I didn't realize the rules allowed as high as 120VDC. I only knew about the 50V rule (hence the plan to use 48VDC.) 120VDC would be nice... But then again, 48V offline supplies are available everywhere, I think I'd struggle to find a suitable 100+VDC offline supply without resorting to custom building my own.

author: SeanB
author_rank: Super Contributor
timestamp: April 06, 2013, 05:35:25 am
content: If going to mains cabling put a big enough cable in. Not much difference in the price for a 20A breaker and a 40A breaker. If going for buried cable you can go with conduit and pull ordinary house wire through ( 3 cores) or use a steel wire armoured cable and not bother with conduit. I use conduit a lot with aerial bundle cable in it ( legal here to bury it in conduit) and it worked out a lot cheaper than the armoured cable. This will give a 6mm or 10mm cable, enough to allow you to have a 30 or 50A circuit board in the shed. This allows you to run high powered tools there easily.

author: peter.mitchell
author_rank: Super Contributor
timestamp: April 06, 2013, 07:03:38 am
content: Electrical conduit is pretty cheap, get bigger stuff, so its easier to pull stuff through and you can add more stuff to it later on, and when you use your pull rope, have 2 on hand, so when you pull your cable through, you can pull a new pull rope through at the same time.

author: SeanB
author_rank: Super Contributor
timestamp: April 06, 2013, 12:28:47 pm
content: My preferred conduit for multiple cables is 50mm drain piping. If you are going to have power and data cabling then place 2 pipe runs in the trench, at opposite sides if possible, so there is some separation between them. If doing a whole bundle of data cabling nothing is better than 110 PVC sewage piping, you can blow the cable through then.

author: peter.mitchell
author_rank: Super Contributor
timestamp: April 06, 2013, 06:55:06 pm
content: Oh, also, for underground conduit, glue it together, above ground its fine not to, but under, you're just asking for water.

author: Harvs
author_rank: Super Contributor
timestamp: April 07, 2013, 01:40:19 am
content: Quote from: SeanB on April 06, 2013, 12:28:47 pmWow, that's some serious data cabling you're doing! (assuming you mean the 110mm ID pipe.) How many CAT5/6 cables do you put through that?

author: Colin55
author_rank: Contributor
timestamp: April 07, 2013, 02:06:12 am
content: Run a lead to the shed. You can run a lead to anywhere.Driving a CFL is very difficult. Use a 15watt fluoro tube. It is much easier to drive.

author: Harvs
author_rank: Super Contributor
timestamp: April 07, 2013, 03:44:20 am
content: Quote from: Colin55 on April 07, 2013, 02:06:12 amHow so? Playing with them on the bench they seem easy as pie. Just give them 340VDC and theyseemhappy.Why is a 15W fluoro any different? Don't they basically use the same circuitry but the CFLs just integrate it into the one object?I'm genuinely interested, as I've said at the start, I really don't know a hell of a lot about them.

author: Strada916
author_rank: Frequent Contributor
timestamp: April 07, 2013, 04:18:21 am
content: in australia mains power needs to be in orange conduit at a MINIMUM 600mm deep. If that can not be achieved orange danger tape and cement must be in place over the conduit. Also Data or comms need 200mm of seperation from mains.

author: SeanB
author_rank: Super Contributor
timestamp: April 07, 2013, 06:50:10 am
content: Quote from: Harvs on April 07, 2013, 01:40:19 amIt was around 80 cables coming out of the server on the top floor and going down a floor. The 110mm hole was easy to drill and make threading cable through easy. There is a 5m cable bundle behind the rack hanging off the wall so that it can be moved to gain access to the back or the sides easily. To get the cabinet in through the safe door ( it is in a built in safety vault) there was the choice of take the safe door off ( done that before, it weighs around 2 tons) or take the rack to pieces and assemble it again inside. Went for making a rack kit and play at Mechanno as it was lighter pieces.