What power supply do I need? Lighting for a Flats Box

[[1ponders] (Paul)]

Ok you guys with electrons flowing in your veins, here's one for you.

I've just finished (well....all but finished) an Eddie Trimarchi flats box, using 20 Watt halogens. (Now bare with me here as I'm not the brightest streetlamp in the street when it comes to things electrical so don't laugh.) I tried to light them up with my trusty ol' 15ah jumpstarter battery and they barely raised a glow, so I tried my trusty ol' D1ck Smith 12V 3 amp transformer. Well it wasn't quite what I'd call spectacular.
What do I need to get these thing to rock my sock?

Oh and where do I get the ultra white halogens, these standard ones look pretty yellow?

Thanks

[acropolite (Phil)]

You can buy a switchmode transformer specifically for halogen downlights for under $20, bunnings should have them, together with different temperature halogen downlights. If 240V is your flavour you may want to try some of the compact flouro downlight bulbs which are now produced in the same small sizes as the halogen ones.

[[1ponders] (Paul)]

Nah, stickin' with 12V Phil. I still remember being 8 years old and getting my first introduction to 240 thanks to a screwdriver and a wall socket.

What sort of terminals are there on the end of the transformer Phil?

[[1ponders] (Paul)]

I'd really like to use these but the price is a killer

[Dennis]

Hi Paul

Are the bulbs wired in series, or in parallel?

Cheers

Dennis

[laika (Brenton)]

1ponders,not sure what one of the so described light boxes is or how many globes you have used but if it has 1 x 20watt globe and it is rated at 12 volts then ohms law is I=W/E where I = Current W = Watts E = Volts.Thus I=20/12 I=1.666..........7 amps lets say 1.7 amps.If each globe is connected in parallel accross 12volts and lets say there are 4 globes then to light them to maximum brilliance you will need a power supply that can deliver 6.8 amps at 12 volts.If they are connected in series then the resistance of each globe affects the total voltage that is required to light them to full brilliance.Hope this helps.

[Dennis]

Wow Paul - you may have too many lumens in that light box if you use those Jaycar LED arrays!

Cheers

Dennis

[[1ponders] (Paul)]

That I know series

[mojo (Terry)]

P = VI

20W / 12V = 1.67A

Did I help, or have I misunderstood the question?

[[1ponders] (Paul)]

I remember your swish little setup Dennis, what did you use?

[[1ponders] (Paul)]

These guys seem to have a range of LEDs that might do the trick at a better price range.

[Dennis]

Hi Paul

I used torch bulbs – 4 of them wired in series. I think each bulb was rated 3V 1A or thereabouts.

This gave me figures of 12V at 1A so I purchased a 12V 1A mains adapter (actually variable 3, 6, 9, 12V) and using the ST7E CCD camera (very sensitive) on the C9.25 my flat field exposures are around ½ second at a setting of 6V on the mains adapter.

I now have to re-think the whole design, as I am moving into the world of LRGB imaging so I think I will need an illumination source more balanced to daylight (5800K) rather than the 2500K of the puny torch bulbs.

I was thinking of high intensity (3000mcd) LEDs if I can find their output spectrum and somehow overcome the narrow field limitations.

Cheers

Dennis

[[1ponders] (Paul)]

I gather with mine in series this is what is causing me problems? Pplease don't suggest I change it now, everything is glued together. I can change the bulbs np but just cant get to the wiring.

[laika (Brenton)]

1Ponders,Ok if the are in series then the ball game has changed and I dont no why you would do this unless you want to reduce the light output or ru it on a higher voltage.Ohms law for resistance in this case is R=ExE/W.Thus R=12x12/20 R=7.2 ohmsIf there are 4 globes then total resistance is 28.8 ohms and total current will be 6.68 amps.Thus to light these to full brilliance ohms law E=IxRThus E=6.68x28.8 E=192.384voltsHope this helps.Regards Brenton.

[Dennis]

Hi Paul

4 globes at 25W will be the equivalent of a 100W light bulb in terms of heat output - very hot in the confined space of a light box and probably too bright for flat fields?

Unless the globes are cool globes?

I presume if you reduce the voltage in the circuit, the bulbs will illuminate proportionally less brighter that full on, although I’m not sure how the reduced intensity may vary from bulb to bulb? Hopefully the manufacturing process is stable enough to minimize variations?

Cheers

Dennis

[[1ponders] (Paul)]

Hi laika, thanks for your input. I joined them in series 'cos thats what the design showed.

I've managed to get everything apart now (liqiud nails is great stuff until you want to get it off your hands) so what should I be doing .

Please excuse me for ten minutes while I dig out the Turps

[[1ponders] (Paul)]

I gather I should be hooking these guys up in parallel rather than series.

[[1ponders] (Paul)]

BTW if you haven't seen it here is Eddies design right at the bottom of the page

[laika (Brenton)]

1Ponders,Not sure what it is for, so please excuss my ignorance, my astronomy experiance to date has been purely observing but recently have been given a neximage ccd camera and have just started imaging the planets.What you need to remember is if in parallel the globes will run from there rated voltage but you need higher current.If they are in series you need the higher current and also the higher voltage to run them at full brilliance.Hope this helps.Regards.

[[1ponders] (Paul)]

Have a look at the link above and you will see what I am building. Up until now I've been taking flats that are very hit and miss. I'm trying to improve on them.