Low Voltage Halogen Question

[jonykaboom]

Hi,
I'm using some low voltage halogen downlighters for some specialized tabletop photography/Video, from reading this site it would appear a lot of you know a lot about these lights

If someone can help for a second, could they see if they could answer some quick questions for me? - (using UK mains 240v)

- I have 2x50w lamps running from a 105va transformer, when I disconnect one lamp I seem to gain far more brightness on the other, is this the norm?, should each lamp not draw same voltage and current always, weather one or 2 lamps connected?

- Why do people use 12v instead of normal 240v lamps of the same kind?, I'm guessing, more economical bulb life, sharper brightness from the low voltage bulbs?, is there also less overall power drawn from the mains perhaps?

- Since I'm using higher current, will longer wire lengths after the transformer dull the brightness slightly?

- Say I want to power one 50w light, I can choose either the 65va or the 105va transformer, is there any benefit from choosing the more expensive 105va transformer?

- For photography, I may take a photo, and then another one minute later, these photos will be blended in a time lapse sort of way, if there is any flicker from the supplies in between this will show up as a flicker, if I want to avoid this, what would be safer, using transformer lamps or mains direct lamps?

Thank you team , any help is BIG !!
JonyKaboom! (..and not called that for nothing!)

 

[Steve]

- I have 2x50w lamps running from a 105va transformer, when I disconnect one lamp I seem to gain far more brightness on the other, is this the norm?, should each lamp not draw same voltage and current always, weather one or 2 lamps connected?

Are you connecting them in series? If so thats wrong for a start.

- Why do people use 12v instead of normal 240v lamps of the same kind?, I'm guessing, more economical bulb life, sharper brightness from the low voltage bulbs?, is there also less overall power drawn from the mains perhaps?

more energy is drawn by ELV, there are small losses in the transformer. But apparently ELV gives a slightly better light.

- Since I'm using higher current, will longer wire lengths after the transformer dull the brightness slightly?

yes. a phenomenon known as voltage drop

- Say I want to power one 50w light, I can choose either the 65va or the 105va transformer, is there any benefit from choosing the more expensive 105va transformer?

no. In fact, you could be under loading it.

- For photography, I may take a photo, and then another one minute later, these photos will be blended in a time lapse sort of way, if there is any flicker from the supplies in between this will show up as a flicker, if I want to avoid this, what would be safer, using transformer lamps or mains direct lamps?

there will be no flicker from halogen lamps. the 50hz cycle is so quick it wont allow the filament to loose brightness on the crest of each wave - it glows at an "average" brightness. combined with the shutter speed lasting at least 5 of the 50hz cycles, there will be no effect on your photography. Fluorescent lighting is a different story, but high frequency ballasts are available now too!

 

[jonykaboom]

Thanks for you time Steve, I'm working from theory and not experience, yes I have connected in parallel and from my calculations both current and voltage should stay exactly the same regardless of one or 2 bulbs connected, therefore why does the bulb brightness increase when I disconnect the other from the circuit? This first question really links up with the 'underloading' answer, as you say I may underload by placing one 50w onto a 105va circuit, because it's designed for say 2x50w's right?

You also say 'slightly better light' from LV halogens, I guess you mean in terms of brightness and sharpness

My last question was answered very accurately, however, I understand the frequency bit ok, but time lapse photographers do tend to get varying light levels sometimes and it can be from the lighting, so in a nutshell, would transformer supplied lights be safer from flicker or mains fed lights you think?

Thanks again Steve, I'll give you a break now !

 

[Steve]

Lighting transformers input 50Hz and output 50Hz AC. The frequency is the same, though obviously the peaks on the ELV side are lower.

The varying light levels experienced by time lapse photographers cannot be to do with mains AC frequency.

Its possible that voltage drops for a period and this causes the light level to decrease - for example when someone turns on an electric shower or a welder on your street. I can see that this would have an adverse effect on photography. Also watch for the ad breaks in coronation street - when everyone turns their kettles on

One way around this voltage drop is to use CFL lamps, since they are relatively immune to it. Or some form of UPS (uninterruptible power supply), one which states that it gives out a regulated voltage of 230 volts AC.

 

[jonykaboom]

" Say I want to power one 50w light, I can choose either the 65va or the 105va transformer, is there any benefit from choosing the more expensive 105va transformer?

no. In fact, you could be under loading it. "


Steve, could you explain?, as I thought the 105va would supply more current, but you say underload?

Cheers
Jon

 

[jonykaboom]

,.. also Steve I presume VA is watts, therefore the 105va would be less economical, ie, why use 105va at all if the 65va is enough power and keeps your bills down?, yes?


Jon

 

[stevelup]

I have 2x50w lamps running from a 105va transformer, when I disconnect one lamp I seem to gain far more brightness on the other, is this the norm?, should each lamp not draw same voltage and current always, weather one or 2 lamps connected?

Are you running two separate cables from the transformer to your lamps, or do you have a common length of cable with both lamps connected at the end?

You should really have two separate cables. How long are the cables and what size are the conductors in the cables?

It's possible that the transformer is poorly regulated but more likely that the cables are undersized.

Steve

 

[securespark]

I thought the 105va would supply more current

Only if a load aks for it.

 

[jonykaboom]

Steve&Secure

from the transformer I connected both lamps in parallel, I understand this should keep volt & current the same regardless of load,. the wire is the recommended wire for these lamps, 0.75mm squ I think, about 2-3 ft in length each, would have to check, dont have here, anyway the dullness is not bad, but I want to keep my lamps at their brightess.

So in general if I use a 105va as opposed to a 65va for one 50w bulb, then I'm not going to get a bigger lecy bill until I put in say a 100w bulb ?

cheers team

 

[Click-Sure]

oops

 

[jonykaboom]

,..now to really mix you guys up,.. I tried 2 x 20w bulbs on the 65va transformer and each bulb is actually brighter with 2 connected as opposed to one??, can someone explain that one??

,,no bend radius involved thee!,.. and I'm happy to use these transformers now as I may keep the 105va for bigger wattage later,.. and did George Michael not get caught doing things wrong,("if you're gonna do it do it right?") in a public toilet ???

thanks guys
J