# Information on this transformer?

Hi everybody,

I’ve just seen this 240v-12v transformer on ebay (http://www.ebay.co.uk/itm/105W-220-240V-to12V-Halogen-Light-LED-Driver-Power-Supply-Electronic-Transformer-/400316050785?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item5d34b22d61&_uhb=1#ht_4809wt_1271) and was wondering a couple of things? Can anybody figure out what the output amps are? And if I spliced my 240v heat cable into the input cables as well as the mains input, would I still safely get 12v out the other side?

Thanks!

105W at 12V means the output current in the range of 8 Amps. Note, this device outputs AC, not DC.

If you tie 2 loads in "parallel" across the mains, they are treated as totally separate loads, and essentially don't affect each other. This is because the mains acts a "voltage source". Do a search on that term to understand what it means.

Hey,

Thanks so much for the quick reply and for pointing out that it outputs AC no DC since that would not have ended well! And also just for future reference, if it outputs about 8amps and my project only requires lets say 4amps will this matter? Or does it only matter if my project requires more than the 8amps?

Also was there a specific calculation you used to change the watts into amps?

Thanks again!

SamuelCB:
Hey,

Thanks so much for the quick reply and for pointing out that it outputs AC no DC since that would not have ended well! And also just for future reference, if it outputs about 8amps and my project only requires lets say 4amps will this matter? Or does it only matter if my project requires more than the 8amps?

No a voltage source can not force a specific current into a load, but rather allows the load to draw what current it requires according to ohms law. Voltage sources rated their current output as the maximum it can supply, but if can of course supply anywhere from 0% to 100% of that current rating.

Also was there a specific calculation you used to change the watts into amps?

If you know the watts and the volts, then amps = watts divided by volts. This however does not account for small losses that would not allow for 100% efficient power transfer across the transformer. Most well constructed transformers work in the high 90%+ range.

Thanks again!

Brilliant thanks, so if I need 5amps I should go for maybe 5.5-6amps to cover possible loss?

Also I am now looking at this one (http://www.ebay.co.uk/itm/AC-100-240V-to-DC-12V-Switching-Power-Supply-Regulated-Transformer-for-LED-Light-/230844619265?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item35bf695a01&_uhb=1#ht_3557wt_1037) and it has 2 -v's and 2 +v's is this just so you can easily attach 2 12v devices at the same time?

Thanks!

V X A = W, A = W/V... Simple

Bob

Thanks! :)

SamuelCB: Brilliant thanks, so if I need 5amps I should go for maybe 5.5-6amps to cover possible loss?

Well everyone has their own comfort level on how much extra 'headroom' they wish to have when they looking to purchase a power supply. As more current capacity also usually means larger volume, it's a trade-off type decision. I like 25%-50% extra current capacity so I would be looking for say 6 to 8 range for a 5 amp continuous load. Have you considered using a PC power supply as they are very cheap (usually free from salvaging old PCs) and have lots of 12vdc current capacity?

Lefty

That's fair enough and makes sense I guess as it also allows for human math error, and future expansions! As for the PC power supply, could you show an example as I am concerned about the size of the for my project and I am really keen on this one (http://www.ebay.co.uk/itm/AC-100-240V-to-DC-12V-Switching-Power-Supply-Regulated-Transformer-for-LED-Light-/230844619265?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item35bf695a01&_uhb=1#ht_3557wt_1037).

Thanks again!

SamuelCB: That's fair enough and makes sense I guess as it also allows for human math error, and future expansions! As for the PC power supply, could you show an example as I am concerned about the size of the for my project and I am really keen on this one (http://www.ebay.co.uk/itm/AC-100-240V-to-DC-12V-Switching-Power-Supply-Regulated-Transformer-for-LED-Light-/230844619265?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item35bf695a01&_uhb=1#ht_3557wt_1037).

Thanks again!