8mm Forum: Calling Electricians

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Posted by Dino Everette (Member # 1378) on September 14, 2012, 01:00 AM:

OK I am getting myself confused on something...If you have a 5A transformer that is stepping down from 120v to 24v does that mean the total wattage it is capable of is 600w or 120w? [Confused]

Posted by Akshay Nanjangud (Member # 2828) on September 14, 2012, 01:45 AM:

Generally, the 5A is the output current. If this is the case, then the output voltage multiplied by the current would give us 120 W.

Posted by Martin Jones (Member # 1163) on September 14, 2012, 03:04 AM:

Confirmed....120W.

Posted by Steve Klare (Member # 12) on September 14, 2012, 08:15 AM:

Usually transformers are rated in Volt-Amperes (sort of like "Watts" but not exactly, it depends on what kind of load they are driving)

Is there a VA rating for this transfomer that you can see?

Posted by Dino Everette (Member # 1378) on September 14, 2012, 11:28 AM:

I am just trying to choose the proper transformer to power 24v 300w lamp..

Posted by Steve Klare (Member # 12) on September 14, 2012, 11:50 AM:

This character will do the job:

24VAC 400VA Transformer

It's capable of 400VA. You will use 300VA, but running power electronics flat out means they run hot, which means they won't last as long.

This is a dual primary and dual secondary transformer. To operate at 115VAC input you put the primaries in parrallel (To operate at 230, in series). For 24VAC you put the secondaries in parallel.(48 in series)

You’d need to put it in some sort of case, a pretty rugged one considering the weight of something like this (almost 10 Lbs.).

Posted by Manuel Tapia (Member # 3249) on September 14, 2012, 12:08 PM:

The transformer are quite expensive and big, look for a electronic transformer could be cheaper and small, if you are doing a lamp conversion, maybe you can try a 120V Lamp.

http://www.ebay.com/itm/EWG-120-VOLT-300-WATT-PROJECTOR-LAMP-PROJECTION-BULB-EIKI-16MM-120V-300W-/200750156928?pt=LH_DefaultDomain_0&hash=item2ebda44c80#ht_500wt_969

Posted by Steve Klare (Member # 12) on September 14, 2012, 12:24 PM:

Another transformer could be cheaper if for example you found one used, but it can't be too much lighter or smaller.

-as Scotty said:

"I canna change the laws of physics!"

You want it to run cool, which means fatter wiring and a heavy metal core.

-and you run cool or pretty soon you won't be running at all!

A 24V(dc) 300W electronic power supply runs $447 in single piece quantities:

300W 24VDC

(Old employer of mine, actually...)

and gives you the bonus of a fan whining in the background.

Power has gotten cheaper, but it still ain't cheap.

Posted by Dino Everette (Member # 1378) on September 14, 2012, 01:26 PM:

Steve what about something like this? It even looks like it has a built in fan.

24V 20A transformer

Posted by Steve Klare (Member # 12) on September 14, 2012, 02:40 PM:

It's a little generic Far-Eastern looking, but then again given the price I really doubt you can go too wrong with it, especially since you'll be running at a little more than half rated power.

Posted by Dino Everette (Member # 1378) on September 14, 2012, 03:36 PM:

OK I'm gonna give it a shot...thanks for the help Steve....

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