Replacement Transformer Question


  #1  
Old 01-28-05, 12:30 PM
BuzzHazzard
Visiting Guest
Posts: n/a
Replacement Transformer Question

A desk lamp stopped working and it appears the transformer failed. It's about12 years old.

INPUT: AC 120V 60Hz 0.46A
OUTPUT: AC 12V
50W max (bulb I assume)

The replacement transformers I find are all rated in milliamps on the secondary, so how big a transformer do I need?

Another transformer (different project) I have is rated at 120VAC and 9.5W on the primary, and 12VDC and 500mA on the secondary.

I can't get the numbers to add up. Someone please refresh my memory.

Thanks.
 
  #2  
Old 01-28-05, 05:06 PM
G
Member
Join Date: Oct 2004
Location: USA
Posts: 676
Upvotes: 0
Received 0 Upvotes on 0 Posts
maybe this will help.

120v / 12v = 10 ratio
10 x 0.46A = 4.6 amps secondary
4.6 amps x 12 volts = 55.2 watt
50 watts / 12 volts = 4.16 amps
You need about a 5amp transformer on the secondary output
5 amps x 12 volts = 60 watts.

0.46A = 460 milliamps
500 milliamps = 1/2 amp. = 0.5A
1000 ma = 1 amp.
 
  #3  
Old 01-28-05, 05:42 PM
J
Member
Join Date: Sep 2000
Location: United States
Posts: 17,733
Upvotes: 0
Received 1 Upvote on 1 Post
Unless you just love this lamp, a new lamp may be cheaper than a new transformer.
 
  #4  
Old 01-29-05, 08:07 AM
BuzzHazzard
Visiting Guest
Posts: n/a
Originally Posted by John Nelson
Unless you just love this lamp, a new lamp may be cheaper than a new transformer.
That's the way I'm leaning too. I did the same math as GWIZ, but figured I had to be making a mistake. The original transformer is only 2-1/2"h x 2"w x 1-3/4"h and pretty lightweight. Hard to believe it's a ~5 amp transformer.
 
  #5  
Old 01-30-05, 01:43 AM
G
Member
Join Date: Oct 2004
Location: USA
Posts: 676
Upvotes: 0
Received 0 Upvotes on 0 Posts
I agree the size is small for 5 amps
I think your bulb may have been 12 volts at 10 watts
using a 50 watt bulb would take out the transformer.
or its a 24 volt bulb
or a switching power supply.

If your sure the transformer is bad. try unwrapping the tape on the transformer look for a break in the wire.
most of the time the break is close to the leads soldered to the transformer.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: