need to find transformer amp rating

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rajesh1987

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hi

if one 12v/5w bulb need 0.416 amp means, if i need to connect 23 bulbs parallely means i need to multiply this amp with 23(no of bulbs) , if so i need to to get 12v/9amp transformer for 23 bulbs to connect parallely, is it correct?

or i need to get higher rating of amp..

regards
 

1. so i need to buy 9amps or higher amps

2. whether if i connect 23 bulbs parallely with 12v/ 9amp transformer means the brightness of bulb will get diminish ?

regards
 

An incandescent light bulb draws 10 times or more current when it is turned on then the current drops to its rating when the filament reaches 2000 degrees C.
So a 9A transformer with a 9A incandescent load might quickly burn out or the lights might never reach full brightness.

A cheap 12V/9A transformer might produce a much higher voltage (18V or more?) when it powers only one or a few light bulbs which makes them VERY bright. Then the voltage drops to 12V when 23 light bulbs are powered and they will have normal brightness.
A high quality 12V/9A transformer might produce 13V when one or a few light bulbs are powered and they will have almost normal brightness.
 

if you need no isolation you can go for a step up transformer it will be less since the transformed volt amp will be below 20W
 

So a 9A transformer with a 9A incandescent load might quickly burn out or the lights might never reach full brightness.
Click to expand...
It's quite normal to operate low voltage lamps with 12 or 24 V transformers up to their rated power, they surely don't burn out. Simply because the transformer's thermal time constant is at least in a minutes range. A fast 9A fuse would most likely blow, however.

The transformer's short circuit current must be sufficient high to overcome the cold filament inrush, but that's surely the case for a regular transformer.

if you need no isolation you can go for a step up transformer it will be less since the transformed volt amp will be below 20W
Click to expand...
Are you suggesting a lamp series circuit? Not a good idea, I think.
- high risk of unequal voltage share and fast lamp burnout
- no light at all if one lamps fails
 
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