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Discuss Voltage Converter (basic question!) in the Industrial Electrician Talk area at ElectriciansForums.net

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CKsam

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Hello,

Just a quick question. I've got a slide projector which takes specialist 100W projector bulbs (A1/21). To cut a long story short, the 115V version of the bulb is cheap as chips (I got 6 for £5) where-as the 240V version is between £15 and £30.

The question is this. Am I OK getting a step-down converter rated at 100W or should is it good practice to have a little bit of room at the top and go for 150W or 200W? If anybody knows any cheap sources that'd be helpful too. Otherwise I'm ordering from Hong Kong on ebay...

Many thanks,

Sam
 
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S

Spudmiester

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  • #2
Can see where you are going and its not a bad idea, however, is the lamp all that is in this unit, or are there any electronics or motors etc.
If there is electronics and other stuff then I would leave it as it is, as the electronics will have been designed to work at 240v via an internal transformer and swapping the lamp to 115 and trying to run the whole thing off a step down transformer will mean the lamp will work and the rest of it wont, and may even be damaged in the process.

If it is just basically a bulb in a box then the tranformer idea will work.
 
C

CKsam

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  • #3
Thanks for the reply. It's a really old manual projector and is really just a bulb in a box, so there are no other components to worry about. I was just worried about using a 100W bulb with a transformer rated at 100W (do they rate it so that 100W is perfectly safe, or is that the very top limit?). In the end I decided to pay a couple more pounds and order a 200W transformer which should make sure there are no burn-out issues ahead...

Thanks for the help!
 
R

rumrunner

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  • #4
Hi
You should have been ok with the 100w one ,if it was a "quality" unit but i think you have done the right thing and gone for the larger one
good luck
 
C

CKsam

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  • #5
Thanks!

The transformer arrived today, and everything seems to be working perfectly. It should all pay off nicely in the long run. Damn those expensive UK bulbs...

Ta for the help.

Sam


EDIT EDIT EDIT

Well that was short lived!

On using the transformer yesterday evening it worked for about 30 minutes before two large POP sounds, a smell of burning and small amounts of smoke came from the unit. Some of the plastic has melted as well. I was only using it with the bulb rated at 115V, 100W - well below the 200W rating. I'd measured the output voltage from the box which was about 122V. So I guess the bulb may have been giving an ouput of more like 115W, but still.

Did I just get a dodgy transformer, or is there something I've missed here?
 
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ian.settle1

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Mentor
Arms
To use at 110v with same wattage means twice the amount of current:rolleyes: if cable is not rated for it cable will start to melt.:eek:
 
C

CKsam

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  • #7
Good point... I hadn't thought about the cable. I don't think there any signs that this had been damaged though, so it'll probably be OK. It seemed to be just the transformer that had overheated and burnt out.

I've read up: it seems like some transformers OK with continuous usage (15 mins or more) where-as others are not. I'm guessing this fell into the latter category, although there was no warning about that.
 
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S

shikun.qian

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  • #8
my english is so poor ,can not understand the meaning. what is "specialist 100W projector bulbs (A1/21)." and what is converter?inverter ?
 

ian.settle1

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Mentor
Arms
Good point... I hadn't thought about the cable. I don't think there any signs that this had been damaged though, so it'll probably be OK. It seemed to be just the transformer that had overheated and burnt out.

I've read up: it seems like some transformers OK with continuous usage (15 mins or more) where-as others are not. I'm guessing this fell into the latter category, although there was no warning about that.
When and if you order a new tranny check that it is continuouis rated one:rolleyes:
 
C

CKsam

  • Thread Starter Thread Starter
  • #10
my english is so poor ,can not understand the meaning. what is "specialist 100W projector bulbs (A1/21)." and what is converter?inverter ?
I have this projector: Minolta Mini 35

which needs this bulb: A1/21 bulb

The "converter" is a 220/240V -> 110/120V transformer so that I can instead use a 115V version of the bulb.

Hope that's clear!

When and if you order a new tranny check that it is continuouis rated one:rolleyes:
Will do! I just wonder whether I can get my money back on the last one...
 
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R

rumrunner

  • Thread Starter Thread Starter
  • #11
Hi
you could always make a resistor,it will get hot but you could use an old electric fire element refactory tube,buy some brightray resistance wire and wind the wire around and then put it in a glass bottle. nice little project ,better than paying out all that dosh for those trannys
enjoy yourself
 
C

CKsam

  • Thread Starter Thread Starter
  • #12
I'd end up with some kind of 100W heater that way! Nice for the winter perhaps...

That's given me another thought, though. I've actually got two of these projectors. Perhaps I should run them in series at all times... double projection! No transformers needed then. I might give that a go, for fun.
 
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