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Simple question about transformers...

Alexizupinhea

Alexizupinhea

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I have a transformer that says it has a 4.5VDC, 400mA output. I was thinking about using it to power this: http://o-like.com/b2b_cpinfo.asp?id=966.

My question is, when I tested the voltage/polarity using a DMM, the voltage measured around 6.7V. Before I was worried that it would've been underpowered (4.5V), but now, I'm worried about blowing it out. So, do you think it would be safe to use this transformer (the circuit inside protects for all this), or no?
 





D

digital_blue

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Is this "transformer" a wall wart or an actual transformer? A 5vdc switching power supply is ideal...
 
lasersbee

lasersbee

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You have a standard non regulated Wall Wart adapter... the voltages indicated
are approximative...
You would be better off using a 5 Volt 500mA (min) Regulated Wall Wart similar
to this type....

http://cgi.ebay.ca/BRAND-NEW-5V-3A-AC-DC-Power-adapter-Power-supply-Well_W0QQitemZ3900565

Or this one...

http://cgi.ebay.ca/Adapter-Adaptor-Charger-AC-120-240-V-DC-5-V-2-A-3-5-mm_W0QQitemZ270404807334QQcmdZViewItemQQptZPDA_Accessories?hash=item3ef561eaa6&_trksid=p3286.c0.m14&_trkparms=65%3A2|66%3A3|39%3A1|240%3A1318|301%3A1|293%3A1|294%3A100


If the input is 100-240 VAC then it is probably a regulated switching supply and the output
will be very close to what is indicated on the label..

Jerry
 
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Alexizupinhea

Alexizupinhea

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That was a fast post lasersbee :), by the time I wrote my response to digital_blue, you've already typed that whole response (including links). Anyway, thanks for the input, and I think I understand now. So, I may order the one I posted above, plus tons of other stuff on their site (fixed shipping cost of $7). However, in the meantime... I just want to test it. So, would it be alright if I connected it to either: 1. The 5V rails of a ATX power supply (w/ a jumper to make it a "lab power supply" if people know what I mean), or 2. Connect it to a regular 5V USB line (they can power up to 500mA correct? This laser says it draws <350mA, so I'd think it should be safe.

Edit: If either is safe, I'll probably go with USB (unless someone believe's one choice is better than the other)
 
lasersbee

lasersbee

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Yeah... that will be good for other Higher Output current projects as well
That's a damn good price for almost 4 Amps of 5Volts...:cool:

Jerry
 
Alexizupinhea

Alexizupinhea

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Yeah, I know.. they're a great site. And also, thanks for all the help :). Also.. I'd hate to bother you again, but maybe someone else will answer it anyway... what exactly is the difference between a wallwart and a switching power supply? You said a switching power supply is more efficient/will be closer to labeled output... but can you tell just by looking at one?
 
Alexizupinhea

Alexizupinhea

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Meatball

Meatball

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your wall wart will work just fine, it unregulated, but the voltage will drop down to a much more ideal voltage once you put your load on it. This is very common transformer design.
 
rog8811

rog8811

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you can change it to DC with a diode
Click to expand...
2 diodes surely for half wave rectification.... 4 diodes for full rectification.... you should be able to use 1N4001 diodes as we all have loads of them:)

Regards rog8811
EDIT, as you were, I have just done some reading you can do it with one diode....Sorry ;)
 
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C

c4r0

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rog8811 said:
you should be able to use 1N4001 diodes as we all have loads of them:)
Click to expand...
This one is not suitable for it. It has only 50V reverse voltage whereas that power supply gives 3kV @ open circuit. Moreover, I believe that HeNe tube can behave like a capacitor on some conditions so there would be possibility of 6kV at the diode. And besided the voltage, the frequency is 30kHz so the 1N4xxx diodes are definitely too slow. I would suggest to use 6 x BA159 diodes in series for instance.
 
Benm

Benm

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Many (even regulated) wall wart transformers can give a somewhat high voltage when operated with no load at all. I suggest putting a 100 ohm resistor over the output and measuring again.
 
rog8811

rog8811

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This one is not suitable for it. It has only 50V reverse voltage whereas that power supply gives 3kV @ open circuit
Click to expand...
I missed the bit where we changed from 400ma to 3kva, I will get my coat....
Regards rog8811
 
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