12 volt power supply now putting our 45 volts??
Joe Collins
My son has a plug-in 12 volt DC power supply that was bought at Radio
Shack sometime ago. Its rated at 12 volts at 1.75amp.
We used it again recently and I noticed the sparks a bit intense.
I measured it with a cheap voltmeter ($12) and it indicated 45 volts!
This could happen with a short within the transformer. But it also
has a thermal reset to prevent overheating of the transformer.
We are now using this power supply to build a simple relay drived
burglar alarm. The alarm is acting a little weird, tripping when it
shouldn't. - the relays are rated at 12vdc but not 40+ volts.
Any thoughts if this power supply is truly putting out 45volts
or should I use a more reliable vom?
Thanks in advance....
HAR...@slacvm.slac.stanford.edu
is not drawing current the voltage goes to the level of its source.
Try plugging it in a looking at the voltage at the input to your circuit.
Harold
Tony stewart
Your supply sounds like it is broken or unregulated like a battery
charger. If the latter, then try using a light bulb for a load, then get
a resister. All transformers run high at no (or small) loads since they
have a voltage rating at full current and are usually conservative. But
you should expect 20Vdc. It could be you need a 2nd opinion on the
voltage. If a 12volt light bulb pops (and it most definitely will at 40V)
then you can use a 3 terminal regulator or better still a better wall
plug voltage regulator/power supply. THey should be cheap. <$10 12V
300ma.
di...@inqmind.bison.mb.ca
The Inquiring Mind BBS, Winnipeg, Manitoba 204 488-1607
Baden de Bari
> I measured it with a cheap voltmeter ($12) and it indicated 45 volts!
>
I think I can solve your problem: The power adapter probably has
a voltage regulator (probably a 7812). It could be that the regulator
is *BLOWN* which would result in you getting the initial output voltage
from the transformer, so I take it it's a stepdown from 112v(whatever) to
45v, correct?... and the 45v's is what you're getting out of it.
As for powering your burglar alarm with it, I wouldn't recomend
it, since you COULD blow that TOO!!!... bad idea.
>>Baden<<
Mr M J Brown
> I think I can solve your problem: The power adapter probably has
>a voltage regulator (probably a 7812). It could be that the regulator
>is *BLOWN* which would result in you getting the initial output voltage
>from the transformer, so I take it it's a stepdown from 112v(whatever) to
>45v, correct?... and the 45v's is what you're getting out of it.
Yes...but there must be something else wrong here too....45volts into a 7812
would make it overheat, it is well past the manufacturers recommended input
voltage....
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_/_/ _/_/ _/ _/_/ _/ | Michael Brown
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_/ _/ _/ _/_/ _/ | cst...@csv.warwick.ac.uk
_/ _/ _/ _/ _/ _/_/_/_/ _/ | m...@dcs.warwick.ac.uk
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