Wall Wart Voltage

Hi,
I've just got a Crust Crawler 6 DOF and having searched through my collection of wall warts I found one with 7.5VDC 2.5A on the case. Long
story short, I went to test the voltage on the jack and I'm reading just over 12V. Any reason for this difference?
I'm assuming that it's not safe to power the arm with.......
TIA,
Michael
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Michael wrote:

It's an unregulated supply. If it is designed to supply up to 2.5A and you're only drawing a few uAs the voltage is going to be a LOT higher than rated, though I have to say >12v sounds a little slack. If you're nervous about the voltage set up a voltage regulator.
- -- Brendan Gillatt brendan brendangillatt co uk http://www.brendangillatt.co.uk PGP Key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xBACD7433 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (MingW32)
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Brendan Gillatt wrote:

Or try loading it slightly - 10Kohm across them and I normally find they drop to a fairly acceptable level.
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Coyoteboy wrote:

I think that is most likely to work with a switching regulator style wall-wart. If it is big/heavy, it is likely to have just a transformer and rectifier inside and relies on the rated current to drag the voltage down to the rated value.
Pete
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If there are spikes that might do something. You need a 3 ohm resistor to get 2.5 amps. Figure up to a 30% voltage increase on a normally cheapo supply. A good unregulated supply can get a 10-15% regulation. Regulated packs are so cheap and reliable, and low RF noise, that I buy them from Jameco all the time.
greg
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