# Spike!

Discussion in 'Electronic Basics' started by Randy Gross, Nov 11, 2004.

1. ### Randy GrossGuest

Greetings,

I read an article on a transformer test recently where the term
"spike" was used. I didn't give it much thought then but, It stuck in
my mind because the last few words in the article contained: "Be
careful when you turn it off, there's a huge spike..."

I recall discussions on Inductors and how they release thier energy
back toward the source but, in this case, once the circuit is broken,
how do the coil/coils discharge? Is the spike fired back into the
mains or into other circuits in the panel? Is this a source of
"Noise"?

Randy

2. ### John PopelishGuest

Any inductance has the following relationship between current and
voltage:

V=L*(di/dt) Or the voltage (volts) across the inductor is
proportional to the time rate of change of the current through it
(amps per second). The inductance (in henries is the constant of
proportionality. If a transformer or other inductor is connected to
an AC source, and happens to be switched off (I goes toward zero very
fast) at the moment when the current happened to be quite large, the
voltage produces can be very high. This is the spike they are talking
about. This is the same process used to produce sparks from an
ignition coil.

If you measure the resistance of a transformer with an ohm meter and
disconnect it while your fingers touch both sides of circuit break,
the transformer may produce enough voltage that the small current
built up by the ohm meter may be pushed through your fingers and give
you a small shock.

3. ### Randy GrossGuest

These are sobering statements. From knowledge gathered from this group
and books on basic electricity, I have reconfigured and tested many
transformers and overlooked one basic fact about them, they are
inductors and capable of delivering a vicious bite when they are
turned off. I've been lucky!!

I try to conduct all of my experiments safely, for myself and those
around me. What safeguards can I institute to guard against an
accidental encounter?

4. ### peterkenGuest

an acidental encounter is an accident, cannot always be avoided when
experimenting...
..... unless you begin building protetion circuits before experimenting, but
i wonder what real techie always does that
at least i've never seen one do it in over 24 years

These are sobering statements. From knowledge gathered from this group
and books on basic electricity, I have reconfigured and tested many
transformers and overlooked one basic fact about them, they are
inductors and capable of delivering a vicious bite when they are
turned off. I've been lucky!!

I try to conduct all of my experiments safely, for myself and those
around me. What safeguards can I institute to guard against an
accidental encounter?

5. ### Steve EvansGuest

don't work drunk; don't work tired. Keep one hand in your back pocket
at all times; eclectricy and water don't mix; don't stand in puddles;
low voltages at *high* currents are just as dangerous; remove all
metallic jewelry.... And more? I'm sure there are! Bring'em on...