# An Absent Amp

Discussion in 'Electronic Basics' started by Randy Gross, Aug 27, 2003.

1. ### Randy GrossGuest

I got curious last night while trying to determine the number of turns in a
trannys' primary.

Primary volts 120vac 60Hz, no load current is 2.38A.

I put a one turn winding in the secondary to determine volts per turn.

Secondary volts 1.8, current .22A under an 8.8 Ohm load. Primary current
rose to 2.51A.

Then (out of curiosity) I put a second one turn winding in parallel with
the first.

Secondary volts 1.8 (expected), current remained .22A under the 8.8 Ohm
load, however, primary current rose to 2.58A, the only appreciable
difference.

I realize that by winding the secondary turns in parallel, this reduced the
resistance of the windings (equal lengths of 18 awg.) by, I *assume* half,
I expected a slight increase in current from the secondary.

The parallel winding reduced the impedance of the primary. Why?

2. ### John PopelishGuest

Did you measure the secondary current to the same 3 digits of
precision that you measured the primary current? In other words, is
the 1.8 amperes actually 1.80 amperes?

3. ### Randy GrossGuest

I ran the test again using a 1.2 Ohm resistor as the load. The 1.8vac held
for the single and parallel measurements.

Secondary amps held at 1.83A for both the single and parallel measurements.

The primary amps were all over the place. I have given an average of 2.83
for single turn, and 2.98 for parallel, however these are suspect. There
are so many items plugged into the circuits, stabilizing the reading was a
......!

Still, it seems the only thing affected by the parallel secondary, is the
impedance of the primary, but to what end?

Randy Gross

<[email protected]>...
: My DVM is an electricians model with a vac scale starting at 200vac, 1
: decimal place, amps to 2 places.
:
: I'll have to raise these values to get the gist. Curiosity in charge now.
: I'll be back.;-)
:
: Randy Gross
:
: <>...
: : Randy Gross wrote:
: : >
: : > I got curious last night while trying to determine the number of
turns
: in a
: : > trannys' primary.
: : >
: : > Primary volts 120vac 60Hz, no load current is 2.38A.
: : >
: : > I put a one turn winding in the secondary to determine volts per
turn.
: : >
: : > Secondary volts 1.8, current .22A under an 8.8 Ohm load.
: Primary current
: : > rose to 2.51A.
: : >
: : > Then (out of curiosity) I put a second one turn winding in parallel
: with
: : > the first.
: : >
: : > Secondary volts 1.8 (expected), current remained .22A under
the
: 8.8 Ohm
: : > load, however, primary current rose to 2.58A, the only appreciable
: : > difference.
: : >
: : > I realize that by winding the secondary turns in parallel, this
reduced
: the
: : > resistance of the windings (equal lengths of 18 awg.) by, I *assume*
: half,
: : > I expected a slight increase in current from the secondary.
: : >
: : > The parallel winding reduced the impedance of the primary. Why?
: :
: : Did you measure the secondary current to the same 3 digits of
: : precision that you measured the primary current? In other words, is
: : the 1.8 amperes actually 1.80 amperes?
: :
: :
: :
: :
: : --
: : John Popelish
: :
:

4. ### Randy GrossGuest

From this exercise, I can see that there is no advantage to having a
parallel secondary (power wise) except to increase the current carrying
capability of the secondary winding.

Thanks

Randy

5. ### Mark ZenierGuest

If your two secondary windings aren't producing indentical voltage,
paralleling them will act like a shorted turn, or part of a shorted turn.
The only thing limiting the current is the resistance of these windings
and the low voltage of the difference.

Hook them up in series with one winding reversed in phase and