I have recently aquired an old Allen Electric Type E30 armature tester.
It's a simple device but I suspect the wiring has been tampered
with/modified. Does anyone know the wiring of these devices? Tnx Jim
H.
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If it's an old-fashioned 'growler' like what I'm thinking, the wiring is
very simple. The winding at the base of the unit is simply connected across
the line to create a nice alternating magnetic field on the pole pieces.
When the armature is set on in the pole pieces, you slowly shift it around.
If at some point the noise of the thing increases (that is, it 'growls' at
you), you've found a shorted winding (the shorted winding acts like a
shorted secondary winding in a transformer and the primary winding is the
growler's. Shorted turns make the current a lot stronger in the primary and
the stronger magnetic field causes the rotor iron to vibrate on the pole
pieces)
Laying a light piece of steel along the slot on top of the rotor as you turn
it can help you find which slots have the shorted turn.
You can also use a meter or low-voltage lightbulb with a couple of leads to
test each circuit on the commutator to look for opens.
Hope this helps
daestrom
In a generator rebuild shop we used a hacksaw blade both to check for
shorted windings and to check for opens by shorting the edge of the
commutator bars and observing the spark intensity.
Note that the growler will rapidly overheat if energized without an
armature in place.
Don Young
Yes, I know essentially how they are used. The existing wiring has two
probes wired directly to the 120V line (not even to the cold side of the
switch!!!) and a 40 watt bulb is simply wired across the switched line (in
parallel with the coil). I suspect the probes are meant to be wired only
to the bulb with no connection to the 120V line. That's the way I'm
rewiring it -- before I get electrocuted ! Jim H.
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A 120 volt test light was often provided for testing the armature for
grounded windings. It was wired in series with the probes so that continuity
between the probes would light the bulb. It was definitely a hazardous
arrangement but those who used them knew to keep away from any contact with
the probes. No matter which side of the line the probes were in, one of them
was hot to ground. If in the neutral side one probe was hot thru the bulb
and would pass enough current to be dangerous.
Those were the days of live front switchboards using knife switches and such
things. People had great respect for the dangers of electricity but
accidents did happen. In order to be safe your test light needs to be
operated from a low voltage transformer and use a low voltage bulb and/or be
energized from a GFCI outlet.
Don Young
OK, Don. Yes, that would have been a dangerous shorts tester. If the
purpose was a shorts tester I can do that with an ohmmeter. I thought
perhaps the bulb would indicate voltage being induced in the windings. I
am familiar with everything you say having retired from an
Electrical/Engineering position (but without a degree). I now have it
rewired.
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The particular subject under discussion was a tester to detect shorts from
windings to the armature frame, not turn-to-turn shorts. An ohmmeter will do
this. The 120V test lamp might be better or worse at detecting partial
high-resistance shorts but either will do a satisfactory job in most cases.
The sequence we used was check for grounded windings first, then for shorted
turns using the hacksaw blade and growler, then for open windings or
commutator joints using the growler and shorting the commutator bars to
check for equal spark intensity. Some growlers did have ammeters connected
to a two prong probe to use instead shorting the commutator bars. A low
voltage bulb might work for this but I never used one.
Don Young
Thanks gentlemen. No, I wouldn't even try to find shorted turns with an
ohmmeter -- would use to look for short to armature structure. If the
windings were 18 guage (just to pick a wire gauge) the resistance would
only be about 6.5 milliohms per foot. Low resistance measurements are
difficult. Even moderately low resistance measurements require a 4-wire
instrument for accuracy. Jim H.
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