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Variable Transformer by Staco Energy Products Model 3PN1210B Variac - $150 (San Marcos (Pioneer)
120 N. Pacific St., Suite L-6 near Descanso
condition:
like new
make / manufacturer:
Staco Energy Products
model name / number:
3PN1210B
size / dimensions:
7 x 5 x 5.5
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Basic Description
A Variac (variable autotransformer) is essentially a single-coil transformer with a movable contact. Turning the knob moves a carbon brush along the winding so you tap the coil at different points, giving you a continuously adjustable AC voltage rather than fixed steps.
The 3PN1210B is a portable, enclosed model with a power cord, switch, fuse, and outlet so you can plug equipment directly into it.
Main Specifications
Electrical
Input voltage: 120 VAC, single-phase
Frequency: 60 Hz (also usable up to ~400 Hz)
Output voltage: 0–120 VAC adjustable
Maximum current: 12 A
Power rating: ~1.44 kVA
Physical
Size: approx 6.96 × 4.62 × 5.5 in
Weight: about 12 lb
Bench portable enclosure with knob and scale dial.
Built-in features
Steel case enclosure
Power cord and plug
Output receptacle (standard outlet)
Lighted ON/OFF switch
Output fuse protection
What It Is Used For
A Variac like this is commonly used when you need precise control of AC voltage.
Typical uses:
1. Electronics testing
Slowly bring up voltage on equipment being repaired
Prevent damage when powering unknown devices
2. Equipment burn-in or stress testing
Run motors, heaters, or electronics at reduced voltage
3. Laboratory power source
Simulate low-line or high-line voltage conditions
4. Lighting and heating control
Adjust brightness of incandescent lights
Control power to resistive heaters
5. Troubleshooting
Safely power old electronics (radios, amplifiers) while monitoring current.
How It Works (Concept)
Inside the device is a toroidal transformer coil. A rotating brush taps the winding at different points:
Dial at 0% → ~0 volts output
Dial at 50% → ~60 volts output
Dial at 100% → ~120 volts output
Because it is an autotransformer, input and output share the same winding, which makes it efficient and compact.
✅ In simple terms:
This device is basically a variable AC power outlet that lets you smoothly dial voltage from 0 to full line voltage at up to 12 amps.
If you want, I can also show you:
How the internal coil and sliding contact work (diagram)
Typical resale value on eBay or surplus markets
How to safely wire one for a test bench (important with Variacs).