Surge Scientific · Model OHS-20D
Overhead Laboratory Stirrer
20 Liter · 20 N·cm Torque
Brushless DC Motor · 50–2000 RPM · Stepless 10 RPM Increment · ±1% Speed Accuracy · Dual Voltage
Most overhead stirrers promise constant speed, then give it up the moment viscosity changes — forcing you to babysit the knob as an emulsion thickens or a polymer sets. The OHS-20D holds your setpoint across the full viscosity curve with a closed-loop brushless DC motor, and if something jams or overheats, an independent overload circuit stops the shaft before the motor — or the sample — takes damage.
Why Constant Speed Under Load Matters
Budget overhead stirrers use open-loop speed control — set the RPM, cross your fingers, watch the number sag as the sample thickens. The problem shows up exactly when you can't afford it: an emulsion breaking because shear dropped mid-run, a polymer reaction stalling because the bulk never fully mixed, a dissolution study losing reproducibility because the impeller slowed as the matrix formed.
The OHS-20D uses a closed-loop brushless DC motor that measures actual shaft speed in real time and pushes more current when viscosity climbs — delivering the same RPM from water-thin to 1,000 mPa·s. The display alternates between set speed and actual speed so you can see the controller working, not just trust it.
Maintenance-Free BLDC Motor
Brushless DC drive with no wear components — no brushes to replace, no carbon dust in the lab, and a service life measured in years of continuous duty, not hours.
±1% Speed Accuracy
50–2000 RPM stepless in 10 RPM increments with closed-loop regulation. Reproducible day to day, sample to sample, viscosity to viscosity.
Multi-Layer Safety
Proprietary overload cutoff if torque exceeds rating, independent over-temperature protection, and an audible alarm with four coded fault states for instant diagnosis.
Through-Shaft Design
Height-adjustable impeller slides through the motor housing — swap samples without re-leveling the stand, and position the blade exactly where the vortex needs it.
"20 N·cm of torque, held flat across the viscosity curve." — Rated for samples up to 1,000 mPa·s and batch volumes up to 20 liters of water-equivalent. The BLDC controller doesn't slow down when your sample resists.
Key Features
- Max torque 20 N·cm at the shaft
- Max batch volume 20 L (water)
- Max viscosity 1,000 mPa·s
- Speed range 50–2000 RPM
- Stepless 10 RPM increment
- ±1% speed accuracy (closed loop)
- Bright LED display — set and actual speed alternating
- Maintenance-free brushless DC motor
- Through-shaft housing — adjustable impeller height
- 0.5–10 mm keyed clamping chuck
- Overload torque cutoff circuit
- Independent over-temperature protection
- Motor protection circuit
- Four fault codes with audible alarm
- Large knob — push to start / stop, turn to set speed
- IP42 dust and splash protection per DIN EN 60529
- Dual voltage: 100–240V, 50/60 Hz
- 60 W max output power
- Compact 71 × 174 × 240 mm drive head
- 2.3 kg head weight — easy to reposition
Ideal Applications
Emulsions & Suspensions
Oil-in-water and water-in-oil mixing at constant shear, even as droplet size and viscosity evolve through the run.
Polymer & Formulation
Polymer synthesis, resin blending, and formulation development where setpoint drift ruins reproducibility.
QC & Dissolution
Pharmaceutical dissolution, food and cosmetic formulation, and any protocol demanding audit-ready mixing consistency.
What's in the Box
Every OHS-20D ships with the components needed to begin stirring — support stand, extension arm, chuck, and drive head. Impellers are sold separately to match your sample's viscosity and geometry.
Technical Specifications
| Parameter | Specification |
|---|---|
| Model / SKU | OHS-20D |
| Max Torque at Shaft | 20 N·cm |
| Max Stirring Quantity | 20 L (H₂O) |
| Max Viscosity | 1,000 mPa·s |
| Speed Range (Normal Load) | 0 / 50–2000 RPM |
| Speed Increment | Stepless, 10 RPM |
| Speed Accuracy | ±1% |
| Motor Type | Brushless DC, maintenance-free |
| Max Output Power | 60 W |
| Rated Power | 65 W |
| Display | LED — set / actual speed alternating |
| Clamping Chuck Range | 0.5–10 mm |
| Overload Protection | Yes |
| Motor Protection | Yes |
| Over-Temperature Protection | Yes |
| Ingress Protection | IP42 (per DIN EN 60529) |
| Permissible Ambient Temp | 5–40°C |
| Permissible Relative Humidity | ≤ 80% |
| Voltage / Frequency | 100–240V, 50/60 Hz |
| Dimensions (D × W × H) | 71 × 174 × 240 mm (without extension arm) |
| Weight | 2.3 kg (with extension arm and chuck) |
Surge Scientific Warranty & Support
This instrument is sold through Surge Scientific, your trusted laboratory equipment partner. Our product specialists are available Monday–Friday for assistance. The OHS-20D is backed by a 2-year all-inclusive manufacturer's warranty. Contact us at info@surgescientific.com or reach out directly to our support team at 855.943.3344 for pre-sales questions, impeller selection, quotes, and technical assistance.