Pick the best style dynamometer for your application! Each type of configuration has its own strengths and weaknesses. The chart below attempts to point out some of the more significant differences.
Custom hybrid configurations using a combination of both an AC Motor/Generator and Eddy-Current (or water brake) absorber can provide the unique characteristics of each – in a single installation. This means it is practical to have instantaneous control, stability, motoring capability, and high power absorption that would be otherwise unaffordable (or impossible) to duplicate. Control of the pair is done using DYNO-MAX “Pro” software. In very high Hp installations it is possible to reduce, significantly, both the dynamometer’s cost and inertia via this method.
| Feature | Water Brake Absorbers | Inertia Rollers | Air-Cooled Eddy Current Absorbers | Liquid-Cooled Eddy Current Absorbers | Friction Brakes | Hydraulic Pumps | AC Motor- Generators | DC Motor- Generators |
| High Hp (steady state) capacity? | Excellent | n/a* | Good | Excellent | Poor (cooling required | Fair (cooler required | Good | Fair |
| High RPM capability? | Excellent | n/a | Fair | Excellent | Good | Poor | Fair | Poor |
| Low RPM torque (steady state) capacity? | Fair | n/a* | Very Good | Very Good | Excellent | Excellent | Excellent | Excellent |
| Stall torque (0 RPM range) test capability? | Poor | Fair (startup only) | Poor | Poor | Very Good | Very Good | Excellent (with encoder) | Excellent (with encoder) |
| Stability of RPM load control? | Good | n/a* | Very Good | Very Good | Poor | Very Good | Excellent | Very Good |
| Typical response time to 90% load change? | Good (less than 0.5 seconds) | n/a* | Very Good (less than 0.1 seconds) | Very Good (less than 0.1 seconds) | Poor (less than 1.0 seconds) | Fair (less than 0.75 seconds) | Excellent (less than 0.01 seconds) | Excellent (less than 0.01 seconds) |
| Testing simulation under computer control? | Good | n/a* | Excellent | Excellent | Fair | Not typically available | Excellent | Excellent |
| Motoring capability? | requires separate motor | requires separate motor | requires separate motor | requires separate motor | requires separate motor | requires separate motor | Excellent | Excellent |
| Suitability to long duration testing? | Excellent | n/a* | Fair | Excellent | Fair (water cooled) | Good (with cooler) | Excellent | Good |
| Ease of engine starting? | requires separate starter | requires separate starter | requires separate starter | requires separate starter | requires separate starter | requires separate starter | Excellent | Excellent |
| Hp capacity vs. weight? | Excellent | Poor | Fair | Fair | Fair | Fair | Poor | Poor |
| Hp capacity vs. size? | Excellent | Excellent | Fair | Good | Good | Good | Fair | Poor |
| Portability of absorption unit | Excellent | Determined by weight | Fair | Poor | Fair | Good | Poor | Poor |
| RPM, Torque, & Hp Accuracy? | Determined by Data Acquisition | Determined by Data Acquisition | Determined by Data Acquisition | Determined by Data Acquisition | Determined by Data Acquisition | Determined by Data Acquisition | Determined by Data Acquisition | Determined by Data Acquisition |
| Data Repeatability? | Determined by Data Acquisition | Determined by Data Acquisition | Determined by Data Acquisition | Determined by Data Acquisition | Determined by Data Acquisition | Determined by Data Acquisition | Determined by Data Acquisition | Determined by Data Acquisition |
| Resistance to hysteresis (breakaway friction) | Good | Excellent | Very Good | Very Good | Good | Poor | Very Good | Good |
| Immunity to un-trunioned parasitic drag losses | Excellent (if mounted directly) | Poor | Good | Excellent | Good | Fair | Excellent (with in-line transducer) | Excellent (with in-line transducer) |
| Affordability per Hp (steady state) capacity? | Excellent | n/a* | Good | Fair | Fair | Fair | Poor | Poor |
| Installation affordability? | Excellent (if water is available) | Fair (if pit or lift required) | Very Good (115v AC required) | Good (115v AC required) | Good (but cooler required) | Good (but cooler required) | Fair (electrician required) | Fair (electrician required) |
| Affordability of maintenance? | Excellent | Excellent | Excellent | Very Good | Fair | Good | Excellent | Good |
*n/a – not applicable, inertia-only “dynos” can not directly measure torque or maintain a steady state load (without also being equipped with some form of absorber and load cell or a parasitic drag source (e.g. a large fan or pump with a known loss curve).
