Dynamometer Absorber Comparisons

Feature	*Water Brake Absorbers*	Inertia Rollers	Inertia+ Parasitic Fan/Pump	Eddy Current Absorbers	*Friction* *Brakes*	*Hydraulic Pumps*	*AC Motor- Generators*	*DC Motor- Generators*
High Hp (steady state) capacity?	Excellent	n/a*	Fair (depends on fan size)	Good	Poor (cooling required	Fair (cooler required	Good	Fair
High RPM capability?	Excellent	n/a	Fair (fan limited)	Fair	Good	Poor	Fair	Poor
Low RPM torque (steady state) capacity?	Fair	n/a*	Poor	Very Good	Excellent	Excellent	Excellent	Excellent
Stall torque (0 RPM range) test capability?	Poor	Fair (startup only)	Fair (startup only)	Poor	Good	Good	Excellent (with encoder)	Excellent (with encoder)
Stability of RPM load control?	Good	n/a*	n/a* (exponential fixed curve)	Very Good	Poor	Fair	Excellent	Very Good
Typical response time to 90% load change?	Good (less than 0.5 seconds)	n/a*	n/a* (exponential fixed curve)	Very Good (less than 0.05 seconds)	Poor (less than 1.0 seconds)	Fair (less than 0.75 seconds)	Excellent (less than 0.005 seconds)	Very Good (less than 0.01 seconds)
Testing simulation under computer control?	Good	n/a*	n/a* (exponential fixed curve)	Excellent	Fair	Not typically available	Excellent	Very Good
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*	Excellent	Excellent(water cooled) Fair (air)	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	Poor	Fair	Fair	Fair	Poor	Poor
Hp capacity vs. size?	Excellent	Excellent	Excellent	Fair	Good	Good	Fair	Poor
Portability of absorption unit	Excellent	Determined by weight	Determined by weight	Fair	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	Excellent	Very Good	Good	Poor	Very Good	Good
Immunity to un-trunioned parasitic drag losses	Excellent (if mounted directly)	Poor	Poor	Good	Good	Fair	Excellent (with in-line transducer)	Excellent (with in-line transducer)
Affordability per Hp (steady state) capacity?	Excellent	n/a*	Fair	Good	Fair	Fair	Poor	Poor
Installation affordability?	Excellent (if water is available)	Fair (if pit or lift required)	Fair (if pit or lift required)	Very Good (115v AC required)	Good (but cooler required)	Good (but cooler required)	Good (electrician required)	Good (electrician required)
Affordability of maintenance?	Excellent	Excellent	Excellent	Excellent	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). © 4/18/2004

Dynamometer Absorber Comparisons

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