Absorber Comparison


View charts that explain the advantages of various configurations.

Basics | 09.28.20

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.

FeatureWater Brake AbsorbersInertia
Rollers
Air-Cooled Eddy Current
Absorbers
Liquid-Cooled Eddy Current
Absorbers
Friction BrakesHydraulic PumpsAC Motor- GeneratorsDC Motor- Generators
High Hp (steady state) capacity?Excellentn/a*GoodExcellentPoor
(cooling required
Fair
(cooler required
GoodFair
High RPM capability?Excellentn/aFairExcellentGoodPoorFairPoor
Low RPM torque
(steady state) capacity?
Fairn/a*Very GoodVery GoodExcellentExcellentExcellentExcellent
Stall torque
(0 RPM range)
test capability?
PoorFair
(startup only)
PoorPoorVery GoodVery GoodExcellent
(with encoder)
Excellent
(with encoder)
Stability of
RPM load control?
Goodn/a*Very GoodVery GoodPoorVery GoodExcellentVery 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?Goodn/a*ExcellentExcellentFairNot typically availableExcellentExcellent
Motoring capability?requires separate motorrequires separate motorrequires separate motorrequires separate motorrequires separate motorrequires separate motorExcellentExcellent
Suitability to long duration testing?Excellentn/a*FairExcellentFair
(water cooled)
Good
(with cooler)
ExcellentGood
Ease of engine starting?requires separate starterrequires separate starterrequires separate starterrequires separate starterrequires separate starterrequires separate starterExcellentExcellent
Hp capacity
vs. weight?
ExcellentPoorFairFairFairFairPoorPoor
Hp capacity
vs. size?
ExcellentExcellentFairGoodGoodGoodFairPoor
Portability of
absorption unit
ExcellentDetermined by weightFairPoorFairGoodPoorPoor
RPM, Torque, &  Hp Accuracy?Determined by Data AcquisitionDetermined by Data AcquisitionDetermined by Data AcquisitionDetermined by Data AcquisitionDetermined by Data AcquisitionDetermined by Data AcquisitionDetermined by Data AcquisitionDetermined by Data Acquisition
Data Repeatability?Determined by Data AcquisitionDetermined by Data AcquisitionDetermined by Data AcquisitionDetermined by Data AcquisitionDetermined by Data AcquisitionDetermined by Data AcquisitionDetermined by Data AcquisitionDetermined by Data Acquisition
Resistance to hysteresis (breakaway friction)GoodExcellentVery GoodVery GoodGoodPoorVery GoodGood
Immunity to un-trunioned parasitic drag lossesExcellent
(if mounted directly)
PoorGoodExcellentGoodFairExcellent
(with in-line transducer)
Excellent
(with in-line transducer)
Affordability per Hp
(steady state) capacity?
Excellentn/a*GoodFairFairFairPoorPoor
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?ExcellentExcellentExcellentVery GoodFairGoodExcellentGood

*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).

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