Eddy current dyno

[Jocke]

Just out of curiosity, how big an AC engine would you need to break a 700Hp BB Chevy ?

[bruce]

700hp at what RPM?

From my experience when you start specing out dyno parts you need to know torque and rpm numbers not HP figures HP figures without rpm's means nothing. HP is mearly a calculation of torque x rpm/5252. My eddy current unit is rated for 280 lbs ft at 8000 rpm max and its about 14" so I would guess it would be a very large AC motor that would be required?

[84-1074663779]

The problem with any eddy current machine is that the available braking torque falls off with falling rpm. It is not like a handbrake where you can actually lock the rotors solid at zero speed.

For a certain level of dc excitation, it takes more and more torque to turn it as the rpm rises, that is how it can maintain a relatively fixed engine Rpm under load.

For lots of torque sinking at low Rpm, as you might require on a chassis dyno, larger diameter brake rotors are going to be needed. Power has to do more with heat dissipation, or how hot is it going to get at that power level.

There is no simple answer to what size, but a torque figure needs to be stated at what Rpm, and power also comes into it as well.

Braking 100 Ft/lb at 8,000 Rpm is not a lot of torque, braking 1,000 Ft/lb of torque at 800Rpm would require a much larger machine, even though both horsepowers would be identical.