Hi, I have heard different things about that. Some say it is fine to overrun the rpm limit, but it seems strange to me that they would put a limit and then it is safe to overrun. 

You can ask on the DIY Dyno forum on Facebook, maybe someone can give better answer!

Yes after reading and rechecking the datasheet 

AC82-45 max rpm 2800

AC82-70 max rpm 2800

AC83-00 max rpm 2100

AC83-31 max rpm 1700

All of these retarders have same physical dimension

Same rotor mass 88lb but differs with stator mass. All same inertia 2.92kgm

Posted by: @ehd-tuning

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Yes after reading and rechecking the datasheet 

AC82-45 max rpm 2800

AC82-70 max rpm 2800

AC83-00 max rpm 2100

AC83-31 max rpm 1700

All of these retarders have same physical dimension

Same rotor mass 88lb but differs with stator mass. All same inertia 2.92kgm

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Hi, very interesting, as you are already aware that those telma retarders share same components.The telma AC83-00 and telma AC82-70 share the same rotor size by weight 86kg/190lb and measures 500mm in diameter hence both have a rotor intertia 2.92kgm2/ 69ib-ft2 from the specs. The stators are different in weight 294kg/648lb and 247kg/544lb respectively. That is a difference of 47kg/104lb i would assume bigger coils ( as in more copper wire turns) to get greater holding force. I didn't check and compare coils was to lazy. But did notice telma AC83-00
runs rotor to stator clearance of 1.5mm and the other 1.2mm. Now the question is why can the telma AC82-70 be turned to 2800 rpm and the telma AC83-00 only to 2100 rpm maximum? Couldn't find out do they both share the same tapered needle bearings ? Is that the difference don't know. Sorry i couldn't contribute any insight into the LOW RPM speed for your hub_dyno build. But very interesting can you find out about the bearings being used all those telma retarders.

AC82-70 max rpm 2800

AC83-00 max rpm 2100

I will disassemble the Retarder and see the specs of the bearing and see if there any upgrade options

@ehd-tuning it may also be related to the rotor balancing spec. 

Somebody corrects me if im wrong , eddy current on rotation : if we apply constant current = constant magnetic force . so as rpm increase the opposing breaking force increases . all of this is internal forces acting in the Retarder .

So i assume that the Retarder AC83-00 if you max the current which max the internal forces in the retarder at 2100 rpm which is max rpm , so increasing the speed more will exceed the internal forces the Retarder can handle .

So by theory lowering the power or the current and increase the speed will not exceed the max internal forces in the Retarder .

been thinking about this in relation to mine, 

if the rotor to all intentes and pourposes is the same dimentions, mass and shape.  they are probally all the same and balanced to same spec  in terms of fast they arn't going round all that fast really so manufactuer should be abel to balance them plenty well enough for the highest speed easy enough. 

bearings  most bearings are good for quite high rpm looking through a few random skf ball bearing spec sheets with shaft sizes of 60 mm  and 85 mm ( larger bearings have lower max rpm  they are all over 5000 RPM for grease lube and higher for oil.

leads me to belive that the units with lower max rpm is not actually limited by the rotor itself so id happily take the rotor upto 2800 rpm

i'm thinking its going to be more a power issue

as the units get higher torque handeling capacity there max rpm drops so within reason i recon there more likely hitting the limite of what the rotor can handel power / heat wise.   

crowbar  max power  handeling  with figures pulled out of all over the place

ac 83 - 31 ( 2432 X 1700 ) / 5252  787 hp 

ac 83 - 00 (2211 x 2100) /  5252 =  884 hp

ac 82 - 70  (1990 x 2800)  / 5252 = 1060  hp

as max torque goes up  max rpm drop       but also dose its ablity to absorb power,  as the rotors are a bit fan like RPM is going to help with cooling so it makes sense to me that as RPM drop  maximum heat disapation also drops   i think the finer details of the ratings will be govened by regulation    they have to be abel to do it for so long ect,    so if you want to handel big torques RPM has to drop due to the power it has to dispate  but droping RPM  affects cooling to the point RPM has to be droped even more.   

thats my guestimation atm    feel free to pick holes in it

@ehd-tuning

Hey I emailed Telma about this exact retarder a while back and this was their response 

Hello Tom