outrunner motor @ 10kw

[gwhy!]

I am wanting to test a controller @ 10kw+ with one of the big outrunners and want it loaded for about 10secs but the problem is loading the motor has anyone got any suggestions of a good/cheap way of doing this. If the motor was geared down enough do you think a motorcycle disc break/hub would be consistant enough to provide this amount of load without getting to hot... Thoughts

 

[Thud]

Just rig yourself a hand actuated brake system to load the motor. It could be as simlpe as mounting it on a bike & using the hand brake. or an in dependant set up for testing.

I asume you will be monitering amp draw to determine you kw output of the controller, so this is a simple set-up-
http://www.me.utexas.edu/~dsclab/labs/pmdc/pronybrake.html
take lotsa photo's or better yet a video.....Have fun,T

 

[gwhy!]

Im gonna need something a lot better that a push bike setup I have already tried that ... loads of smell and smoke and that was only 4kw, I have a old motorcycle wheel kicking around and a 4 pot caliper ( wish i had a twin disc wheel ) that may be better at getting rid of the heat, the voltage will be 50-60v so yes monitoring the current , I will take some vid when Im all setup and ready to go. The idea is to put the scope on the important signals when under this sort of load to try and work out what is going on with the hall/phase signals ( if anything ).

 

[jag]

How about a 2nd motor running as generator, then sink the power in some electric heaters or other resistive domestic electric appliance?

 

[gwhy!]

How about a 2nd motor running as generator, then sink the power in some electric heaters or other resistive domestic electric appliance?

That will be a much better way of doing it but It will have to be a hefty motor to produce 10kw, that I dont have I will be looking out for one thou ( kerbside) or may be even a car wheel hub that should be better to get rid of the heat even better with a wheel attached.

 

[jag]

How about a 2nd motor running as generator, then sink the power in some electric heaters or other resistive domestic electric appliance?

That will be a much better way of doing it but It will have to be a hefty motor to produce 10kw, that I dont have I will be looking out for one thou ( kerbside) or may be even a car wheel hub that should be better to get rid of the heat even better with a wheel attached.

You just need to get a second 10kW outrunner for the test. Then you can build a dual drive bike!

Cheaper possibilities from recycled equipment:
Car alternators: Take current directly off windings, bypassing diodes. Usually rated at 1-2kW, but can probably take more for short durations.
Bus or truck alternator.
Appliance motor: Usually need some rewiring to separate stator and rotor windings (so you can induce a magnetic field like in an alternator). Lots of agricultural and industrial equipment have 10+kW motors. Larger washing machines may have 1+kW motors. Not all motors will like the 4000-6000rpm your test presumably will take place under if you directly couple the axles.

 

[gwhy!]

I already have 2 of the large outrunners 8) spose i could force cool the gen windings if it gets to hot, I also have access to a few 3kw electric heaters for a load, I was reluctant to use my other motor for the just in case senorio but thinking about it now, with a bit of forced cooling it may be be ok .

 

[rhitee05]

The disc brake from a car should be able to handle that, easy. Grab a rotor and caliper from your local junkyard, and you could probably rig up a lever system to move the caliper manually and not worry about the hydraulics.

10 seconds at 10kW is 100 kJ of energy. If you assume a disc rotor is somewhere around 10 kg of steel (460 J/kg-K), that would only raise the temp of the rotor by about 22 C. It could easily take several times that and it shouldn't bother the pad very much either.

 

[gwhy!]

The disc brake from a car should be able to handle that, easy. Grab a rotor and caliper from your local junkyard, and you could probably rig up a lever system to move the caliper manually and not worry about the hydraulics.

10 seconds at 10kW is 100 kJ of energy. If you assume a disc rotor is somewhere around 10 kg of steel (460 J/kg-K), that would only raise the temp of the rotor by about 22 C. It could easily take several times that and it shouldn't bother the pad very much either.

The more i think about this setup the more im liking it, It would make adjusting the load a lot easier and can also be a variable load instead of static. Maybe just a disk ( I have a disk and a caliper ) on a shaft geared down from the motor.. with some forced cooling 8) like what they use on a fixed axle on a kart... also if it gets to hot it would be easy enough to add a additional disk and caliper yes thats the way I think Im gonna go as I have nearly everthing here to put it together. Thanks guys :wink:

 

[jag]

The disc brake from a car should be able to handle that, easy. Grab a rotor and caliper from your local junkyard, and you could probably rig up a lever system to move the caliper manually and not worry about the hydraulics.

10 seconds at 10kW is 100 kJ of energy. If you assume a disc rotor is somewhere around 10 kg of steel (460 J/kg-K), that would only raise the temp of the rotor by about 22 C. It could easily take several times that and it shouldn't bother the pad very much either.

How come everyone just thinks of rigging a brake to dump the energy into? That's so 1970's! I live near a bakery and the bakers can attest to that working next to a 10kW heat source is no fun this time of the year.

Now following the above numerical example, suppose we instead use a 10kg alternator/generator. If we just shorted the armature windings and then gave it a field current, results would be exactly as above: it would heat by 22C per 10s. However, if we instead use it as intended, generating electricity we could expect 70-80% efficiency, and instead of running 10s, we could run a full minute with the same temperature rise even if considered a thermally isolated system. Furthermore, if reasonably sized and cooled it would allow for continuous operation at some reasonable temperature (~100C), locally dumping only about 2kW of the 10, the other 8kW that could be lead away to some other location.

Now this reasoning of course leads to the obvious refinement: If like gwhy we have two identical motors and the matching controllers also happen to be able to do regen, then we just couple the motor shafts together, set one controller to power the experiment, and the other to capture the energy and feed it back to the battery. Thus we significantly lessen the load on the battery used for bench testing as well. A good motor has pretty much the same efficiency as a generator, so the heat load and stress on the "generator" motor will be the similar to the driving motor. If typical ebike controllers will hold up to do this type of regen is a bit of an unknown though. Controllers used in hybrid cars are more likely to be purposively sized for substantial regen power in the design stage.

 

[AussieJester]

Best of luck GWhy...if she dont blow how much too build me one hahaa

KiM

 

[Jeremy Harris]

10kW for 10 secs is a puny amount of energy for a brake to get rid of. Even a small motorcycle disc brake will handle this amount of energy, provided you don't keep the load on for minutes at a time.

If you use a quick 'rule of thumb' comparison, and make some crude assumptions, then if a motorcycle takes the same time to slow down under braking as it does to accelerate, you can fairly assume that roughly the same amount of power was being absorbed by the brakes as was being generated by the engine. If the motorcycle can slow down faster than it will accelerate (which is usually the case) then the brakes will absorb even more power.

90% + of the braking will come from the front wheel, so if your motorcycle wheel/disc is from a machine with more than about 10 to 15kW then it should be fine, although it'll get a bit warm.

The key is that you only need intermittent use, for no more than maybe 10 secs at a time, which should give the disc time to cool down.

You might want to think about a conventional band brake dyno. Many years ago I used one of these at college to measure the torque of a big (multi hp) electric motor as a lab experiment. It had a steel (or maybe cast iron) drum around a foot or so in diameter, with a flexible friction material band half wrapped around the outside. This band was attached to a tension adjuster and a spring balance, which was calibrated to directly read the torque applied to the drum. The drum was hollow, with a lip around the outer edge. It was partially filled with maybe 4 or 5 litres of water. Cooling was simply by evaporation through the central filling hole. IIRC this thing would run for several minutes absorbing quite a few hp without boiling the water. Not really surprising when you think how long it takes an electric kettle, with maybe 2.5kW of power, to boil a litre or so of water.

Jeremy

 

[liveforphysics]

If you take a car brake, use a rear brake with a mechanical cable-actuated parking brake. Way easier to have a lever on a cable than to mess with a hydrolic setup. You could actually rig a lever from the mounting bracket the tugs the cable, and have the pulling point adjustable by sliding up and down the lever. It could be a crude analog adjustable constant-torque setup this way. It could handle many 10's of KWs for 10-20second bursts easily.

 

[Biff]

Just to throw my 2cents in here

I have built a 12kW (sustained) resistive bank load and used a Mars7809 (the bigger one) as a generator to make a load.

If I were to do it again, This time I would use nichrome wire rather than purchasing resistors or heating elements.

The other options I have though of are the car or large motorcycle bakes you have discussed.

The last thing, that hasn't been discussed here yet is to use an eddy current brake. Grab some hard drive magnets (or other strong magnets) and put them on a balanced rotor near a thick steel, copper or aluminum plate. Build it so you you have control of the distance between the plate and the rotor. Then you can move the plate closer to increase the resistance. I was thinking that the eddy current plate would be part of a box which you could fill with water to keep it cool. That should operate for a long time and have no parts (other than the cooling liquid) that need replacing.

-ryan