Jeff:
Baffles me, the idea to overlook cooling air in the design of the motor...why not mae the housing of aluminum with cooling fins or just have fins in the existing frame
The etek was probably extensively tested in its designed-for application. I bet if you stayed within the manufacturer specs the motor would run fine for an acceptable life. Whats not understood is that the 300 amp for 30 sec limit is probably starting at room temp while the motor is cool. This is an unrealistic spec for real world design. If you run it at 100 amps until the temperature stabilizes, than it may be out-of-spec to go over 100 amps without cooling down first. Chrisj:
I wonder if the new brushless version has those copper clippys? My guess is no - I'll bet B&S has received lots of complaints and did what they could to make them go away.
It shouldn't, as the PM magnets are always the rotating component in a brushless DC motor. Chris:
Just took a look at Mike's pictures. I wonder if you could wrap the armature with a Kevlar band to take some of the load off the solder joints?
Someone I talked to at Electric Vehicles USA mentioned doing that for racing I think. I'm sure either they or the guys at thunderstruck would know how. Jonathan:
in a brushless motor the windings should be mechanically part of the casting and able to conduct heat away better.
Quite a bit better to my understanding. The stator can get extremely hot very quickly in a conventional brushed motor design with high current. The casing temp is a poor indication of how hot the critical rotating buss bars get. Kind of like an electric stove heating element or a toaster, if you turn it on it'll heat up quickly, and also cool down pretty quick from the very high temps if you shut it off. I'll bet Mike's etek got much hotter than 160 internally. Jeff:
I can control the heat build-up in the motor by very gradually applying throttle. If I spin the throttle to full most of the 200+ amps will turn into heat and I still won't get wheel spinning take-off anyway. Until WE find a nice small 2 speed trans, acceleration is going to be just less than a land speed record machine (okay not that bad) but when you gear for 60 MPH top the compromise in take-off is fairly significant
Or, why not thrown on another etek? Half the resistance (with the motors wired in parallel) and you half the losses in heating, and each motor must dissipate 1/4 the energy in heat. Say you are pulling 200 amps with one etek running at any voltage: 200 * .033 ohms (terminal resistance) = 6.6v * 200 = 1320 watts in heat that one etek must dissipate without frying. Throw an etek into the mix: 200 * .0165 ohms = 3.3 * 200 = 660 watts in heat that is divided between two eteks, so each etek must dissipate 330 watts without frying. Darn, I guess its not magical that my duel eteks stay really cool even under very high loads. Additinally, because I'm wasting less in heat, I get less pack voltage drop when accelerating. And because the motors are heating up less, the terminal resistance does not rise much (meaning they run more efficiently). The PMG uses clips like the ETEK but I still see no evidence my motor is
being over-amped... the PMG is actually rated for 72 volts the ETEK is rated for 48 volts. That might explain the price difference, I haven't heard of someone frying a PMG (yet).
I have heard of one frying running in the wrong direction. I'd bet that the larger slots in the sides help keep the bars cooler than on those on the etek. Johnathan:
Maybe I should rephrase... I haven'l blown up a motor or controller or anything yet....
You have yet to be initiated... Regards, Andrew
