BMS Q-series hub question

[eddiecycle]

Hey y'all, I'm planning a build with a Q100C hub and have a question. I've read numerous places that these hubs need to be kept at or above about half the max RPMs. So pretty straightforward, the 201 would need to be kept above about 100 RPMs to keep from toasting it (frying the gears correct?). What happens when the hub is overvolted? If I run the hub at 52v, the max speed (at least on a downhill) becomes 290 RPMs. Do I now need to keep the hub at or above 145 RPMs, or will it still be fine at around 100 RPMs?

If the answer is that the overvolted hub now needs to be kept above 145 RPMs, my next question would be about battery sourcing since 36V options are becoming much less common and the ones that are available from reputable sources are all in bottle cases

If the answer is that the overvolted hub will still be fine at 100 RPMs, the next question would be about controllers. BMS has very little information about a large selection of controllers. I know a lot of people are using the S12S for overvolting. Would the S09 controllers also work fine since they also support 48v? Will all their controllers that say 48v also support 52v? Does the number that comes after the "S" denote the number of fets?

 

[amberwolf]

The problem you're referring to has to do with putting a high load on it while at a low speed, because there wouldn't be enough back-EMF to prevent phase currents from being so high they cause overheating.

Simply running at a higher voltage or higher speed doesn't fix the problem.

It's easier to understand what is happening in such situations, and see how to prevent them, if you go to the https://ebikes.ca/tools/simulator.html and setup the type of system you wish to use, under the conditions you wish to use it at, and vary the throttle input to the system to see when or if overheating will occur. There is also a trip simulator that will use the same principles to help you figure out if your system can do what you need it to on a particular trip's conditions.

It's not a perfect simulation, but it does help to visualise everything.

 

[eddiecycle]

I wasn't trying to fix the problem by increasing voltage, just wondering whether increasing voltage makes the problem worse or not. In other words, I'm fine with the "minimum speed", but I'm wondering if a voltage increase also increases that minimum speed.