Advice for a heavy rider

[Teejay]

After years of reading Pedelecs off and on, I'd understood the the BMS controls things like keeping all the battery's cells balanced, cutting off the juice when the voltage falls too low, that kind of thing. Whereas the current to the motor was controlled by the Controller - and to get more go you change the controller for one that allows more amps, or you 'solder the shunt'. But now were told they're uprating the BMS on the Big Bear to give it more grunt. Can somebody explain, please, 'cos I'm obviously not understanding something and frankly I'm confused?

 

[trex]

When you see a label on the controller '17A max' - like many things in electronics, it's approximate. It can vary a little around 17A, allowing short surges to peak over that 17A. Without a high discharge BMS, the large current draw causes the voltage to sag.
So even when the current is allowed to peak, the battery voltage can sag as much as 3-5V. This sag reduces the true output power of the motor. A high discharge rate BMS needs to work with high discharge rate cells, but it essentially eliminates this voltage sag and allows the controller a much wider margin on power.
Bikes fitted with high discharge rate batteries are perkier to ride.

 

[Deleted member 4366]

Uprating the BMS doesn't affect the performance of the bike in any way. It also works like a fuse. It'll cut-off if your current goes too high, and there's often on-board temperature control, so it'll also shut down if it gets too hot. If the BMS was uprated, it would have been to reduce the risk of cut-offs or to reduce the risk of something in the BMS blowing.

My guess is that the controller was uprated and then someone tested it and found that the BMS would cut off occasionally on steep hills, probably because it got too hot.

Even though the controller has a maximum current control, It's not always quick to react, so it'll allow a lot more current for a short time before it cuts it back. This can trip a BMS, which often has a much faster current limit, so you normally need a higher rated BMS than the controller; however, you can get more expensive modern microprocessor controlled BMSs where everything is programmable, so you can adjust the time you'll allow a peak before something reacts.

 

[trex]

I think the cells got uprated too.

 

[rolando177]

This post asked for advice for a heavier rider - something I have a lot of experience with.

It is not really an issue of the motor but the wheels. Most cheap, machine-made wheels will break if you are too heavy or the road is too rough. I had to resort to getting a rear wheel made (touring rim, extra-strong spokes etc). It cost £90 and I have not had a problem since.

Other changes I made include a wide saddle, a mirror, a pannier rack and good lights.

I ride across the South Downs and I couldn't do it without a crank-drive ebike.

I find that I can do it two or three times per week but I don't want to do it every day.

Oh....and it is fantastic,

 

[Deleted member 4366]

This post asked for advice for a heavier rider - something I have a lot of experience with.

I ride across the South Downs and I couldn't do it without a crank-drive ebike.

I'm sure you have a lot of experience of being a heavy rider, but it's clear that you don't have a lot of experience of electric bikes when you make statements like that, which are very misleading to the uninformed. There's many hub-motored bikes that will get you across the South Downs with less effort than your present bike, especially if you still have your Raleigh Dover that couldn't pull the skin off a rice pudding.

Sorry for being so abrupt, but statements like that wind me up. We used to hear that sort of thing a lot years ago, but, thankfully, it's not so often now.

Come to Bristol next Sunday to try the modern bikes, and you'll change your opinion.