Riding downhill

[Michael Vu]

So as I understand it, battery cut-off on many EUCs occurs not really because of speed, but because of power exceeding the threshold that the battery is able to supply to the wheel. So while my wheel might cut-out going 18 mph on flat surface, it might also cut-out going just 10 mph up a 30 degree incline.

But what about going downhill? If everything I said has been correct, then shouldn't you in theory be able to go as fast as you can downhill since all the power from the battery no longer has to propel you forward, just keep you balanced upright? I have always made sure to lean back a little going downhill so I don't go too fast for fear that my EUC might cut off but I will gladly go faster if I know that my wheel will still keep me upright. I'm tired of bikes passing me going downhill. 

[esaj]

In theory, maybe, but I really have no idea. Want to be the test monkey?  Don't forget to take a video... And wear tons of protection

Wikipedias entry for Battery Management System lists the following common protections:  https://en.wikipedia.org/wiki/Battery_management_system#Protection

A BMS may protect its battery by preventing it from operating outside its safe operating area, such as:

• Over-current (may be different in charging and discharging modes)
• Over-voltage (during charging)
• Under-voltage (during discharging), especially important for lead–acid and Li-ion cells
• Over-temperature
• Under-temperature
• Over-pressure (NiMH batteries)
• Ground fault or leakage current detection (system monitoring that the high voltage battery is electrically disconnected from any conductive object touchable to use like vehicle body)

The BMS may prevent operation outside the battery's safe operating area by:

• Including an internal switch (such as a relay or solid state device) which is opened if the battery is operated outside its safe operating area
• Requesting the devices to which the battery is connected to reduce or even terminate using the battery.
• Actively controlling the environment, such as through heaters, fans, air conditioning or liquid cooling

Don't know if over-current or over-voltage protections could trigger a cut-out due to regenerative breaking? When a motor is turned by outside force, it becomes a generator...

These pages seem to also contain lots of information: http://www.mpoweruk.com/bms.htm  http://www.mpoweruk.com/protection.htm   http://www.mpoweruk.com/chargers.htm

In general cell protection should address the following undesirable events or conditions:

• Excessive current during charging or discharging.
• Short circuit
• Over voltage - Overcharging
• Under voltage - Exceeding preset depth of discharge (DOD) limits
• High ambient temperature
• Overheating - Exceeding the cell temperature limit
• Pressure build up inside the cell
• System isolation in case of an accident
• Abuse

 

• Random charging There are many applications where the energy to charge the battery is only available, or is delivered, in some random, uncontrolled way. This applies to automotive applications where the energy depends on the engine speed which is continuously changing. The problem is more acute in EV and HEV applications which use regenerative braking since this generates large power spikes during braking which the battery must absorb. More benign applications are in solar panel installations which can only be charged when the sun is shining. These all require special techniques to limit the charging current or voltage to levels which the battery can tolerate.

 

Apparently "Automotive" BMSs have lots of stuff to handle regenerative braking, including using it for cell balancing and dumping (offloading) extra charge to something else to prevent batteries from overcharging, but I doubt the wheels use that "intelligent" BMSs.

[Michael Vu]

The regenerative braking makes sense and that's basically what I am doing right now. I guess if I brake too hard or resist going down a steep decline that the battery would cut off too? But even with all of that, my main question is what if you do not brake nor actively move forward? But instead just let gravity and the decline determine how fast you go and all you have to do is just remained balanced..... like a bicycle.

[esaj]

This isn't a topic I know that much about really, but I'd guess that during really hard braking, the regenerative energy isn't enough to slow you down, and instead the wheel actually needs to use some of the battery charge to slow you down... What comes to the just "free rolling" down hill, ie. the wheel just needs to maintain the balance, its coils are still switching "on" and "off" with varying power as they pass the magnets, whether the energy comes either way. What I'd guess comes to play next, is the electromagnetic forces, which really goes waaayyy over my head, but refer to this image which other people have posted here a couple of times:

I'm not sure, but I suspect that once the motor is turning at the "No load speed" RPMs, the motor cannot balance you anymore, regardless of how much power the batteries can push into it, as the coils cannot produce any more torque... but could be wrong. I'm pretty sure I'm not the one who wants to try this, though   

EDIT: Could this be actually tested by placing the wheel on a treadmill, with something holding the wheel upright (but not prevent it from falling, unless the motor keeps it up) and then gradually raising the speed?

[Gimlet]

I only know from experience that I've had more motor cut off problems going down steep hills than I have had from going fast.

My problem has always been that despite the surface looking smooth there always seems to be slight dips in it which when going down hill really ramps up the acceleration and it is when I've tried to control these sudden bursts of extra acceleration that the motor has cut out leaving me sitting on the road. I'm afraid I haven't got the kahunnas to try riding it out without controlling the speed as I have a feeling that it would just build and build.

[Luiz]

I have never had a cut off going down hill Although i  always have the speed under control. The sheer thought of having a cut off while descending a steep hill is very scarry  not so much for the fall but the idea of the wheel falling on the hill and possibly hiting people on the way is terrifying. Concusion again is always use leash and protective gear.

[^tom^]

A cut off I never had, but a not longer regeneration (during driving with a fully loaded wheel) and so the wheel will not longer break and becomes faster and faster and you better jump off (what I did).

I do not know of the wheel turns off because of overspeed but I think so and then you better learn fly first!

[dmethvin]

If everything I said has been correct, then shouldn't you in theory be able to go as fast as you can downhill since all the power from the battery no longer has to propel you forward, just keep you balanced upright?

The basic torque-speed curve of the motor still applies, the zero-torque point is there whether you're applying battery power or not. When moving downhill and braking you need some sort of "sink" to generate the braking torque by using up the power generated by the motor. Either it has to be put back into the battery (storing the energy) or dumped onto a load resistor (creating heat).

[K.Ronko]

This is something I've been wandering for a while, if you go down a long hill with fully charged batteries, what effect will the overcharge have? I know that in theory the Solowheel code  is designed so that in an overcharge scenario, it trigger a similar reaction to when the battery is low (shaking and pedals tilting backwards) but have never experienced it.  I don't know what would happen on other wheels.

Gimlet I see you are from Bath?  I went to Bath Uni so I am familiar with the steep hills there; have you ever ridden down from the top of one of the hills and encountered any problems?

[Gimlet]

I live just off the top of Lansdown so I regularly go up and down to Bath and back.

I can't say I've ever had any overcharge problems, according to Jason McNeil my IPS eucs burn of the charge with resisters and heat sinks and I believe the Gotways have pedal tilt back on overcharge and I've never had that happen.

[Michael Vu]

So it seems there is still no clear consensus on this? My buddy has a treadmill and we've been talking about testing my Firewheel on it to see when the motor does go out. 

[esaj]

So it seems there is still no clear consensus on this? My buddy has a treadmill and we've been talking about testing my Firewheel on it to see when the motor does go out. 

​If it has handrails on the sides, you could (probably, maybe) try standing on top of the wheel yourself, holding the rails and ready to catch yourself if/when the wheel shuts down... then at least you'd get results with "real" weight.

Edit: I'd be interested to know the results also, but am not able to test this myself, because I don't have a treadmill and am not willing to try it out on a real downhill