Question about regen braking

[Bonzo Banana]

On direct drive hub motors, even entry level models do they have regen when going down hill with the electric circuit live but the motor not being operated if not where does the power generated go?

If you lived at the top of a long steep hill and your destination was at the bottom of the hill would a fully charged battery be damaged by the regen and would not switching on the circuit prevent the battery from being over-charged, i.e. coasting down the hill.

 

[Danidl]

My understanding is that there is no regen.in the terms you are thinking about. If the motor rotates faster than the switching wants it to, the excess current induced in the windings just makes them warmer!. Basically there is no path backwards into the battery with the correct polarities. Were the motor a pure AC induction motor, then it would create an AC voltage ..but its not.

 

[Woosh]

Analysis of regen on an ebike

This June I gave a presentation at the monthly VEVA meeting ( http://www.veva.bc.ca/events/pastevents.htm ) about among other things regen braking on electric bicycles. This was before the cross-canada ebike trip but after doing some quantitative tests riding around Vancouver with various early...

endless-sphere.com

On direct drive hub motors, even entry level models do they have regen when going down hill with the electric circuit live but the motor not being operated if not where does the power generated go?

nowhere on a normal controller. The FETs block the reverse current unless you have a controller with regen function.
Read the analysis of Justin Lemore in the ES thread.
Regen gives back usually less than 1% of the battery you use, plus increase risk of damage to the battery BMS because the regen current flows back through the BMS' FETs in the wrong direction, although that works when the junction (in the BMS FETs) is conductive, the gate voltage may be wrong, so not worth it.

 

[BazP]

Analysis of regen on an ebike

This June I gave a presentation at the monthly VEVA meeting ( http://www.veva.bc.ca/events/pastevents.htm ) about among other things regen braking on electric bicycles. This was before the cross-canada ebike trip but after doing some quantitative tests riding around Vancouver with various early...

endless-sphere.com

nowhere on a normal controller. The FETs block the reverse current unless you have a controller with regen function.
Read the analysis of Justin Lemore in the ES thread.
Regen gives back usually less than 1% of the battery you use, plus increase risk of damage to the battery BMS because the regen current flows back through the BMS' FETs in the wrong direction, although that works when the junction (in the BMS FETs) is conductive, the gate voltage may be wrong, so not worth it.

The thread you pointed to was started in 2008 and it seems that things have moved on a bit since then.
Reading the latest posts the figures look more like 15% and this is for a speed Pedelec with figures for a 25kph bike looking to be better than this.
Not sure if the problem of overcharging an already full battery has been overcome but maybe a manual cut off could be used.

 

[Woosh]

Reading the latest posts the figures look more like 15% and this is for a speed Pedelec with figures for a 25kph bike looking to be better than this.

if you don't have regen, your bike wastes about 2%-3% battery on braking.
You can only recuperate some of that 2%-3%.
If regen is 25% efficient, then you recover 25% of the 2%-3% - that means your mileage is going to be extended by about 0.5%.
There are sophistcated regen controllers that cater for different strategies and speed, but 25% is the ball park figure. You'll need extra winding and ultracapacitors if you want higher yield. 0.5% on a 500WH battery is 2.5WH, less than a minute of charging time, not worth the effort.

 

[Wisper Bikes]

A Grace bike with Re-Gen was my bike of choice for a year or so. Woosh is absolutely correct, the benefit was infinitesimal and there are cost implications. Better to spend that money on a higher spec battery.

The kinetic energy stored in rider and bike at 15mph is simply not enough to put much power back into the system, unlike a 2 ton family car at 70mph. You do save on brake pads though!!

All the best, David

 

[Wicky]