# Cheap regenerative braking of RC BLDC motor.



## ryan27968 (Mar 1, 2016)

So I'm planning on doing an electric conversion of my Chinese 150 cc scooter as soon as funds will permit. The motor I'm planning on using is this 100A/2400W brushless DC RC motor. http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=22036. I will be using a normal RC ESC to power it from a 24v lead acid system. I will make a separate thread some point soon about the build itself. But as I was browsing babyhood.com for random electrical crap I'll need for the build, I found this: http://www.banggood.com/MDS150A-150A-1600V-3-Phase-Diode-Bridge-Rectifier-p-1027732.html. It's a three phase AC rectifier. As I'm sure most of you know, a BLDC motor is the same as a three phase AC motor. In other words, this would be a really simple way to get regen. I will pair it with a high power boost converter so that as the motor slows down it can still push 28 volts into the battery. (1200watts should be enough right? From what I've read, you get about 1/3 amperage back when decelerating as you use when accelerating so 1200 watts should be plenty considering a 2400 watt motor.) And a solid state high current relay to enable it when I want to brake. This whole system will only cost around 60$ for a regen setup. Thoughts?


----------



## WolfTronix (Feb 8, 2016)

Or just buy a 4 quadrant controller...

It will PWM the MOSFETs (using the inductance of motor coils) to boost the voltage higher than the battery pack, and thus regeneratively brake.


----------



## dcb (Dec 5, 2009)

I hadn't thought much about bldc regen, but isn't it just a matter of using the inverter 6 pack (which is a buck converter in the direction of battery->motor) as a boost converter? It *should* be a software problem, I think.


----------



## ryan27968 (Mar 1, 2016)

Where can you buy those? How much for a 100amp controller?


----------



## ryan27968 (Mar 1, 2016)

dcb said:


> I hadn't thought much about bldc regen, but isn't it just a matter of using the inverter 6 pack (which is a buck converter in the direction of battery->motor) as a boost converter? It *should* be a software problem, I think.


No because the RC ESC uses MOSFETs which are directional so they won't be able to put energy back into the battery. The way that an c car ESC does brakes is my using a separate set of MOSFETs to short out all of the motor terminals, essentially throwing away all that energy.


----------



## WolfTronix (Feb 8, 2016)

Use your favorite search engine:
"4 quadrant regenerative braking"
"mosfet reverse conduction"

Enjoy.


----------



## ryan27968 (Mar 1, 2016)

The cheapest I could find is a Kelly controller that supports 150a(but for some reason only 2.0 kw?) For 60 dollars more than my system+ a 200 amp esc not including shipping. It's quite a bit pricier. That said, it will probably be smoother breaking and it'll certainly be easier. But I'm a tinkerer at heart and imho it's just much more fun to put together your own system(and it's cheaper too)


Edit: that Kelly controller is 60 amps constant, 150 peak. Hence the lower wattage rating. I'm looking through their website now to see if there's a better one, but I'm fairly sure it'll cost significantly more.


----------



## ryan27968 (Mar 1, 2016)

OK so the best option seems to be the kbl36101x. It's 150 amps peak, 100 for 1 minute. So it should work fine for my needs, but it's 170 USD before shipping. My system will be around 100 USD and shipping would be around 20 USD. 50 dollars is a lot of money for me. Are their any cheaper controllers?


----------



## dcb (Dec 5, 2009)

ryan27968 said:


> (and it's cheaper too)


Usually not, at least not initially (educational expenses, aka mistakes and time), nor when the market catches up on production (again a function of time).

And this is for a 30v 1 pound motor, with more rpm than it knows what to do with and perhaps 4 foot lbs of torque? Low voltage/high current systems are the worst of both worlds, combined with high rpm low torque is the worst of all 4.

I think you would be better off w/a freewheel fwiw, light vehicles aren't as good as regen, and you can coast (or pedal power off) better with the motor decoupled.


----------



## ken will (Dec 19, 2009)

ryan27968 said:


> The motor I'm planning on using is this 100A/2400W brushless DC RC motor. http://www.hobbyking.com/hobbyking/store
> Thoughts?


Those motors are designed to be cooled by the prop wash.
Sitting in a scooter they might over heat.


----------



## Karter2 (Nov 17, 2011)

1) you wont get near that 2400W output from that motor
2) most RC ESC s die very quickly trying to drive motors on EVs
3) there are better controllers, with adjustable regen setting, made specifically for Ebikes.
Go read a while over on ES.


----------



## ryan27968 (Mar 1, 2016)

Don't worry about cooling. I've got plans for that.


----------



## ryan27968 (Mar 1, 2016)

Karter2 said:


> 1) you wont get near that 2400W output from that motor
> 2) most RC ESC s die very quickly trying to drive motors on EVs
> 3) there are better controllers, with adjustable regen setting, made specifically for Ebikes.
> Go read a while over on ES.


Why wouldn't it run 2400w? It's rated for 100 amps... anyway, I've changed my mind. Instead of running the motor through the CVT as originally intended, I'm thinking of just running it at higher speed and putting it directly into the final drive gearbox.(It's a 8.67:1 reduction gearbox.) The motor I'm thinking of using after reconsideration is a 620kv water-cooled motor designed for those big RC boats. Rated at 105 amps I'm planning to run 25.9 volts worth of lithium ion 18650s. This gives me a motor rpm of 16k, and a wheel rpm of 1850 rpm. This gives me a top speed of 80km/h(50mph) which is my target. This will give me close to 3kw of power. But my only concern is whether the motor will have the torque to even get to that speed. The numbers and gear ratios seem to support that speed, but i wanna know from you guys. Can you get 80km/h on a 3kw system?


----------



## dcb (Dec 5, 2009)

ryan27968 said:


> Can you get 80km/h on a 3kw system?


You look at the rolling resistance and coefficient of drag and frontal area basically to determine that. But probably you can get there, though you may have to trade acceleration to do so and pay some heed to aerodynamics.
i.e.: department store mountain bike vs well maintained racing bike.










from:
http://users.frii.com/katana/biketext.html


----------



## ryan27968 (Mar 1, 2016)

I seem to remember there being a website that calculates the HP required to maintain a specific speed. You enter weight, coefficient of drag, etc and it figures it all out. But I can't find that website any more. Does anyone have a link?


----------

