Regenerative Braking

ankanphukan

10 mW
Joined
Oct 1, 2021
Messages
32
Do regenerative braking uses bidirectional dc dc converter? I have read a few papers where they are using bidirectional DC-DC converters for regenerative braking. I know the concept of regenerative braking. But how to incorporate the BDC in regenerative braking? One more thing, in BDC, we need to know the value of two voltages (i.e. input and output voltages). How to find out the value of voltage generated due to braking? Please help
 
You need a motor controller that has regen braking capability. The controller will likely use the motor winding inductances to boost the voltage as needed to push current into the battery. The voltage attained will depend on the battery voltage, it's internal resistance, and the resistance of the rest of the circuit vs the current flowing.
 
ankanphukan said:
Do regenerative braking uses bidirectional dc dc converter? I have read a few papers where they are using bidirectional DC-DC converters for regenerative braking. I know the concept of regenerative braking. But how to incorporate the BDC in regenerative braking? One more thing, in BDC, we need to know the value of two voltages (i.e. input and output voltages). How to find out the value of voltage generated due to braking? Please help

The same circuitry in the controller that converts the DC in from the battery to 3-phase out to the motor, converts the 3-phase in from the motor (under regen) to DC out to the battery. No DC-DC converter involved.
 
Every hub motor controler, Voliamart ect. has regn braking. You just have to coonect two pins in any cv ontroller to activate it.
 
Thank you everyone for your valuable suggestions.

I just have another question.

Let us suppose, I am using the Votol Em 100. It has inbuilt regen. But the pins have no direct indication of the same. However, there are two connections namely : Low Brake (0- 5V) and High Brake (0-12V). Are these pins related to regen?

What should I connect to each of these brake connections, to implement regen in my vehicle?

I tried searching about it in google and youtube. But I couldn't figure it out. Please help !!
 
ankanphukan said:
Let us suppose, I am using the Votol Em 100. It has inbuilt regen. But the pins have no direct indication of the same. However, there are two connections namely : Low Brake (0- 5V) and High Brake (0-12V). Are these pins related to regen?

What should I connect to each of these brake connections, to implement regen in my vehicle?

Votol controllers are programmable, so either the one you buy it from sets everything based on your setup, or you get the free software and data cable and program it yourself.

LOW BRAKE pin will have +5v that gets pulled to ground when you activate the brake level.

HIGH BRAKE pin is 0v and you send high voltage (+12 to ???) when you pull the brake level.

In the software you can check the “Low beake” box and that tells the controller to use that signal for brake and regen. The regen amount (EBS%) is set in the program.

Normal controller allows battery voltage to be used for high brake, so its simple. +Battery goes to both normally open brake level sensors, then back to the high brake connector as well as the brake light (which is destroyed for battery voltage not 12v). Ive seen the drawing showing +12v and ive seen resident experts saying battery voltage is also fine for the Votol. I asked Carrie at Siaecosys and waiting for her answer. To work on all applications, +12v to full battery voltage would be allowed. There is no 12v on my bike.

The Votol controller allowed you to use LOW BRAKE pin as a side stand safely switch. Down closes the switch and disables the motor, up opens the switch and its ready to roll if the brakes are off (which used the HIGH BRAKE) pin.
 
Hello Everyone,

Please help me in understanding this concept.

Let us suppose, I am using a 48V motor for my e-bike. I have a controller which is capable of regenerative braking. Since the motor is a 48V motor, so I am using a 48V battery pack.

How much voltage is generated during regenerative braking from the 48V motor? How can I measure that?

Is it like this: In order to charge the 48V battery (if only one battery pack is used) during regenerative braking, the motor controller combination should also supply 48V right? Kindly correct me if I am wrong.

My main concern here is, I want to use two battery packs (Let A and B). Battery pack A is 48V. I want the regenerated energy to charge battery pack B, which is much smaller than pack A. How can I route the regenerated energy to battery pack B?

The main purpose of this question here is, if the regenerated voltage is 48V, then there is no necessity of using the second battery pack B. I thought of using the second battery pack, if at all the regenerated voltage is less than 48V.

Please help me. I would be very grateful.
 
2 points I can share.
First, MOST people aren't going to recoup enough charge from the regen process to be concerned about the issues you raise. Sales people and add copy are all hype when it comes to where the rubber hits the road. Folks living in an area with big hills will enjoy regen's ability to help control their speed coming down a big hill. Flat landers could care less.....

There's one exception to the above I know of, and that would be Grin's GMAC setup. It sort of makes all new rules when it comes to regen.

2nd, if your regen is triggered, and it's trying to charge a fully charged battery (say while descending a big hill as you leave home for instance) "stuff" can and does happen. Point being, regen will not over charge a fully charged battery. There IS power being generated, and it's going to go somewhere....
 
Motors become Generators.

So there is no such thing as a "48 volt motor".

That's the area you need to focus on... the very basic ideas of energy "out" vs energy "in".

In each direction "in" or "out" this device of "magnetic to electric transmutation" will charge a FEE.

That "fee" is the losses in the system.

So you put energy "in" and lose 10% - 50%.

And you pull it out and lose 10% - 50%.

On an ebike your recovery in total is usually in the single digits percentage wise.

The entire regen thing is a silly sort of Virtue Signal.

It's a real thing, but it's really not worth building an entire bike around.
 
Motor controllers manage voltage and current as they see fit. They are always trading voltage and current. If your controller was set for max regen voltage at 48v and your motor was only spinning fast enough to produce 24v then the controller will step up that voltage to 48v and send it to your pack.

A really simplified example:
You have a motor that goes 20mph at 48v
Your controller is pulling 2.5 amps at 48v from the battery
You are traveling at 10mph so your controller is sending out 5amps at 24v
You regen 5 amps at 24v at 10mph
Your controller sends 48v 2.5amps to the battery.

If you have 2 battery packs on your bike and they are the same voltage then you should either parallel them together to make one large capacity pack OR use only one pack at a time.

I suppose if you wanted to get really creative you could use diodes to only let regen into one pack while drawing from both. There is really no reason to go through all of that trouble.
 
Thank you for all your insights.

Could you kindly guide me as to how can I measure the regenerated voltage during braking or deacceleration?

During regenerative braking, the motor acts as a generator. How can we measure, how much voltage is generated by the motor (generator) during that time?

Please help.
 
larsb said:
..And if you start regen at a higher speed than your max noload speed then the created voltage can burn both your pack and controller, if it’s a simple controller. Smart ones limit regen to safe speeds/voltages

DanGT86 said:
Motor controllers manage voltage and current as they see fit. They are always trading voltage and current. If your controller was set for max regen voltage at 48v and your motor was only spinning fast enough to produce 24v then the controller will step up that voltage to 48v and send it to your pack.

A really simplified example:
You have a motor that goes 20mph at 48v
Your controller is pulling 2.5 amps at 48v from the battery
You are traveling at 10mph so your controller is sending out 5amps at 24v
You regen 5 amps at 24v at 10mph
Your controller sends 48v 2.5amps to the battery.

If you have 2 battery packs on your bike and they are the same voltage then you should either parallel them together to make one large capacity pack OR use only one pack at a time.

I suppose if you wanted to get really creative you could use diodes to only let regen into one pack while drawing from both. There is really no reason to go through all of that trouble.

SafeDiscDancing said:
Motors become Generators.

So there is no such thing as a "48 volt motor".

That's the area you need to focus on... the very basic ideas of energy "out" vs energy "in".

In each direction "in" or "out" this device of "magnetic to electric transmutation" will charge a FEE.

That "fee" is the losses in the system.

So you put energy "in" and lose 10% - 50%.

And you pull it out and lose 10% - 50%.

On an ebike your recovery in total is usually in the single digits percentage wise.

The entire regen thing is a silly sort of Virtue Signal.

It's a real thing, but it's really not worth building an entire bike around.

AHicks said:
2 points I can share.
First, MOST people aren't going to recoup enough charge from the regen process to be concerned about the issues you raise. Sales people and add copy are all hype when it comes to where the rubber hits the road. Folks living in an area with big hills will enjoy regen's ability to help control their speed coming down a big hill. Flat landers could care less.....

There's one exception to the above I know of, and that would be Grin's GMAC setup. It sort of makes all new rules when it comes to regen.

2nd, if your regen is triggered, and it's trying to charge a fully charged battery (say while descending a big hill as you leave home for instance) "stuff" can and does happen. Point being, regen will not over charge a fully charged battery. There IS power being generated, and it's going to go somewhere....



Thank you for all your insights.

Could you kindly guide me as to how can I measure the regenerated voltage during braking or deacceleration?

During regenerative braking, the motor acts as a generator. How can we measure, how much voltage is generated by the motor (generator) during that time?

Please help.
 
Regarding measuring power created by regen, I think it likely something could be cobbled up, an ammeter for instance. Grin's CA3 display has a function if you need/can use something like that. Scroll down to display #6 here:
https://ebikes.ca/product-info/grin-products/cycle-analyst-3.html
 
ankanphukan said:
Thank you for all your insights.

Could you kindly guide me as to how can I measure the regenerated voltage during braking or deacceleration?
Are you asking this for a school project?
 
Yes, it is all about knowing the kV of the motor.

Lets imagine a kV of 100.

Motor side:

10 volts -> 1000 rpm.
20 volts -> 2000 rpm.
30 volts -> 3000 rpm.

Generator side:

1000 rpm -> 10 volts.
2000 rpm -> 20 volts.
3000 rpm -> 30 volts.

Minus losses of course which are 10% - 50% in either direction depending on circumstances.

But what happens when you get:

8000 rpm -> 80 volts

...and your battery and controller cannot handle the excess and blows it's capacitors?

And it does happen.
 
I have to ask here, how likely are we going to see the rpm numbers above? I'm thinking 500 rpm would be on the high side. That's actually one of the reasons regen is pretty much ineffective at providing much of a charge....

See the motor rpms bottom left here:
https://ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=B4816_GA&cont=C35
 
It’s more of an issue for happy hotrodders. Let’s say you get a controller with 100V internal parts, get a 22S battery, this system is already on the limits for the voltage peaks that inevitably occurs. Max it out on any downhill slope around you - regen brake. Boom.
 
ankanphukan said:
Could you kindly guide me as to how can I measure the regenerated voltage during braking or deacceleration?

I'm assuming, because you say you have a controller that supports regenerative braking, that you're working with a brushless motor.

The back EMF of a brushless motor is variable frequency, variable voltage, 3 phase AC. You can measure it by placing multimeter probes (in AC voltage mode) across any two of the phase wires leading to the motor, and rolling the bike around.

The peak voltage will be a function of motor RPM. Peak or RMS voltage under load (like a charging battery, or a braking resistor) will depend on the characteristics of that load.

A brushless controller with regenerative braking capabilities takes in wild AC from the motor, rectifies it, and converts the voltage to a level higher than that of the battery pack.
 
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