# what is needed for regen braking?



## dmac257 (Jun 30, 2010)

I am still trying to sort motors in my head and some seem to overlap so I am persistantly confused.

I thought you couldn't do regen with a brushed motor yet I read a thread today that mentioned higher voltage large diameter DC motor with interpoles or something doing regen.

I have also read that you can use PM motors and sepEx motors for regen and they didnt sound like they was talking about the same thing.

I am trying to straighten out which motors are which.

Do PMDC motors have brushes? What exactly is a Brushless DC motor and can it be used for regen? I have heard that sepEx motors are more versatile and more expensive .. what would be good reason for sepEx over a brushed DC motor (or do sepEx have brushes also)??

Don


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## Georgia Tech (Dec 5, 2008)

In theory you can do regen with any motor. But some are more suited and practical than others. A series motor is the most difficult to do regen while an ac motor is eaiser. The interpoles are in brushed motors that allow the motor to do regem better and more reliable! Interpoles keep the flux more aligned where it needs to be while either motoring or generating. without interpoles regen on high voltage/high performance applications become impracticle. From time to time you will here of golf karts with Sep X motors doing regen but again....48 Volts...not 120 or let alone 144 volts!


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## Guest (Aug 4, 2010)

There are a few Higher voltage SepEx controllers that will do regen with a large SepEx motor but they are few and far between. You can buy them but they are quite expensive. Zapi makes one that is a 120 volt SepEx controller that works well but is hard to get. The programmer is extra. Besides that Kelly has one for the SepEx motors and it is also 120 volt model. Not as high of amperage as the Zapi but pretty darn good. I think those are your choices for higher voltage SepEx with regen. Plenty to choose from for your Series DC motors. Tiny to Race. You choose. You really don't need regen but it could be good to have. My Ghia does not have regen and stops just fine. I coast and save that way. 

Pete


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## major (Apr 4, 2008)

dmac257 said:


> I am still trying to sort motors in my head and some seem to overlap so I am persistantly confused.
> 
> I thought you couldn't do regen with a brushed motor yet I read a thread today that mentioned higher voltage large diameter DC motor with interpoles or something doing regen.
> 
> ...


Hi Don,

You ask a lot of questions. Here goes 

What is needed for regen braking? A generator. And a method to condition the power converted from vehicle kinetic energy to electrical for acceptance by the energy storage system (most times batteries).

Because all motors can operate as generator (if properly excited), most EV propulsion systems use the traction motor as a generator to regen. IMO, it rarely makes sense to add an additional machine (generator) to regen. By the time you consider the mass and cost of doing that, you're miles ahead devoting that mass and cost to additional battery (in most cases).

You can regenerate with any type of EV propulsion motor. But resulting problems make it impractical with series wound brushed DC motors. While we're on it:

DC motors include all motors with brushes and commutators. These can have various fields (which in almost all cases are the stators). The types of fields include PM (Permanent Magnet), SepEx (Separately Excited, sometimes called shunt) and series. There are also compound motors (combo of series and shunt).

AC motors do not have brushes and commutators (the inverter does the commutation electronically). Although misleading, the BLDC is an AC motor. It needs an inverter to commutate for it. The inverter switches the applied current positive to negative many times a second making an AC waveform. It may not be a sine wave, but alternates, so is AC.

Also you have ACIM. That is induction motors. Induction motors also require an inverter to make AC from the battery DC. They differ from the BLDC because they do not have magnets on the rotor. They have bars or wires on the rotor which are excited thru induction, hence the name induction motor.

With AC motors and drives (drives meaning the electronic controllers or inverters), regeneration is a SMOP (simple matter of programming). In other words, no additional hardware is required. So it is essentially free. Why not use it?

For DC motors (those guys with brushes), regeneration presents difficulty with commutation, regardless of which type. It is least noticeable with PM brushed motors, but these are rarely used above a few kilowatts. When they are, regen can zorch them. 

Regen with series wound DC motors, forgetaboutit.

With the SepEx DC brushed motor, regen is practical. The motor controller needs to have one additional power switch and logic. This works well up to about 5 or 10 kW, depending on voltage and other things, then commutation gets messy. So for higher power regen capable SepEx motors, interpoles are needed to commutate successfully. And that adds expense and mass to the motor.

There you go in a nut shell 

major


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## Overlander23 (Jun 15, 2009)

major said:


> Regen with series wound DC motors, forgetaboutit.
> major



I keep hearing this, but then I also hear that neutrally-timed, series-wound, DC motors with interpoles can regen... Before I do something, sometime, that I might regret... what's the deal???

BTW, if I were to regen, it would be primarily for a degree of braking (like engine braking). The recoup of energy would be icing.


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## major (Apr 4, 2008)

Overlander23 said:


> I keep hearing this, but then I also hear that neutrally-timed, series-wound, DC motors with interpoles can regen... Before I do something, sometime, that I might regret... what's the deal???


Hi Over,

Yes, regeneration with series motors is possible. It's just not easy  If you can figure it out, go ahead.

Why do you think no controllers are available for series motors which include regen? It is not a good idea. The series generator is unstable. And you have to disconnect the series field and reconnect it to bump start the generator current, so this requires a reversing contactor set. Not a small item. 

There is literature out there on how it is done. Cafe Electric used to have a nice article. Go for it. I'll bet you'll be unhappy with your results.

major


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## Guest (Aug 4, 2010)

> ............to have a nice article


I believe that the article was about using a standard series motor and not one neutrally timed with interpoles. That was the big issue that drove folks away from regen with those types of motors. Oh it can't be done. But they fail to mention that they tried with advanced standard series motors and they fried them. So comes the bad rap. But saying that the series motor even with interpoles is not as good as a SepEx and those just don't have the following of controllers needed for HV setups. Next comes the expensive AC drives. We know about AC. If you have a small car and a SepEx motor you could get a Kelly controller for one and tweek it to work for you. If you want a large HV car your out of luck on regen except with AC. For the most part you won't find much on Regen with the DC motors except like in small lower speed golf carts or industrial carts or forklifts and even those are moving into AC territory. 

Pete


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## major (Apr 4, 2008)

gottdi said:


> I believe that the article was about using a standard series motor and not one neutrally timed with interpoles. That was the big issue that drove folks away from regen with those types of motors.


Pete,

Brush timing and interpoles have little to do with instability and bump start. And I think Ot was smart enough to set his motor to neutral, IIRC 

major


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## TX_Dj (Jul 25, 2008)

major said:


> And I think Ot was smart enough to set his motor to neutral, IIRC


Ot is a smart guy.

I find it humorous some people read that exact article and spew garbage from their mouths and/or fingers about it, and then almost in the same breath will say something like "whoever designed the Zilla is a genius."


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## umurali2000 (May 3, 2010)

Yes. PMDC motor will have brushes. 

Yes, BLDC Motor can be used for Regen braking. 

Regen braking occurs when the motor is running at a speed which is greater than nominal speed where the current will be flowing from motor winding to the mains or power supply. This condition is called regen braking.


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