# discussion on DC regen



## dtbaker (Jan 5, 2008)

I occasionally see ads for Zapi h3d HV controllers, which are supposed to be able to do DC regen..... The disclaimers I have picked up from a little reading are that the motor brushes have to be 'not advanced', and it can generate TOO MUCH regen if used at high speeds.

Can somebody chime and a post a little more ifo on the pros/cons of using a DC controller with regen? why are we NOT all doing this? what are the implications of de-advancing a DC motor brush position?


----------



## major (Apr 4, 2008)

dtbaker said:


> I occasionally see ads for Zapi h3d HV controllers, which are supposed to be able to do DC regen..... The disclaimers I have picked up from a little reading are that the motor brushes have to be 'not advanced', and it can generate TOO MUCH regen if used at high speeds.
> 
> Can somebody chime and a post a little more ifo on the pros/cons of using a DC controller with regen? why are we NOT all doing this? what are the implications of de-advancing a DC motor brush position?


Hi dt,

I'll give it a shot. Let's talk about series wound motors. When in regeneration, the motor is excited as a generator, right? Series generators are unstable. A little more current makes more voltage which makes more current which makes more voltage and so on. And, generator current is opposite flow direction thru the armature. Since the armature and field are in series, you must disconnect at zero current and then somehow reinitiate current in the proper directions. Then the series generator is not inherently self exciting.

So by the nature of the series machine, initiation, control and regulation of regeneration is a bitch. It can be done. Curtis at one time had a regen capable model but it didn't last on the market long at all. I suspect there were just too many problems and they deemed it unworthwhile in the interest of their business. I've heard of this Zapi regen controller. Never seen one. Have you? If it is so great, why don't we see them used all over the place?

The other problem with regeneration on series motors as EVers use them is that the brushes have been advanced to get acceptable commutation as a motor. This brush advance is right for motoring but the wrong direction for generating. So would you want a fireball in your motor everytime you braked? Setting the brushes back to neutral is an option. But then, for the higher voltage EV (above 72V), you have commutation difficulty both on motoring and generating. Solution: interpoles. But those are an expensive feature to build into a motor. And for what? So you can regen? It does not do anything to solve the stability issue.

In short, regeneration with series motors isn't worth it. It will cost you a lot, in dollars and reliability. And is unlikely to buy you much in tangible outcome. Most that use regen in EV cars are hard pressed to quantify an increased range.

Don't get me wrong. I like regenerative braking. I have it on lower voltage DC SepEx machines and high voltage AC large EVs and HEVs. Works great and especially on AC I see no reason to be without it.

But on your EV cars using DC series motors, forgetaboutit 

My take,

major


----------



## dtbaker (Jan 5, 2008)

thanks for details.  I have read the basic conclusion elsewhere, but not gotten many details... As an engineer I hate throwing away all that braking energy, but as a pragmatic builder I agree it is probably not a great choice. Looking to the future, I just can't justify an expensive AC motor+controller in a DIY conversion for a questionable amount of return.

I am thinking that if I were building a delivery vehicle with many stops/starts, or had very hilly terrain on my usual commute it MIGHT be worth it.


----------



## green caveman (Oct 2, 2009)

dtbaker said:


> I am thinking that if I were building a delivery vehicle with many stops/starts, or had very hilly terrain on my usual commute it MIGHT be worth it.


My interest in regen is primarily the braking action on downhill runs. Especially with the car made heavier by batteries I wouldn't want to use the brakes exclusively down a long hill.

No idea how much more range this will lead to. The problem is that, while the downhill has a big positive effect, at some point you have to get back up that hill.

For a Metro, you could use a sepex motor and a regen controller. Comments from users using some of the GE motors suggest that up to about 120V you're OK, although 96V seems to be considered the safe limit. 72V should give you good round-town performance for a Metro and Li. Of course, round town it probably doesn't make much sense.


----------



## piotrsko (Dec 9, 2007)

major said:


> I've heard of this Zapi regen controller. Never seen one. Have you? If it is so great, why don't we see them used all over the place?
> major



Pretty sure the NEW electric car we just bought at work had one (until the boss fried it on the first test drive). Ours is mosfet with a 500 amp limit. Sales idiot has no technical background, but label on blue controller box says Zapi. I will hunt around when they fix it, bring it back and get better details.


----------



## dtbaker (Jan 5, 2008)

piotrsko said:


> Pretty sure the NEW electric car we just bought at work had one (until the boss fried it on the first test drive). Ours is mosfet with a 500 amp limit. Sales idiot has no technical background, but label on blue controller box says Zapi. I will hunt around when they fix it, bring it back and get better details.



hhhmmm, not exactly impressive if it is so 'fryable'.


----------



## major (Apr 4, 2008)

major said:


> I've heard of this Zapi regen controller. Never seen one. Have you? If it is so great, why don't we see them used all over the place?





piotrsko said:


> Pretty sure the NEW electric car we just bought at work had one (until the boss fried it on the first test drive).


Hmmm,

Sorta supports my points.

major


----------



## ga2500ev (Apr 20, 2008)

How about attaching a permanent magnet alternator into the system like one of these:

http://www.windbluepower.com/category_s/1.htm

They run up to 10000 RPM and regen a lot of energy. Only problem I see is regulating it in such a way that it can reused. Charging supercaps maybe?

ga2500ev


----------



## Tesseract (Sep 27, 2008)

dtbaker said:


> ...
> Can somebody chime and a post a little more ifo on the pros/cons of using a DC controller with regen? why are we NOT all doing this? what are the implications of de-advancing a DC motor brush position?


This has been covered in exhaustive detail... Major makes the usual good arguments but I wrote a post back n July of 2009 where I break down the actual "return" you get for regen (which, unlike with AC, is not "free" in a DC controller): Tesseract's take on regen efficiency.

If anything I was being generous with some of my efficiency estimates... I know, for example, that the interpoled HV Kostovs (and likely the new NetGain 11HV) plummet in efficiency at high amps... down to as low as 55-65%.

Also keep in mind you can only recapture the energy that went into acceleration/hill-climbing... if you accelerate onto a flat highway and drive at a constant speed for 20 miles when you exit the highway the only energy you can recapture is a portion of what was used to get the vehicle up to speed (maybe a couple of joules?).

The Soliton1 is a two quadrant converter, so in conjunction with the ability to flip the field polarity it is theoretically capable of regeneratively braking a series dc motor. Whether we will ever develop the code to implement regen, and, furthermore, whether we will ever unleash that on the public, though, are two questions that I wouldn't hold my breath waiting for answers!


----------



## JRP3 (Mar 7, 2008)

Seems as if the best way to do regen on a series DC motor is with an external generator or alternator.


----------



## few2many (Jun 23, 2009)

JRP3 said:


> Seems as if the best way to do regen on a series DC motor is with an external generator or alternator.


Would you be referring to something like a couple car alternators on the non-driven wheels? Why does it seem like everyone wants the traction motor to regen? A couple alternators, one on each non-driven wheel would work, powerd up with the brake switch. Shouldnt weigh much. If/when I do a conversion using an auto tranny, regen would be weak, unless driven directly from the wheels seperate of the drivetrain.


----------



## JRP3 (Mar 7, 2008)

No just a single unit on the CE output shaft of the motor with an electric clutch, people use A/C clutches. That way it's not inducing any drag when driving, a switch would turn it on when the brakes are pressed.


----------



## dtbaker (Jan 5, 2008)

few2many said:


> Would you be referring to something like a couple car alternators on the non-driven wheels? Why does it seem like everyone wants the traction motor to regen? A couple alternators, one on each non-driven wheel would work, powerd up with the brake switch. Shouldnt weigh much. If/when I do a conversion using an auto tranny, regen would be weak, unless driven directly from the wheels seperate of the drivetrain.


using the tailshaft of the traction motor, you (could) hook to a beefy 8hp or 10hp generator and some considerable regen, albiet for brief periods unless you have long downhills. Generator heads without engines are available at HarborFreight; but they are pretty big, heavy, and in most cases probably less cost effective than just buying bigger batteries. An 80amp ICE alternator (at 12v) hardly would generate enough to be worth the cost, weight and trouble....


----------



## JRP3 (Mar 7, 2008)

People usually rewind the alternator for higher voltage and it works quite well.


----------



## Guest (Mar 30, 2010)

If you do the alternator trick go to the wrecking yard and get a used one because you will be rewinding it to make it work for your needs. They do work. Don't remember off the top of my head where you'd find the info but it's out there. 

Pete


----------



## dtbaker (Jan 5, 2008)

I am curious now... how much can a re-wound alternator put out?


----------



## JRP3 (Mar 7, 2008)

Here's an extensive writeup with lots of pictures http://www.waynesev.com/ev/regeneration.html


----------



## few2many (Jun 23, 2009)

JRP3 said:


> No just a single unit on the CE output shaft of the motor with an electric clutch, people use A/C clutches. That way it's not inducing any drag when driving, a switch would turn it on when the brakes are pressed.


but an alternator wont have much drag until the coils are powered either.


----------



## Tesseract (Sep 27, 2008)

dtbaker said:


> I am curious now... how much can a re-wound alternator put out?


If it started life as as 13.8V/70A alternator then it can put out about 1kw max no matter what voltage you rewind it for... that's it. 

Also keep in mind that the "claw pole wound rotor synchronous" alternator (the most common by far...) is about 50% efficient at converting mechanical power into electrical.

So, you have to go through a lot of work for very little return. I mean, if you can't recapture at least 10kW of power during braking neither you nor your batteries will notice it.


----------



## jackbauer (Jan 12, 2008)

I hope to do regen with the compound motor. Ive measured the armature voltage while coasting (admittedly on no load) and its a little over 100v with full shunt field.


----------



## few2many (Jun 23, 2009)

JRP3 said:


> Here's an extensive writeup with lots of pictures http://www.waynesev.com/ev/regeneration.html


Very good read, This is what alot of people do for converting the common chevy/gm alternator to a wind power alternator. I have a couple 100amp gm alternators I was trying to do this with, just slacked off on the project. Also, there is good luck with pulling the rotor apart and replacing it with neo magnets. check out http://www.windstuffnow.com/main/gm_alt_mod.htm
No way to use the internal regulator and it powers full time, though. 
Also, most alts are internally regulated for the 13.8 volts, 26-27volts for the 24volt systems. You can replace the internal regulator with something else to get more voltage.


----------



## jehan12413 (Feb 4, 2010)

Just my two cents worth, but I would not use a PM (permanent magnet) alternator for a regen application, I would keep the original wound rotor. That is the plan for my EV as I have some experience with wind generators using GM 10si and 12si alternators. The way I see it is with a PM machine there is no way to control the field strength and hence there is always power loss unless a clutch is used as mentioned previously. With a wound rotor you can produce much more power for short periods of time such as regen by simply increasing the voltage to the rotor. A stock rotor will draw in the 2-5 amp range depending on the alternator rating but can handle much more than that. I'm not saying not to use a clutch but it is an option as there is very little drag with the rotor unpowered. In addition this will alow the field to cool down relatively quickly. Two points I have learned from wind generators
1. At power levels of about 8KW the stock pulley will slip (it's clamped on by the nut). Use a keyway.
2. A belt will also not handle that much power. I would use a chain or gears.
Regarding the stator there are many aftermarket ones out there ranging from 335 amp at 12V to considerably lower current at over 500v. An e-bay search for PMA coil should turn up some results.
Good luck


----------

