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Regenerative braking

Technical discussion on converting internal combustion to electric
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acmotor
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Regenerative braking

Post by acmotor »

I have regenerative braking on my AC motor conversion.
The controller will regenerate down to stop with as much torque as it will accelerate. So much so that I rarely use the brake pedal at all. Surely you would only not have regenerative braking if you ran a series DC motor and regeneration was not an option or only available in small amounts at high revs with a clever controller. I have heard claims of 10 to 30% improvement in range with regenerative braking depending on terrain and depending on how lower revs your system will regenerate at. I shall gather some data on my conversion.
There is a down side for me at present, down hill on full batteries I have no-where to put the power and I need to run an electric frypan as a braking resistor ! Image
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Regenerative braking

Post by Turtle »

A question please *acmotor*?

Where and when did you get your AC motor conversion done?
Did you acquire parts & undertake the job yourself?

I am looking at such a conversion, rather than a smaller DC job.

You can contact me offlist if you wish.
drysdale@iinet.net.au

Cheers, have a good one mate! :-)

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Regenerative braking

Post by acmotor »

Hi Turtle,
Home grown conversion. Guess you're talking red suzi here.
Like a working man's version of an AC Propulsions AC-150
http://www.acpropulsion.com/ nice bit of kit, but at $35k + some serious batteries you start to look $100k in the face ! Image
My EV project was to show it could be done off the shelf with industrial parts.
Image



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Regenerative braking

Post by jpcw »

You can do regen with a series DC motor. I'm doing a conversion using a ZAPI H2 controller that has regen on the Series DC motors. Not as efficient but from what I have heard very good for brake assist.

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acmotor
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Regenerative braking

Post by acmotor »

True there is limited regen available from a cleaver controller at higher revs from a series DC motor.... but AC systems can provide 90% efficient regen up to the max motor torque at nearly all speeds !! Completely different beast ! Image
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Regenerative braking

Post by Mesuge »

acmotor wrote: There is a down side for me at present, down hill on full batteries I have no-where to put the power and I need to run an electric frypan as a braking resistor ! Image


Hi Tuarn, I'm about to crack down quite similar problem, very hilly country/part of the city overhere and full batteries to start => challenge..

Would you pls. share some more details, like wiring, nominal watts of your frypan, mechanics - were did you mount it in the vehicle (safely), etc..? I thought you are using some Danfoss stock braking resistor like in that greatly interesting "a4x4kiwi Hilux" conversion blog.. ?

I'm wondering how did you make it eat 750VDC, was it just plug and play/pray? Perhaps, frypans could be used in this diy fashion instead of new braking resistors, frypans also usually have got that red signal (power_on) light so this link could be also used on the dash etc..
(perhaps with some opto in between for safety)
Last edited by Mesuge on Tue, 04 Mar 2008, 21:17, edited 1 time in total.
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Regenerative braking

Post by a4x4kiwi »

Something I have been thinking about is not using the braking resistor and enabling the setting to delay the braking time if the bus voltage exceeds a threshold. The important thing is that the voltage threshold is equal or less than the maximum cyclic charge voltage for the pack. This is dependant on the controller.

The implication is that when you are going down hill or slowing down on a full charge you will need to use the brakes more than if the batteries were discharged. It might make the regenerative braking a little unpredictable.

Cheers,
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Post by Sparky Brother »

I`m a little scared of the price of the worth of the conv. kit you mention about.
I my self am pretty far from the physical conversion however already set some milestones though. Here is the picture. Donor car Land Rover Discovery!!! 2.7 t. in weight. I want to keep it as a4WD so obviously the plan is to get 2 x AC Motors (have no intention to even speak about DCs) and put them where the gear box was. Question; While the V8 Petrol engine is designed for 134kW, 304Nm at some 2600rpm (got some idea combustion engines are kW rated differently) What should be the combined (Peak) power of the two AC motors. Speaking of ACs we`ve got several types of Inductive AC Motors and while the big hassle is the regenerative braking what exactly is the motor I should go for. I can only guess we are talking a Squirrel Cage Inductive Motor. Right?

Also how about using some sort of capacitors set in regard of making it less harsh to the bateries when accellerating/breaking. The talk about the invertor is yet to come because I`m still struggling to understand what`s the difference between "controller, drive and invertor". As for a beginning if someone lights the bulb will be really something.

Any idea - much appreciated

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Post by a4x4kiwi »

Hi Sparky brother,

All good questions Image

The weight of the vehicle for you will be the biggest factor in defining your motor and drive requirements. My Hilux will have a kerb mass (before conversion) of 1250kg. I am advised that this is too heavy but I will see how I go.

For motors, I believe that GE does some new aluminium framed motors. Otherwise check M&E equipment in Sydney for used ASEA motors. An aluminium frame is vital because they are light. My 15kw unit weighs in at 95kg.

The 2 motors can be run electrically in parallel in open loop control mode.

In a perfect world the motors would be 240v star wound. These can be run off the 600v DC bus and produce torque up to 85hz rather than 50hz in delta. This is to do with differing saturation voltage/frequency in star configuration.


An Inverter / Drive / Controller are all the same thing. I probably use the terms interchangeably in my blog.

The inverter will have to be a bit of a monster to cope with the load of 2 motors, but with some know-how much of the mass can be removed from the controller as it is redundant in a DC situation. The input filtering, rectifiers, capacitors and soft charge circuits can all be eliminated if the inverter can function without them.

I like your idea of using ultracaps to ease the load on the batteries. See the recent Silicon Chip magazine article on these.

A lot of the fun is in the design and planning.

Regards,
Mal.
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Post by Mesuge »

Lets add few interesting regen hints from the pros (ACP), mainly from their Scion bx (Ebox) project and general ACP150gen2 powertrain properties. I think many of these can be utilized in diy "Danfoss" drivetrain setups as well..

ACP is probably the most advanced system on the planet, so take their >30% regen, as reported from highway/downtown test rides in Calif. as the theoretical limit (disregarding ultracaps and other unbotanium substances) Image

--
1/Specifications of ACP150gen2:
http://www.acpropulsion.com/technology/gen2.htm
!!!http://www.evbones.com/acp150gen2.pdf
http://www.acpropulsion.com/ebox/

Readup on the regen related information (pdf), very interesting,
for instance about the crude anti-slip/block protection which is just reading wheel revolution from opposing axle and that I/O is fed back to the inverter logic to limit/shutdown regen etc..


--
2/Quote from 3d party testing:

"In case you are wondering about aggressive regen and notifying drivers behind you of your deceleration via brake lights, don't worry because AC Propulsion has already figured this out. Their motor control samples motor speed at something like 10Hz, and since the motor drives through a fixed ratio, motor speed is an unambiguous indicator of vehicle speed. So, by continually sampling speed one knows when the car is slowing down, and the brake lights are turned on automatically if the deceleration exceeds a low threshold. It works in reverse too. The brake lights also come on with actuation of the brake pedal as in a normal car. Interestingly, you can be using quite strong regen holding speed steady on a downhill and the brake light will not come on. "
http://www.stefanoparis.com/piaev/acpro ... /ebox.html

--
3/ Real driving test data plus pictures of system ifno lcd panel incl. regen statistic, regen tuning knob, regen braking activates special "regen warning" LED on the dash and other goodies in the cockpit..
http://www.stefanoparis.com/piaev/acpro ... index.html

PS Tuarn, pls. describe more your frypan braking resistor - regen offloading technology, namely how to put safely~750VDC into that old kitchen critter, thanks..
Last edited by Mesuge on Sat, 14 Jun 2008, 05:56, edited 1 time in total.
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Regenerative braking

Post by Rob M »

I have to ask why you would waste energy by heating a frypan when the whole idea of regen is to conserve energy. Why not start out with a less than full battery?
Unless you live in a very hilly environment or drive a stop/start passenger bus, regen is always going to be more expensive than carrying a couple of extra cells or Ah's.
If you use your EV regularly, say going to work and back, count and time the seconds you are actually applying the brakes. Multiply this by the watt.hrs you could recover to get the total regen. I think you will be surprised by what a small amount of energy it is.
The saving on brake pads is minimal anyway.

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Post by acmotor »

Sorry I ever mentioned the frypan !!!

It is gone now anyway. I have a genuine Danfoss braking resistor. 40kW at 10% duty, designed for the job. Don't worry Rob, it very rarely sees any power.

When I consider the measured battery kW each way there seems to be around 20% benefit, more depending on traffic than terrain. Stopping at a red light is far more satisfying nowadays. The more the stops the more the return. This is on SLA, I am hoping for better on TS as they accept the fast recharge better.

Rolling resistance is less with direct drive and an AC motor than with a gearbox and a brushed DC motor (or two). AC induction motors spins incredibly freely at thousands of RPM. No brush drag.

The difference is even more than putting an ICE in neutral since there is no gearbox drag.
Don't be misled by brakes they get through a lot of energy and they are a lot stronger than motors !

The truth is that the regen on full batteries is not that much of an issue since batteries are never full for long in an EV !

Rob, your point about not starting with full batteries is a good one.
The EVpower lithium BMS seems to be doing just that. It starts with 3.8V not 4.2V on the batteries. I understand that there are technical compromises that choose that voltage however it seems to be less than 100% charge, maybe 95%. We'll have to talk to Rod about Mk2.
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Post by Mesuge »

acmotor wrote: Sorry I ever mentioned the frypan !!!

Rolling resistance is less with direct drive and an AC motor than with a gearbox and a brushed DC motor (or two). AC induction motors spins incredibly freely at thousands of RPM. No brush drag.

The difference is even more than putting an ICE in neutral since there is no gearbox drag. Don't be misled by brakes they get through a lot of energy and they are a lot stronger than motors !


Thanks for the answer.
The problem with direct drive is that most of the euro/asian econoboxes these days are FWD only, so to use original transmission as a reductor without clutch/flywheel attached seems necessary. Another option could be some special reductor ang go direct but I doubt there would be any significant efficiency gain, also take into account the price/eff. ratio. So is it possible to conclude having list of the highest efficency as follows for FWD cars?


1. Direct drive with reductor for traction applications,
professionaly made (ala ACP) or other, will be expensive.

2. Hacked original tranny without clutch and flywheel coupled directly to emotor (see Gavin's Tredia or various similar on Austin EV - album). In small cars these trannies are really lightweight anyway.

3. Original tranny (incl. clutch and flywheel) coupled to emotor.

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Post by acmotor »

Image
Your thoughts on drive trains are correct. But don't discount the losses of a gearbox. 85% efficiency is all you are likey to expect in top gear. Rob Mason is correct, just put in a few more batteries to make up for the losses. An EV conversion should be kept simple and low (?) cost.
The thing is that all the losses weigh up. Battery ESR losses, controller losses, wiring losses, motor losses, gearbox losses, diff losses, rolling resistance, wind resistance. If you don't address all of them in some way then you won't go far.
If going F(front)WD means you have to retain the gearbox then it would put me off.
Don't get me wrong. A DC conversion with a gearbox and lead acid batteries works and is easy to do, low cost and will suit a lot of people's requirements. You don't have to try for the Holy Grail !
Remember that a compact FWD is low energy consuming because it is small, not because it is efficient. A hummer Image is likely be more efficient in kg moved/litre of fuel, but not that efficient at transporting 1 person.

Efficiency is one of the reasons I think Hybrids like the prius are bad news, and in reality, such old technology touted up with a CAN bus and digital readout. (google their drive train for yourself)

Lower revving motors are desirable, although this usually means bigger / heavier although developments are being made.

Inevitably, as people think about motors and drive systems they will end up in one place for the reason of efficiency if nothing else....

>>>>>> Wheel (Hub) motors.Image

They are nothing new. It is a 100 year old idea (Baker electric). But direct drive with no gears in the hub is more recent. PM AC of course.
I am not quite convinced with these yet, although they are eventually the way to go. (pros are well known)
My reservations are....
- Unsprung mass (alloy wheels weren't invented for looks you know).
- Wet, high g, dirty environment.
- Cost (at this stage at least).
- Unsuitability to the EV conversion market, the IMMEDIATE market.

Hub motors will most likely be part of the new generation of vehicles to come, designed from scratch for the different suspension and dynamics of the hub motor.

It would be great to think of buying a set of 4 hub motors from the local hardware store for an EV conversion. However not likey.

What a lot of waffle. I'm going out to migrate some electrons.
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Post by Thalass »

Just because a small FWD car has it's diff inside the gearbox, doesn't mean you can't substitute another vehicle's rear diff and mount it in the front. If you're going to put batteries in the engine bay area, then you're going to have to make up mounting brackets anyway, so modifying that to include mounting points for the diff wouldn't be that difficult.

It's extra work, sure, but a mechanically simpler result, I'd say.
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Post by woody »

And if you are putting a diff in the front, you don't have to hang the motor off the back, you could put the motor on the front or on the top to give you easier access/better cooling/ better weight distribution / better aesthetics :-)

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Post by Mesuge »

Here is some interesting info on gearbox efficiency optimization, e.g. getting rid of the 5th gear, reverse etc. Might not be applicable on other manuf. designs..

Both clutch/freewheel and completely clutchless (gutted tranny) conversion methods could benefit:
http://www.amphibike.org/index.cgi?page ... ssion_mods

More links on Gav's site and EValbum (Fiats)
http://kiwiev.com/Step%20Five%20-%20The ... emoval.htm
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Post by Mesuge »

acmotor wrote: ..If going F(front)WD means you have to retain the gearbox then it would put me off..


Again, that takes us back to the ever elusive question of suitable donor platform options! The problem is there are not that many choices in the RWD passanger car segment with reasonable ~1ton weight for the direct drive AC conversion. Basically the only preferable compromise in weight/aerodynamic/emotor&batt. access/cargo space/price/esthetics is the BMW 316i/32x 4seat coupe from the mid-late 1990s..

http://www.bmwinfo.com/pictures/00866.jpg
http://www.evdrive.com/BMW_project/motorpull.html
http://www.pelicanparts.com/bmw/techart ... eplace.htm

There is a giant space under the shifter console/former tranny home, so as the emotor being closer to the rear differential most of the engine bay now empty there can go many batteries and inverter,..

And even this "ideal" 1ton passanger car is so much last century anyway, while for instance aluminum chassis cars (upscale german and japanese) do exist they are very expensive even after 5-10yrs from production and logged 200kkm..

And after all this deliberation, it sounds viable only on the condition of at least 50-100km or more range type of project. Because ~1ton passanger glider (not pickup/workmule) for shorter errands is just stupid way for transportation in the first place, this should be the domain of 600-700kg platform at max..

I'm afraid this renders the concept of efficient/affordable RWD passanger car donor under 10yrs age for AC direct drive project as pointless. Obviously if someone wants to burn cash and race on the highway, these 3-series bmws after 2000 are one of the best candidates for luxurious EV conversions.. It will take ACP150 and big doze of lithium or Nilar NiMH though. In the DC world high voltage Zilla option might do as well.
Last edited by Mesuge on Mon, 30 Jun 2008, 21:46, edited 1 time in total.
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Post by Johny »

Has anyone direct coupled an AC motor to a tailshaft yet?
I have a problem with mating a slip-yoke on the tail shaft to the motor drive shaft.
Any ideas?
John

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Post by acmotor »

Do you mean - to retain the splined coupling that used to go into the gearbox ?

see www.evalbum.com/1149
I used a 100mm dia by 120 long aluminium block, bored to 42mm ID and a keyway cut for the motor end and turned at the tailshaft end to suit the spiggot of the uni joint on the front end of the tailshaft. The ali was drilled and tapped for the 4 bolts of the uni.
I used a suzuki tailshaft that had a sliding spline between two flanged uni's.

Truth is the system would work without the spline but probably put more load on the bearings.

You could look for a completely different tailshaft with an inline sliding spline coupling and fit a rear uni flange at the front (by re-assembling the front uni) as above. Or butcher the gearbox to get the other half of the spline.
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Post by Johny »

Hi Tuarn
I have visited your evalbum page many times over the last month and I must admit your were the person who switched on the light re AC industrial drive and 3 phase motor etc. with me.

It would make it heaps easier if I had a spline on the motor but I would need some method of lubricating it etc.

I was wondering if a dirty great rubber coupling would take up enough movement to let the tailshaft and rear axle run free.
Just musing...

I actually don't mind using bits of the gearbox, maybe tail housing and shaft. Anyway that's my current mechanical design block.

While you are reading this. I read up on the Danfoss VLT5042 that you used (lots more question on this but I'll ask them later) and it says 160% torque. Where does the 466% you mention on the evalbum page come in. I contacted a guy at ABB and the small frame 11kW can do 200%. I'm not being picky but I have to plan if I can do this with a 3.89 diff ratio.
Thanks
John


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Post by acmotor »

A suitable rubber coupling is a fenner coupling,
http://www.fptgroup.com/products/hub_couplings.asp
sometimes known as a tyre coupling. It would provide the required movement. But if used in a tail shaft then it would require an intermediate bearing to stop the whole thing getting out of control.
My Izusu (next conv.) uses an intermediate bearing so I may use a fenner.

Rat the gearbox if you have to for the spline.

The VLT5042 is a 30kW + 160% controller, 52kVA rated max and the motor is 11kW. Dial it all in and the controller says it can supply 466% of the 11kW motor's 73 Nm nominal torque. The ABB data shows the pullout torque of the 11kW motor is around 300% of nominal and this assumes standard constant V/F ratios. The VLT drive produces load dependent V/F ratios and basically pumps the motor for all its worth. That is, increased voltage at low revs.
This 466% torque is available up to around 500RPM. It reduces to 300% at 1500RPM (50Hz synchronous speed) and has reduced to around 150% at 3000 RPM. These are all intermittent ratings (1 minute or so)
Remember here that if you want incresed torque your controller must be capable of the extra current.

Most motor manufacturers think 415V 50Hz and nominal torque with fixed kW. Put a cleaver controller to work and allow increased voltages, revs and intermittent operation and an 11kW motor comes alive.

Siemens have been doing it for years.
Check the Evisol Thorr Ev thread on this forum.

My ratio, emotor to back wheels is 6.5:1
With a 3.89:1 diff you would need to check your calcs for expected performance. You might need an 18.5 or 22kW motor.
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Post by a4x4kiwi »

Hi John,

I too have been inspired by Tuarns work. See my blog for progress with my Hilux ute.

For the tail shaft connection, I am adding a sliding joint shaft from the intermediate bearing (middle uni) to the diff. I am going to use a fixed shaft between the motor drive flange and the intermediate Bering and middle uni.

I should have a picture on my blog in a week or so.

Regards,
Mal.



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Post by Johny »

Thanks guys
I'm glad to here that I'm not alone in the tail shaft fiddle.
There are enough split tail shaft vehicles out there so I should be able to adapt something.

Thanks for the drive/motor description Tuarn. It looks like I have to be a bit careful which motor. Among the new ABB motors there is a smaller 11kW but It's rated lower than the full size.

I have already contacted someone with the same(ish) car as me who has a 4.78 diff and perhaps even a 5.1 so that's my fallback. I don't want to go too heavy on the motor as weight is my opponent here. Wife desperately wants to keep the 4 seats in the EV and I can't afford Lithium power for this first EV (unless I take a REALLY long time converting it).



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Post by Johny »


I have been chasing controller prices and am astounded at the prices. Generally over $6000.
There has been one lower price response at $2800 for a WEG CFW 09 so that's my backup for now.

While I wait for my lotto win or another one to come up on eBay I have been checking out the possibility of a DIY controller and found quite a few custom chips. I have a service request in with one of the manufacturers asking about torque control but meantime...
(Microchip also have an AC controller now which also looks good)

Tuarn mentioned at some point that the shaft encoder wasn't absolutely necessary. How does the trottle control differ in practical use when you are using the controller to estimate RPM. This sort of dictates how simple the controller can be if a DIY is a reasonable course.

I think this has to be simple as I don't have time to do SW development of any complexity (not do I want to go down the track of high-power experiments with all the device blow-ups it would probably entail) given the amount of work to do on the EV overall. Doing a host controller in a PIC or something would be fairly straightforward so that's OK.
(I do embedded software for a living but don't have heaps of spare time.)

The controller devices available make it look deceptively simple.
I would appeciate comments, whichever way.

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