Plug Braking

Technical discussion on converting internal combustion to electric
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ohmboy
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Plug Braking

Post by ohmboy » Fri, 18 Jan 2013, 00:20

In an attempt to get faster gear changes I am considering hooking up my DC motor and Curtis controller for Plug breaking. A momentry switch on the gearstick would bypass the throttle pot micro switch which cuts power to the controller.

I wouldn't expect the controller to get much hotter as plug breaking would only be used to slow the armature down when I'm changing up gears.

Could also come in handy on those rare occasions that the motor gets a free rev and takes forever to wind down again.

Good idea or bad?

Mark
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acmotor
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Plug Braking

Post by acmotor » Fri, 18 Jan 2013, 01:43

Just thinking this through without researching first....

So with a series DC motor you can't extract power from the armature without applying some current to the field windings. i.e. setting up a regen configuration. Then feeding armature voltage back to battery.

If you just wanted to brake the emotor (as is done in many electric hand drills for fast stop, AKA plug braking) then short the armature (i.e. at brushes) and supply a small DC current to field. Probably only a few volts required. From a floating 12V battery ?

So a contactor (or mosfet / bipolar) shorting the armature and a tiny squeeze of throttle via normal controller could potentially work. Risk is lack of inductance for the controller to switch into may damage it.

Probably all been done.

I will resist suggesting you get an AC motor. Image
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Plug Braking

Post by Canberra32 » Fri, 18 Jan 2013, 04:34

DC = HP = :D
AC = hippie


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acmotor
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Post by acmotor » Fri, 18 Jan 2013, 05:49

Oh well.... I guess I left myself open for that. Image
DC = Dinosaur Car. Great in a straight line, should try pikes peak.
AC = Advanced Car. I never knew Elon Musk was a hippie ? Image
Seen the model S reviews ? There are some great vids on youtube to get you up to date. Image

The fact is they are all EVs and that is what counts.

Anyone done some research on plug braking ?
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Richo
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Post by Richo » Fri, 18 Jan 2013, 07:15

Could always put the switch on the clutch pedal to bypass accelerator pot - or set it to Zero.
Slightest tap on the clutch pedal makes sure there is no chance of accendental free revving.
Downside - would probably prevent burnouts...

Another switch on the clutch pedal can "allow" plug braking when it's fully depressed ie when the motor is free wheeling.
If you press the button on the gearstick and the clutch pedal is fully engaged only then it momentary plug brakes.


Depends on what the controller does when the pot goes to zero or open circuit.
Would you need another contactor across the one set of windings activated by the momantary switch and still have the controller set at like 1% for it to work?


Here is the results of my plug braking reasearch:
Image
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Post by ohmboy » Fri, 18 Jan 2013, 13:18

I like your plug breaking research Image
I don't have a clutch or clutch pedal so will just be a button on the gear stick. It's a good time to experiment as I may replace the Curtis with a Soliton soon because it has some issues. Doesn't matter if it goes out with a bang Image
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Post by Johny » Fri, 18 Jan 2013, 21:36

Just disconnecting the controller input or grounding it isn't going to help you much. It will have the same effect as removing your foot from the accelerator.

If you want to actively slow the motor down you are going to have to do something like acmotor suggested which will get complex very quickly. That is: excite the field in the reverse direction and short the armature. If you are careful with the experiments and slowly increase field excitation, noting the effect, there shouldn't be any smoke. After all, you are just slowing the motor down quickly which shouldn't involve much energy.

Edit: fixed the throttle
Last edited by Johny on Sat, 19 Jan 2013, 18:19, edited 1 time in total.

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acmotor
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Post by acmotor » Fri, 18 Jan 2013, 21:55

ohmboy wrote: ....Doesn't matter if it goes out with a bang Image


Universal logic suggests then that it won't fail !

No need to excite field in reverse, just excite it. Shorted armature doesn't care for polarity.
i.e. if the field were PM then shorting the armature creates braking both directions. Perhaps a low value resistor as the armature short rather than fence wire ?
Just take care not to overload controller.
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acmotor
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Post by acmotor » Fri, 18 Jan 2013, 21:59

Johny wrote: ... eccelerator.


You saw it here first folks. emotor, email, etc... now

An EV's electronic accelerator is called an eccelerator ! Image
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Post by Canberra32 » Sat, 19 Jan 2013, 00:02

Yeah good in a straight line :) but also good in corners be ause cornering has nothing to do with AC or DC :)
Hippie :)

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Post by acmotor » Sat, 19 Jan 2013, 01:44

Agreed.

BTW, taken a AC motored Leaf for a fang through the hills at 140kmph with instant 80kW power/30kW regen all on the accel...oh yeah, eccelerator pedal, all in one gear ? I have. Image

Trivia... did you know that the White Zombie has the same 1/4 mile times as a Bugatti Veyron ?
What's that got to do with plug braking ?    Image
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Plug Braking

Post by PeterS » Sun, 20 Jan 2013, 19:11

Ohmboy, If you're upgrading to a Soliton controller which presumably has more grunt than a Curtis, then you won't have to change gear.

My Holden Combo is fitted with a Zapi controller and goes everywhere in 3rd gear; from starts on steep hills to 100kph, all in the one gear (I have to watch the revs though!). The Zapi has 800A capacity but I rarely draw more than 400A.

What is the current capacity of a Soliton?
PeterS

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Post by Mark T » Sun, 20 Jan 2013, 23:37

Hi Peter. The Solaton Jr. is rated at 450-500 Amp. Peak at 600 Amp. May also need to update motor from 8 to 9 inch or add some cooling fans.
But the car has been so good I really don't want to change anything until I have to.
Mark

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Post by Richo » Mon, 21 Jan 2013, 21:03

ohmboy wrote:I don't have a clutch or clutch pedal


So how does the motor accedently free spin and take forever to wind down?

Have you been getting your eV on 2 wheels?!? Image

Official now:   eccelerator™

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Post by Mark T » Tue, 22 Jan 2013, 02:20

Motor usually spins up if I miss a gear, trying to show the ICE cars who's boss.
Don't like to strain my little Suzuki gearbox trying to slow the motor down to get a gear again.
Getting my EV on two wheels doesn't usually last for long and revs stay at a manageable level.

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Post by 4Springs » Tue, 22 Jan 2013, 02:22

The way I drive my vehicle I'm glad to have a clutch. I'll often sit at about 80kph (in 2nd), which is about 5000rpm, the maximum for my motor. Apparently it is more efficient at that speed, and gets more air through to cool it. So if I didn't have a clutch, and I wanted to change up a gear, I would put it into neutral and have to wait for it to wind down to the right speed to mesh the gears into 3rd. I'm guessing, but I'd be surprised if it took less than 20 seconds to go from 5000 to 2000 rpm. Is this the problem you have Mark?
Since I do have a clutch and a flywheel it would be much more pronounced on mine - the flywheel weighs near 10kg.

Brainstorming ways to slow down a motor:
Do you have an unused shaft from your motor? I wonder what sorts of brakes are available from bike shops, and whether one could be fitted. Doesn't sound like an elegant way to change though, pulling on a lever attached to a cable...
Another thought is to attach an alternator to that (quite possibly non-existant) shaft. It would freewheel most of the time, but when you click in a relay it shorts it out, causing a braking force. If you have a switch on your potbox you could hook it up so that taking your foot off the eccelerator fully causes the relay to cut in and brake the motor.

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Post by Mark T » Tue, 22 Jan 2013, 22:54

I'm only fine tuning what is a great car to drive. Max delay between gear changes is only around 3 seconds, which doesn't sound like much, but I would like to try circuit racing or drag racing this year. I like to keep my EV as mechanically simple as possible. I like Peter's suggestion, bigger motor and ditch the gearbox.

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