Range: 156Volts vs 312 volts

[Zeke Yewdall]

True....  It must have been a situation where the engine failed so they lost
engine braking, then the brakes overheated and stopped functioning.

Z

On Tue, May 13, 2008 at 7:26 AM, Karl Bellve <Karl.Bellve@...>
wrote:

> Zeke Yewdall wrote:
> >  Schools
> > busses for use in the mountains here are required to have an electric
> > retarder on the driveshaft in case the brakes fail (I think a bus full
> of
> > kids went over a cliff around 1977 when the engine (and hence airbrakes)
> > failed, and that law was implemented shortly after).
>
>
> When air brakes fail, the brakes fail in the on position. Air is used to
> compress the springs to keep the brakes shoes off of the drum. No air,
> brakes activate.
> -------------- next part --------------
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> email;internet:Karl.Bellve@...<email%3Binternet%3AKarl.Bellve@...>
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[Roland Wiench]

My old CableForm controller had resistance braking.  It consist of another
main contactor and a resistor in series with that contactor. As the
accelerator was de-press, the main contactor would open and this resistance
braking contactor would close if I had a control switch on, which it allow
to do so.

A DC series motor with compensating fields normally become a generator when
a mechanical force is use to turn it.  The problem here, is when you put in
100 percent battery power to become a motor, it will only become a 75
percent generator, because you lose about 25 percent by iron saturation.

The DC series type motor is connected to a large 300 amp diode which is
place in the direction that battery current cannot flow from the battery to
the motor.  It is same type of diode that is across the main contactor which
is call a free wheel diode.

There is several ways that the energy can be use from the main motor during
the coast down time.  One is where the resistance braking contactor is
connected directly to a very large resistor that will accept any level of
voltage and provide some load to the motor which slows the EV.

One way, which is call rheostatic braking.  This involves disconnecting the
motor from the supply, reversing the field connections relative to the
armature and connecting a resistance across the motor.  The then acts as a
series generator supplying the resistance load.

Another method which was tested on my EV, which was use to help slow the
7850 lb EV on a very steep 2 mile hill, is to reversed the two main lines
coming off the motor and connected to a very large resistor to limit the
current while still connected to the supply source.  The motor now tends to
run in the opposite direction of the vehicle motion.

The second method was more effective which is call plug braking than the
resistance only braking.  It gave greater torque, but current is drawn from
the battery.  We had to use a 30 inch long resistor that was 15 inches
square that was 0.5 ohm with tapes at 0.16 and 0.32 ohms.  It was hang off
the front of the EV, and would glow red which would slow the EV from 90 mph
down to 60 mph.

Today, I use a 7kw invertor-alternator that is connected to the main motor
pilot shaft, that is connected by a electric clutch.  It can provide over
100 amps of power to all my accessories at the REGEN time.

Roland





We had to use a very large resistance that was hung off the front of the EV.
This resistor is a 0.50 ohm resistor that had two center taps of 0.16 and
0.32 ohms.

The size of this resistor is about 30 inches long and 15 by 15 inches wide
stainless steel plates.  This resistor is normally use for a test load bank.






----- Original Message -----
From: "Mark Grasser" <markgrasser@...>
To: <evdl@...>; "'Electric Vehicle Discussion List'"
<ev@...>
Sent: Tuesday, May 13, 2008 6:38 AM
Subject: Re: [EVDL] Range: 156Volts vs 312 volts

> I don't know if going downhill in a car that now has no engine breaking
> and
> is probably over the design weight of the brakes on the car would be
> considered a non issue, of course the first trip down the hill will be the
> deciding factor. I do like the idea of the resistor across the motor for
> engine braking but would you not have to put some voltage to the field to
> get it to work?
>
> Mark Grasser
>
>
> -----Original Message-----
> From: ev-bounces@... [mailto:ev-bounces@...] On
> Behalf
> Of Peter VanDerWal
> Sent: Monday, May 12, 2008 3:29 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] Range: 156Volts vs 312 volts
>
> Diesel powered cars have very little compression braking and seem to be
> able to descend hills safely.
>
> Considering the limited amount of hill that you can climb, I don't think
> you'll have enough downhill to cause any serious problems for the brakes.
>
> I think this is practically a non-issue.
>
> > On Mon, May 12, 2008 at 1:59 PM, storm connors <stormconnors@...>
> > wrote:
> >
> >> I have a similar situation re elevation. Regen won't buy you anything
> >> if your batteries are fully charged when you leave home. Electric cars
> >> are happier when you live in the valley rather than the mountaintop.
> >>
> >
> >>From an energy perspective, it might not, but from a not crashing
> > perspective, if you add a giant resistor bank to burn it up as you
> > descend
> > the hill, it still might be useful....
> >
> > Z
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>
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[Roger Stockton]

David Nelson wrote:

> On the cost side of things it looks like I'd be ahead to go
> with 6v flooded and a low voltage Zilla. If I read Otmar's
> web site correctly that if I needed to go to a higher voltage
> later I could have him upgrade my controller.

Double-check Otmar's site before placing your order; I may be mistaken, but my recollection is that he can upgrade a Z1K to a Z2K of the same voltage, but that you cannot upgrade a controller from one voltage model to another.  If you think you might later upgrade beyond 156V, then I'd suggest it is best to just spend the couple hundred more for the -HV model up front.  This is probably less than you would pay for the upgrade and return shipping later, and Otmar has suggested that he is looking at selling the business, so there may never be a later... :(

Cheers,

Roger.

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[Roger Stockton]

Mark Grasser wrote:

> I don't know if going downhill in a car that now has no
> engine breaking and is probably over the design weight of the
> brakes on the car would be considered a non issue, of course
> the first trip down the hill will be the deciding factor.

My auto-tranny ICE has essentially no compression braking unless I manually downshift it to 2nd; I don't think many drivers rely on compression braking anymore.

If the vehicle is over the design weight of the brakes, it really has no business on the road in the first place!  Keep the conversion within the GVWR and you shouldn't have to worry about the braking ability.  Or, if you know you are going to end up over GVWR, upgrade the brakes with beefier parts from another member of the vehicle family that had a GVWR like that of your conversion.

Cheers,

Roger.

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Mark Grasser wrote:

>I do like the idea of the resistor across the motor for engine braking,
>but would you not have to put some voltage to the field to get it to work?

Check the archives for posts by Lee Hart mentioning Dynamic Braking and
Residual Magnetism.  Lee believes that most motors will develop a small
residual magnetism from the field windings, and if you put a low-ohm
resistor across the armature (like .01 or .1 ohms), you can generate
significant braking power.

Bill Dennis

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[markgrasser]

Roger,
I would have to disagree with you. Just an easy example, go down a small
hill near you in drive then go back to the top and go down in neutral.
Anyone with any knowledge of hill descending knows to split the decal work
between the brakes and the engine.

Mark Grasser
 

-----Original Message-----
From: ev-bounces@... [mailto:ev-bounces@...] On Behalf
Of Roger Stockton
Sent: Tuesday, May 13, 2008 1:49 PM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Range: 156Volts vs 312 volts

Mark Grasser wrote:

> I don't know if going downhill in a car that now has no
> engine breaking and is probably over the design weight of the
> brakes on the car would be considered a non issue, of course
> the first trip down the hill will be the deciding factor.

My auto-tranny ICE has essentially no compression braking unless I manually
downshift it to 2nd; I don't think many drivers rely on compression braking
anymore.

If the vehicle is over the design weight of the brakes, it really has no
business on the road in the first place!  Keep the conversion within the
GVWR and you shouldn't have to worry about the braking ability.  Or, if you
know you are going to end up over GVWR, upgrade the brakes with beefier
parts from another member of the vehicle family that had a GVWR like that of
your conversion.

Cheers,

Roger.

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[Roger Stockton]

Mark Grasser wrote:

> I would have to disagree with you.

Well, OK, if you must.  I didn't realise you'd driven my car...  ;^>

> Just an easy example, go
> down a small hill near you in drive then go back to the top
> and go down in neutral.

Like so many other EVers, I live on a hill, and just to add insult to injury, my work is at the top of a steep hill across a valley from my home.  Unless I apply the brakes or downshift to 2nd (and still touch the brakes), I will accelerate to about 60mph by the bottom of the hill from work.

As I stated, there is essentially no compression braking on my ICE unless I manually downshift my automatic tranny.  I did not say there is no braking, just not a useful amount.  Your vehicle may certainly differ.

> Anyone with any knowledge of hill descending knows to split
> the decal work between the brakes and the engine.

I'm not disagreeing.  I'm just saying that in my experience few people with automatic trannies *ever* use anything but P, D, and R; they will ride the brakes down a hill instead of downshifting to take advantage of the compression braking that might be available.

I do not believe that compression braking is required to safely slow or stop any modern passenger car, and do not believe that auto OEMs design their braking systems on the assumption that some minimum amount of compression braking will always be present.  I could be wrong, but I have seen nothing that would lead me to believe otherwise.

My DC EV has absolutely no compression braking and its (stock) brakes have no problem with stopping the vehicle or slowing it on any of the hills I've driven it on.  Of course, my EV is within the factory GVWR.

Cheers,

Roger.

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[Zeke Yewdall]

> I do not believe that compression braking is required to safely slow or
> stop any modern passenger car,
>
> I hope you never drive up Pikes peak then.......

Z
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[Bob Rice-2]

----- Original Message -----
From: "Zeke Yewdall" <zyewdall@...>
To: "Electric Vehicle Discussion List" <ev@...>
Sent: Tuesday, May 13, 2008 6:16 PM
Subject: Re: [EVDL] Range: 156Volts vs 312 volts


>> I do not believe that compression braking is required to safely slow or
>> stop any modern passenger car,
>>
>> I hope you never drive up Pikes peak then.......

       Hell! It's DOWN Pikes Peek, ya gotta worry!

    Bob, 01 Prius, been there.

> Z
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[Lee Hart]

wjdennis@... wrote:

> Mark Grasser wrote:
>
>> I do like the idea of the resistor across the motor for engine braking,
>> but would you not have to put some voltage to the field to get it to work?
>
> Check the archives for posts by Lee Hart mentioning Dynamic Braking and
> Residual Magnetism.  Lee believes that most motors will develop a small
> residual magnetism from the field windings, and if you put a low-ohm
> resistor across the armature (like .01 or .1 ohms), you can generate
> significant braking power.

Not exactly "significant"; more like ICE engine braking. With no field
current, there is only a weak field from the residual magnetism, so even
shorting the armature only produces a weak torque.

--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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