Reversing Contactors Yet Again

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Reversing Contactors Yet Again

m_radtke
Hello,

I apologize if I missed the answer to my questions in the archives.

I have a Jet ElectraVan that I am replacing the old GE EV-1 SCR
controller with an Open Revolt controller.  I've used a home made
reversing switch for years, but it's slow and showing some wear.  I
picked up a Contact Industries CT200C-12B1 200 amp reversing switch to
replace my home made unit.  Now I have some questions:

1) Is 200 amps enough?  The car is 102 volts with a 20 HP motor.  The
motor current should average well under 200 amps, but I am a little
concerned about the size of the bus bars on the contactor.  They
measure 1/2" X 5/32" and the supplied jumpers are 1/2" X 1/8"

2) This reversing contactor is built like every other reversing
contactor that I have seen in that it has two contactors in tandem and
one or the other is activated for either forward or reverse.  It
doesn't have a mechanical interlock.  Why not change the jumpers so
that both contactors are activated for reverse and neither for
forward?  

The coils are 12 volts @ 2 amps.  25 coil watts doesn't seem to be
continuous duty, so I built a driver to use PWM after the initial pull
in to reduce the current to about 200 mA.  The driver works fine and
includes the interlocking logic for the throttle.  But, I would rather
not waste the power since the car goes forward 99% of the time.

Thanks,
Mike
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Re: Reversing Contactors Yet Again

Jeff Major
Hi Mike,

I am not familiar with that brand of contactor, but if it is DC rated at 200A and comes with jumper/bus bars, they should be sufficient.  The current density is a bit high IMO but not out of sight.  If they were totally enclosed and run for many hours continuously at 200A, I might be concerned.  You can help draw heat by using large cables and lugs.


I guess you might be able to reconfigure bus bars/jumpers such that forward would be with neither coil energized and reverse with both coils energized.  I've never seen it done and it might be hairy.  Most of these DC reversing contactors go into fork lifts which have a 50/50 forward/reverse duty, so one coil on makes sense.  Also, without either coil on, it is automatically in neutral, so to speak.

And beware of reduced holding current if the contactors are not made for it.  Bumps in the road may cause the contacts to separate and arc.

Jeff M



________________________________
 From: Michael A. Radtke <[hidden email]>
To: [hidden email]
Sent: Tuesday, April 9, 2013 2:50 PM
Subject: [EVDL] Reversing Contactors Yet Again
 
Hello,

I apologize if I missed the answer to my questions in the archives.

I have a Jet ElectraVan
 that I am replacing the old GE EV-1 SCR
controller with an Open Revolt controller.  I've used a home made
reversing switch for years, but it's slow and showing some wear.  I
picked up a Contact Industries CT200C-12B1 200 amp reversing switch to
replace my home made unit.  Now I have some questions:

1) Is 200 amps enough?  The car is 102 volts with a 20 HP motor.  The
motor current should average well under 200 amps, but I am a little
concerned about the size of the bus bars on the contactor.  They
measure 1/2" X 5/32" and the supplied jumpers are 1/2" X 1/8"

2) This reversing contactor is built like every other reversing
contactor that I have seen in that it has two contactors in tandem and
one or the other is activated for either forward or reverse.  It
doesn't have a mechanical interlock.  Why not change the jumpers so
that both contactors are activated for reverse
 and neither for
forward? 

The coils are 12 volts @ 2 amps.  25 coil watts doesn't seem to be
continuous duty, so I built a driver to use PWM after the initial pull
in to reduce the current to about 200 mA.  The driver works fine and
includes the interlocking logic for the throttle.  But, I would rather
not waste the power since the car goes forward 99% of the time.

Thanks,
Mike
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Re: Reversing Contactors Yet Again

Lee Hart
In reply to this post by m_radtke
On 4/9/2013 1:50 PM, Michael A. Radtke wrote:
> Contact Industries CT200C-12B1...
 > 1) Is 200 amps enough?

It looks a little bit on the small side. But the price was right and you
already have it; so go ahead and give it a try!

You will certainly want the motor current to be able to exceed 200 amps,
or your acceleration will be abysmal. The Electravan is probably going
to draw 100 amps just to cruise at a constant speed (like 45 mph).
You're going to want at least 500 amps for accelerating, going faster,
and climbing hills.

But you shouldn't be running at these high currents for very long.
Contactors are good at handling high peak currents for minutes at a
time. You also won't (shouldn't!) be switching these high currents.

 > 2) Why not change the jumpers so that both contactors are activated
 >    for reverse and neither for forward?

The normally-closed contact of relays and contactors have a lower
current rating. There is only a spring holding it closed, and it has to
be weaker than the coil's force (or the coil couldn't overcome the
spring to pull it in).

So, you don't want to use the normally-closed contacts to carry normal
forward current. If you're going to rewire it, wire it so you energize
both coils for forward, and neither coil for reverse.

One other thing: Be sure to wire it to reverse the field; not the
armature. When both coils are off, a reversing contactor typically
*snorts* the field. That's OK. But you do *not* want to let it short the
armature! You can get ruinously high currents if it shorts the armature
while the vehicle is moving!
--
An engineer can do for a nickel what any damn fool can do for a dollar.
        -- Henry Ford
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Reversing Contactors Yet Again

Paul Wujek-2

On 13-04-10 12:49 PM, Lee Hart wrote:
> a reversing contactor typically *snorts* the field
I hope you meant *shorts* or there is a term I have not heard of before.
--
*Paul Wujek* <[hidden email]>
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Re: Reversing Contactors Yet Again

Lee Hart
Lee Hart wrote:
>> a reversing contactor typically *snorts* the field

Paul Wujek wrote:
> I hope you meant *shorts* or there is a term I have not heard of before.

Ooh, that's a good one! Don't you just love it when the spell checker
has a sense of humor. :-)

--
The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of
destruction without making any audible or visible signs of distress.
  -- Electrical Review, 1902
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Reversing Contactors Yet Again

rodhower
Lee Hart wrote:
>> a reversing contactor typically *snorts* the field


Brings back memories of Bob Rice.  I kind of like the new description!


----- Original Message ----
From: Lee Hart <[hidden email]>
To: Electric Vehicle Discussion List <[hidden email]>
Sent: Wed, April 10, 2013 11:31:18 PM
Subject: Re: [EVDL] Reversing Contactors Yet Again

Lee Hart wrote:
>> a reversing contactor typically *snorts* the field

Paul Wujek wrote:
> I hope you meant *shorts* or there is a term I have not heard of before.

Ooh, that's a good one! Don't you just love it when the spell checker has a
sense of humor. :-)

-- The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of
destruction without making any audible or visible signs of distress.
-- Electrical Review, 1902
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
_______________________________________________
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Re: Reversing Contactors Yet Again

Bill Dennis
I always thought it was the freewheel diode that snorts the magnetic field.

Bill

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Rod Hower
Sent: Thursday, April 11, 2013 9:00 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Reversing Contactors Yet Again

Lee Hart wrote:
>> a reversing contactor typically *snorts* the field


Brings back memories of Bob Rice.  I kind of like the new description!


----- Original Message ----
From: Lee Hart <[hidden email]>
To: Electric Vehicle Discussion List <[hidden email]>
Sent: Wed, April 10, 2013 11:31:18 PM
Subject: Re: [EVDL] Reversing Contactors Yet Again

Lee Hart wrote:
>> a reversing contactor typically *snorts* the field

Paul Wujek wrote:
> I hope you meant *shorts* or there is a term I have not heard of before.

Ooh, that's a good one! Don't you just love it when the spell checker has a
sense of humor. :-)

-- The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of destruction
without making any audible or visible signs of distress.
-- Electrical Review, 1902
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
_______________________________________________
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
http://lists.evdl.org/listinfo.cgi/ev-evdl.org
For EV drag racing discussion, please use NEDRA
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Re: Reversing Contactors Yet Again

Lee Hart
In reply to this post by rodhower
>>> a reversing contactor typically *snorts* the field

Rod Hower wrote:
> Brings back memories of Bob Rice.  I kind of like the new description!

I don't think it's even in the same league as Bob's stench cords,
rectumfires, badderies, desistors, crapacitors, etc. :-)

--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
         -- Antoine de Saint Exupery
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Reversing Contactors Yet Again

Cor van de Water
In reply to this post by Bill Dennis
You are thinking about the coil of the contactor, which typically has an
anti-parallel diode or surge suppressor to catch the high voltage
kick-back when the power to the coil is interrupted - you do not want to
blow the switching transistor when it tries to turn off the contactor
(it might fail shorted and cause the contactor to stay on, defeating the
purpose).

Lee is talking about the switching arrangement of the contacts to
achieve reversing of a DC motor. Since the common setup is to use two
single contact
units to reverse the motor, you have some choices how to wire the
contacts.
- you can connect the center contacts to the supply (controller) side
and
  connect the motor leads to the NO and NC contacts, but this has the
  drawback that when one contactor switches faster than the other, it
  will short the controller.
- you can connect the center contacts to the two motor leads and connect
the
  controller between the NO and NC contacts. That way, if one contactor
  switches before the other, it will short the motor but not the
controller.

Lee remarked that if you short the armature of a running motor with
magnetised field, then you get unpredictable currents, you lock up the
motor and since this typically is a direct drive situation, you may
cause
the EV to lock the wheels, skid and get into a crash.
Better to switch the field, because a collapsing field does not result
in the same magnitude of problems.

BTW, "SNORT" is a known word, typically referring to forceful inhaling,
but it has also been used to name a tool that captures large amounts of
data from wireless networks (either to try to catch sensitive
information that could lead to finding security keys of a network or to
defend the network by detecting unauthorized transmissions). It is a
software hacking tool.
http://www.snort.org/

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email] Private: http://www.cvandewater.info
Skype: cor_van_de_water Tel: +1 408 383 7626


-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Bill Dennis
Sent: Thursday, April 11, 2013 8:58 AM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Reversing Contactors Yet Again

I always thought it was the freewheel diode that snorts the magnetic
field.

Bill

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf
Of Rod Hower
Sent: Thursday, April 11, 2013 9:00 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Reversing Contactors Yet Again

Lee Hart wrote:
>> a reversing contactor typically *snorts* the field


Brings back memories of Bob Rice.  I kind of like the new description!


----- Original Message ----
From: Lee Hart <[hidden email]>
To: Electric Vehicle Discussion List <[hidden email]>
Sent: Wed, April 10, 2013 11:31:18 PM
Subject: Re: [EVDL] Reversing Contactors Yet Again

Lee Hart wrote:
>> a reversing contactor typically *snorts* the field

Paul Wujek wrote:
> I hope you meant *shorts* or there is a term I have not heard of
before.

Ooh, that's a good one! Don't you just love it when the spell checker
has a
sense of humor. :-)

-- The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of
destruction
without making any audible or visible signs of distress.
-- Electrical Review, 1902
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
_______________________________________________
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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For EV drag racing discussion, please use NEDRA
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For EV drag racing discussion, please use NEDRA
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Re: Reversing Contactors Yet Again

m_radtke
In reply to this post by Jeff Major
Jeff and Lee,

Thanks for your responses.

> 50/50 forward/reverse duty

That seems reasonable.  So there really is no issue with rewiring.

> beware of reduced holding current

I checked it out and once the solenoid bottoms out, the reduced current
keeps it very solid.  If the van hits a bump hard enough to dislodge
it, I'll have a few broken bones as well.

> both coils energized.  I've never seen it done and it might
> be hairy

In this case it is quite straight forward.  Just replace a || with an
X.  Spacers will avoid the obvious short.

> There is only a spring holding it closed, and it has to
> be weaker than the coil's force

Not so on this contactor.  The actuator is a solenoid.  However, the
contacts are isolated from the actuator by springs.  So, at either end
of the actuator's throw, the isolation springs are compressed the same
amount ensuring that the contact pressure is the same in either
position.  So, at least in the case of this contactor there should be
no difference in current carrying capacity.

> can get ruinously high currents if it shorts the armature
> while the vehicle is moving

I didn't think of that.  I guess that's because of the residual
magnetism in the field.  That armature sees an alternating current so
has less residual magnetism and thus generates a much smaller AC current
in a shorted field on coasting.  The paired contactors could have a
shorting overlap while switching.  My old home made switch could not.
Perhaps I should re-consider rebuilding my old switch.

Thanks for your advice,
Mike
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Re: Reversing Contactors Yet Again

Bill Dennis
In reply to this post by Cor van de Water
I should have put a smiley face after my comment; it was meant to be a joke.
Guess I'd better stop planning for that future career as a comedy writer.
:)

Sorry for the confusion,

Bill

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Cor van de Water
Sent: Thursday, April 11, 2013 1:20 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Reversing Contactors Yet Again

You are thinking about the coil of the contactor, which typically has an
anti-parallel diode or surge suppressor to catch the high voltage kick-back
when the power to the coil is interrupted - you do not want to blow the
switching transistor when it tries to turn off the contactor (it might fail
shorted and cause the contactor to stay on, defeating the purpose).

Lee is talking about the switching arrangement of the contacts to achieve
reversing of a DC motor. Since the common setup is to use two single contact
units to reverse the motor, you have some choices how to wire the contacts.
- you can connect the center contacts to the supply (controller) side and
  connect the motor leads to the NO and NC contacts, but this has the
  drawback that when one contactor switches faster than the other, it
  will short the controller.
- you can connect the center contacts to the two motor leads and connect the
  controller between the NO and NC contacts. That way, if one contactor
  switches before the other, it will short the motor but not the controller.

Lee remarked that if you short the armature of a running motor with
magnetised field, then you get unpredictable currents, you lock up the motor
and since this typically is a direct drive situation, you may cause the EV
to lock the wheels, skid and get into a crash.
Better to switch the field, because a collapsing field does not result in
the same magnitude of problems.

BTW, "SNORT" is a known word, typically referring to forceful inhaling, but
it has also been used to name a tool that captures large amounts of data
from wireless networks (either to try to catch sensitive information that
could lead to finding security keys of a network or to defend the network by
detecting unauthorized transmissions). It is a software hacking tool.
http://www.snort.org/

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email] Private: http://www.cvandewater.info
Skype: cor_van_de_water Tel: +1 408 383 7626


-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Bill Dennis
Sent: Thursday, April 11, 2013 8:58 AM
To: 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] Reversing Contactors Yet Again

I always thought it was the freewheel diode that snorts the magnetic field.

Bill

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Rod Hower
Sent: Thursday, April 11, 2013 9:00 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Reversing Contactors Yet Again

Lee Hart wrote:
>> a reversing contactor typically *snorts* the field


Brings back memories of Bob Rice.  I kind of like the new description!


----- Original Message ----
From: Lee Hart <[hidden email]>
To: Electric Vehicle Discussion List <[hidden email]>
Sent: Wed, April 10, 2013 11:31:18 PM
Subject: Re: [EVDL] Reversing Contactors Yet Again

Lee Hart wrote:
>> a reversing contactor typically *snorts* the field

Paul Wujek wrote:
> I hope you meant *shorts* or there is a term I have not heard of
before.

Ooh, that's a good one! Don't you just love it when the spell checker has a
sense of humor. :-)

-- The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of destruction
without making any audible or visible signs of distress.
-- Electrical Review, 1902
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
_______________________________________________
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
http://lists.evdl.org/listinfo.cgi/ev-evdl.org
For EV drag racing discussion, please use NEDRA
(http://groups.yahoo.com/group/NEDRA)
_______________________________________________
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Re: Reversing Contactors Yet Again

Dwain Swick
In reply to this post by m_radtke
I always built my conversions with a solenoid connecting power from the controller to the motor and the throttle controlling the solenoid. When the throttle was off the power was off. If you reversed with your foot in the throttle, then you deserved what you get. Where is common sense and safety?

--- On Thu, 4/11/13, Michael A. Radtke <[hidden email]> wrote:

From: Michael A. Radtke <[hidden email]>
Subject: Re: [EVDL] Reversing Contactors Yet Again
To: "Electric Vehicle Discussion List" <[hidden email]>
Date: Thursday, April 11, 2013, 3:32 PM

Jeff and Lee,

Thanks for your responses.

> 50/50 forward/reverse duty

That seems reasonable.  So there really is no issue with rewiring.

> beware of reduced holding current

I checked it out and once the solenoid bottoms out, the reduced current
keeps it very solid.  If the van hits a bump hard enough to dislodge
it, I'll have a few broken bones as well.

> both coils energized.  I've never seen it done and it might
> be hairy

In this case it is quite straight forward.  Just replace a || with an
X.  Spacers will avoid the obvious short.

> There is only a spring holding it closed, and it has to
> be weaker than the coil's force

Not so on this contactor.  The actuator is a solenoid.  However, the
contacts are isolated from the actuator by springs.  So, at either end
of the actuator's throw, the isolation springs are compressed the same
amount ensuring that the contact pressure is the same in either
position.  So, at least in the case of this contactor there should be
no difference in current carrying capacity.

> can get ruinously high currents if it shorts the armature
> while the vehicle is moving

I didn't think of that.  I guess that's because of the residual
magnetism in the field.  That armature sees an alternating current so
has less residual magnetism and thus generates a much smaller AC current
in a shorted field on coasting.  The paired contactors could have a
shorting overlap while switching.  My old home made switch could not.
Perhaps I should re-consider rebuilding my old switch.

Thanks for your advice,
Mike
_______________________________________________
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Re: Reversing Contactors Yet Again

Lee Hart
On 4/11/2013 11:02 PM, Dwain Swick wrote:
> I always built my conversions with a solenoid connecting power from the controller to the motor and the throttle controlling the solenoid. When the throttle was off the power was off. If you reversed with your foot in the throttle, then you deserved what you get. Where is common sense and safety?

To be fair, there are sometimes reasons to switch rapidly between
forward and reverse. When you're stuck in snow for example, you may need
to "rock" the car forward and backward every second or so to it unstuck.

Warning: a quirk of series DC motors is that you do not want it rotating
slowly in the wrong direction when you apply power. When rotated
backwards from the direction it wants to run as a motor, it becomes a
series generator. Unless your controller is set up for regen, it can't
control the generated current. The motor can generate a huge current, to
murder the freewheel diodes in the controller, or break something in the
drive train.
--
The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of
destruction without making any audible or visible signs of distress.
  -- Electrical Review, 1902
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Reversing Contactors Yet Again

Dwain Swick
Hey Lee, I'm always fair. I'm picturing an S10 with a 11" motor. Your foot in it, shift it a couple times and get out and sweep up the pieces of u-joint on the ground. You can choose an action and nature's law will choose the consequence. With an ICE, you have the cushion of the clutch or torque converter, but with an electric motor hooked up direct to the wheels and full torque at zero rpm something has to give.

--- On Thu, 4/11/13, Lee Hart <[hidden email]> wrote:

From: Lee Hart <[hidden email]>
Subject: Re: [EVDL] Reversing Contactors Yet Again
To: "Electric Vehicle Discussion List" <[hidden email]>
Date: Thursday, April 11, 2013, 11:59 PM

On 4/11/2013 11:02 PM, Dwain Swick wrote:
> I always built my conversions with a solenoid connecting power from the controller to the motor and the throttle controlling the solenoid. When the throttle was off the power was off. If you reversed with your foot in the throttle, then you deserved what you get. Where is common sense and safety?

To be fair, there are sometimes reasons to switch rapidly between forward and reverse. When you're stuck in snow for example, you may need to "rock" the car forward and backward every second or so to it unstuck.

Warning: a quirk of series DC motors is that you do not want it rotating slowly in the wrong direction when you apply power. When rotated backwards from the direction it wants to run as a motor, it becomes a series generator. Unless your controller is set up for regen, it can't control the generated current. The motor can generate a huge current, to murder the freewheel diodes in the controller, or break something in the drive train.
-- The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of
destruction without making any audible or visible signs of distress.
 -- Electrical Review, 1902
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Reversing Contactors Yet Again

Lee Hart
Dwain Swick wrote:
> Hey Lee, I'm always fair. I'm picturing an S10 with a 11" motor. Your
> foot in it, shift it a couple times and get out and sweep up the
> pieces of u-joint on the ground.

If you have a big enough motor (and controller and batteries), you can
easily produce far more torque than the stock drive train can handle. No
doubt about it! But this has nothing to do with your reversing setup.

I was just observing that you don't want to make it *too* hard to go
from forward to reverse quickly, because there are times you may need to
do it.

Most EV controllers are in fact derived from industrial EV controllers
for fork lifts etc. They already have an adjustable ramp-up time, so
they won't go from 0 to full current instantly. They also have
adjustable current limits, which limit motor torque. Some even have
interlocks to limit current in case of rapid forward/reverse
transitions. These features are there so you *won't* break things by
careless operation.

Obviously, you can set up your controller to defeat these limiters. Then
you are free to go very fast and/or break the vehicle, as you choose.
--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
         -- Antoine de Saint Exupery
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Reversing Contactors Yet Again

m_radtke
In reply to this post by Dwain Swick
Hello,

So, it's a good plan to block the reverse switching while the motor is
still spinning.  Any suggestions for a simple way to detect that?

Thanks,
Mike
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Re: Reversing Contactors Yet Again

Lee Hart
On 4/12/2013 11:48 AM, Michael A. Radtke wrote:
> So, it's a good plan to block the reverse switching while the motor is
> still spinning.  Any suggestions for a simple way to detect that?

If the controller doesn't have this feature built-in, you can add a
relay to do it. The coil goes across the motor armature, so it pulls in
whenever there is voltage. To switch to reverse, this relay has to drop out.

Pick a relay whose DC coil voltage is about the same as your maximum
motor voltage. For example, a 110vdc coil for an EV with a 120v pack.
Put a resistor or light bulb in series to drop the voltage if you can't
find a relay with a high enough coil voltage.

Relays drop out with about 10% of their rated voltage across the coil. A
110vdc coil drops out at 11v, etc. So this relay turns off when the
motor is at less than 11v average (barely idling).

Wire this relay's contacts to control your forward/reverse contactor's
coils. If your forward/reverse contactors have auxiliary switches, it
would be wired something like this (view with a fixed width font like
Courier):
                           /  <------
                       ___o  o___    \
              forward |  S2  NO  |    \
                      |          |    _\_ _
            o_________|___o--o___|___| | | |_____
           /             K1a NC      forward     |
  +12v____O   o neutral              contactor  gnd
        S1                 /  <------
            o_____________o  o___    \
              reverse |  S3  NO  |    \
                      |          |    _\_ _
                      |___o--o___|___| | | |_____
                         K1b NC      reverse     |
                                     contactor  gnd

K1 is the new forward/reverse motor speed detection relay. It has two
normally-closed contacts, K1a and K1b. When the motor is stopped, K1a
and K1b are closed. They open when the motor is running.

S1 is your forward/reverse switch on the dashboard or shift lever.

The forward contactor has an auxiliary switch S2, which is closed when
the contactor is on. The reverse contactor has an auxiliary switch S3,
which is closed when the contactor is on.

Set S1 for the desired direction; let's say forward. Then the reverse
contactor has no coil power and must be off. If the motor is stopped,
the forward coil gets power through S1 and K1a, and pulls in. Once it
has pulled in, S2 closes and holds the forward contactor on even when
the motor starts turning and K1a opens.

When you switch to reverse, the forward contactor drops out immediately.
But the reverse contactor won't turn on until the motor (almost) stops,
allowing K1b to close.

--
Ring the bells that still can ring
Forget your perfect offering
There is a crack in everything
That's how the light gets in.
        -- Leonard Cohen, from "Anthem"
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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Re: Reversing Contactors Yet Again

Roland Wiench
In reply to this post by Lee Hart
Not simple.

My first controller was a Cable Form controller normally design for
industrial vehicles that did not have a mechanical reverse gear.

It use 600 amp reversing contactors with a surge rating of 2000 amps.  There
are mechanical interlocks, electrical interlocks and a control relays that
also have mechanical and electrical interlocks.

This reversing circuit could switch on the dynamic braking which also
activates plug braking which disconnect the armature circuit and shorts it
out. This circuit was never use in my EV because it had a transmission.

There was three modes of dynamic braking that can be adjusted. Violent,
Standard and Soft.  The violent mode shatter the motor coupler when I
accelerated and than stop the motor. So it was recommended to choose the
soft mode and come to a complete stop.

Not only the two contactors were switch out, but there was a free wheeling
diode for each contactor which was switch out.  A current sensor circuit was
install in series on the wire that came from the field of the motor to the
free wheeling diode.

This current sensor circuit is like a current relay which you can get in
open frame or in a factory assembly package that has adjustments to limit
the amount of current to a low level where it then will activate the other
contactor.

This current sensor circuit is available from any electrical supply company.

Roland



----- Original Message -----
From: "Michael A. Radtke" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Sent: Friday, April 12, 2013 10:48 AM
Subject: Re: [EVDL] Reversing Contactors Yet Again


> Hello,
>
> So, it's a good plan to block the reverse switching while the motor is
> still spinning.  Any suggestions for a simple way to detect that?
>
> Thanks,
> Mike
> _______________________________________________
> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
> For EV drag racing discussion, please use NEDRA
> (http://groups.yahoo.com/group/NEDRA)
>
>
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Re: Reversing Contactors Yet Again

m_radtke
Thanks Lee and Roland.

I think that I am only concerned with detecting the motor coasting with
the controller off.  I already have an interlock with the throttle and
the reversing switch done with my microprocessor software.  I was
considering blocking the switch while the motor was spinning as well.
Detecting the spin in some simple way was the goal.

I think that Lee's circuit will do that, but I think that the sensing
relay won't energize unless the motor has been spun up to a high enough
speed under power.  There may be a range where the relay never
energized but there still was enough speed to cause damage: such as
coasting.

Roland suggests current sensing which implies a current path.  I think
that there is no current path unless the reversing switch is already
switched, and I was hoping to block that until the motor stops or at
least is quite slow.

Both ideas make me think that I could use a high voltage transistor
connected as a current source across the armature to drive an
opto-isolator. The circuit would be self powered by the armature
voltage and result in an isolated binary signal to the microprocessor
to represent the motor's state.  What I don't know is about how much
voltage to expect from the armature vs. speed based on residual field
magnetism.

Another choice is to ignore the problem and let common sense prevail.
I wouldn't put my manual transmission car in reverse while travelling
forward.  To do so would probably cost as much as switching my
ElectraVan into reverse under the same circumstances.

Thanks for your suggestions,
Mike

------------------------ Original Message ------------------------
Date: Fri, 12 Apr 2013 12:43:30 -0600
From: "Roland Wiench" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Subject: Re: [EVDL] Reversing Contactors Yet Again


Not simple.

My first controller was a Cable Form controller normally design for
industrial vehicles that did not have a mechanical reverse gear.

It use 600 amp reversing contactors with a surge rating of 2000 amps.
There are mechanical interlocks, electrical interlocks and a control
relays that also have mechanical and electrical interlocks.

This reversing circuit could switch on the dynamic braking which also
activates plug braking which disconnect the armature circuit and shorts
it out. This circuit was never use in my EV because it had a
transmission.

There was three modes of dynamic braking that can be adjusted. Violent,
Standard and Soft.  The violent mode shatter the motor coupler when I
accelerated and than stop the motor. So it was recommended to choose
the soft mode and come to a complete stop.

Not only the two contactors were switch out, but there was a free
wheeling diode for each contactor which was switch out.  A current
sensor circuit was install in series on the wire that came from the
field of the motor to the free wheeling diode.

This current sensor circuit is like a current relay which you can get
in open frame or in a factory assembly package that has adjustments to
limit the amount of current to a low level where it then will activate
the other contactor.

This current sensor circuit is available from any electrical supply
company.

Roland



----- Original Message -----
From: "Michael A. Radtke" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Sent: Friday, April 12, 2013 10:48 AM
Subject: Re: [EVDL] Reversing Contactors Yet Again


> Hello,
>
> So, it's a good plan to block the reverse switching while the motor is
> still spinning.  Any suggestions for a simple way to detect that?
>
> Thanks,
> Mike
> _______________________________________________
> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
> For EV drag racing discussion, please use NEDRA
> (http://groups.yahoo.com/group/NEDRA)
>
>
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Re: Reversing Contactors Yet Again

Lee Hart
Michael A. Radtke wrote:
> I think that I am only concerned with detecting the motor coasting with
> the controller off.

That can be pretty easy. Measure the armature voltage of your motor
versus RPM. Figure out what voltage corresponds to what RPM with no
field current.

It will probably be something like 500 RPM per volt. Let's say you want
to know when it is under 1000 RPM; then you need to detect an armature
voltage under 2v.

The relay trick I mentioned won't be sensitive enough to do this.
Instead, I'd use an optocoupler. Its infrared LED will turn on above 1v.
Put a resistor in series to the armature, chosen so the LED current at
maximum motor voltage is about half the LEDs maximum current rating. Put
a trimpot across the LED, and you can adjust the exact voltage.

> I think that Lee's circuit will do that, but I think that the sensing
> relay won't energize unless the motor has been spun up to a high enough
> speed under power. There may be a range where the relay never
> energized but there still was enough speed to cause damage: such as
> coasting.

That's true. The relay is cheap and easy, but not very sensitive. The
opto circuit is more sensitive and repeatable. It just takes more parts.

> Both ideas make me think that I could use a high voltage transistor
> connected as a current source across the armature to drive an
> opto-isolator. The circuit would be self powered by the armature
> voltage and result in an isolated binary signal to the microprocessor
> to represent the motor's state.

That can work, too. Just be aware that the armature voltage is
incredibly noisy, and can have monstrous spikes. It would be a tough job
for a transistor.

> Another choice is to ignore the problem and let common sense prevail.

That's fine if you are the only driver. But, are you sure your wife or a
friend will *never* drive your EV? I have had cases where someone got in
an EV, pressed the clutch, and revved up the motor "to see how it
sounds". Well, it will hit about 10,000 RPM in about 1 second. It sounds
like "whine... BANG!"

--
Anyone can make the simple complicated. Creativity is making the
complicated simple. -- Charles Mingus
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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