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Discussion Starter #1
A single string of 17 group 34 batts (like Optima YTs)
could fit into my Geo Metro EV for 204 volts nominal.

Is there any way to step down that pack voltage to
around 150-160 volts for input into the existing
Curtis 1231 controller (rated 144v nominal max)?

The Geo EV's original converter did such a nice job
with the controller/heatsink/cooling fan installation,
that i can't bear the thought of ripping that all out
even if it meant replacing it with a zilla.

Mark




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Discussion Starter #2
Mark Freidberg wrote:
> A single string of 17 group 34 batts (like Optima YTs)
> could fit into my Geo Metro EV for 204 volts nominal.
>
> Is there any way to step down that pack voltage to
> around 150-160 volts for input into the existing
> Curtis 1231 controller (rated 144v nominal max)?

The Curtis 1231 is rated for a *nominal* 144v pack maximum. You really
don't want to run it with a nominal pack voltage above this. The parts
inside are rated at 200v peak. A 144v pack freshly off a 2.5v/cell
charge will be at 180v, and there will be voltage spikes that go above this.

So, I'd look for ways to stay with twelve 12v batteries, but increase
the amphours of each one to whatever weight you feel you can carry. For
example, my LeCar EV (about the same size as your Metro) has twelve 12v
100ah AGMs (about 750 lbs; same as 17 Optimas). Each battery is 13" x
6.6" x 9". This has worked out fine with my Curtis 1231 controller.
--
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
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Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
 

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Discussion Starter #3
--- Lee Hart <[email protected]> wrote:

> The Curtis 1231 is rated for a *nominal* 144v pack
> maximum. You really don't want to run it with a
> nominal pack voltage above this. The parts
> inside are rated at 200v peak. A 144v pack freshly
> off a 2.5v/cell charge will be at 180v, and there
> will be voltage spikes that go above this.

Would it be possible to connect the hypothetical 204v
pack to a device like a step-down transformer, and
then connect the output side of that to the rest of
the drive circuit? The transformer would reduce 204v
pack voltage to 144v or less for Curtis COntroller.


> So, I'd look for ways to stay with twelve 12v
> batteries, but increase the amphours of each one to
> whatever weight you feel you can carry. For
> example, my LeCar EV (about the same size as your
> Metro) has twelve 12v 100ah AGMs (about 750 lbs;
> same as 17 Optimas). Each battery is 13" x
> 6.6" x 9". This has worked out fine with my Curtis
> 1231 controller.

I'm all for staying with 12 large 12v batts as long as
my stinky batt woes can be resolved.


Mark




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Discussion Starter #4
Lee Hart wrote:
>> The Curtis 1231 is rated for a *nominal* 144v pack maximum...

Mark Freidberg wrote:
> Would it be possible to connect the hypothetical 204v
> pack to a device like a step-down transformer, and
> then connect the output side of that to the rest of
> the drive circuit? The transformer would reduce 204v
> pack voltage to 144v or less for Curtis Controller.

The Curtis controller *is* such a step-down device. Unfortunately, its
maximum input pack voltage is 144v. To go higher, you need to buy a more
expensive controller; and that's what you are trying to avoid.

>> I'd look for ways to stay with twelve 12v batteries, but increase
>> the amphours of each one to whatever weight you feel you can carry.

> I'm all for staying with 12 large 12v batts as long as
> my stinky batt woes can be resolved.

We haven't figured out what is causing it yet, but I'm quite sure it's
not the batteries themselves. Something you or your charger are doing is
causing them to vent and smell.

--
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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Discussion Starter #5
What you'd need is a DC-DC converter. A very powerful converter, in fact
at least as powerful as your motor controller.

Since a motor controller is basically a DC-DC converter, what you would
need is basically a motor controller (plus a huge inductor) to feed your
curtis motor controller.

It would be simpler, cheaper, and more efficient to just replaced the
Curtis with a different controller that can work with a 204V battery pack.

Either that or use different batteries that add up to 144V or less.

> A single string of 17 group 34 batts (like Optima YTs)
> could fit into my Geo Metro EV for 204 volts nominal.
>
> Is there any way to step down that pack voltage to
> around 150-160 volts for input into the existing
> Curtis 1231 controller (rated 144v nominal max)?
>
> The Geo EV's original converter did such a nice job
> with the controller/heatsink/cooling fan installation,
> that i can't bear the thought of ripping that all out
> even if it meant replacing it with a zilla.
>
> Mark
>
>
>
>
> ____________________________________________________________________________________
> Sick sense of humor? Visit Yahoo! TV's
> Comedy with an Edge to see what's on, when.
> http://tv.yahoo.com/collections/222
>
>


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Discussion Starter #6
For a transformer to work one of two things must happen - There has to
be a change in the voltage presented to the secondary windings. You can
accomplish this by moving the secondary in relation to the primary or
vary the voltage at the primary. When the voltage changes the field the
primary presents will start to collapse or increase. The movement of
the field intersects the secondary inducing voltage into the secondary.
Without this field intersection the secondary will see no voltage
induced. Straight DC will not go across a transformer except for the
brief moment in time when the primary field is being created. Once the
DC stabilizes in the primary no voltage will induce over to the
secondary.

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Mark Freidberg
Sent: Monday, July 30, 2007 14:50
To: [email protected]
Subject: Re: Could higher pack voltage be stepped down for Curtis input?

--- Lee Hart <[email protected]> wrote:

> The Curtis 1231 is rated for a *nominal* 144v pack maximum. You really

> don't want to run it with a nominal pack voltage above this. The parts

> inside are rated at 200v peak. A 144v pack freshly off a 2.5v/cell
> charge will be at 180v, and there will be voltage spikes that go above

> this.

Would it be possible to connect the hypothetical 204v pack to a device
like a step-down transformer, and then connect the output side of that
to the rest of the drive circuit? The transformer would reduce 204v pack
voltage to 144v or less for Curtis COntroller.


> So, I'd look for ways to stay with twelve 12v batteries, but increase
> the amphours of each one to whatever weight you feel you can carry.
> For example, my LeCar EV (about the same size as your
> Metro) has twelve 12v 100ah AGMs (about 750 lbs; same as 17 Optimas).
> Each battery is 13" x 6.6" x 9". This has worked out fine with my
> Curtis
> 1231 controller.

I'm all for staying with 12 large 12v batts as long as my stinky batt
woes can be resolved.


Mark





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Discussion Starter #7
Dewey, Jody R ATC COMNAVAIRLANT, N422G5G wrote:
> For a transformer to work one of two things must happen...

This sparked an idea. A standard buck converter (i.e. a normal PWM
series motor controller) can only step the pack voltage down. It has a
single untapped inductor (usually the motor's field winding).

But... there are buck converters that use a tapped inductor. This does
interesting things. It lets you change the relative stress on the diode
and transistor, and the duty cycle / output voltage relationship. For
example, you can reduce the stress on the transistor by increasing the
stress on the diode; useful because high breakdown voltage diodes are
cheaper and easier to get.

The field winding of a motor *is* a tapped inductor; it normally
consists of four coils (for a 4-pole motor), which can be connected in
various series/parallel arrangements. If it has two pairs in series, for
example, the tap between them will behave like a center-tapped inductor.
--
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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Discussion Starter #8
How about just hooking the Curtis to its max pack voltage and then have
a bypass contactor to add in the additional batteries for full throttle
operation? I know you would have balance issues but with proper
equalization each day the pack wouldn't suffer too badly.

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Lee Hart
Sent: Tuesday, July 31, 2007 11:43
To: [email protected]
Subject: Re: Could higher pack voltage be stepped down for Curtis input?

Dewey, Jody R ATC COMNAVAIRLANT, N422G5G wrote:
> For a transformer to work one of two things must happen...

This sparked an idea. A standard buck converter (i.e. a normal PWM
series motor controller) can only step the pack voltage down. It has a
single untapped inductor (usually the motor's field winding).

But... there are buck converters that use a tapped inductor. This does
interesting things. It lets you change the relative stress on the diode
and transistor, and the duty cycle / output voltage relationship. For
example, you can reduce the stress on the transistor by increasing the
stress on the diode; useful because high breakdown voltage diodes are
cheaper and easier to get.

The field winding of a motor *is* a tapped inductor; it normally
consists of four coils (for a 4-pole motor), which can be connected in
various series/parallel arrangements. If it has two pairs in series, for
example, the tap between them will behave like a center-tapped inductor.
--
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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Discussion Starter #9
I have been considering a system like this too. Basically use a controller to handle all the voltage it can, and then have a second battery pack on a breaker. When the accelerator is depressed all the way, the controller will be at "full throttle" and the breaker will also be engaged. This is the simple version of what I have been kicking around anyway. I would have trouble verbalizing the actual design in detail.
 

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Discussion Starter #10
This type of idea comes up frequently on the list, usually from folks who
are newer to EVs. It sounds easier and less expensive, but when the details
are all worked out it turns it out is best to get the right controller and
use all your batteries at the same time. You can always give it a shot, but
at some point and time you will realize it wasn't easy or cheap to get it to
work well. It is also very possible that you will destroy the cotroller you
already have and maybe even end up in a dangerous situation. I would avoid
any of these schemes.

damon


>From: Brian Jackson <[email protected]>
>Reply-To: [email protected]
>To: [email protected]
>CC: Dan Frederiksen <[email protected]>
>Subject: RE: Could higher pack voltage be stepped down for Curtis input?
>Date: Tue, 31 Jul 2007 12:51:33 -0700
>
>I have been considering a system like this too. Basically use a controller
>to handle all the voltage it can, and then have a second battery pack on a
>breaker. When the accelerator is depressed all the way, the controller will
>be at "full throttle" and the breaker will also be engaged. This is the
>simple version of what I have been kicking around anyway. I would have
>trouble verbalizing the actual design in detail.
>

_________________________________________________________________
http://liveearth.msn.com
 

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Discussion Starter #11
How about something like this (modified from a post by Lee Hart on Oct.
28, 2006):

_______________________________________
| | _|_
__|__ + | / \ armature
___ 36v / S1 \___/
| - | _________ | series
|____/_____|____________|_____ | |_ motor
S2 | B+| _|_ | _|
| | D1 /_\ | _| field
__|__ + | |___|_____|
___ 144 | |_| |M-
| - | -||_ Q1 |
| | | | |
|____________|_____| | Controller
B-|_________|

Close either S1 or S2 to be using 14-cell mode or 17-cell mode, respectively.
Start off in 14-cell mode, then switch to 17-cell mode when up to speed.
Controller never sees more the 144V across it.
Charge the two battery strings separately.

Bill Dennis
 

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Discussion Starter #12
Bill Dennis wrote:
> _____________________________________
> | | _|_
> __|__ + | / \ armature
> ___ 36v / S1 \___/
> | - | _________ | series
> |____/_____|____________|_____ | |_ motor
> S2 | B+| _|_ | _|
> | | D1 /_\ | _| field
> __|__ + | |___|_____|
> ___ 144v | |_| |M-
> | - | -||_ Q1 |
> | | | | |
> |____________|_____| | Controller
> B-|_________|
>
> Close either S1 or S2 to be using 14-cell mode or 17-cell mode,
> respectively.
> Start off in 14-cell mode, then switch to 17-cell mode when up to speed.
> Controller never sees more the 144V across it. Charge the two battery
> strings separately.

This should work. S1 and S2 obviously can't both be closed at once! Both
strings of batteries should have fuses just in case.

You would also have to be sure to turn the controller fully off, then
switch pack voltages, then resume controller operation. Switching S1 or
S2 while the controller is operating would do nasty things.

You also don't want to allow S2 to be closed if it would put the
controller in current limit. With the extra batteries, the controller
can't limit motor current. The 36v pack would force current to keep
flowing in the freewheel diodes (D1) even with the MOSFETs (Q1) totally off.
--
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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Discussion Starter #13
Lee Hart wrote:
>S1 and S2 obviously can't both be closed at once! Both strings of
batteries should have fuses just in case.
Yes, perhaps a SPDT contactor, either separate from the main contactor
or with a neutral "off" position.

>Switching S1 or S2 while the controller is operating would do nasty
things.
An extra freewheel diode across the motor is probably a good idea. When
in 17-battery mode, there's still current flowing, even when the
controller is off. So an extra diode across the motor would allow S2 to
be opened without arcing.

Bill Dennis

>> _____________________________________
>> | | _|_
>> __|__ + | / \ armature
>> ___ 36v / S1 \___/
>> | - | _________ | series
>> |____/_____|____________|_____ | |_ motor
>> S2 | B+| _|_ | _|
>> | | D1 /_\ | _| field
>> __|__ + | |___|_____|
>> ___ 144v | |_| |M-
>> | - | -||_ Q1 |
>> | | | | |
>> |____________|_____| | Controller
>> B-|_________|
>>
>
 

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Discussion Starter #15
Andre' Blanchard wrote:
> Would adding a diode in parallel with S1 (D2) make it possible to
> switch the 36V pack in and out without having the controller fully off?
>
> Then there is still a current path for both Q1 and D1 even with both S1
> and S2 open, and at the moment I am not seeing how it would short
> anything out. Or you could replace S1 with the diode and just accept
> the extra voltage drop?
> _____________________________________
> | | | _|_
> __|__ + | _|_ / \ armature
> ___ 36v / S1 /_\ D2 \___/
> | - | | _________ | series
> |____/_____|_______|____|_____ | |_ motor
> S2 | B+| _|_ | _|
> | | D1 /_\ | _| field
> __|__ + | |___|_____|
> ___ 144v | |_| |M-
> | - | -||_ Q1 |
> | | | | |
> |____________|_____| | Controller
> B-|_________|

Adding D2 looks like a good move. It should work if you get the details
right. You could indeed eliminate S1 in this case, if you didn't mind D2
carrying the full motor current at all times.

You still don't want to have the controller going at full power when you
close S2. When S2 closes, motor current may not ramp down during the
controller's off time; it will continue to flow through the 36v pack,
the motor, D1, and S2. Nothing limits this current, so it could rise to
ruinous levels. If the motor is at low RPM, the current would be high
enough to exceed the controller diode's ratings. If the controller turns
back on, the MOSFETs could also die from this excessive current.

--
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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Discussion Starter #17
What about adding an inductor to ramp down current when S1 opens?


David C. Wilker Jr.
USAF (RET)

---- Andre' Blanchard <[email protected]> wrote:
At 12:29 PM 8/1/2007, you wrote:

>Adding D2 looks like a good move. It should work if you get the details
>right. You could indeed eliminate S1 in this case, if you didn't mind D2
>carrying the full motor current at all times.
>
>You still don't want to have the controller going at full power when you
>close S2. When S2 closes, motor current may not ramp down during the
>controller's off time; it will continue to flow through the 36v pack, the
>motor, D1, and S2. Nothing limits this current, so it could rise to
>ruinous levels. If the motor is at low RPM, the current would be high
>enough to exceed the controller diode's ratings. If the controller turns
>back on, the MOSFETs could also die from this excessive current.
>
>--
>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

So now we need a circuit the will only allow S2 to close or remain closed
when the motor current is low enough, and the controler is not too hot, and
etc..

This is the point at which it gets cheaper to buy the right speed control
because learning when it is safe to have S2 closed is going to burn up a
few of the cheaper controls unless you are real lucky.
__________
Andre' B. Clear Lake, Wi.
 

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Discussion Starter #18
Andre', this doesn't like much more than a series of switches, and not
all that expensive. A reed switch on one cable, and a heat sensor
switch on the controller. What else did you have in mind that drives up
the cost to new controller range?

Bill Dennis

Andre' Blanchard wrote:
> So now we need a circuit the will only allow S2 to close or remain
> closed when the motor current is low enough, and the controler is not
> too hot, and etc..
> This is the point at which it gets cheaper to buy the right speed
> control because learning when it is safe to have S2 closed is going to
> burn up a few of the cheaper controls unless you are real lucky.
 

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Discussion Starter #19
> Andre', this doesn't like much more than a series of switches, and not
> all that expensive. A reed switch on one cable, and a heat sensor
> switch on the controller. What else did you have in mind that drives up
> the cost to new controller range?

Hmm well, a pair of highpower contactors (S1 and S2), a high power diode,
and of course the cost of any extra low voltage controllers you happen to
fry trying to get everything right.

>
> Bill Dennis
>
> Andre' Blanchard wrote:
>> So now we need a circuit the will only allow S2 to close or remain
>> closed when the motor current is low enough, and the controler is not
>> too hot, and etc..
>> This is the point at which it gets cheaper to buy the right speed
>> control because learning when it is safe to have S2 closed is going to
>> burn up a few of the cheaper controls unless you are real lucky.
>
>


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Discussion Starter #20
> What about adding an inductor to ramp down current when S1 opens?

I must be missing something. Why would you want to do that? Wouldn't
that make matters worse?

>
>
> David C. Wilker Jr.
> USAF (RET)
>
> ---- Andre' Blanchard <[email protected]> wrote:
> At 12:29 PM 8/1/2007, you wrote:
>
>>Adding D2 looks like a good move. It should work if you get the details
>>right. You could indeed eliminate S1 in this case, if you didn't mind D2
>>carrying the full motor current at all times.
>>
>>You still don't want to have the controller going at full power when you
>>close S2. When S2 closes, motor current may not ramp down during the
>>controller's off time; it will continue to flow through the 36v pack, the
>>motor, D1, and S2. Nothing limits this current, so it could rise to
>>ruinous levels. If the motor is at low RPM, the current would be high
>>enough to exceed the controller diode's ratings. If the controller turns
>>back on, the MOSFETs could also die from this excessive current.
>>
>>--
>>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
>
> So now we need a circuit the will only allow S2 to close or remain closed
> when the motor current is low enough, and the controler is not too hot,
> and
> etc..
>
> This is the point at which it gets cheaper to buy the right speed control
> because learning when it is safe to have S2 closed is going to burn up a
> few of the cheaper controls unless you are real lucky.
> __________
> Andre' B. Clear Lake, Wi.
>
>


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