# Could higher pack voltage be stepped down for Curtis input?



## EVDL List (Jul 27, 2007)

> 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.
> >
> ...


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## EVDL List (Jul 27, 2007)

> --- 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
> ...


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## EVDL List (Jul 27, 2007)

> Lee Hart wrote:
> >> The Curtis 1231 is rated for a *nominal* 144v pack maximum...
> 
> Mark Freidberg wrote:
> ...


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## EVDL List (Jul 27, 2007)

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
>
>
>
>
> ____________________________________________________________________________________
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## EVDL List (Jul 27, 2007)

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
> 
> ...


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## EVDL List (Jul 27, 2007)

> 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
> ...


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## EVDL List (Jul 27, 2007)

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
> ...


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## EVDL List (Jul 27, 2007)

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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## EVDL List (Jul 27, 2007)

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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## EVDL List (Jul 27, 2007)

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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## EVDL List (Jul 27, 2007)

> Bill Dennis wrote:
> > _____________________________________
> > | | _|_
> > __|__ + | / \ armature
> ...


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## EVDL List (Jul 27, 2007)

> 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
> ...


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## EVDL List (Jul 27, 2007)

[No message]


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## EVDL List (Jul 27, 2007)

> 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?
> >
> ...


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## EVDL List (Jul 27, 2007)

[No message]


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## EVDL List (Jul 27, 2007)

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
> ...


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## EVDL List (Jul 27, 2007)

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..
> ...


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## EVDL List (Jul 27, 2007)

> 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..
> ...


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## EVDL List (Jul 27, 2007)

> 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
> ...


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