Re: (ET) Speed controller

["Steve & Sandy Naugler" <snaugler earthlink net>]

David and others,
    If you gave up field weakening, you'd turn your E15 or E20 into the
functional equivalent of an E12S, which is an E12 with the E15's wound 
field
motor.  It has three motor speeds, like an standard E12, but with the more
rugged shunt wound motor.
    If you connected the field in parallel with the armature, you'd have 
two
competing effects that would turn your motor into a nearly constant speed
motor.  As your armature voltage dropped, your motor speed would want to
also drop.  Except in this case, as your field voltage dropped, your field
current would drop proportionately, and as filed current drops, the motor
would want to speed up.  If, for example, your 36 VFC motor was running on
18 V, both armature and field, your speed would not change.  Base speed at
36 VDC x (18V/36V) / (18V/36V) = base speed.  The numerator would be the
effect of dropped voltage to the armature, and the denominator would be the
effect of dropped field voltage.
    As the field takes little power compared to the armature, you might
consider leaving the GE original field dropping resistors and related
circuitry intact.  There is much, much more to be gained by eliminating the
armature dropping resistors and updating the drive to solid state controls.
Unfortuneately, you'd end up with stepwise control.

Steve N.

----- Original Message -----
From: "David Roden (Akron OH USA)" <roden ald net>
To: "electrak list" <elec-trak cosmos5 phy tufts edu>
Sent: Saturday, December 11, 1999 11:52 PM
Subject: Re: (ET) Speed controller


> I've looked into the 4QD controllers and I think they are probably a good
> candidate for the ET.  I'm waiting to learn how yours works before taking
> the plunge.
>
> Here are some of the things I've been thinking about.  Since I haven't
> tried any of these, take them as random ramblings.  If you know more
> about this stuff than I do (which wouldn't take much), please don't
> hesitate to comment or correct.
>
> I can see a couple of ways to handle the field.  One is, as you suggest,
> to connect it to full battery voltage through the main contactor and
> leave it.  However I don't think I'd want to leave it energized when the
> motor is not running.  So I'd want to to find a way to shut it down when
> the potbox is released, or better yet when the motor actually stops (so I
> can have regen braking).
>
> Another way would be to simply parallel it to the armature.  I wonder if,
> with the field paralleled to the armature, I'd still get regen.  Maybe
> the residual magnetism would keep the current flowing and therefore
> maintain the field strength.
>
> I don't know which would work better; I'd experiment with both.
>
> With either of these schemes, I would lose the higher GE speeds achieved
> by field weakening.  To get the higher speeds back, I could (1) retain
> the GE's speed lever (linking the potbox to it), card 3, and FW relay;
> (2) add a second PWM controller to control the field; or (3) increase the
> pack voltage to 48 volts or more.
>
> Curtis used to say their controllers could be used with shunt motors if
> the field were paralleled with the armature.  The reason I'm reluctant to
> try this is that I've heard recently that newer Curtis controllers act
> strangely if the motor inductance is too low -- it reportedly fools the
> current limit so the maximum current isn't available, and can also cause
> jerky starts.  I believe most shunt and sep-ex motors (as in the ET) have
> lower inductance than the series motors usually used in golf cars.
>
> To answer the question of "what controls the controller," any 5000 ohm
> potentiometer can do so.  Obviously you want a high quality, sturdy, well
> made pot rather than the cheap Chinese knockoffs sold at Radio Shack.
> Most controller makers will sell you a good quality pot enclosed in a
> rugged metal box, set up for use with an accelerator cable or linkage.
> Curtis has a complete potbox assembly that looks like a sewing machine
> pedal.
>
> Some advice for those who want to try rolling their own.  Designing a
> controller for the currents involved in running an ET is not trivial.
> Unless you are an electronic engineer with considerable experience in
> electric vehicle control design, you are likely to smoke a lot of silicon
> before you have a reliable design.  In the end, you'll most likely spend
> more on sacrificial silicon than you would have on a good factory built
> controller.
>
> If you really want to do it yourself, email Mark Hanson
> (mhanson valcom com).  He's an electrical engineer who used to work for
> GE's EV division before they essentially closed it down a year or so ago.
> Mark designed a controller for his own ET running at 48 volts (using 8-
> volt golf car batteries), and he'll sell you the plans for a few bucks.
> That's a lot cheaper than exploding large quantities of high power
> silicon.  But I think you'll still find that you're money ahead to buy a
> mass-produced controller -- it's just a matter of finding the right one.
>
> If you're looking for cheap, you might look into Wilde Evolutions'
> rebuilt Curtis controllers (http://www.Wilde-EVolutions.com/PriceList.htm
> -- page down to see the rebuilt controllers branded as "Wilde
> Evolutions").  If you go this route, please let us know how it works out.
>
>
> David Roden - Akron, Ohio, USA
> 1991 Solectria Force 144vac
> 1991 Ford Escort Green/EV 128vdc
> 1979 General Engines ElectroPed 24vdc
> 1974 Honda Civic EV 96vdc
> 1970 GE Elec-trak E15 36vdc
>