3-29-06 Re: Fast Street Car with Twin DC Motors

Hello to Don and All,

I see my buddy Jim has already responded, but I’ll throw my two cents worth in as well.

Don Cameron wrote:

I am **very** interested in this DC siamese motor config of John’s and

Cool. It’s not everyday where we see an AC guy who’s also interested in DC systems, especially high performance DC systems  :-)   Yes, the extreme power delivery of twin DC motors in a series-parallel and fed with 2000 motor amps is addicting. As Jim pointed out, currently, White Zombie’s Siamese 8 is the only one of its kind. I’m hoping there’ll be more to come, though.

Here is what I undestand so far (from what I have read here, the
archives and off the net):

- single Zilla 2K controller
- 300+ volts of high current batteries
- two 9″ Warp motors, mechanically in series, with the brushes advanced

Or….two 8″ ADC. Warp, GE, or whatever.

- no transmission, just a rear end (around 4.1:1)

Yes, no tranny. White Zombie runs with a 4:57 ratio and smallish (but big for a Datsun 1200) 24″ diameter rear tires. It still hits 106 mph in the 1/4 mile due to its expertly crafted 8 inch Siamese motor spinning at around 6800 rpm with so far, no apparent damage from high rpm (fingers still crossed) I am planning on a rear ratio change to in fact, a 4:11 to allow the car to hit 115-120 mph and stay within a safe rpm range. I believe there’s enough off-line torque, so that the taller gear set will not detract from the 1.59 60 ft. time it presently does with the 4:57 ratio.

- electrically the motors are initially series for lots of torque, then via
BF contactors (Bubbas) are switched to parallel for lots of power

When I did the ‘Afterburner’ bypass with the 240V pack of Orbitals, it was indeed, done with twin Bubbas. The controller was completely out of circuit at that point and the motors were connected in parallel directly to the pack….quite the rush when the button was hit! Now, with the 348V Z2K setup, I uses a trio of Albright SW200 contactors….one for the series connection, the other two for the parallel connection, Both modes are with the controller always in circuit.

- in series each motor only see half pack voltage (obviously)
- in parallel the motors can see full pack voltage, however this is limited
by the controller to 170V to prevent arc-over.
- about a 6000RPM redline on the 9″ motors

Yes, and as stated, 6800 rpm @ 106 mph. The car actually goes faster than this, and with the pedal still down as it flashes through the traps, the speed is still rising to probably 110 mph or close to 6900 rpm with the Siamese 8 before we get out of it.

So, a few questions:

- it appears there is going to be a lot of contactors if this is going to be
a street vehicle as well as a fast race car:
2 contactors for main power

I use one, plus a manual disconnect.

2 contactors for series-parallel switch

I assume you’re talking 2 reversing type contactors. It can be done with three SP/ST contactors as well.

1 contactor for reverse (or is it two?)

With twin motors, it’s one reversing set per motor.

- how does one switch from series to parallel? If it was just the
contactors, that would be understandable, but it appears to be controlled
from the Zilla controller.

Actually, it’s controlled by the Zilla’s Hairball, not the Zilla itself. It can be done automatically by virtue of full throttle and the current ramping down to 1/2 the max selected current, or, with a manual control via a push button.

- is the series/parallel switched under full load?  Is it a real rough shift
(like drag race scarey – BANG?)

It doesn’t have to be when manually controlled, but if under automatic mode, yes….full throttle, yes, a big BANG with your  head against the seatback! For a more sane street driving experience, a manual control over the series-parallel contactors, where you switch them off throttle, results in very smooth operation that is seamless in effect with no banging, no tire squealing at switch-over.

See Ya……John Wayland

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