OK, it’s Monday 5:57 am…cobwebs are clearing, the day after day 3 of a crazed weekend of racing and fellowship with the best of friends.
In response to Jim Husted’s first part of his Late Night Nationals post, James Massey wrote:
So how did John do reverse in Zombie? Did he go with the tried-and-not-so-true reversing contactors that he had trouble with before, or do something less conventional?
C’mon, wanna know…
James has been great helping me with ideas on the best way to reverse the not-so- conventional motor & contactor setup in my car, so I want to thank him for all his support. In the end, I went back to the way I had done it two years ago, only in a much more aggressive design. To clarify, I reverse the front motor section only while the rear motor section is off line and is just along for the ride. Here’s how it gets done…
Much to my not wanting to do so, I replaced the beefy 4/0 external field-to-armature cable connection (~ 1ft. long) on the front motor section, with two short 4/0 cables and an SW200 Albright contactor with a single set of contact tips normally open (NO), the same model as the three I use for the series/parallel switchers. The racer in me was convinced the added extra set of high current contacts would add too much resistance and negatively affect the car’s performance at the drag strip. When you’re hunting 100ths of a second, even small losses affect things.
Fast forward to this weekend’s runs…the car ran 12.3 ETs, the same as before the reverse mods, so I’m happy to report that I was wrong , and boy is it sa-weeeet! Flip a switch, and it silently goes the other way!
Back to the reversing project…In my car’s original design, I wanted to avoid using the array of F-R type contactor sets used for series, parallel, forward and reverse (times two) as is the norm for a Zilla equipped EV that takes advantage of its ability to drive twin motors. From my extensive experience with forklift contactors, I’ve learned that despite claims from contactor manufacturers to the contrary, the F-R contactors burn their normally closed tips that rely on spring pressure much worse, than their normally open tips that are closed under high pressure via the magnetic pull of the contactor coil. In White Zombie running at 2000 amps, all those spring-closed tip sets add up to unwanted problems. Thus, the way I wire the sections of my Siamese 8 requires just three single pole type contactors (NO tips) to accomplish the series and parallel modes. For the series mode, just on SW200 slams shut and connects the motor sections in line for the high torque series configuration launch mode. To switch to parallel, the series contactor opens and a pair of parallel SW200s slam shut connecting the motor sections across each other for the parallel configuration max hp top end mode. Simple, and no NC spring pressure contact tips, and just three easy to see and easy to replace NO contact tip sets, and after two years in service they look almost as new still! To continue…with the 4th SW200 inserted between the field and armature of the front motor section’s field-to-armature series connection, with it energized and pulled in I can still operate the Siamese 8 motor as I had been doing, or, by opening this ‘field contactor’, the front motor section can now be reconfigured for reverse via a set of 300 amp GE single pole NO contactors. These are the same heavy duty contactors I had installed and experimented with for field weakening. Yes, in the forward direction series mode of operation, the Siamese 8 now has two SW200 Albright contactors to loop the 2000 amps through instead of just one, but when I looked at the tip condition of the series mode contactor and saw they had not burned at all the last two years in service, I figured there must not be all that much resistance to worry about, and the results from this weekend’s runs backs this up.
Soooo…that’s how reverse was accomplished, at least from the high current high voltage path perspective. The other ‘control logic’ circuit is a whole ‘nuther story! I wanted to use the Hairball’s great set of convenience and safety features, especially the ‘roll detect’ circuit Otmar built into its design (inspired by yours truly back in the formative days of the Hairball) that prevents catastrophic reversing of the motors during an apposing direction under detectable rpm. I also wanted a true ‘Neutral’ direction position with the dash mounted three position toggle switch, so that nothing can run when the switch is in neutral. I also wanted all the fault code options intact….etc. etc.
The high current reversing wiring was actually completed a week ago and had been tested in a crude ‘disconnect all these wires, hook up all these’ wheels off the ground trial operation. The control logic job was intense and required lots of new wire looms, a lot more relays, more switches, a new bracket, and more stuff too boring to keep listing. Tim Brehm and Chris Brune literally sweated through a day long under-hood ordeal getting it ready for racing Friday night while I hung out on the shaded deck sipping lemonade through an interview with Car and Driver’s Ted West. Thanks to both of these guys for taking on the challenge and taking the pressure off me.
In the end, it all worked as planned…..oh yeah, there ‘was’ that little glitch of frying 25 amp fuse! Seems the last minute snubber we installed across the reversing contactor coils couldn’t handle the inductive kick-back and failed in a shorted condition! Once we figured that out though, reverse was available at the mere flip of a switch…beautiful!